In Situ Mechanistic Insights for the Oxygen Reduction Reaction in Chemically Modulated Ordered Intermetallic Catalyst Promoting Complete Electron Transfer

Superoxide anion radicals mediated degradation of tetrachloropicolinic acid in biochars-FexP@Fe-FexC/O2 system with excellent reactivity durability

Activation of oxygen by zero-valent iron (ZVI) to in-situ produce reactive oxidant species (ROS) provides a promising low-carbon and "green" technology for water purification. However, poor ROS yields and easy inactivation limit its engineering application for organic pollutants elimination. Herein, we fabricated a novel Fe-based catalyst with Fe(II)-regenerative surface derived from phosphatized sewage sludge and iron salts. The achieved materials were composed of sludge biochars, FexP, Fe, and FexC (SL-FexP@Fe-FexC) and possessed core/shell structure. SL-FexP@Fe-FexC showed high efficiency in degrading recalcitrant organic pollutants 3,4,5,6-tetrachloropicolinic acid (TCPA) from water at pH 3-10 or in different salts solution without the need of exogenous H2O2. When sludge was pretreated with 1.0 M H3PO4 and then soaked in 50 mM FeCl3 solution before carbonization, the obtained SL1.0M-FexP@Fe-FexC50mM could degrade TCPA with almost 100 % efficiency in ten consecutive recycle runs. This material demonstrates better activity persistence than most of the reported Fe-based catalysts. The EPR and quenching tests indicated that O2•- radicals generated from Fe(II)/O2 reaction were the main active species for TCPA degradation. The electrochemical experiments revealed that strong affinity of O2 and fast electron transfer from inner Fe/FexC to SL-FexP shell improved the yields of O2•- and regeneration of Fe(II) species.

2D Rhodium-Isocyanide Frameworks

2D metal-organic frameworks (2D MOFs) are emerging organic van der Waals materials with great potential in various applications owing to their structural diversity, and tunable optoelectronic properties. So far, most reported 2D MOFs rely on metal-heteroatom coordination (e.g., metal-nitrogen, metal-oxygen, and metal-sulfur); synthesis of metal-carbon coordination based 2D MOFs remains a formidable challenge. This study reports the rhodium-carbon (Rh-C) coordination-based 2D MOFs, using isocyanide as the ligand and Rh(I) as metal node. The synthesized MOFs show excellent crystallinity with quasi-square lattice networks. These MOFs show ultra-narrow bandgaps (0.1-0.28 eV) resulting from the interaction between Rh(I) and isocyano groups. Terahertz spectroscopy demonstrates exceptional short-range charge mobilities up to 560 ± 46 cm2 V-1 s-1 in the as-synthesized MOFs. Moreover, these MOFs are used as electrocatalysts for nitrogen reduction reaction and show an excellent NH3 yield rate of 56.0 ± 1.5 µg h-1 mgcat -1 and a record Faradaic efficiency of 87.1 ± 1.8%. In situ experiments reveal dual pathways involving Rh(I) during the catalytic process. This work represents a pioneering step toward 2D MOFs based on metal-carbon coordination and paves the way for novel reticular materials with ultra-high carrier mobility and for versatile optoelectronic devices.

Harnessing Bio-Inspired Axial Coordination to Boost Synergistic Effects for Enhanced Bifunctional Oxygen Electrocatalysis

Strategic alteration of the chelating atoms around the metal center can modify the electronic band structure of the electrocatalyst, improving its performance in oxygen evolution and reduction reactions (OER/ORR). Advancements in the development of catalysts with heteroatoms and axial modifications in the coordination sphere are mostly limited to single-molecule electrocatalysts or elevated temperature-mediated pyrolysis approaches for oxygen electrocatalysis. Inspired by biological catalytic systems with axial coordination, a pyrolysis-free strategic methodology is adopted for the synthesis of an iron-metaled covalent organic polymer matrix axially laminated over cobalt-based metal-organic framework through an imidazole moiety. Precise engineering of coordination atoms in synthesized core-shell material, featuring dual metal sites with distinct neighboring atom exhibits mutual synergy due to the presence of bridging imidazole moiety between two metal sites. Modulated synergism navigates the electronic structure such that it favors specific reactant adsorption on specific metal sites during bifunctional O2 electrocatalysis as confirmed through in situ Raman spectroscopy and in situ attenuated total reflection infrared (ATR-IR) spectroscopy. Through dynamic correlation between the in-situ studies and modified d-band center obtained theoretically, the pivotal role of axial coordination linkage mediated synergism favoring ORR/OER process via target-specific reactant adsorption is demonstrated.

eg Electron Occupancy as a Descriptor for Designing Iron Single-Atom Electrocatalysts

A quantitative electronic structure-performance relationship is highly desired for the design of single-atom catalysts (SACs). The Fe single-atom catalysts supported by ordered mesoporous carbon with the eg electron occupancy from 1.7 to 0.7 are synthesized. A linear relationship has been established between the eg electron occupancy of the Fe site and the catalytic activity/activation entropy of oxygen-related intermediates. Fe SAC with an eg electron occupancy of 0.7 alters the rate determining step from *OH desorption to *OOH formation. The value of the turn-over frequency is ≈28 times that of the Fe SAC site with an eg electron occupancy of 1.7 e, and the mass activity is ≈6.3 times that of commercial Pt/C. When used in a zinc-air battery, the Fe SAC gives a remarkable power density of 196.3 mW cm-2 and a long-term stability exceeding 1500 h. The discovery of eg electron occupancy descriptor provides valuable insights for designing single-atom electrocatalysts.

d-Orbital Single Electron Filling O─O π* Bonds on WO3S1 Sites for Highly Selective Generation of Hydroxyl Radicals

Hydroxyl radical (•OH) stemming from dissolved oxygen (O2) via photocatalysis is very attractive, but its poor selectivity and generation efficiency greatly limit its application. Herein, a kind of tungsten single site co-coordinated with O and S atoms (WO3S1) is established on ZnIn2S4 (W-ZIS). The strong interactions in WO3S1 shift the d-band center toward the Fermi level, enhancing the adsorption of O2. These interactions improve the accumulation of photo-generated electrons on WO3S1, facilitating the dissociation of O─O bonds in crucial intermediates and promoting the selective conversion from O2 into •OH. This brings a state-of-the-art selectivity (40.2%) and generation efficiency (1668.90 mmol. g-1. L-1. h-1) of •OH production. Experimental results and theoretical simulations have elucidated that O2 can be reduced by d-orbitals single electron (↑, _, _, _, _, _) of WO3S1 transfer to 2p-orbital O─O pi anti-bonding (π*: px and py), initially activating O2. Additionally, WO3S1 sites facilitate the cleavage of H2O, optimizing proton adsorption through W─O orbital coupling in WO3S1 and promoting the transformation of oxygen-containing intermediates. More importantly, d-orbitals single electron can fill O─O π* bond in •OOH intermediate, weakening the covalency of the O─O bond, mitigating the formation of H2O2 and shortening the pathway for •OH generation.).

Linkage Microenvironment and Oxygen Electroreduction Reaction Performance Correlationship of Iron Phthalocyanine-based Polymers

Iron phthalocyanine-based conjugated polymers (PFePc) offer well-defined sites, rendering them ideal model systems to elucidate structure-property relationships towards oxygen reduction reaction (ORR), but have struggled to achieve improved catalytic activity due to uniform electron distribution of iron center and difficulty in molecular-level structure design. Although rationally linkage microenvironmental regulation is an effective approach to adjusting activity, the underlying fundamental mechanism is incompletely understood. Herein, systematic DFT calculations and experimental investigation of PFePc analogous reveal that the incorporation of the electron-withdrawing benzophenone linkage into the PFePc backbone (PFePc-3) drives the delocalization of Fe d-orbital electrons, downshifts the d-band energy level, thereby tailoring the key OH* intermediate interaction, demonstrating enhanced ORR performance with a half-wave potential of 0.91 V, a high mass activity of 21.43 A g-1, and a high turnover frequency of 2.18 e s-1 site-1. Magnetic susceptibility measurements and electron paramagnetic resonance spectroscopy reveal that linkage regulation can induce a 3d electron with high spin-state (t2g 3eg 2) of PFePc-3, significantly accelerating the ORR kinetics. In situ scanning electrochemical microscopy and variable-frequency square wave voltammetry further highlight the rapid kinetics of PFePc-3 to the high accessible site density (6.14×1019 site g-1) and fast electron outbound propagation mechanism.

Atomically Dispersed Metal Catalysts for Oxygen Reduction Reaction: Two-Electron vs. Four-Electron Pathways

Developing eco-friendly electrochemical devices for electrosynthesis, fuel cells (FCs), and metal-air batteries (MABs) requires precisely designing the electronic pathway in the oxygen reduction reaction (ORR) process. Understanding the principle of developing low-cost, highly active, and stable catalysts helps to reduce the usage of noble metals in ORR. Atomically dispersed metal catalysts (ADMCs) emerge as promising alternatives to replace commercial noble metals due to their high utilization of active metal atoms, high intrinsic activity, and controllable coordination environments. In this review, the research tendency and reaction mechanisms in ORR are first summarized. The basic principles concerning the geometric size and chemical coordination of two-electron ORR (2e- ORR) catalysts were then discussed, aiming to outline the evolution of material design from 2e- ORR to four-electron ORR (4e- ORR). Subsequently, recent advances in ADMCs primarily investigated for the 4e- ORR are well-documented. These advances encompass studies on M-N-C coordination, light heteroatom doping, dual-metal atoms-based coordination, and interaction between nanoparticle (NPs)/nanoclusters (NCs) and atomically dispersed metals (ADMs). Finally, the setups for 2/4e- ORR applications, key challenges, and opportunities in the future design of ADMCs for the ORR are highlighted.

High-Performance Overall Water Splitting Dominated by Direct Ligand-to-Cluster Photoexcitation in Metal-Organic Frameworks

Expanding the spectral response of photocatalysts to facilitate overall water splitting (OWS) represents an effective approach for improving solar spectrum utilization efficiency. However, the majority of single-phase photocatalysts designed for OWS primarily respond to the ultraviolet region, which accounts for a small proportion of sunlight. Herein, we present a versatile strategy to achieve broad visible-light-responsive OWS photocatalysis dominated by direct ligand-to-cluster charge transfer (LCCT) within metal-organic frameworks (MOFs). Three synthesized OWS MOFs, namely Fe2MCbz (M2+ = Mn2+, Co2+, Ni2+), exhibited intrinsic OWS capability without the requirement for extra photosensitizer or sacrificial agent or cocatalyst. Among these, Fe2NiCbz was identified as the superior performer, and when dispersed with polyacrylonitrile nanofibers using electrospinning technology, it achieved the highest OWS rates of 170.2 and 85.1 μmol g-1 h-1 for H2 and O2 evolution, surpassing all previously documented MOF-based photocatalysts. Experimental and theoretical analyses revealed that direct LCCT played a crucial role in enhancing the photocatalytic efficiency, with exceptional performance of Fe2NiCbz attributed to its well-optimized energy level structures and highly efficient charge transfer mechanism. This work not only sets a benchmark in OWS MOF photocatalysts but also paves the way for maximizing solar spectrum utilization, thereby advancing renewable hydrogen production strategy.

Constructing Pentagonal Topological Defects in Carbon Aerogels for Flexible Zinc-Air Batteries

In the context of energy conversion, the design and synthesis of high-performance metal-free carbon electrocatalysts for the oxygen reduction reaction (ORR) is crucial. Herein, a one-step nitrogen doping/extraction strategy is proposed to fabricate 3D nitrogen-doped carbon aerogels (NCA-Cl) with rich pentagonal carbon topological defects. The NCA-Cl electrocatalyst exhibits superb ORR activity, displaying a half-wave potential of 0.89 V vs RHE and 0.74 V vs RHE under alkaline (0.1 m KOH) and acidic (0.1 m HClO4) media, respectively, thanks to the balanced *OOH intermediate adsorption and desorption induced by the pentagonal carbon topological defects and nitrogen dopants. The aqueous zinc-air battery (ZAB) equipped with the NCA-Cl cathode delivers a peak power density of 206.6 mW cm-2, a specific capacity of 810.6 mAh g-1, and a durability of 400 h, and the flexible ZAB also performed convincingly. This work provides an effective strategy for the formation of topological carbon defects for the enhancement of the electrocatalytic activity of carbon-based catalysts.

Embedding Coupled Pd/Fe Sites in Electrospun MOF-Derived Carbon Nanofibers Achieves Efficient and Durable Oxygen Reduction Catalysis

High costs, poor durability of Pt electrocatalysts, and the low performance of non-precious metals hinder the large-scale commercialization of fuel cells. To address these challenges, a bimetallic, highly dispersed catalyst containing Pd and Fe uniformly distributed on porous nitrogen-doped carbon nanofibers was developed. This catalyst demonstrated remarkable oxygen reduction catalytic performance. The Pd-Fe-N-C catalyst exhibited catalytic activity 4.6 times higher than that of the JM 20 % Pt/C catalyst, despite containing only 0.62 wt. % Pd. Moreover, it achieved a half-wave potential (E1/2=0.953 V vs. RHE) that is 40 mV higher than the JM 20 % Pt/C catalyst (0.913 V vs. RHE). Significantly, with a total metal content of just 1.19 wt. %, the E1/2 of Pd-Fe-N-C catalyst decreased by only 1 mV after 10,000 cycles, highlighting its exceptional durability. Furthermore, a stability test revealed a current retention rate of 84.87 % after 50,000 s of operation, with no evidence of agglomeration. These results suggest that combining electrostatic spinning of MOFs with pyrolysis provides an effective and innovative method for synthesizing electrocatalysts with reduced reliance on precious metals.

Reducing Intrinsic Carrier Recombination in Au/CuTCPP(Fe) Schottky Junction Through Spin Polarization Manipulation for Sensitive Photoelectrochemical Biosensing

Schottky junctions have been widely applied to facilitate charge carrier separation through the formation of an internal electric field (IEF). However, the notably restricted spatial distribution of the IEF weakens the promotion of intrinsic carrier separation. In this study, we unveil that Au nanoparticles (NPs) in the Au/CuTCPP(Fe) Schottky junction can manipulate the spin polarization of CuTCPP(Fe) to inhibit inner carrier recombination. Experimental investigations and theoretical calculations reveal that the introduction of Au NPs leads to an increased population of spin-polarized electrons, effectively suppressing inner charge carrier recombination in CuTCPP(Fe) by employing the spin mismatch between spin-polarized photoexcited carriers. Moreover, as a typical active site for the oxygen reduction reaction, the oxygen adsorption configuration on spin-polarized Fe single-atom sites in Au/CuTCPP(Fe) is further optimized, resulting in boosted interfacial reactions. Leveraging the thiocholine-induced poisoning of the active sites and the magnetic-enhanced photoelectric response, Au/CuTCPP(Fe) is harnessed to develop a photoelectrochemical biosensing platform for organophosphorus pesticides. This work offers a promising method for manipulating the spin polarization of semiconductors in heterojunctions to mitigate intrinsic charge carrier recombination.

Fe─N4 and Fe7Co3 Nanoalloy Dual-Site Modulation by Skeleton Defect in N-Doped Graphene Aerogel for Enhanced Bifunctional Oxygen Electrocatalyst in Zinc-air Battery

The dual-site electrocatalysts formed by metal single atoms combines with metal nanoparticles represent a promising strategy to enhance both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance. Herein, defect engineering is applied to dual-site ORR and OER electrocatalysts. Its design, synthesis, structural properties, and catalytic performance experimentally and theoretically are insightfully studied for the single-atomic Fe─N4 and the adjacent Fe7Co3 nanoalloy (FeCoNA) as dual-site loading on nitrogen-doped graphene aerogel (Fe─N/FeCo@NGA). The high-density dual-sites, together with the good electronic conductivity of NGA, synergistically improve the electronic structure for superior electrocatalytic activity. The half-wave potential of Fe─N/FeCo@NGA in ORR is 0.92 V and the overpotential of it in OER is 1.58 V. Corresponding all-solid-state Zn-air battery demonstrates a peak power density of 147.6 mW cm-2 and charge/discharge durability for over 140 h. Theoretical calculations reveal that the single-atomic Fe-N4 and FeCoNA dual-site on the skeleton defect optimized NGA, further refine the local electronic structure, modulating the tensile force on the O─O bond in *OOH intermediate, leading to its spontaneous dissociation and facilitating a significantly reduced energy barrier. This work takes a promising shortcut in the application of defect engineering for the development of highly efficient dual-site bifunctional oxygen electrocatalysts with single atoms.

A(CoFe)(S2)2/CoFe heterostructure constructed in S, N co-doped carbon nanotubes as an efficient oxygen electrocatalyst for zinc-air battery

Transition metal alloys can exhibit synergistic intermetallic effects to obtain high activities for oxygen reduction/evolution reactions (ORR/OER). However, due to the insufficient stability of active sites in alkaline electrolytes, conventional alloy catalysts still do not meet practical needs. Herein, by using polypyrrole tubes and cobalt-iron (CoFe) Prussian blue analogs as precursors, CoFe sulfides is in-situ formed on CoFe alloys to construct (CoFe)(S2)2/CoFe heterostructure in sulfur (S) and nitrogen (N) co-doped carbon nanotubes (CoFe@NCNTs-nS) via a low-temperature sulfidation strategy. The as-marked CoFe@NCNTs-12.5S exhibits a comparable ORR activity (half-wave potential of 0.901 V) to Pt/C (0.903 V) and a superior OER activity (overpotential of 272 mV at 10 mA cm-2) to RuO2 (299 mV). CoFe@NCNTs-12.5S also exhibits ultralow charge transfer resistances (ORR-6.36 Ω and OER-0.21 Ω) and an excellent potential difference of 0.617 V. The sulfidation-induced (CoFe)(S2)2/CoFe heterojunctions can accelerate interfacial charge transfer process. Tubular structure not only disperses the (CoFe)(S2)2/CoFe heterostructure, but also reduces the corrosion of active-sites to enhance catalysis stability. Zinc-air battery with CoFe@NCNTs-12.5S achieves a high specific capacity (718.1 mAh g-1), maintaining a voltage gap of 0.957 V after 400 h. This work reveals the potential of interface engineering for boosting ORR/OER activities of alloys via in-situ heterogenization.

Densely populated macrocyclic dicobalt sites in ladder polymers for low-overpotential oxygen reduction catalysis

Dual-atom catalysts featuring synergetic dinuclear active sites, have the potential of breaking the linear scaling relationship of the well-established single-atom catalysts for oxygen reduction reaction; however, the design of dual-atom catalysts with rationalized local microenvironment for high activity and selectivity remains a great challenge. Here we design a bisalphen ladder polymer with well-defined densely populated binuclear cobalt sites on Ketjenblack substrates. The strong electron coupling effect between the fully-conjugated ladder structure and carbon substrates enhances the electron transfer between the cobalt center and oxygen intermediates, inducing the low-to-high spin transition for the 3d electron of Co(II). In situ techniques and theoretical calculations reveal the dynamic evolution of Co2N4O2 active sites and reaction intermediates. In alkaline conditions, the catalyst exhibits impressive oxygen reduction reaction activity featuring an onset potential of 1.10 V and a half-wave potential of 1.00 V, insignificant decay after 30,000 cycles, pushing the overpotential boundaries of ORR electrocatalysis to a low level. This work provides a platform for designing efficient dual-atom catalysts with well-defined coordination and electronic structures in energy conversion technologies.

Unprecedented Photocatalytic Hydrogen Peroxide Production via Covalent Triazine Frameworks Constructed from Fused Building Blocks

Covalent organic frameworks (COFs) have garnered attention for their potential in photocatalytic hydrogen peroxide (H2O2) production. However, their photocatalytic efficiency is impeded by insufficient exciton dissociation and charge carrier transport. Constructing COFs with superior planarity is an effective way to enhance the π-conjugation degree and facilitate electron-hole separation. Nonetheless, the conventional linear linkers of COFs inevitably introduce torsional strain that disrupts coplanarity. Herein, we address this issue by introducing inherently coplanar triazine rings as linkers and fused building blocks as monomers to create covalent triazine frameworks (CTFs) with superior coplanarity. Both experimental and theoretical calculations confirm that CTFs constructed from fused building blocks significantly enhance the electron-hole separation efficiency and improve the photocatalytic performance, compared to the CTFs constructed with non-fused building blocks. The frontier molecular orbitals and electrostatic potentials (ESP) revealed that the oxygen reduction reaction (ORR) is preferentially facilitated by the triazine rings, with the water oxidation reaction (WOR) likely occurring at the thiophene-containing moiety. Remarkably, CTF-BTT achieved an exceptional H2O2 production rate of 74956 μmol g-1 h-1 when employing 10 % benzyl alcohol (V/V) as a sacrificial agent in an O2-saturated atmosphere, surpassing existing photocatalysts by nearly an order of magnitude. Our findings provide valuable insights for designing highly coplanar polymer-based photocatalysts that enhance the solar-to-chemical energy conversion process.

Decoding Dual-Functionality in N-doped Defective Carbon: Unveiling Active Sites for Bifunctional Oxygen Electrocatalysis

Oxygen electrocatalysis plays a pivotal role in energy conversion and storage technologies. The precise identification of active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for developing an efficient bifunctional electrocatalyst. However, this remains a challenging endeavor. Here, it is demonstrated that metal-free N-doped defective carbon material derived from triazene derivative exhibits excellent bifunctional activity, achieving a notable ΔE value of 0.72 V. Through comprehensive X-ray photoelectron spectroscopy and Raman spectroscopic analyses, the active sites responsible for oxygen electrocatalysis are elucidated, resolving a long-standing issue. Specifically, pyridinic-N sites are crucial for ORR, while graphitic-N are good for OER. A predictive model utilizing π-electron descriptors further aids in identifying these sites, with theoretical insights aligning with experimental results. Additionally, in situ ATR-FTIR spectroscopy provides clarity on reaction intermediates for both reactions. This research paves the way for developing metal-free, site-specific electrocatalysts for practical applications in energy technologies.

The Interfacial Interpenetration Effect for Controlled Reaction Stability of Palladium Catalysts

Tailoring well-defined interfacial structures of heterogeneous metal catalysts has become an effective strategy for identifying the interface relationships and facilitating the reactions involving multiple intermediates. Here, a particle-particle heterostructure catalyst consisting of Pd and copper oxide nanoparticles is designed to achieve high-performance alkaline methanol oxidation electrocatalysis. The strong coupling particle-particle heterostructure catalyst induced a unique interfacial interpenetration effect to improve the interfacial charge redistribution and regulate the d-band structure for optimizing the adsorption of CO intermediates on the catalyst. The resulting catalyst shows impressive mass activity (4.0 A mgPd-1) and current density (215.8 mA cm-2) for the methanol oxidation reaction (MOR) in alkaline media, which is 80.0 and 154.1 times higher than 10% Pd/C. The catalyst also exhibited outstanding stability for the MOR without obvious mass activity decay after 30,000 cycles. Experimental results and theoretical simulation (DFT) studies show that the chemical bond of the Cu-O-Pd interface can be regulated by the Pd penetration effect, greatly improving the activity and stability of the MOR. The present work exhibits the superiority of the metal particle-metal oxide heterostructure interface toward the rational design of advanced electrocatalysts.

Well-Defined Co2 Dual-Atom Catalyst Breaks Scaling Relations of Oxygen Reduction Reaction

The 4-electron oxygen reduction reaction (ORR) under alkaline conditions is central to the development of non-noble metal-based hydrogen fuel cell technologies. However, the kinetics of ORR are constrained by scaling relations, where the adsorption free energy of *OOH is intrinsically linked to that of *OH with a nearly constant difference larger than the optimal value. In this study, a well-defined binuclear Co2 complex was synthesized and adsorbed onto carbon black, serving as a model dual-atom catalyst. This catalyst achieved a record half-wave potential of 0.972 V versus the reversible hydrogen electrode in an alkaline electrolyte. Density functional theory simulations and in situ infrared spectroscopy revealed that the dual-atom site stabilizes the *OOH intermediate through bidentate coordination, thereby reducing the free energy gap between *OOH and *OH. By altering the adsorption configuration of *OOH on the dual-atom site, the scaling relations are effectively disrupted, leading to a significant enhancement in ORR activity.

Spin-Polarized PdCu-Fe3O4 In-Plane Heterostructures with Tandem Catalytic Mechanism for Oxygen Reduction Catalysis

Alloying has significantly upgraded the oxygen reduction reaction (ORR) of Pd-based catalysts through regulating the thermodynamics of oxygenated intermediates. However, the unsatisfactory activation ability of Pd-based alloys toward O2 molecules limits further improvement of ORR kinetics. Herein, the precise synthesis of nanosheet assemblies of spin-polarized PdCu-Fe3O4 in-plane heterostructures for drastically activating O2 molecules and boosting ORR kinetics is reported. It is demonstrated that the deliberate-engineered in-plane heterostructures not only tailor the d-band center of Pd sites with weakened adsorption of oxygenated intermediates but also endow electrophilic Fe sites with strong ability to activate O2 molecules, which make PdCu-Fe3O4 in-plane heterostructures exhibit the highest ORR specific activity among the state-of-art Pd-based catalysts so far. In situ electrochemical spectroscopy and theoretical investigations reveal a tandem catalytic mechanism on PdCu-Fe3O4─Fe sites that initially activate molecular O2 and generate oxygenated intermediates being transferred to Pd sites to finish the subsequent proton-coupled electron transfer steps.

Building Cobalt-Nickel Diatomic Sites as Oxygenophilic ORR Catalyst with Strong Cl--Corrosion Resistance for Seawater Batteries

The seawater battery (SWB) holds great potential as the next-generation energy supply system for marine electrical equipment. However, its efficiency and durability are hindered by low oxygen concentration and harmful Cl- adsorption and corrosion in seawater. Herein, a host-guest strategy is developed to fabricate diatomic catalysts with adjacent Co and Ni sites on nitrogen-doped carbon (CoNi-DAC), where Co and Ni atoms are each coordinated to three nitrogen atoms. Theoretical calculations and in situ characterization reveal that the synchronized reduction of Co and Ni valence states enhances ORR kinetics by optimizing the O2 adsorption energy barrier, facilitating direct O─O bond cleavage and preventing *OOH intermediate formation. This electronic modulation enhances oxygenophilicity and Cl- corrosion resistance. The Co/Ni diatomic sites synergistically improve ORR catalytic activity, achieving a half-wave potential (E1/2) of 0.79 V and exceptional long-term durability of nearly 700 h in natural seawater. The assembled SWB with CoNi-DAC coated carbon brush electrode attains a peak power density of 3.3 W L-1. This work offers valuable insights into the design and development of advanced ORR electrocatalysts for natural seawater environments.

A Perspective on Electrochemical Point Source Utilization of CO2 and Other Flue Gas Components to Value Added Chemicals

Electrochemical CO2 reduction reaction (eCO2RR) has been explored extensively for mitigation of noxious CO2 gas generating C1 and C2+ hydrocarbons and oxygenates as value-added fuels and chemicals with remarkable selectivity. The source of CO2 being a pure CO2 feed, it does not fully satisfy the real-time digestion of industrial exhausts. Besides the detrimental effect of noxious gas mixture leading to global warming, there is a huge capital investment in purifying the flue gas mixtures from industries. The presence of other impurity gases affects the eCO2RR mechanism and its activity and selectivity toward C2+ products dwindle drastically. Impurities like NOx, SOx, O2, N2, and halide ions present in flue gas mixture reduce the conversion and selectivity of eCO2RR significantly. Instead of wiping out these impurities via separation processes, new strategies from material chemistry and electrochemistry can open new avenues for turning foes to friends! In this perspective, the co-electroreduction will vividly discussed and supporting role of different heteroatom-containing impurity gases with CO2, generating highly stable C─N, C─S, C─X bonds, and highlight the existing limitations and providing probable solutions for attaining further success in this field and translating this to industrial exhaust streams.

Manipulation of d-Orbital Electron Configurations in Nonplanar Fe-Based Electrocatalysts for Efficient Oxygen Reduction

Manipulation of the spin state holds great promise to improve the electrochemical activity of transition metal-based catalysts. However, the underlying relationship between the nonplanar metal coordination environment and spin states remains to be explored. Herein, we report the precise regulation of nonplanar Fe atomic d-orbital energy level into an irregular tetrahedral crystal field configuration by introducing P atoms. With the increase of P coordination number, the spin magnetic moment decreases linearly from 3.8 μB to 0.2 μB, and the high spin content decreases linearly from 31% to 5%. Significantly, a volcanic curve between the spin states of Fe-based catalysts (Fe-NxPy) and oxygen reduction reaction (ORR) activity has been unequivocally established based on the thermodynamic results. Thus, the Fe-N3P1 catalyst with a 19% medium spin state experimentally exhibits the optimal reaction activity with a high half-wave potential of 0.92 V. These findings indicate that regulating electron spin moments through coordination engineering is a promising catalyst design strategy, providing important insights into spin catalysis.

Iridium Single Atoms to Nanoparticles: Nurturing the Local Synergy with Cobalt-Oxide Supported Palladium Nanoparticles for Oxygen Reduction Reaction

A ternary catalyst comprising Iridium (Ir) single-atoms (SA)s decorated on the Co-oxide supported palladium (Pd) nanoparticles (denoted as CPI-SA) is developed in this work. The CPI-SA with 1 wt.% of Ir exhibits unprecedented high mass activity (MA) of 7173 and 770 mA mgIr -1, respectively, at 0.85 and 0.90 V versus RHE in alkaline ORR (0.1 m KOH), outperforming the commercial Johnson Matthey Pt catalyst (J.M.-Pt/C; 20 wt.% Pt) by 107-folds. More importantly, the high structural reliability of the Ir single-atoms endows the CPI-SA with outstanding durability, where it shows progressively increasing MA of 13 342 and 1372 mA mgIr -1, respectively, at 0.85 and 0.90 V versus RHE up to 69 000 cycles (3 months) in the accelerated degradation test (ADT). Evidence from the in situ partial fluorescence yield X-ray absorption spectroscopy (PFY-XAS) and the electrochemical analysis indicate that the Ir single-atoms and adjacent Pd domains synergistically promote the O2 splitting and subsequent desorption of hydroxide ions (OH-), respectively. Whereas the Co-atoms underneath serve as electron injectors to boost the ORR activity of the Ir single-atoms. Besides, a progressive and sharp drop in the ORR performance is observed when Ir-clusters and Ir nanoparticles are decorated on the Co-oxide-supported Pd nanoparticles.

IR-EcoSpectra: Exploring sustainable ex situ and in situ FTIR applications for green chemical and pharmaceutical analysis

In various industries, particularly in the chemical and pharmaceutical fields, Fourier transform infrared spectroscopy (FTIR) spectroscopy provides a unique capacity to detect and characterise complex chemicals while minimising environmental damage by minimal waste generation and reducing the need for extensive sample preparation or use of harmful reagents. This review showcases the versatility of ex situ and in situ FTIR applications for substance identification, analysis, and dynamic monitoring. Ex situ FTIR spectroscopy's accuracy in identifying impurities, monitoring crystallisation processes, and regulating medication release patterns improves product quality, safety, and efficacy. Furthermore, its quantification capabilities enable more effective drug development, dosage procedures, and quality control practices, all of which are consistent with green analytical principles. On the other hand, in situ FTIR spectroscopy appears to be a novel tool for the real-time investigation of molecular changes during reactions and processes, allowing for the monitoring of drug release kinetics, crystallisation dynamics, and surface contacts, as well as providing vital insights into material behaviour. The combination of ex situ FTIR precision and in situ FTIR dynamic capabilities gives a comprehensive analytical framework for developing green practices, quality control, and innovation in the chemical and pharmaceutical industries. This review presents the wide range of applications of ex situ and in situ FTIR spectroscopy in chemical, pharmaceutical and medical fields as an analytical green chemistry tool. However, further study is required to fully realise FTIR's potential and develop new applications that improve sustainability in these areas.

Oxygen-bridged W-Pd atomic pairs enable H2O2 activation for sensitive immunoassays

Regulating the performance of peroxidase (POD)-like nanozymes is a prerequisite for achieving highly sensitive and accurate immunoassays. Inspired by natural enzyme catalysis, we design a highly active and selective nanozyme by loading atomically dispersed tungsten (W) sites on Pd metallene (W-O-Pdene) to construct an artificial three-dimensional (3D) catalytic center. The 3D asymmetric W-O-Pd atomic pairs can effectively stretch the O-O bonds in H2O2 and further promote the desorption of H2O to enhance POD-like activity. Moreover, the W-O-Pd sites with unique spatial structures demonstrate satisfactory specificity for H2O2 activation, effectively preventing the interference of dissolved oxygen. Accordingly, the highly active and specific W-O-Pdene nanozymes are utilized for sensitive and accurate prostate-specific antigen (PSA) immunoassay with a low detection limit of 1.92 pg mL-1, superior to commercial enzyme-linked immunosorbent assay.

Semimetal-triggered covalent interaction in Pt-based intermetallics for fuel-cell electrocatalysis

Platinum-based intermetallic compounds (IMCs) play a vital role as electrocatalysts in a range of energy and environmental technologies, such as proton exchange membrane fuel cells. However, the synthesis of IMCs necessitates recombination of ordered Pt-M metallic bonds with high temperature driving, which is generally accompanied by side effects for catalysts' structure and performance. In this work, we highlight that semimetal atoms can trigger covalent interactions to break the synthesis-temperature limitation of platinum-based intermetallic compounds and benefit fuel-cell electrocatalysis. Attributed to partial fillings of p-block in semimetal elements, the strong covalent interaction of d-p π backbonding can benefit the recombination of ordered Pt-M metallic bonds (PtGe, PtSb and PtTe) in the synthesis process. Moreover, this covalent interaction in metallic states can further promote both electron transport and orbital fillings of active sites in fuel cells. The semimetal-Pt IMCs were obtained with a temperature 300 K lower than that needed for the synthesis of metal-Pt intermetallic compounds and reached the highest CO-tolerant oxygen reduction activity (0.794 A mg-1 at 0.9 V and 5.1% decay under CO poisoning) among reported electrocatalysts. We anticipate that semimetal-Pt IMCs will offer new insights for the rational design of advanced electrocatalysts for fuel cells.

Improvement in ORR Durability of Fe Single-Atom Carbon Catalysts Hybridized with CeO2 Nanozyme

FeNC catalysts are considered one of the most promising alternatives to platinum group metals for the oxygen reduction reaction (ORR). Despite the extensive research on improving ORR activity, the undesirable durability of FeNC is still a critical issue for its practical application. Herein, inspired by the antioxidant mechanism of natural enzymes, CeO2 nanozymes featuring catalase-like and superoxide dismutase-like activities were coupled with FeNC to mitigate the attack of reactive oxygen species (ROS) for improving durability. Benefiting from the multienzyme-like activities of CeO2, ROS generated from FeNC is instantaneously eliminated to alleviate the corrosion of carbon and demetallization of metal sites. Consequently, FeNC/CeO2 exhibits better ORR durability with a decay of only 5 mV compared to FeNC (18 mV) in neutral electrolyte after 10k cycles. The FeNC/CeO2-based zinc-air battery also shows minimal voltage decay over 140 h in galvanostatic discharge-charge cycling tests, outperforming FeNC and commercial Pt/C.

Selective oxygen reduction reaction: mechanism understanding, catalyst design and practical application

The oxygen reduction reaction (ORR) is a key component for many clean energy technologies and other industrial processes. However, the low selectivity and the sluggish reaction kinetics of ORR catalysts have hampered the energy conversion efficiency and real application of these new technologies mentioned before. Recently, tremendous efforts have been made in mechanism understanding, electrocatalyst development and system design. Here, a comprehensive and critical review is provided to present the recent advances in the field of the electrocatalytic ORR. The two-electron and four-electron transfer catalytic mechanisms and key evaluation parameters of the ORR are discussed first. Then, the up-to-date synthetic strategies and in situ characterization techniques for ORR electrocatalysts are systematically summarized. Lastly, a brief overview of various renewable energy conversion devices and systems involving the ORR, including fuel cells, metal-air batteries, production of hydrogen peroxide and other chemical synthesis processes, along with some challenges and opportunities, is presented.

Ligand Isomerization Driven Electrocatalytic Switching

The prevailing view about molecular catalysts is that the central metal ion is responsible for the reaction mechanism and selectivity, whereas the ligands mainly affect the reaction kinetics. Here, we question this paradigm and show that ligands have a dramatic influence on the selectivity of the product. We show how even a seemingly small change in ligand isomerization sharply alters the selectivity of the well-researched oxygen reduction reaction (ORR) Co phthalocyanine catalyst from an indirect 2e- to a direct 4e- pathway. Detailed analysis reveals that intramolecular hydrogen-bond interactions in the ligand activate the catalytic Co, directing the oxygen binding and thus deciding the final product. The resulting catalyst is the first example of a Co-based molecular catalyst catalyzing a direct 4e- ORR via ligand isomerization, for which it shows an activity close to the benchmark Pt in an actual H2-O2 fuel cell. The effect of the ligand isomerism is demonstrated with different central metal ions, thus highlighting the generalizability of the findings and their potential to open new possibilities in the design of molecular catalysts.

Microwave Assisted Fast Synthesis of a Donor-Acceptor COF Towards Photooxidative Amidation Catalysis

The synthesis of covalent organic frameworks (COFs) at bulk scale require robust, straightforward, and cost-effective techniques. However, the traditional solvothermal synthetic methods of COFs suffer low scalability as well as requirement of sensitive reaction environment and multiday reaction time (2-10 days) which greatly restricts their practical application. Here, we report microwave assisted rapid and optimized synthesis of a donor-acceptor (D-A) based highly crystalline COF, TzPm-COF in second (10 sec) to minute (10 min) time scale. With increasing the reaction time from seconds to minutes crystallinity, porosity and morphological changes are observed for TzPm-COF. Owing to visible range light absorption, suitable band alignment, and low exciton binding energy (Eb=64.6 meV), TzPm-COF can efficaciously produce superoxide radical anion (O2 .-) after activating molecular oxygen (O2) which eventually drives aerobic photooxidative amidation reaction with high recyclability. This photocatalytic approach works well with a variety of substituted aromatic aldehydes having electron-withdrawing or donating groups and cyclic, acyclic, primary or secondary amines with moderate to high yield. Furthermore, catalytic mechanism was established by monitoring the real-time reaction progress through in situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study.

Linker Mediated Electronic-State Manipulation of Conjugated Organic Polymers Enabling Highly Efficient Oxygen Reduction

Conjugated polymers with tailorable composition and microarchitecture are propitious for modulating catalytic properties and deciphering inherent structure-performance relationships. Herein, we report a facile linker engineering strategy to manipulate the electronic states of metallophthalocyanine conjugated polymers and uncover the vital role of organic linkers in facilitating electrocatalytic oxygen reduction reaction (ORR). Specifically, a set of cobalt phthalocyanine conjugated polymers (CoPc-CPs) wrapped onto carbon nanotubes (denoted CNTs@CoPc-CPs) are judiciously crafted via in situ assembling square-planar cobalt tetraaminophthalocyanine (CoPc(NH2)4) with different linear aromatic dialdehyde-based organic linkers in the presence of CNTs. Intriguingly, upon varying the electronic characteristic of organic linkers from terephthalaldehyde (TA) to 2,5-thiophenedicarboxaldehyde (TDA) and then to thieno/thiophene-2,5-dicarboxaldehyde (bTDA), their corresponding CNTs@CoPc-CPs exhibit gradually improved electrocatalytic ORR performance. More importantly, theoretical calculations reveal that the charge transfer from CoPc units to electron-withdrawing linkers (i.e., TDA and bTDA) drives the delocalization of Co d-orbital electrons, thereby downshifting the Co d-band energy level. Accordingly, the active Co centers with more positive valence state exhibit optimized binding energy toward ORR-relevant intermediates and thus a balanced adsorption/desorption pathway that endows significant enhancement in electrocatalytic ORR. This work demonstrates a molecular-level engineering route for rationally designing efficient polymer catalysts and gaining insightful understanding of electrocatalytic mechanisms.

Selective Oxidation of sp-Bonded Carbon in Graphdiyne/Carbon Nanotubes Heterostructures to Form Dominant Epoxy Groups for Two-Electron Oxygen Reduction

Two-electron oxygen reduction reaction (2e- ORR) is of great significance to H2O2 production and reversible nonalkaline Zn-air batteries (ZABs). Multiple oxygen-containing sp2-bonded nanocarbons have been developed as electrocatalysts for 2e- ORR, but they still suffer from poor activity and stability due to the limited and mixed active sites at the edges as well as hydrophilic character. Herein, graphdiyne (GDY) with rich sp-C bonds is studied for enhanced 2e- ORR. First, computational studies show that GDY has a favorable formation energy for producing five-membered epoxy ring-dominated groups, which is selective toward the 2e- ORR pathway. Then based on the difference in chemical activity of sp-C bonds in GDY and sp2-C bonds in CNTs, we experimentally achieved conductive and hydrophobic carbon nanotubes (CNTs) covering O-modified GDY (CNTs/GDY-O) through a mild oxidation treatment combined with an in situ CNTs growth approach. Consequently, the CNTs/GDY-O exhibits an average Faraday efficiency of 91.8% toward H2O2 production and record stability over 330 h in neutral media. As a cathode electrocatalyst, it greatly extends the lifetime of 2e- nonalkaline ZABs at both room and subzero temperatures.

Understanding Advanced Transition Metal-Based Two Electron Oxygen Reduction Electrocatalysts from the Perspective of Phase Engineering

Non-noble transition metal (TM)-based compounds have recently become a focal point of extensive research interest as electrocatalysts for the two electron oxygen reduction (2e- ORR) process. To efficiently drive this reaction, these TM-based electrocatalysts must bear unique physiochemical properties, which are strongly dependent on their phase structures. Consequently, adopting engineering strategies toward the phase structure has emerged as a cutting-edge scientific pursuit, crucial for achieving high activity, selectivity, and stability in the electrocatalytic process. This comprehensive review addresses the intricate field of phase engineering applied to non-noble TM-based compounds for 2e- ORR. First, the connotation of phase engineering and fundamental concepts related to oxygen reduction kinetics and thermodynamics are succinctly elucidated. Subsequently, the focus shifts to a detailed discussion of various phase engineering approaches, including elemental doping, defect creation, heterostructure construction, coordination tuning, crystalline design, and polymorphic transformation to boost or revive the 2e- ORR performance (selectivity, activity, and stability) of TM-based catalysts, accompanied by an insightful exploration of the phase-performance correlation. Finally, the review proposes fresh perspectives on the current challenges and opportunities in this burgeoning field, together with several critical research directions for the future development of non-noble TM-based electrocatalysts.

Unveiling Nanoscale Heterogeneities at the Bias-Dependent Gold-Electrolyte Interface

Electrified solid-liquid interfaces (SLIs) are extremely complex and dynamic, affecting both the dynamics and selectivity of reaction pathways at electrochemical interfaces. Enabling access to the structure and arrangement of interfacial water in situ with nanoscale resolution is essential to develop efficient electrocatalysts. Here, we probe the SLI energy of a polycrystalline Au(111) electrode in a neutral aqueous electrolyte through in situ electrochemical atomic force microscopy. We acquire potential-dependent maps of the local interfacial adhesion forces, which we associate with the formation energy of the electric double layer. We observe nanoscale inhomogeneities of interfacial adhesion force across the entire map area, indicating local differences in the ordering of the solvent/ions at the interface. Anion adsorption has a clear influence on the observed interfacial adhesion forces. Strikingly, the adhesion forces exhibit potential-dependent hysteresis, which depends on the local gold grain curvature. Our findings on a model electrode extend the use of scanning probe microscopy to gain insights into the local molecular arrangement of the SLI in situ, which can be extended to other electrocatalysts.

Boosting CO2 Electroreduction over a Covalent Organic Framework in the Presence of Oxygen

Herein, we propose an oxygen-containing species coordination strategy to boost CO2 electroreduction in the presence of O2. A two-dimensional (2D) conjugated metal-covalent organic framework (MCOF), denoted as NiPc-Salen(Co)2-COF that is composed of the Ni-phthalocyanine (NiPc) unit with well-defined Ni-N4-O sites and the salen(Co)2 moiety with binuclear Co-N2O2 sites, is developed and synthesized for enhancing the CO2RR under aerobic condition. In the presence of O2, one of the Co sites in the NiPc-Salen(Co)2-COF that coordinated with the intermediate of *OOH from ORR could decrease the energy barrier of the activation of CO2 molecules and stabilize the key intermediate *COOH of the CO2RR over the adjacent Co center. Besides, the oxygen species axially coordinated Ni-N4-O sites can favor in reducing the energy barrier of the intermediate *COOH formation for the CO2RR. Thus, NiPc-Salen(Co)2-COF exhibits high oxygen-tolerant CO2RR performance and achieves outstanding CO Faradaic efficiency (FECO) of 97.2 % at -1.0 V vs. the reversible hydrogen electrode (RHE) and a high CO partial current density of 40.3 mA cm-2 at -1.1 V in the presence of 0.5 % O2, which is superior to that in pure CO2 feed gas (FECO=94.8 %, jCO=19.9 mA cm-2). Notably, the NiPc-Salen(Co)2-COF achieves an industrial-level current density of 128.3 mA cm-2 in the flow-cell reactor with 0.5 % O2 at -0.8 V, which is higher than that in pure CO2 atmosphere (jCO=104.8 mA cm-2). It is worth noting that an excellent FECO of 86.8 % is still achieved in the presence of 5 % O2 at -1.0 V. This work provides an effective strategy to enable the CO2RR under O2 atmosphere by utilizing the *OOH intermediates of ORR to boost CO2 electroreduction.

p-d Orbital Hybridization-Engineered PdSn Nanozymes for a Sensitive Immunoassay

Nanozymes with peroxidase-like activity have been extensively studied for colorimetric biosensing. However, their catalytic activity and specificity still lag far behind those of natural enzymes, which significantly affects the accuracy and sensitivity of colorimetric biosensing. To address this issue, we design PdSn nanozymes with selectively enhanced peroxidase-like activity, which improves the sensitivity and accuracy of a colorimetric immunoassay. The peroxidase-like activity of PdSn nanozymes is significantly higher than that of Pd nanozymes. Theoretical calculations reveal that the p-d orbital hybridization of Pd and Sn not only results in an upward shift of the d-band center to enhance hydrogen peroxide (H2O2) adsorption but also regulates the O-O bonding strength of H2O2 to achieve selective H2O2 activation. Ultimately, the nanozyme-linked immunosorbent assay has been successfully developed to sensitively and accurately detect the prostate-specific antigen (PSA), achieving a low detection limit of 1.696 pg mL-1. This work demonstrates a promising approach for detecting PSA in a clinical diagnosis.

Pd "Kills Two Birds with One Stone" for the Synthesis of Catalyst: Dual Active Sites of Pd Triggers the Kinetics of O2 Electrocatalysis

Noble metal-based catalyst, despite their exorbitant cost, are the only successful catalyst for bifunctional oxygen electrocatalysis owing to their capability to drive forward the reaction rate kinetically. Therefore, it is desirable to diminish the noble metal loading without any compromise in the catalyst performance. In this study, the aim to achieve two goals with one action via a single-step route to have ultra-low loading of Pd in the catalyst. The Pd is used as a catalyst for C─C bond formation followed by complexation reactions or vice versa, in conventional Suzuki-Miyaura cross-coupling (SMCC) reaction, which yields a Pd-based porous organic polymer. Interestingly, it is found that dispersed Pd nanocluster (PdNC ) is present together with Pd single atom doped into nanocarbon (Pd-NC) matrix in the catalyst (PdNC /Pd-NC800 ) that obtained after pyrolysis of the porous polymer. The catalyst exhibits remarkable bifunctional activity and durability towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Further, it is studied that the in situ attenuated total reflection infrared (ATR-IR) spectroscopy at different electrochemical potentials during ORR and OER to observe the reaction intermediates. The homemade zinc-air battery with the catalyst displayed great performance, establishing the significance of PdNC /Pd-NC800 as a bifunctional oxygen electrocatalyst.

Single-Chain Conjugated Polymer Guests Confined inside Metal-Organic Frameworks (MOFs): Boosting the Detection and Degradation of a Sulfur Mustard Simulant

Real-time detection and effective degradation of toxic gases have attracted considerable attention in environmental monitoring and human health. Here, we demonstrate a solvent-assisted dynamic assembly strategy to strongly enhance the detection and degradation performance for 2-chloroethyl ethyl sulfide (CEES, as a sulfur mustard simulant) via confinement of a conjugated polymer in metal-organic frameworks (MOFs). The conjugated polymer poly(9,9-di-n-octylfluorene-altbenzothiadiazole) (F8BT) is infiltrated into one-dimensional nanochannels of the Zr-based topological MOF NU-1000 in a single-chain manner, which is caused by the nanoconfinement effect and the steric hindrance between 9,9-dioctylfluorene units and benzothiadiazole units. The obtained F8BT⊂NU-1000 composites provide a high specific surface area and abundant active sites. Based on the cooperative effect of F8BT and NU-1000, rapid and sensitive detection of CEES has been achieved. Moreover, the F8BT⊂NU-1000 composites can selectively oxidize CEES into 2-chloroethyl ethyl sulfoxide (CEESO) under mild photooxidation conditions. Overall, this study opens a new avenue for the fabrication of conjugated polymer/MOF hybrid materials that show great potential for the sensitive detection and effective removal of hazardous chemicals.

Revealing the Orbital Interactions between Dissimilar Metal Sites during Oxygen Reduction Process

A FeCo/DA@NC catalyst with the well-defined FeCoN6 moiety is customized through a novel and ultrafast Joule heating technique. This catalyst demonstrates superior oxygen reduction reaction activity and stability in an alkaline environment. The power density and charge-discharge cycling of znic-air batteries driven by FeCo/DA@NC also surpass those of Pt/C catalyst. The source of the excellent oxygen reduction reaction activity of FeCo/DA@NC originates from the significantly changed charge environment and 3d orbital spin state. These not only improve the bonding strength between active sites and oxygen-containing intermediates, but also provide spare reaction sites for oxygen-containing intermediates. Moreover, various in situ detection techniques reveal that the rate-determining step in the four-electron oxygen reduction reaction is *O2 protonation. This work provides strong support for the precise design and rapid preparation of bimetallic catalysts and opens up new ideas for understanding orbital interactions during oxygen reduction reactions.

Metal-Free Covalent Organic Frameworks for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is the key reaction in metal air and fuel cells. Among the catalysts that promote ORR, carbon-based metal-free catalysts are getting more attention because of their maximum atom utilization, effective active sites and satisfactory catalytic activity and stability. However, the pyrolysis synthesis of these carbons resulted in disordered porosities and uncontrolled catalytic sites, which hindered us in realizing the catalysts' design, the optimization of catalyst performance and the elucidation of structure-property relationship at the molecular level. Covalent organic frameworks (COFs) constructed with designable building blocks have been employed as metal-free electrocatalysts for the ORR due to their controlled skeletons, tailored pores size and environments, as well as well-defined location and kinds of catalytic sites. In this Concept article, the development of metal-free COFs for the ORR is summarized, and different strategies including skeletons regulation, linkages engineering and edge-sites modulation to improve the catalytic selectivity and activity are discussed. Furthermore, this Concept provides prospectives for designing and constructing powerful electrocatalysts based on the catalytic COFs.

Well-defined N3 C1 -anchored Single-Metal-Sites for Oxygen Reduction Reaction

N-, C-, O-, S-coordinated single-metal-sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well-defined such SMSs, and the fundamental comprehension has long been impeded in case-by-case reports using carbon materials as investigation targets. In this work, the well-defined molecular catalysts with N3 C1 -anchored SMSs, i.e., N-confused metalloporphyrins (NCPor-Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor-Ms with corresponding N4 -anchored SMSs (metalloporphyrins, Por-Ms), are synthesized for catalytic activity evaluation. Among all, NCPor-Co reaches the top in established volcano plots. NCPor-Co also shows the highest half-wave potential of 0.83 V vs. RHE, which is much better than that of Por-Co (0.77 V vs. RHE). Electron-rich, low band gap and regulated d-band center contribute to the high activity of NCPor-Co. This study delves into the examination of well-defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high-performance asymmetric SMS catalysts.

Tuning Coordination Structures of Zn Sites Through Symmetry-Breaking Accelerates Electrocatalysis

Manipulating the coordination environment of individual active sites in a precise manner remains an important challenge in electrocatalytic reactions. Herein, inspired by theoretical predictions, a facile procedure to synthesize a series of symmetry-breaking zinc metal-organic framework (Zn-MOF) catalysts with well-defined structures is presented. Benefiting from the optimized coordination microenvironment regulated by symmetry-breaking, Zn-N2 S2 -MOF exhibits the best performance of nitrogen (N2 ) reduction reaction (NRR) with NH3 yield rate of 25.07 ± 1.57 µg h-1  cm-2 and Faradaic efficiency of 44.57 ± 2.79% compared with reported Zn-based NRR catalysts. X-ray absorption near-edge structure shows that the symmetry-breaking distorts the coordination environment and modulates the delocalized electrons around the Zn sites, which favors the formation of unpaired low-valence Znδ+ , thereby facilitating the adsorption/activation of N2 . Theoretical calculations elucidate that low-valence Znδ+ in Zn-N2 S2 -MOF can effectively lower the energy barrier of potential determining step, promoting the kinetics and boosting the NRR activity. This work highlights the relationship between the precise coordination environment of metal sites and the catalytic activity, which offers insightful guidance for rationally designing high-efficiency electrocatalysts.

Defect-Engineered Charge Transfer in a PtCu/PrxCe1-xO2 Carbon-Free Catalyst for Promoting the Methanol Oxidation and Oxygen Reduction Reactions

Platinum (Pt) and Pt-based alloys have been extensively studied as efficient catalysts for both the anode and cathode of direct methanol fuel cells (DMFC). Defect engineering has been revealed to be practicable in tuning the charge transfer between Pt and transition metals/supports, which leads to the charge density rearrangement and facilitates the electrocatalytic performance. Herein, Pr-doped CeO2 nanocubes were used as the noncarbon support of a PtCu catalyst. The concentration and structure of oxygen vacancy (Vo) defects were engineered by Pr doping. Besides the Vo monomer, the oxygen vacancy with a linear structure is also observed, leading to the one-dimensional PtCu. The Vo concentration shows the volcanic scenario as Pr increased. Accordingly, the activities of PtCu/PrxCe1-xO2 toward methanol oxidation and oxygen reduction reactions exhibit the volcanic scenario. PtCu/Pr0.15Ce0.85O2 exhibits the optimal catalytic performance with the specific activity 3.57 times higher than that of Pt/C toward MOR and 1.34 times higher toward ORR. The MOR and ORR mass activities of PtCu/Pr0.15Ce0.85O2 reached 1.05 and 0.12 A·mg-1, which are 3.09 and 0.92 times the values of Pt/C, respectively. The abundant Vo afforded surplus electrons, which tailored the electron transfer between PtCu and PrxCe1-xO2, leading to enhanced catalytic performance of PtCu/PrxCe1-xO2. DFT calculations on PtCu/Pr0.15Ce0.85O2 revealed that Pr doping reduced the band gap of CeO2 and lowered the overpotential.

Electrocatalytic Deep Dehalogenation and Mineralization of Florfenicol: Synergy of Atomic Hydrogen Reduction and Hydroxyl Radical Oxidation over Bifunctional Cathode Catalyst

It is difficult to achieve deep dehalogenation or mineralization for halogenated antibiotics using traditional reduction or oxidation processes, posing the risk of microbial activity inhibition and bacterial resistance. Herein, an efficient electrocatalytic process coupling atomic hydrogen (H*) reduction with hydroxyl radical (•OH) oxidation on a bifunctional cathode catalyst is developed for the deep dehalogenation and mineralization of florfenicol (FLO). Atomically dispersed NiFe bimetallic catalyst on nitrogen-doped carbon as a bifunctional cathode catalyst can simultaneously generate H* and •OH through H2O/H+ reduction and O2 reduction, respectively. The H* performs nucleophilic hydro-dehalogenation, and the •OH performs electrophilic oxidization of the carbon skeleton. The experimental results and theoretical calculations indicate that reductive dehalogenation and oxidative mineralization processes can promote each other mutually, showing an effect of 1 + 1 > 2. 100% removal, 100% dechlorination, 70.8% defluorination, and 65.1% total organic carbon removal for FLO are achieved within 20 min (C0 = 20 mg·L-1, -0.5 V vs SCE, pH 7). The relative abundance of the FLO resistance gene can be significantly reduced in the subsequent biodegradation system. This study demonstrates that the synergy of reduction dehalogenation and oxidation degradation can achieve the deep removal of refractory halogenated organic contaminants.

Distortion-Induced Interfacial Charge Transfer at Single Cobalt Atom Secured on Ordered Intermetallic Surface Enhances Pure Oxygen Production

In this work, atomic cobalt (Co) incorporation into the Pd2Ge intermetallic lattice facilitates operando generation of a thin layer of CoO over Co-substituted Pd2Ge, with Co in the CoO surface layer functioning as single metal sites. Hence the catalyst has been titled Co1-CoO-Pd2Ge. High-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy confirm the existence of CoO, with some of the Co bonded to Ge by substitution of Pd sites in the Pd2Ge lattice. The role of the CoO layer in the oxygen evolution reaction (OER) has been verified by its selective removal using argon sputtering and conducting the OER on the etched catalyst. In situ X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopy demonstrate that CoO gets transformed to CoOOH (Co3+) in operando condition with faster charge transfer through Pd atoms in the core Pd2Ge lattice. In situ Raman spectroscopy depicts the emergence of a CoOOH phase on applying potential and shows that the phase is stable with increasing potential and time without getting converted to CoO2. Density functional theory calculations indicate that the Pd2Ge lattice induces distortion in the CoO phase and generates unpaired spins in a nonmagnetic CoOOH system resulting in an increase in the OER activity and durability. The existence of spin density even after electrocatalysis is verified from electron paramagnetic resonance spectroscopy. We have thus successfully synthesized intermetallic supported CoO during synthesis and rigorously verified the role played by an intermetallic Pd2Ge core in enhancing charge transfer, generating spin density, improving electrochemical durability, and imparting mechanical stability to a thin CoOOH overlayer. Differential electrochemical mass spectrometry has been explored to visualize the instantaneous generation of oxygen gas during the onset of the reaction.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Zn/N/S Co-doped hierarchical porous carbon as a high-efficiency oxygen reduction catalyst in Zn-air batteries

Zn-N-C catalysts have garnered attention as potential electrocatalysts for the oxygen reduction reaction (ORR). However, their intrinsic limitations, including poor activity and a low density of active sites, continue to hinder their electrocatalytic performance. In this study, we have devised a dual-template strategy for the synthesis of Zn, N, S co-doped nanoporous carbon-based catalysts (Zn-N/S-C(S, Z)) with a substantial specific surface area and a graded pore structure. The introduction of S enhances electron localization around the Zn-Nx active centers, facilitating interactions with oxygen-containing substances. The resulting Zn-N/S-C(S, Z) sample exhibits outstanding performance in an alkaline solution, demonstrating a half-wave potential of 0.89 V. This value surpasses that of commercial Pt/C by 40 mV. Furthermore, when combined with RuO2 (Zn-N/S-C(S, Z) + RuO2), the catalyst demonstrates exceptional performance in a Zn-air battery, offering an open-circuit voltage (OCV) of 1.47 V and a peak power density of 290.8 mW cm-2. This study paves the way for the development of highly dispersed and highly active Zn-metal site catalysts, potentially replacing traditional Pt-based catalysts in various electrochemical devices.

Highly efficient and continuous activation of O2 by a novel FexP-FeCu composite for water purification and insights into the activation mechanisms through DFT calculation

Degradation of organic pollutants through O2 activation catalyzed by transitional metals is challenging without addition of external chemicals and input of energy. We prepare a novel Fe based catalyst by compositing carbon, iron phosphide (FexP), iron carbide (FexC), Fe0 and Cu NPs, which can continuously activate O2 to produce high amount of 1O2,·O2- and·OH radicals in a wide pH range. DFT calculation discloses that O2 molecules are dissociated into *O or exist as O-O in various configurations. The Fe-O2, Cu-O2 and FeP-O2 surfaces can react with H2O molecules to generate *OOH, *OH and/or OH-. The sorbed-O2 intermediates on FexC surface might be released as 1O2 or·O2-. The oxidative O2-sorbed surfaces and in-situ produced oxygen reactive species contribute to the efficient and pH-indenpendent degradation of organic pollutants. Cu NPs accelerate Fe2+/Fe3+ cycles and offer impetus to initiate O2 activation due to the potential difference between Fe and Cu. The recycling test and XPS results confirm that the mutual electron transferring among carbon, FexC, FexP, Fe and Cu maintains reactivity and stability of the catalysts.

Architecting FeNx on High Graphitization Carbon for High-Performance Oxygen Reduction by Regulating d-Band Center

Fe single atoms and N co-doped carbon nanomaterials (Fe-N-C) are the most promising oxygen reduction reaction (ORR) catalysts to replace platinum group metals. However, high-activity Fe single-atom catalysts suffer from poor stability owing to the low graphitization degree. Here, an effective phase-transition strategy is reported to enhance the stability of Fe-N-C catalysts by inducing increased degree of graphitization and incorporation of Fe nanoparticles encapsulated by graphitic carbon layer without sacrificing activity. Remarkably, the resulted Fe@Fe-N-C catalysts achieved excellent ORR activity (E_1/2  = 0.829 V) and stability (19 mV loss after 30K cycles) in acid media. Density functional theory (DFT) calculations agree with experimental phenomena that additional Fe nanoparticles not only favor to the activation of O₂ by tailoring d-band center position but also inhibit the demetallization of Fe active center from FeN₄ sites. This work provides a new insight into the rational design of highly efficient and durable Fe-N-C catalysts for ORR.

Recent Advances of Electrocatalyst and Cell Design for Hydrogen Peroxide Production

Electrochemical synthesis of H2O2 via a selective two-electron oxygen reduction reaction has emerged as an attractive alternative to the current energy-consuming anthraquinone process. Herein, the progress on electrocatalysts for H2O2 generation, including noble metal, transition metal-based, and carbon-based materials, is summarized. At first, the design strategies employed to obtain electrocatalysts with high electroactivity and high selectivity are highlighted. Then, the critical roles of the geometry of the electrodes and the type of reactor in striking a balance to boost the H2O2 selectivity and reaction rate are systematically discussed. After that, a potential strategy to combine the complementary properties of the catalysts and the reactor for optimal selectivity and overall yield is illustrated. Finally, the remaining challenges and promising opportunities for high-efficient H2O2 electrochemical production are highlighted for future studies.