Atomically Dispersed Zn/Co-N-C as ORR Electrocatalysts for Alkaline Fuel Cells

Cobalt nanoclusters promoted coordination-field enhancement of manganese single atoms for robust alkaline oxygen reduction reaction

Bimetallic component catalysts, especially those with heteronucleation active sites, have recently attracted significant attention due to multi-component synergism and fast electron transfers. Herein, we report an architecture of dual-metal Mn/Co components loaded catalyst (MnSACsCoNPs-20) derived from metal-organic frameworks (MOFs) through simple wet-chemical synthesis followed by pyrolysis. By using various advanced characterization techniques, we confirm that Co exists in the form of nanoclusters and Mn exists as single atoms on the nitrogen-doped carbon support. Compared with single-metal counterparts, our MnSACsCoNPs-20 shows significantly higher electrocatalytic performance in the oxygen reduction reaction (ORR), with a half-wave potential as high as 0.912 V, even superior to the commercial Pt/C catalyst. X-ray absorption spectroscopy experiments and density functional theory (DFT) calculations indicate that the MnN4 site mainly acts as the functional unit. As the Co nanoclusters tune the coordination field of the Mn active site by changing the charge distribution, their synergy significantly accelerates ORR kinetics. DFT calculations demonstrate that Co nanoclusters effectively lower the d-band center of Mn sites, thereby optimizing the adsorption and desorption energies of key oxygen intermediates (*OOH, *O, *OH). Such precise modulation reduces the Gibbs free energy barriers associated with ORR steps, facilitating a highly efficient four-electron transfer pathway under alkaline conditions. It opens up a new path for the design of high-performance, low-cost ORR catalysts and also provides a new insight into the ORR mechanism.

Static magnetic field-enhanced cathodic electrocatalysis of Fe3O4-based nitrogen-doped carbon for improving the performance of microbial fuel cells

Enhancing oxygen reduction reaction (ORR) electrocatalysis through an external static magnetic field to improve the performance of microbial fuel cells (MFCs) is technically feasible, but its application in MFCs remains largely unexplored. Herein, we present a Fe3O4-based nitrogen-doped carbon (Fe3O4@NC2) magnetic catalyst that significantly boosts ORR catalytic activity, increasing the half-wave potential (E1/2) of the ORR by approximately 20 mV with a magnetic field strength of 140 mT. When the Fe3O4@NC2 cathode is combined with an external magnetic field into the MFCs, the maximum power density of the MFC can reach 553.17 ± 7.16 mW m-2. This performance notably exceeds that of the same MFCs operated without a magnetic field (522.26 ± 4.25 m-2) and that of MFCs equipped with a Pt/C cathode (447.29 ± 2.16 mW m-2). This study introduces an effective and straightforward cathodic magnetic enhancement approach, offering promising avenues for advancing MFCs technology.

Enhancing Rechargeable Zinc-Air Batteries with Atomically Dispersed Zinc Iron Cobalt Planar Sites on Porous Nitrogen-Doped Carbon

Rechargeable zinc-air batteries (ZABs) face significant challenges in achieving both high power density and long-term stability, primarily due to limitations in catalytic materials for oxygen electrodes. Here, we present a trimetal planar heterogeneous metal catalyst featuring atomically dispersed ZnN4, FeN4, and CoN4 sites supported on a porous nitrogen-doped carbon substrate (ZnFeCo-NC) through a templating approach. By fine-tuning the content of each metal, the optimized ZnFeCo-NC-based ZAB achieves a high peak power density of 244 mW cm-2 and maintains durable performance for 500 h at 10 mA cm-2. Ab initio molecular dynamics simulations reveal that the ZnFeCo-NC catalyst configuration remains stable at 300 K during the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) process. Further theoretical calculations demonstrate that the introduction of adsorbed OH groups effectively tunes the electronic structure redistribution of metal active sites, particularly improving the catalytic performance at the Fe site for ORR and the Co site for the OER. These findings provide insights into the rational design of high-performance electrocatalysts in energy storage technologies.

Nanoengineering of P, Se co-doped hollow microspheres induced charge redistribution with P-Se-M bond as multifunctional electrocatalysts

Exploring a multifunctional catalyst that possesses excellent catalytic activities for the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and oxygen evolution reaction (OER) is essential for the storage and conversion of renewable energy. Here, a newfangled trifunctional P decorated and nitrogen-doped carbon (NC) coated selenide material (CoSe2@FeSe2/P2.5/NC) was fabricated by in-situ heteroatom doping and selenylation strategy. CoFe2O4 particles were firstly fabricated by hydrothermal, next blended with 2-methylimidazole and Zn(NO3)2·6H2O, followed by two-step pyrolysis and phosphating to form the CoSe2@FeSe2/P2.5/NC catalyst. The hollow structure possesses a large void size and a specific surface area was constructed by encapsulating CoFe2O4 particles with a zeolitic imidazolate framework-8 (ZIF-8) derived NC cube layer. The bonding of Se with the highly electronegative P and metal causes the charge to redistribute through the P-Se-M (M= Co, Fe) structure, thereby weakening the adsorption energy of P-containing substances. Its unique hollow structure and high conductivity made the screened CoSe2@FeSe2/P2.5/NC have superior ORR properties with the onset potential (E0) of 0.96 V and half-wave potential (E1/2) of 0.85 V. In alkaline electrolytes, the lower overpotential of 289 mV (10 mA/cm2) and the 526 mV (100 mA/cm2) also exhibited distinguished OER and HER catalytic activities. Besides, the density functional theory (DFT) results concurrently demonstrated that CoSe2@FeSe2/P2.5/NC optimized the adsorption of O*/OOH* (adsorbed O/OOH atoms) intermediates for OER and H* (adsorbed H atoms) intermediates for HER. The excellent trifunctional catalytic effect was put down to the charges redistribution effect at the interface of various components constructed by the Se element and the effect of the P element on enhancing conductivity. This study reveals that heteroatom-doped nanoengineering is an effective technique for optimizing electronic structures and boosting the electrocatalytic performance of catalysts.

Engineering Local Coordination and Electronic Structures of Dual-Atom Catalysts

Heterogeneous dual-atom catalysts (DACs), defined by atomically precise and isolated metal pairs on solid supports, have garnered significant interest in advancing catalytic processes and technologies aimed at achieving sustainable energy and chemical production. DACs present board opportunities for atomic-level structural and property engineering to enhance catalytic performance, which can effectively address the limitations of single-atom catalysts, including restricted active sites, spatial constraints, and the typically positive charge nature of supported single metal species. Despite the rapid progress in this field, the intricate relationship between local atomic environments and the catalytic behavior of dual-metal active sites remains insufficiently understood. This review highlights recent progress and major challenges in this field. We begin by discussing the local modulation of coordination and electronic structures in DACs and its impact on catalytic performance. Through specific case studies, we demonstrate the importance of optimizing the entire catalytic ensemble to achieve efficient, selective, and stable performance in both model and industrially relevant reactions. Additionally, we also outline future research directions, emphasizing the challenges and opportunities in synthesis, characterization, and practical applications, aiming to fully unlock the potential of these advanced catalysts.

Engineering Triple Phase Interface and Axial Coordination Design of Single-Atom Electrocatalysts for Rechargeable Zn─air Batteries

Bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desirable for rechargeable Zn─air batteries (rZABs). Herein, a space optimized 3D heterostructure Co-N-C@MoS2 catalyst with Co single atom and Co cluster sites is developed by pyrolysis of ZIF-67 and in situ grown ultrathin MoS2 nanosheets. The introduced MoS2 not only has abundant defective structures, but also regulates the Co electronic distribution, thus introducing additional active sites and enhancing Co-Nx activity. In addition, the MoS2 modification leads to an appropriate increase in hydrophilicity which can make a stable liquid/gas/solid triple phase interface, facilitating the approachability of electrolytes into the porous channels and promotes the mass transfer through ensuring a favorite contact among the catalyst, electrolyte and reactants and enhancing utility of active reaction sites. Comprehensive analysis and theoretical simulation indicate that the enhancement of activity stems from the axial coordination of Co cluster over Co single-atom active sites to regulate local electronic structure, thereby optimizing the adsorption of ORR intermediates and enhancing the catalytic activity. Compared with the commercial Pt/C and IrO2, the structurally optimized Co-N-C@MoS2 catalyst displays exceptional bifunctional electrocatalytic activity and long-time stability toward both OER and ORR. Moreover, the Co-N-C@MoS2 catalyst exhibits higher peak power density and superior stability in liquid and flexible ZABs compared to the commercial Pt/C + IrO2 catalyst.

Interfacial Charge Transfer in ZnO/COF S-Scheme Photocatalyst via Zn─N Bond

Photocatalysis is a promising solution to global energy shortage and environmental problems. Inspired by photosynthesis, multicomponent heterostructured photocatalysts are extensively investigated, and step-scheme (S-scheme) heterojunction has emerged as the theoretical basis for delineating charge transfer processes in predominant heterostructured photocatalysts. However, the specific charge transfer pathway across an S-scheme heterojunction remains elusive from an atomic/molecular perspective. Herein, it is demonstrated that in S-scheme heterojunction photocatalysts composed of imine-based covalent organic frameworks and nanostructured zinc oxide, interfacial Zn─N bonds are formed between the two components and play critical roles as a charge transfer gateway in the S-scheme heterojunction, based on theoretical calculations, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Moreover, mechanisms for enhanced charge transfer across the S-scheme heterojunction are elucidated using femtosecond transient absorption spectroscopy. This work provides new insights into molecular-level understanding of charge transfer mechanisms in S-scheme heterojunction photocatalysts for promoting energy and environmental applications of artificial photosynthesis.

Highly Defective Ultrafine Carbon Nanoreactors Enriched with Edge-Type Zn-N3P1 Moiety Boosting Oxygen Electrocatalysis

High-active nonplatinum group metal oxygen reduction reaction (ORR) catalysts have great potential to improve fuel cell and metal-air battery performance due to their efficiency and cost-effectiveness. However, a fundamental understanding of their size-dependent structure-performance relationships remain elusive. Here a mesoporous-dominant carbon nanoreactor with dimensions in the range of 15-43 nm with edge-rich defective atomic Zn sites is designed. The crystal size and pore diameter of this carbon nanoreactors can be precisely adjusted to enable tunable mass diffusion pathways and porosities. Importantly, the hydrophobic nature of 25 nm nanoreactors maximizes the nonkinetic advantages of active site exposure and rapid O2 mass transfer at the triple-phase interface. The developed Zn-N-P/NPC catalysts delivers outstanding alkaline and acidic ORR performance with half-wave potentials of 0.92 and 0.80 V, respectively, as well as excellent zinc-air battery performance with charge/discharge over 400 h under 20 mA cm-2. X-ray absorption spectroscopy and theoretical calculations indicate that the enhanced ORR catalytic activity of Zn-N-P/NPC stems from the introduction of P atoms and edge carbon defects effectively exciting the localized electronic asymmetric distribution of Zn species. The findings provide new perspectives on the size effect of porous carbon supports for the development of efficient cathodes catalysts with multifunctionality.

Altering the Symmetry of Fe-N-C by Axial Cl-Mediation for High-Performance Zinc-Air Batteries

Fe-N-C catalyst is acknowledged as a promising alternative for the state-of-the-art Pt/C in oxygen reduction reaction (ORR) toward cutting-edge electrochemical energy conversion/storage applications. Herein, a "Cl-mediation" strategy is proposed on Fe-N-C for modulating the catalyst's electronic structure toward achieving remarkable ORR activity. By coordinating axial Cl atoms to iron phthalocyanine (FePc) molecules on carbon nanotubes (CNTs) matrix, a Cl-modulated Fe-N-C (FePc-Cl-CNTs) catalyst is synthesized. The as-prepared FePc-Cl-CNTs exhibit an improved ORR activity with a half-wave potential of 0.91 V versus RHE in alkaline solution, significantly outperforming the parent FePc-CNTs (0.88 V versus RHE). The advanced nature of the as-prepared FePc-Cl-CNTs is evidenced by a configured high-performance rechargeable Zn-air battery, which operates stably for over 150 h. The experiments and density functional theory calculations unveil that axial Cl atoms induce the transformation of FePc from its original D4h to C4v symmetry, effectively altering the electrons distribution around the Fe-center, by which it optimizes *OH desorption and subsequently boosts the reaction kinetics. This work paves ways for resolving the dilemma of Fe-N-C catalysts' exploration via engineering Fe-N-C configuration.

Cluster-Scale Multisite Interface Reinforces Ruthenium-Based Anode Catalysts for Alkaline Anion Exchange Membrane Fuel Cells

Ruthenium (Ru) is a more cost-effective alternative to platinum anode catalysts for alkaline anion-exchange membrane fuel cells (AEMFCs), but suffers from severe competitive adsorption of hydrogen (Had) and hydroxyl (OHad). To address this concern, a strongly coupled multisite electrocatalyst with highly active cluster-scale ruthenium-tungsten oxide (Ru-WOx) interface, which could eliminate the competitive adsorption phenomenon and achieve high coverage of OHad and Had at Ru and WOx domains, respectively, is designed. The experimental and theoretical results demonstrate that WOx domain functions as a proton sponge to perpetually accommodate the activated hydrogen species that spillover from the adjacent Ru domain, and the resulting WO-Had species are readily coupled with Ru-OHad at the heterointerface to finish the hydrogen oxidation reaction with faster kinetics via the thermodynamically favorable Tafel-Volmer mechanism. The AEMFC delivers a high peak power density of 1.36 W cm-2 with a low anode catalyst loading of 0.05 mgRu cm-2 and outstanding durability (negligible voltage decay over 80-h operation at 500 mA cm-2). This work offers completely new insights into understanding the alkaline HOR mechanism and designing advanced anode catalysts for AEMFCs.

Rational Design of Covalent Organic Frameworks-Based Single Atom Catalysts for Oxygen Evolution Reaction and Oxygen Reduction Reaction

The rational design of high-performance catalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is essential for the development of clean and renewable energy technologies, particularly in fuel cells and metal-air batteries. Two-dimensional (2D) covalent organic frameworks (COFs) possess numerous hollow sites, which contribute to the stable anchoring of transition metal (TM) atoms and become promising supports for single atom catalysts (SACs). Herein, the OER and ORR catalytic performance of a series of SACs based on TQBQ-COFs were systematically investigated through density functional theory (DFT) calculations, with particular emphasis on the role of the coordination environment in modulating catalytic activity. The results reveal that Rh/TQBQ exhibits the most effective OER catalytic performance, with an overpotential of 0.34 V, while Au/TQBQ demonstrates superior ORR catalytic performance with an overpotential of 0.50 V. A critical mechanistic insight lies in the distinct role of boundary oxygen atoms in TQBQ, which perturb the adsorption energetics of reaction intermediates, thereby circumventing conventional scaling relationships governing OER and ORR pathways. Furthermore, we established the adsorption energy of TM atoms (Ead) as a robust descriptor for predicting catalytic activity, enabling a streamlined screening strategy for SAC design. This study emphasizes the significance of the coordination environment in determining the performance of catalysts and offers a new perspective on the design of novel and effective OER/ORR COFs-based SACs.

Spin polarization regulation of Fe-N4 by Fe3 atomic clusters for highly active oxygen reduction reaction

The Fe-N4 motif is regarded as a leading non-precious metal catalyst for the oxygen reduction reaction (ORR) with the potential to replace platinum (Pt), yet achieving or surpassing the performance of Pt-based catalysts remains a significant challenge. In this study, we introduce a modification strategy employing homogeneous few-atom Fe3 cluster to regulate the spin polarization of Fe-N4. Experimental research and theoretical calculations show that the incorporation of the Fe3 cluster significantly enhances the adsorption of Fe-N4 motif toward OH ligands, leading to a structural transformation from a square-planar field (Fe-N4) to a square-pyramid field structure (Fe(OH) -N4). This structural transformation reduces the spin polarization of 3dxz, 3dyz, and 3dz2 orbitals of Fe-N4, resulting in a decrease in unpaired electrons within 3d orbitals. As a result, this modulation leads to moderate adsorption/desorption energies of reaction intermediates, thereby facilitating the ORR process. Moreover, the in-situ spectroscopy confirms that the desorption of OH* on Fe3/Fe(OH) -NC motif is more favorable compared to atomic Fe-NC, indicating a lower energy barrier for ORR. Consequently, the Fe3/Fe-NC catalyst demonstrates outstanding ORR performance with a half-wave potential of 0.836 V vs. reversible hydrogen electrode (RHE) in 0.1 mol L-1 HClO4 solution and 0.936 V vs. RHE in 0.1 mol L-1 KOH solution, even surpassing commercial Pt/C catalyst. It also exhibits excellent Zn-air battery efficiency. Our study introduces a novel approach to modulating the electronic structure of single atoms catalysts by leveraging the robust interaction between single atoms and atomic clusters.

A Highly Dispersed Heterogeneous Cobalt Catalyst for Efficient Domino Hydroformylation Reductive Amination of Olefins

The hydroaminomethylation of alkenes using CO and H2 proceeds efficiently in the presence of a heterogeneous Co-N/C catalyst with highly dispersed metal centers. Various secondary and tertiary amines can be effectively synthesized from cyclic and linear aliphatic alkenes using this specific material. The active sites of the optimal catalyst result from the synergistic effect of atomically dispersed Co sites with their surrounding N atoms, and the high surface area as well as structural defects of the NC support. The broad applicability (>54 examples), including pharmaceutically relevant molecules, together with the high activity and reusability, underline the general applicability of this catalytic system.

Applications of Metal-Organic Frameworks and Their Derivatives in Fuel Cells

Metal-organic frameworks (MOFs) and their derivatives represent a novel class of porous crystalline materials characterized by exceptional porosity, high specific surface areas, and uniquely tunable physicochemical properties. These attributes render them highly promising for applications in the field of fuel cells. This review provides a comprehensive overview of the classification of MOFs and their current applications as catalysts, catalyst supports, and membranes in fuel cells. Additionally, the potential prospects and challenges associated with using MOFs and their derivatives in fuel cells are discussed, aiming to advance their development and offer valuable insights for researchers in this field.

Energetic MOF-derived Fe3C nanoparticles encased in N,S-codoped mesoporous pod-like carbon nanotubes for efficient oxygen reduction reaction

The rational design of advanced oxygen reduction reaction (ORR) catalysts is essential to improve the performance of energy conversion devices. However, it remains a huge challenge to construct hierarchical micro-/meso-/macroporous nanostructures, especially mesoporous transport channels in catalysts, to enhance catalytic capability. Herein, motivated by the characteristics of energetic metal-organic frameworks (EMOFs) that produce an abundance of gases during high-temperature pyrolysis, we prepared a unique tetrazine-based EMOF-derived electrocatalyst (denoted as Fe3C@NSC-900) consisting of highly dispersed Fe3C nanoparticles and N,S-codoped mesoporous carbon nanotubes. The mesopore-dominated core-shell structure endows Fe3C@NSC-900 with excellent catalytic activity and efficient mass transfer. Thus, optimal Fe3C@NSC-900 demonstrates a high half-wave potential of 0.922 V and great stability in 0.1 M KOH, outperforming commercial Pt/C and most of the reported ORR catalysts. As far as we know, this work is the first application of a tetrazine-based EMOF derivative for the electrocatalytic ORR and is expected to offer some constructive insights into potential of EMOFs for new-generation catalyst design.

Multiscale Understanding of Anion Exchange Membrane Fuel Cells: Mechanisms, Electrocatalysts, Polymers, and Cell Management

Anion exchange membrane fuel cells (AEMFCs) are among the most promising sustainable electrochemical technologies to help solve energy challenges. Compared to proton exchange membrane fuel cells (PEMFCs), AEMFCs offer a broader choice of catalyst materials and a less corrosive operating environment for the bipolar plates and the membrane. This can lead to potentially lower costs and longer operational life than PEMFCs. These significant advantages have made AEMFCs highly competitive in the future fuel cell market, particularly after advancements in developing non-platinum-group-metal anode electrocatalysts, anion exchange membranes and ionomers, and in understanding the relationships between cell operating conditions and mass transport in AEMFCs. This review aims to compile recent literature to provide a comprehensive understanding of AEMFCs in three key areas: i) the mechanisms of the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) in alkaline media; ii) recent advancements in the synthesis routes and structure-property relationships of cutting-edge HOR and ORR electrocatalysts, as well as anion exchange membranes and ionomers; and iii) fuel cell operating conditions, including water management and impact of CO2. Finally, based on these aspects, the future development and perspectives of AEMFCs are proposed.

Balancing Activity and Selectivity in Two-Electron Oxygen Reduction through First Coordination Shell Engineering in Cobalt Single Atom Catalysts

The electrochemical two-electron oxygen reduction reaction (2e- ORR) offers a potentially cost-effective and eco-friendly route for the production of hydrogen peroxide (H2O2). However, the competing 4e- ORR that converts oxygen to water limits the selectivity towards hydrogen peroxide. Accordingly, achieving highly selective H2O2 production under low voltage conditions remains challenging. Herein, guided by first-principles density functional theory (DFT) calculations, we show that modulation the first coordination sphere in Co single atom catalysts (Co-N-C catalysts with Co-NxO4-x sites), specifically the replacement of Co-N bonds with Co-O bonds, can weaken the *OOH adsorption strength to boost the selectivity towards H2O2 (albeit with a slight decrease in ORR activity). Further, by synthesizing a series of N-doped carbon-supported catalysts with Co-NxO4-x active sites, we were able to validate the DFT findings and explore the trade-off between catalytic activity and selectivity for 2e- ORR. A catalyst with trans-Co-N2O2 sites exhibited excellent catalytic activity and H2O2 selectivity, affording a H2O2 production rate of 12.86 m o l g c a t . - 1 h - 1 ${mol\ {g}_{cat.}^{-1}{h}^{-1}{\rm \ }}$ and an half-cell energy-efficiency of 0.07 m o l H 2 O 2 g c a t . - 1 J - 1 ${{mol}_{{H}_{2}{O}_{2}}\ {g}_{cat.}^{-1}\ {J}^{-1}}$ during a 100-hours H2O2 production test in a flow-cell.

Tailoring d-Band Center of Single-Atom Nickel Sites for Boosted Photocatalytic Reduction of Diluted CO2 from Flue Gas

Photocatalytic reduction of diluted CO2 from anthropogenic sources holds tremendous potential for achieving carbon neutrality, while the huge barrier to forming *COOH key intermediate considerably limits catalytic effectiveness. Herein, via coordination engineering of atomically scattered Ni sites in conductive metal-organic frameworks (CMOFs), we propose a facile strategy for tailoring the d-band center of metal active sites towards high-efficiency photoreduction of diluted CO2. Under visible-light irradiation in pure CO2, CMOFs with Ni-O4 sites (Ni-O4 CMOFs) exhibits an outstanding rate for CO generation of 13.3 μmol h-1 with a selectivity of 94.5 %, which is almost double that of its isostructural counterpart with traditional Ni-N4 sites (Ni-N4 CMOFs), outperforming most reported systems under comparable conditions. Interestingly, in simulated flue gas, the CO selectivity of Ni-N4 CMOFs decreases significantly while that of Ni-O4 CMOFs is mostly unchanged, signifying the supremacy for Ni-O4 CMOFs in leveraging anthropogenic diluted CO2. In situ spectroscopy and density functional theory (DFT) investigations demonstrate that O coordination can move the center of the Ni sites' d-band closer to the Fermi level, benefiting the generation of *COOH key intermediate as well as the desorption of *CO and hence leading to significantly boosted activity and selectivity for CO2-to-CO photoreduction.

Building Asymmetric Zn-N3 Bridge between 2D Photocatalyst and Co-catalyst for Directed Charge Transfer toward Efficient H2O2 Synthesis

Two-dimensional (2D) polymeric semiconductors are a class of promising photocatalysts; however, it remains challenging to facilitate their interlayer charge transfer for suppressed in-plane charge recombination and thus improved quantum efficiency. Although some strategies, such as π-π stacking and van der Waals interaction, have been developed so far, directed interlayer charge transfer still cannot be achieved. Herein, we report a strategy of forming asymmetric Zn-N3 units that can bridge nitrogen (N)-doped carbon layers with polymeric carbon nitride nanosheets (C3N4-Zn-N(C)) to address this challenge. The symmetry-breaking Zn-N3 moiety, which has an asymmetric local charge distribution, enables directed interfacial charge transfer between the C3N4 photocatalyst and the N-doped carbon co-catalyst. As evidenced by femtosecond transient absorption spectroscopy, charge separation can be significantly enhanced by the interfacial asymmetric Zn-N3 bonding bridges. As a result, the designed C3N4-Zn-N(C) catalyst exhibits dramatically enhanced H2O2 photosynthesis activity, outperforming most of the reported C3N4-based catalysts. This work highlights the importance of tailoring interfacial chemical bonding channels in polymeric photocatalysts at the molecular level to achieve effective spatial charge separation.

Activating the Mn Single Atomic Center for an Efficient Actual Active Site of the Oxygen Reduction Reaction by Spin-State Regulation

The ligand engineering for single-atom catalysts (SACs) is considered a cutting-edge strategy to tailor their electrocatalytic activity. However, the fundamental reasons underlying the reaction mechanism and the contemplation for which the actual active site for the catalytic reaction depends on the pyrrolic and pyridinic N ligand structure remain to be fully understood. Herein, we first reveal the relationship between the oxygen reduction reaction (ORR) activity and the N ligand structure for the manganese (Mn) single atomic site by the precisely regulated pyrrolic and pyridinic N4 coordination environment. Experimental and theoretical analyses reveal that the long Mn-N distance in Mn-pyrrolic N4 enables a high spin state of the Mn center, which is beneficial to reduce the adsorption strength of oxygen intermediates by the high filling state in antibond orbitals, thereby activating the Mn single atomic site to achieve a half-wave potential of 0.896 V vs RHE with outstanding stability in acidic media. This work provides a new fundamental insight into understanding the ORR catalytic origin of Mn SACs and the rational design strategy of SACs for various electrocatalytic reactions.

Modification d x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ Orbital Electronic States in Nickel-Based Hydroxides Via Cobalt/Iron Co-Doping for High-Efficiency Methanol Electrooxidation

The nickel hydroxide-based (Ni(OH)2) methanol-to-formate electrooxidation reaction (MOR) performance is greatly related to thed x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ orbital electronic states. Hence, optimizing thed x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ orbital electronic states to achieve enhanced MOR activities are highly desired. Here, cobalt (Co) and iron (Fe) doping are used to modify thed x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ orbital electronic states. Although both dopants can broaden thed x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ orbital; however, Co doping leads to an elevation in the energy level ofd x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ highest occupied crystal orbital (HOCO), whereas Fe doping results in its reduction. Such a discrepancy in the regulation ofd x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ orbital electronic states stems from the disparate partial electron transfer mechanisms amongst these transition metal ions, which possess distinct energy level and occupancy of d orbitals. Motivated by this finding, the NiCoFe hydroxide is prepared and exhibited an excellent MOR performance. The results showed that the Co dopants effectively suppress the partial electron transfer from Ni to Fe, combined with thed x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ orbital broadening induced by NiO6 octahedra distortion, endowing NiCoFe hydroxide with highd x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ HOCO and broadd x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ orbital. It is believed that the work gives an in-depth understanding ond x 2 - y 2 ${{d}_{{{x}^2} - {{y}^2}}}$ orbital electronic states regulation in Ni(OH)2, which is beneficial for designing Ni(OH)2-based catalysts with high MOR performance.

Inhibiting carbon corrosion of cobalt-nitrogen-carbon materials via Mn sites for highly durable oxygen reduction reaction in acidic media

Cobalt-nitrogen-carbon (CoNxC) materials are regarded as promising low-cost electrocatalysts for the oxygen reduction reaction (ORR). However, their susceptibility to deactivation and poor stability in acidic media limits their practical applications. In this study, we develop cobalt (Co) and manganese (Mn) embedded in nitrogen-doped carbon (CoMnNxC) dual-site catalysts by incorporating Mn into CoNxC and leverage a synergistic dual-catalysis strategy to optimize both activity and stability. The dynamic evolution of *OOH intermediate on the catalyst surface is monitored via in situ Raman spectroscopy, confirming that Mn introduction modulates the reaction pathway. Due to electron transfer from Mn to the Co-Nx center in CoMnNxC, *OOH activation on the surface is enhanced, and the two-electron ORR process is inhibited. Consequently, the CoMnNxC catalyst exhibits excellent ORR activity (E1/2 = 0.76 V vs. reversible hydrogen electrode) and a very low hydrogen peroxide (H2O2) yield (<2.9 %) in acidic electrolyte. Additionally, the dynamic evolution of *OH on the Mn-Nx site confirms that Mn-Nx can serve as a potential catalytic site for the hydrogen peroxide reduction reaction (HPRR), facilitating H2O2 decomposition. Differential electrochemical mass spectrometry (DEMS) demonstrates that this parallel catalytic pathway effectively weaks the oxidative corrosion of H2O2 on the carbon carrier. The results indicate that the negative half-wave potential shift of CoMnNxC catalysts in acidic electrolyte after 10,000 accelerated durability tests (ADT) is only 11 mV. The synergistic dual-catalytic strategy proposed in this work offers a novel approach for designing high-efficiency and stable transition metal-nitrogen-carbon catalysts.

Nitrogen, sulfur co-coordinated iron single-atom catalysts with the optimized electronic structure for highly efficient oxygen reduction in Zn-air battery and fuel cell

Atomically dispersed iron-nitrogen-carbon (FesbndNsbndC) materials have been considered ideal catalysts for the oxygen reduction. Unfortunately, designing and adjusting the electronic structure of single-atom Fe sites to boost the kinetics and activity still faces grand challenges. In this work, the coordination environment engineering is developed to synthesize the FeSA/NSC catalyst with the tailored N, S co-coordinated Fe atomic site (Fe-N3S site). The structural characterizations and theoretical calculations demonstrate that the incorporation of sulfur can optimize the charge distribution of Fe atoms to weaken the adsorption of OH* and facilitate the desorption of OH*, thus leading to enhanced kinetics process and intrinsic activity. As a result, the S-modified FeSA/NSC exhibits outstanding catalytic activity with the half-wave potentials (E1/2) of 0.915 V and 0.797 V, as well as good stability, in alkaline and acidic electrolytes, respectively. Impressively, the excellent performance of FeSA/NSC is further confirmed in Zn-air batteries (ZABs) and fuel cells, with high peak power densities (146 mW cm-2 and 0.259 W cm-2).

Constructing Asymmetric Fe-Nb Diatomic Sites to Enhance ORR Activity and Durability

Iron-nitrogen-carbon (Fe-N-C) materials have been identified as a promising class of platinum (Pt)-free catalysts for the oxygen reduction reaction (ORR). However, the dissolution and oxidation of Fe atoms severely restrict their long-term stability and performance. Modulating the active microstructure of Fe-N-C is a feasible strategy to enhance the ORR activity and stability. Compared with common 3d transition metals (Co, Ni, etc.), the 4d transition metal atom Nb has fewer d electrons and more unoccupied orbitals, which could potentially forge a more robust interaction with the Fe site to optimize the binding energy of the oxygen-containing intermediates while maintaining stability. Herein, an asymmetric Fe-Nb diatomic site catalyst (FeNb/c-SNC) was synthesized, which exhibited superior ORR performance and stability compared with those of Fe single-atom catalysts (SACs). The strong interaction within the Fe-Nb diatomic sites optimized the desorption energy of key intermediates (*OH), so that the adsorption energy of Fe-*OH approaches the apex of the volcano plot, thus exhibiting optimal ORR activity. More importantly, introducing Nb atoms could effectively strengthen the Fe-N bonding and suppress Fe demetalation, causing an outstanding stability. The zinc-air battery (ZAB) and hydroxide exchange membrane fuel cell (HEMFC) equipped with our FeNb/c-SNC could deliver high peak power densities of 314 mW cm-2 and 1.18 W cm-2, respectively. Notably, the stable operation time for ZAB and HEMFC increased by 9.1 and 5.8 times compared to Fe SACs, respectively. This research offers further insights into developing stable Fe-based atomic-level catalytic materials for the energy conversion process.

Synthesis of Metal-Nitrogen-Carbon Electrocatalysts with Atomically Regulated Nitrogen-Doped Polycyclic Aromatic Hydrocarbons

Tuning the active site structure of metal-nitrogen-carbon electrocatalysts has recently attracted increasing interest. Herein, we report a bottom-up synthesis strategy in which atomically regulated N-doped polycyclic aromatic hydrocarbons (N-PAHs) of NxC42-x (x = 1, 2, 3, 4) were used as ligands to allow tuning of the active site's structures of M-Nx and establish correlations between the structures and electrocatalytic properties. Based on the synthesis process, detailed characterization, and DFT calculation results, active structures of Nx-Fe1-Nx in Fe1-Nx/RGO catalysts were constructed. The results demonstrated that the extra uncoordinated N atoms around the Fe1-N4 moieties disrupted the π-conjugated NxC42-x ligands, which led to more localized electronic state in the Fe1-N4 moieties and superior catalytic performance. Especially, the Fe1-N4/RGO exhibited optimized performance for ORR with E1/2 increasing by 80 mV and Jk at 0.85 V improved 18 times (compared with Fe1-N1/RGO). This synthesis strategy utilizing N-PAHs holds significant promise for enhancing the controllability of metal-nitrogen-carbon electrocatalyst preparation.