Engineering unsymmetrically coordinated Cu-S1N3 single atom sites with enhanced oxygen reduction activity

Switching alkaline hydrogen oxidation reaction pathway via microenvironment modulation of Ru catalysts

Ruthenium (Ru) has emerged as a promising catalyst for alkaline hydrogen oxidation reaction (HOR). Nevertheless, its catalytic performance still remains substantially inferior to the requirements of practical applications. Strategic modulation of the Ru micro-environment offers significant potential for optimizing its intrinsic catalytic activity. In this study, by elaborately designing a micro-environment of asymmetrically coordinated cobalt single-atom (Co-N3O-C) structures for Ru, the obtained Ru/Co-N3O-C achieves an exceptional HOR activity of 0.98 mA μg-1Ru, which is 4.5-folds higher than Pt/C and 3.4-folds higher than Ru/Co-N4-C. Combined experimental and theoretical investigations uncover that the outstanding HOR activity originates from three positive influences brought by the precisely engineered asymmetric coordination of Co sites, as compared to the symmetric Co-N4-C environment, i.e., (i) through the electronic interaction between Ru and Co-N3O-C, the excessively high hydrogen binding energy (HBE) at Ru sites is suppressed, (ii) by lowering the d-band center of Co, the strong hydroxide binding energy (OHBE) on Co sites is alleviated and (iii) the hydrogen bonding network within the electronic double layer is more connective, facilitating the OH- transfer to react with Had, thus switching the HOR pathway from the OHBE mechanism to the apparent HBE mechanism. This work accentuates the critical role of microenvironment modulation in regulating the HOR pathway and provides a novel strategy for devising superior-performance HOR catalysts.

Deciphering Local Microstrain-Induced Optimization of Asymmetric Fe Single Atomic Sites for Efficient Oxygen Reduction

Disrupting the symmetric electron distribution of porphyrin-like Fe single-atom catalysts has been considered as an effective way to harvest high intrinsic activity. Understanding the catalytic performance governed by geometric microstrains is highly desirable for further optimization of such efficient sites. Here, we decipher the crucial role of local microstrain in boosting intrinsic activity and durability of asymmetric Fe single-atom catalysts (Fe-N3S1) by replacing one N atom with S atom. The high-curvature hollow carbon nanosphere substrate introduces 1.3% local compressive strain to Fe-N bonds and 1.5% tensile strain to Fe-S bonds, downshifting the d-band center and accelerating the kinetics of *OH reduction. Consequently, highly curved Fe-N3S1 sites anchored on hollow carbon nanosphere (FeNS-HNS-20) exhibit negligible current loss, a high half-wave potential of 0.922 V vs. RHE and turnover frequency of 6.2 e-1 s-1 site-1, which are 53 mV more positive and 1.7 times that of flat Fe-N-S counterpart, respectively. More importantly, multiple operando spectroscopies monitored the dynamic optimization of strained Fe-N3S1 sites into Fe-N3 sites, further mitigating the overadsorption of *OH intermediates. This work not only sheds new light on local microstrain-induced catalytic enhancement, but also provides a plausible direction for optimizing efficient asymmetric sites via geometric configurations.

Phosphorus-Doped Single Atom Copper Catalyst as a Redox Mediator in the Cathodic Reduction of Quinazolinones

The use of clean electric energy to activate inert compounds has garnered significant attention. Homogeneous redox mediators (RMs) in organic electrosynthesis are effective platforms for this purpose. However, understanding the RM's electronic structure under operational conditions, electron transport processes at the electrode surface, and substrate adsorption-desorption dynamics remains challenging. Here, we synthesized a Cu single-atom catalyst (SAC, named Cu─N─P@NC) with a CuN3P1 micro-coordination structure, employing it as a unique cathode redox mediator. Introducing phosphine atoms into the coordination system allowed modulation of the SAC's electronic metal-support interaction, optimizing catalyst-substrate adsorption-desorption dynamics and accelerating electrochemical reactions. Utilizing the heterogeneous SAC strategy, we achieved a novel electro-reduction coupling ring-opening reaction of inert quinazolinone frameworks. The Cu-SAC exhibited exceptionally high catalytic activity and substrate compatibility, operating smoothly at gram-scale production. Additionally, we applied the SAC to modify 11 natural product molecules. Integrating micro-coordination environment regulation and theoretical adsorption models elucidated the significant influence of electrode-RMs-substrate interactions on reaction kinetics and catalytic efficiency-a feat challenging for homogeneous RMs. This approach offers a novel pathway for advancing efficient organic electrosynthesis reactions and provides critical insights for mechanistic studies.

Photocatalytic H2O2 Production with >30% Quantum Efficiency via Monovalent Copper Dynamics

Photocatalytic O2 reduction to H2O2 is a green and promising technology with advantages in cost-effectiveness, sustainability, and environmental friendliness, but its efficiency is constrained by limited selectivity for the two-electron oxygen reduction reaction (ORR) pathway. Here, we anchored isolated Cu atoms with tunable oxidation states onto WO3 as effective active centers to enhance photocatalytic H2O2 production. Due to the charge compensation between single atoms and the support, the oxidation state of Cu species exhibited a loading-dependent transition between +2 and +1 valence. Experimental and theoretical analyses indicate that Cu(I) sites exhibit outstanding O2 adsorption and activation capabilities, transforming the thermodynamically unfavorable hydrogenation of the *OOH intermediate (the rate-determining step in the two-electron ORR pathway) into an exothermic process, thereby significantly improving selectivity and efficiency. The Cu(I)-SA/WO3 photocatalyst exhibited a H2O2 production rate of 102 μmol h-1 under visible light irradiation, much higher than other reported photocatalysts. More importantly, it achieves an impressive apparent quantum efficiency of 30% at 420 nm, making a significant breakthrough in this field. This work provides novel perspectives for designing single-atom catalysts for efficient H2O2 synthesis via electronic state modulation.

Asymmetrically tailored catalysts towards electrochemical energy conversion with non-precious materials

Electrocatalytic technologies, such as water electrolysis and metal-air batteries, enable a path to sustainable energy storage and conversion into high-value chemicals. These systems rely on electrocatalysts to drive redox reactions that define key performance metrics such as activity and selectivity. However, conventional electrocatalysts face inherent trade-offs between activity, stability, and scalability particularly due to the reliance on noble metals. Asymmetrically tailored electrocatalysts (ATEs) - systems that are being exploited for non-symmetric designs in composition, size, shape, and coordination environments - offer a path to overcome these barriers. Here, we summarize recent developments in ATEs, focusing on asymmetric coupling strategies employed in designing these systems with non-precious transition metal catalysts (TMCs). We explore tailored asymmetries in composition, size, and coordination environments, highlighting their impact on catalytic performance. We analyze the electrocatalytic mechanisms underlying ATEs with an emphasis on their roles in water-splitting and metal-air batteries. Finally, we discuss the challenges and opportunities in advancing the performance of these technologies through rational ATE designs.

Bioengineered iron-based heterojunction orientation in optimizing activation pathways for superoxide radical-mediated photoreduction of Cr(VI) from water

Photocatalytic technology has been widely employed for Cr(VI) remediation. However, the inadequate generation of reactive oxygen species associated with the Cr(VI) reduction, caused by the uncontrollable photo-Fenton reaction, significantly restricts the reduction efficiency. Herein, a bioengineered iron-based heterojunction (Bio-Fe2O3/Fe2(WO4)3) was fabricated via a two-step process of biomineralization and calcination, where tungstate was doped into the precursor during iron metabolism in acidophilic bacteria to optimize the heterojunction structure. Bio-Fe2O3/Fe2(WO4)3 exhibited a short-range ordered structure and superior photocatalytic performance, achieving 100 % reduction of 20 mg/L Cr(VI) within 60 min by photocatalytic oxalic acid (OA) under simulated light conditions. The system provided robust operation in complex environments, notably, operating effectively under mild solar radiation as an alternative to the simulated light. The heterojunction structure intensified the H2O2 activation and selectively boosted the yield of superoxide radical (O2·-), the primary Cr(VI)-reducing species, from 48.02 % to 72.96 %. The high oxidation state of Fe in Bio-Fe2O3/Fe2(WO4)3 contributed to stronger adsorption performance towards OA and H2O2, accompanied with the tendency to take the O2·--generated activation pathway. This work provides a broader perspective on the rational design of photocatalysts to modulate the OA photocatalysis and the H2O2 activation pathway, selectively elevating the yield of O2·- for Cr(VI) reduction.

Importance of local coordination microenvironment in regulating CO2 electroreduction catalyzed by Cr-corrole-based single-atom catalysts

Single-atom catalysts (SACs) with MN4 active sites are a promising type of electrocatalyst for CO2 reduction reactions (CO2RR). Here, we designed a novel corrole-based CO2RR single-atom catalyst Cr-N4-Cz with a metal center supported by conjugated N4-macrocyclic ligand of corrole, which can serve as an excellent model for regulating the active center microenvironment, thereby achieving the goal of regulating the catalytic activity and selectivity. Density functional theory (DFT) calculations are performed to investigate the stability of Cr-N3X-Cz (X = N, C, O, S, P) and the mechanism of local coordination microenvironment regulating catalytic selectivity. The calculation results show that Cr-N4-Cz demonstrates high electrocatalytic activity for CO2RR with a limiting potential of -0.25 V, and the main product is CO. However, the selectivity of CO2RR is compromised due to the low limiting potential (-0.28 V) of the competitive hydrogen evolution reaction (HER). By substituting one N atom of Cr-N4-Cz with C, O, S and P, the corresponding main products become HCOOH, CO, CO, and CH3OH (or CH4). Moreover, the competing HER reaction is suppressed, thus remarkably increasing the selectivity of electrocatalytic CO2RR. Further mechanism investigation reveals different atomic substitution alters local coordination microenvironment of Cr metal center, resulting in the rising of d-orbital center and stabilizing the key intermediates of the potential determining step (PDS) by enhancing the integrated crystal orbital Hamilton population (ICOHP) between Cr and adsorbed intermediates, thereby regulating the CO2RR process. Especially, P substitution improves charge transfer, thus facilitating hydrogenation CO2 to form CH3OH (or CH4) in CO2RR.

Precise Construction of Asymmetrically Coordinated PtCuZn Trimetallic Atom Catalysts for Efficient Oxygen Reduction

With advancements in the study of catalysts at atomic sites, the unique and predictable characteristics of atomic models have enabled the exploration of catalysts with monoatomic, diatomic, and polymetallic centers. In this study, a platinum-copper-zinc trimetallic catalyst (named PtCuZn/SNC) was synthesized by the spatial confinement method and polymer coating method. This triatomic catalyst facilitates electronic interaction and charge redistribution among the three metal atoms, optimizing the adsorption and desorption of reaction intermediates and thereby exhibiting excellent performance in acidic oxygen reduction reactions. In the oxygen reduction reaction test, a high half-wave potential of 0.859 V and an impressive energy density of 532 mW cm-2 were achieved in fuel cell tests, demonstrating the outstanding catalytic performance of the catalyst. These findings suggest that the design and synthesis of monodisperse triatomic catalysts provide a promising route to improve the efficiency of H2/O2 fuel cells.

Sulfur-modified charge-asymmetry FeNi nanoalloy catalysts anchored on N-doped carbon nanosheets for efficient electrochemical CO2 reduction

The electrochemical carbon dioxide reduction reaction (CO2RR) plays a crucial role in mitigating global CO2 emissions and achieving carbon neutrality. In this study, we present a sulfur-doped FeNi alloy on a nitrogen-doped carbon substrate (FeNi Alloy/SNC) as a highly active CO2RR catalyst. This advanced charge-asymmetric nanocluster catalyst features sulfur-doped Fe-Ni bimetallic sites. X-ray absorption spectroscopy (XAS) was used to verify the presence of these S-doped asymmetric bimetallic sites. The charge-asymmetric catalysts exhibited 98.1% CO conversion efficiency, which significantly surpassed that of S-containing Fe cluster/SNC, Ni cluster/SNC, and S-free FeNi/NC, Ni/NC, and Fe/NC catalysts. Furthermore, in situ synchrotron radiation XAS analysis revealed that the S-doped Fe-Ni bimetallic sites enhanced charge transfer between the metal centers, thereby facilitating the accelerated production of CO.

Catalytic Performance of Highly Dispersed Bimetallic Catalysts for CO Hydrogenation to DME

Highly dispersed bimetallic atomic-scale catalysts have garnered significant attention in syngas conversion filed due to the synergistic effects of the precisely structured bimetallic site, which facilitate the effective activation of CO. Despite their potential, synthesizing these catalysts to meet the specific application requirements remains challenging. Herein, various bimetallic catalysts were synthesized through the pyrolysis of the bimetallic ZIF precursors which were prepared by in situ doping of different metals (Mn, Fe, Co, Ni and Cu) into the ZIF-8 structure. In the presence of a highly dispersed and highly loaded Zn, the doping content in the ultimate second metallic catalysts varied between 0.15-1.20 wt % for different metals. The catalysts were systematically characterized using XRD, BET, TEM, XPS, Raman, ICP, and H2-TPD techniques. Among them, the Zn-NC regulated with Cu or Ni exhibited superior catalytic performance. Notably, the Cu-Zn-NC catalyst showed the highest activity, achieving a CO conversion of 32.8 % and optimal DME selectivity approaching 95.2 % in CO hydrogenation reactions. These enhanced performance metrics were attributed to the synergetic effects of bimetallic components. The incorporation of Cu not only preserved the original Zn-N structure but also preserved the catalytic performance unchanged. This preparation strategy is expected to filter out new research targets to use in diverse catalytic applications.

Construction of Asymmetric Fe-N3P1 Sites on Freestanding Nitrogen/Phosphorus Co-Doped Carbon Nanofibers for Boosting Oxygen Electrocatalysis and Zinc-Air Batteries

The construction of freestanding carbon nanofiber membrane with single-atomic metal active sites and interconnected microchannels as air electrodes is vital for boosting the performance of zinc-air batteries (ZABs). Herein, single-atomic Fe sites is prepared on freestanding hierarchical nitrogen/phosphorus co-doped carbon nanofibers (Fe SACs@PNCNFs) by loading Fe-doped zeolitic imidazolate framework-8 with leaf-like structures on electrospun polyacrylonitrile (PAN) nanofibers with subsequent multi-step pyrolysis in the presence of sodium monophosphate, which are confirmed to be in the form of Fe-N3P1 by X-ray adsorption spectra. The asymmetric N/P coordinated Fe sites is theoretically demonstrated to boost the ORR performance with a half-wave potential of 0.89 V due to the weakened *O adsorption while stabilizing *OOH adsorption arising from the increased charge density of Fe sites compared to symmetric N coordinated Fe sites with Fe-N4. Moreover, when liquid and quasi-solid ZABs are assembled, excellent battery performance is also achieved with peak power density of 163 and 72 mW cm-2 as well as good stability for more than 190 and 65 h, respectively.

Ligand Regulated the Coordination Environment of Cobalt-Group-MOF for Efficient Electrocatalytic Oxygen Reduction/Evolution Catalysis

In recent years, the TMN4 moieties have demonstrated significant catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in graphene, CxNy, and other carbon-based two-dimensional (2D) support materials. Modifying the coordination number and species of N atoms in the TMN4 moieties has proven to be an effective approach to regulate their catalytic activity. In this research, by incorporating different triphenylene ligands, we have successfully constructed TMA2B2 (TM = Co, Rh, Ir; A/B = N, O, S, Se) moieties with varying coordination environments within 2D metal organic frameworks (MOFs), which are linked by TM and triphenylene. These moieties serve as an effective model to elucidate the structure-property relationship of two-dimensional 2D-MOFs in OER and ORR. Our findings confirm that alterations in the coordination environment can finely tune the d-band electron distribution of the TM within the TMA2B2 unit, particularly activating the dyz and dz2 orbitals of O2, thereby influencing the interactions between TM and key intermediates. We discovered that the regulatory effect of the coordination environment is closely linked to the electronegativity of the coordinating atoms, which led us to establish reliable descriptors such as φ1 and φ2 to elucidate the impact of coordination environments on the performance of OER/ORR. This criterion can be applied to numerous other 2D-MOFs and provides an in-depth understanding of the structure-activity relationship facilitates the development of highly efficient bifunctional electrocatalysts for OER and ORR applications.

In Situ Time-Resolved X-ray Absorption Spectroscopy Unveils Partial Re-Oxidation of Tellurium Cluster for Prolonged Lifespan in Hydrogen Evolution

Efficient and long-lasting electrocatalysts are one of the key factors in determining their large-scale commercial viability. Although the fundamentals of deactivation and regeneration of electrocatalysts are crucial for understanding and sustaining durable activity, little has been conducted on metalloids compared to metal-derived ones. Herein, by virtue of in situ seconds-resolved X-ray absorption spectroscopy, we discovered the chemical evolution during the deactivation-regeneration cycles of tellurium clusters supported by nitrogen-doped carbon (termed Te-ACs@NC) as a high-performance electrocatalyst in the hydrogen evolution reaction (HER). Through in situ electrochemical reduction, Te-ACs@NC, which had been deactivated due to surface phase transitions in a previous HER process, was reactivated and regenerated for the next run, where partially oxidized Te was found, surprisingly, to perform better than its nonoxidized state. After 10 consecutive deactivation-regeneration cycles over 480 h, the Te-ACs@NC retained 85% of its initial catalytic activity. Theoretical studies suggest that local oxidation modulates the electronic distribution within individual Te clusters to optimize the adsorption energy of water molecules and reduce dissociation energy. This study provides fundamental insights into the rarely explored metalloid cluster catalysts during deactivation and regeneration and will assist in the future design and development of supported catalysts with high activity and long durability.

Oxygen-Mediated Hydrogen Spillover Promotes Stable Synthesis of Vinyl Chloride on Ru Single-Atom Catalysts

Ru single-atom catalysts hold great promise for the robust synthesis of vinyl chloride through acetylene hydrochlorination. However, the easy over-chlorination of Ru atoms during reaction suppress the catalytic activity and stability. Herein, we have synthesized an oxygen doped Ru single-atom catalyst by a sequential oxygen etching strategy, which delivers the remarkable yield of vinyl chloride monomer (>99.38 %) and stability (>900 h, 180 h-1), far beyond those reported Ru counterparts. Experimental results and theoretical calculations reveal that the asymmetric structure of single-atom Ru promotes an unconventional oxygen-mediated hydrogen spillover after the activation of hydrogen chloride, which enables the reaction to proceed through Eley-Rideal mechanism with a reduced energy barrier of acetylene hydrochlorination compared to the traditional Langmuir-Hinshelwood pathway. As a result, the enhanced reaction kinetics further restrict over-chlorination of single-atom Ru, thereby ensuring the excellent durability. This work offers a strategy for designing multifunctional catalysts with enhanced performances for acetylene hydrochlorination.

Single-Atom Catalysts for Converting CO2 into High Value-Added Products: From Photocatalysis and Electrocatalysis to Photoelectrocatalysis

Converting CO2 into valuable products via photo-, electro-, and photoelectrocatalysis offers the possibility of simultaneously mitigating global warming and energy shortages. Single-atom catalysts (SACs) have garnered significant interest from researchers owing to their optimal atom use, suitable coordination environments, distinctive electronic structures, and highly dispersed active sites. This work offers a thorough examination of the progress of research on SACs for photocatalytic, electrocatalytic, and photoelectrocatalytic conversion of carbon dioxide. The fundamental concepts of photo-, electro-, and photoelectrocatalytic reduction of CO2 are briefly described, respectively. Second, the preparation approaches and characterization techniques of SACs are summarized, with a focus on how to increase the single-atom loading rate and achieve scale-up preparation. Finally, the specific applications of SACs for photo-, electro-, and photoelectrocatalytic conversion of CO2 are discussed, and the future development of SACs in the field of CO2 catalytic reduction is summarized and prospected. Herein, the aim is to provide guidance and insights for the systematic design of SACs used in CO2 reduction reactions, serving as a reference for the further advancement of photo-, electro-, and photoelectrocatalytic reduction of CO2.

Impregnation of Single-Atom Iron from Metallosurfactants onto MOF-Derived Porous N-Doped Carbon for Efficient Wastewater Treatment via Peroxymonosulfate Activation

Herein, a Fe-MOF-derived single iron atom impregnated on porous N-doped carbon (FeSAC/NC) was synthesized using an iron-based metallosurfactant (FeCTAC) as the precursor. The formation of isolated single atoms and their surrounding environment after pyrolysis at 900 °C was confirmed by XPS and EXAFS analysis. The use of FeCTAC facilitated the exposure of more single iron atoms on the porous NC matrix and prevented their aggregation, as verified by elemental analysis and HAADEF-TEM. The resulting FeSAC/NC was applied in the Fenton reaction for the degradation of tetracycline (TC) by activating peroxymonosulfate (PMS). It achieved 92% TC removal in 40 min compared to only 23% with PMS alone. Free radical scavenging experiments indicated that a nonradical pathway, involving singlet oxygen and electron transfer, dominated the degradation process. Additionally, pyrrolic and graphitic nitrogen sites in the NC matrix contributed significantly to TC adsorption. This exceptional catalytic performance provides valuable insights for designing highly efficient catalysts for wastewater treatment.

Accelerated Design of Fenton-Like Copper Single-Atom Catalysts by Adaptive Learning with Genetic Programming

Traditional trial-and-error methods for optimizing catalyst synthesis are time-consuming and costly, exploring only a small fraction of the vast combinatorial space. Machine learning (ML) offers a promising alternative but still has the limitation of relying on well-selected initial datasets, which the recent development of active learning (AL) could be addressed. Here, we novelly integrate an AL-derived algorithm, the adaptive learning genetic algorithm (ALGA), into experimental workflows to optimize the synthesis of Fenton-like single-atom catalysts (SACs). Our results show that the closed-loop ALGA framework effectively learns from limited and sparse datasets, greatly reducing the research cycle compared to traditional ML and AL frameworks. By iteratively retaining better-performing genetic information and proactively expanding the search space through mutation and crossover, ALGA identifies the highest-performing Fenton-like Cu SACs with less than 90 experiments. The maximum phenol degradation rate k-value (0.147 min-1) achieved within the ALGA framework is approximately three times higher than that of the initial dataset and surpasses the reported best Fenton-like Cu SACs. Our successful implementation of ALGA signifies an advancement in SACs synthesis assisted by the AL-derived algorithm, offering a guiding methodology for the exploration of other functional materials.

Accurate Thermal Resection of Atomically Precise Copper Clusters to Achieve Near-IR Light-Driven CO2 Reduction

Atomically precise copper clusters are desirable as catalysts for elaborating the structure-activity relationships. The challenge, however, lies in their tendency to sinter when protective ligands are removed, resulting in the destruction of the structural integrity of the model system. Herein, a copper-sulfur-nitrogen cluster [Cu8(StBu)4(PymS)4] (denoted as Cu8SN) is synthesized by using a mixed ligand approach with strong chelating 2-mercaptopyrimidine (PymSH) ligands and relatively weak monodentate tert-butyl mercaptan ligands. A precise thermal-resection strategy is applied to selectively peel only the targeted weak ligands off, which induces a structural transformation of the initial Cu8 cluster into a new and more stable Cu-S-N cluster [Cu8(S)2(PymS)4] (denoted as Cu8SN-T). The residual bridging S2- within the metal core forms asymmetric Cu-S species with a near-infrared (NIR) response, which endows Cu8SN-T with the capability for full-spectrum responsive CO2 photoreduction, achieving a ≈100% CO2-to-CO selectivity. Especially for NIR-driven CO2 reduction, it has a CO evolution of 42.5 µmol g-1 under λ > 780 nm. Importantly, this work represents the first NIR light-responsive copper cluster for efficient CO2 photoreduction and opens an avenue for the precise manipulation of metal cluster structures via a novel thermolysis strategy to develop unprecedented functionalized metal cluster materials.

Theory-Guided Design of Surface-Enhanced Ni-Mn Diatomic Site Catalysts for Efficient Seawater Electrolysis via the Degradation of High Ionization Potential Organic Pollutants

In response to energy shortages and hard-to-degrade chemical pollution, especially high ionization potential (IP) organic pollutants, this study developed a novel photoelectrocatalyst, Ni-Mn@OBN, for degrading IP pollutants in seawater and generating hydrogen. Incorporating Ni-Mn dual atoms into an O-doped boron nitride (OBN) framework, Ni-Mn@OBN, shows excellent stability and HER performance. Density functional theory (DFT) analysis revealed its low Gibbs free energy change (ΔGH* = 0.03 eV) for HER, outperforming Pt (111). Achieving an ultralow overpotential of 43.8 mV at 500 mA cm⁻2 under AM 1.5G, simulated light surpasses commercial Pt/C catalysts. High IP pollutants enhance hydrogen evolution rates, indicating a synergistic effect. Theoretical calculations elucidated the interplay between seawater electrolytes and high IP values on the photoelectrocatalytic performance. Ni-Mn@OBN demonstrated excellent stability and a solar-to-hydrogen (STH) efficiency of 3.72%, offering a sustainable solution for marine pollution control and clean energy production.

Tailoring Single Co-N4 Sites Within the Second Coordination Shell for Enhanced Natural Light-Driven Photosynthetic H2O2 Production

Rational regulation of the coordination environment of single-atom catalysts (SACs) is a promising yet challenging strategy to enhance their activity. Here, we introduce an O atom into the second coordination shell of Co-N4 sites via a simple thermal treatment, forming a Co-N4-ON matrix to boost photosynthetic hydrogen peroxide (H2O2) production. This modification significantly alters the electronic structure of the Co site, bringing the d-band center closer to the Fermi energy and elevating the conduction band of Co-N4-CN to enhance its reducing capacity. Density functional theory (DFT) calculations reveal intensified charge redistribution and a reduced work function in Co-N4-ON, facilitating O2 adsorption. Notably, Co-N4-ON exhibits the lowest O2 adsorption energy, indicating a stronger interaction between Co-N4-O and O2, which is further strengthened by orbital hybridization and charge transfer at their interface, leading to enhanced O2 activation. The optimized Co-N4-ON catalyst demonstrates superior O2 reduction capabilities with the lowest energy barrier during H2O2 desorption. Consequently, it achieves a H2O2 production rate of 3098.18 μmol g-1 h-1 under neutral conditions, which is 2.6 times higher than that of Co-N4-CN. Moreover, it maintains a production rate of 1967.79 μmol g-1 h-1 over 10 h in a continuous flow reactor under natural sunlight and ambient air, highlighting its durability and practicality. This study underscores the crucial role of the second coordination shell in SACs and offers valuable insights into their atomic-level structure-activity relationships, thus contributing to advancements in catalyst design for efficient photosynthetic H2O2 production.

Ultrafast Water Purification by Template-Free Nanoconfined Catalysts Derived from Municipal Sludge

Nanoconfinement at the interface of heterogeneous Fenton-like catalysts offers promising avenues for advancing oxidation processes in water purification. Herein, we introduce a template-free strategy for synthesizing nanoconfined catalysts from municipal sludge (S-NCCs), specifically engineered to optimize reactive oxygen species (ROS) generation and utilization for rapid pollutant degradation. Using selective hydrofluoric acid corrosion, we create an architecture that confines atomically dispersed Fe centers within a micro-mesoporous carbon matrix in situ. This method maximizes the utilization of silicon and aluminum content from sludge, prevents metal agglomeration, and precisely regulates the chemical environment of Fe active sites. As a result, the S-NCCs promote a transition from nonradical to hybrid radical/nonradical reaction mechanisms, significantly enhancing ROS efficiency, stability, and pollutant degradation rates. These catalysts demonstrate exceptional pollutant removal performance, achieving a 261-fold increase in degradation efficiency for compounds such as phenol and sulfamethoxazole compared to unconfined analogs, outperforming most state-of-the-art Fenton-like systems. Our findings highlight the transformative potential of nanoconfined catalysis in environmental applications, providing an effective and scalable solution for sustainable water purification.

Interfacial hydrogen bonds induced by porous FeCr bimetallic atomic sites for efficient oxygen reduction reaction

Interfacial hydrogen bonds are pivotal in enhancing proton activity and accelerating the kinetics of proton-coupled electron transfer during electrocatalytic oxygen reduction reaction (ORR). Here we propose a novel FeCr bimetallic atomic sites catalyst supported on a honeycomb-like porous carbon layer, designed to optimize the microenvironment for efficient electrocatalytic ORR through the induction of interfacial hydrogen bonds. Characterizations, including X-ray absorption spectroscopy and in situ infrared spectroscopy, disclose the rearrangement of delocalized electrons due to the formation of FeCr sites, which facilitates the dissociation of interfacial water molecules and the subsequent formation of hydrogen bonds. This process significantly accelerates the proton-coupled electron transfer process and enhances the ORR reaction kinetics. As a result, the catalyst FeCrNC achieves a remarkable half-wave potential of 0.92 V and exhibits superior four-electron selectivity in 0.1 M KOH solution. Moreover, the zinc-air battery assembled by FeCrNC demonstrates a high power density of 207 mW cm-2 and negligible degradation over 240 h at a current density of 10 mA cm-2.

Quantifying Asymmetric Coordination to Correlate with Oxygen Reduction Activity in Fe-Based Single-Atom Catalysts

Precisely manipulating asymmetric coordination configurations and examining electronic effects enable to tunethe intrinsic oxygen reduction reaction (ORR) activity of single-atom catalysts (SACs). However, the lackof a definite relationship between coordination asymmetry and catalytic activity makes the rational design of SACs ambiguous. Here, we propose a concept of "asymmetry degree" to quantify asymmetric coordination configurations and assess the effectiveness of active moieties in Fe-based SACs. A theoretical framework is established, elucidating the volcanic relationship between asymmetry degree and ORR activity by constructing a series of Fe-based SAC models doped with non-metal atoms (B, P, S, Se, and Te) in the first or second coordination sphere, which aligns with Sabatier principle. The predicted ORR activity of Fe asymmetric active moieties is then experimentally validated using asymmetry degree. The combined computational and experimental results suggest that single-atom moiety with a moderate asymmetry degree exhibits optimal intrinsic ORR activity, because breaking the square-planar symmetry of FeN4 can alter the electronic population of the Fe 3d-orbital, thereby optimizing the adsorption-desorption strength of intermediates and thus enhancing the intrinsic ORR activity. This fundamental understanding of catalytic activity from geometric and electronic aspects offers a rational guidance to design high-performance SACs with asymmetric configurations.

Isolated Metal Centers Activate Small Molecule Electrooxidation: Mechanisms and Applications

Electrochemical oxidation of small molecules shows great promise to substitute oxygen evolution reaction (OER) or hydrogen oxidation reaction (HOR) to enhance reaction kinetics and reduce energy consumption, as well as produce high-valued chemicals or serve as fuels. For these oxidation reactions, high-valence metal sites generated at oxidative potentials are typically considered as active sites to trigger the oxidation process of small molecules. Isolated atom site catalysts (IASCs) have been developed as an ideal system to precisely regulate the oxidation state and coordination environment of single-metal centers, and thus optimize their catalytic property. The isolated metal sites in IASCs inherently possess a positive oxidation state, and can be more readily produce homogeneous high-valence active sites under oxidative potentials than their nanoparticle counterparts. Meanwhile, IASCs merely possess the isolated metal centers but lack ensemble metal sites, which can alter the adsorption configurations of small molecules as compared with nanoparticle counterparts, and thus induce various reaction pathways and mechanisms to change product selectivity. More importantly, the construction of isolated metal centers is discovered to limit metal d-electron back donation to CO 2p* orbital and reduce the overly strong adsorption of CO on ensemble metal sites, which resolve the CO poisoning problems in most small molecules electro-oxidation reactions and thus improve catalytic stability. Based on these advantages of IASCs in the fields of electrochemical oxidation of small molecules, this review summarizes recent developments and advancements in IASCs in small molecules electro-oxidation reactions, focusing on anodic HOR in fuel cells and OER in electrolytic cells as well as their alternative reactions, such as formic acid/methanol/ethanol/glycerol/urea/5-hydroxymethylfurfural (HMF) oxidation reactions as key reactions. The catalytic merits of different oxidation reactions and the decoding of structure-activity relationships are specifically discussed to guide the precise design and structural regulation of IASCs from the perspective of a comprehensive reaction mechanism. Finally, future prospects and challenges are put forward, aiming to motivate more application possibilities for diverse functional IASCs.

Lanthanide single-atom catalysts for efficient CO2-to-CO electroreduction

Single-atom catalysts (SACs) have received increasing attention due to their 100% atomic utilization efficiency. The electrochemical CO2 reduction reaction (CO2RR) to CO using SAC offers a promising approach for CO2 utilization, but achieving facile CO2 adsorption and CO desorption remains challenging for traditional SACs. Instead of singling out specific atoms, we propose a strategy utilizing atoms from the entire lanthanide (Ln) group to facilitate the CO2RR. Density functional theory calculations, operando spectroscopy, and X-ray absorption spectroscopy elucidate the bridging adsorption mechanism for a representative erbium (Er) single-atom catalyst. As a result, we realize a series of Ln SACs spanning 14 elements that exhibit CO Faradaic efficiencies exceeding 90%. The Er catalyst achieves a high turnover frequency of ~130,000 h-1 at 500 mA cm-2. Moreover, 34.7% full-cell energy efficiency and 70.4% single-pass CO2 conversion efficiency are obtained at 200 mA cm-2 with acidic electrolyte. This catalytic platform leverages the collective potential of the lanthanide group, introducing new possibilities for efficient CO2-to-CO conversion and beyond through the exploration of unique bonding motifs in single-atom catalysts.

Increasing the local electron density of carbons for enhanced O2 activation at room temperature

Room-temperature activation of O2 into a super dioxide radical (O2˙-) is a crucial step in oxidation processes. Here, the concept of tuning the local electron density of carbons is adopted to develop highly efficient catalysts for molecular oxygen activation. We demonstrate that the π electron of sp2 carbons is essential for activating O2 with the assistance of ultra-micropores, while varying defects or functional groups induce local electron rearrangement of carbons, thereby altering their catalytic capacity. Electron rich non-metallic doping can increase the local electron intensity of modified carbons with improved oxygen activation. In addition, transition-metal-sp2-carbon nano-composites that readily surrender electrons are constructed, achieving O2˙- formation without spatial confinement. Our findings provide fundamental insights into the intrinsic mechanism of O2 activation and offer a general protocol for the design and development of advanced carbon catalysts for low-temperature oxidations.

Symmetry Breaking of FeN4 Moiety via Edge Defects for Acidic Oxygen Reduction Reaction

Fe-N-C catalysts, with a planar D4h symmetric FeN4 structure, show promising as noble metal-free oxygen reduction reaction catalysts. Nonetheless, the highly symmetric structure restricts the effective manipulation of its geometric and electronic structures, impeding further enhancements in oxygen reduction reaction performance. Here, a high proportion of asymmetric edge-carbon was successfully introduced into Fe-N-C catalysts through morphology engineering, enabling the precise modulation of the FeN4 active site. Electrochemical experimental results demonstrate that FeN4@porous carbon (FeN4@PC), featuring enriched asymmetric edge-FeN4 active sites, exhibits higher acidic oxygen reduction reaction catalytic activity compared to FeN4@flaky carbon (FeN4@FC), where symmetric FeN4 is primarily distributed within the basal-plane. Synchrotron X-ray absorption spectra, X-ray emission spectra, and theoretical calculations indicate that the enhanced oxygen reduction reaction catalytic activity of FeN4@PC is attributed to the higher oxidation state of Fe species in the edge structure of FeN4@PC. This finding paves the way for controlling the local geometric and electronic structures of single-atom active sites, leading to the development of novel and efficient Fe-N-C catalysts.

Sulfur-doping tunes p-d orbital coupling over asymmetric Zn-Sn dual-atom for boosting CO2 electroreduction to formate

The interaction of p-d orbitals at bimetallic sites plays a crucial role in determining the catalytic reactivity, which facilitates the modulation of charges and enhances the efficiency of CO2 electroreduction process. Here, we show a ligand co-etching approach to create asymmetric Zn-Sn dual-atom sites (DASs) within metal-organic framework (MOF)-derived yolk-shell carbon frameworks (named Zn1Sn1/SNC). The DASs comprise one Sn center (p-block) partially doped with sulfur and one Zn center (d-block) with N coordination, facilitating the coupling of p-d orbitals between the Zn-Sn dimer. The N-Zn-Sn-S/N arrangement displays an asymmetric distribution of charges and atoms, leading to a stable adsorption configuration of HCOO* intermediates. In H-type cell, Zn1Sn1/SNC exhibits an impressive formate Faraday efficiency of 94.6% at -0.84 V. In flow cell, the asymmetric electronic architecture of Zn1Sn1/SNC facilitates high accessibility, leading to a high current density of -315.2 mA cm-2 at -0.90 V. Theoretical calculations show the asymmetric sites in Zn1Sn1/SNC with ideal adsorption affinity lower the CO2 reduction barrier, thus improve the overall efficiency of CO2 reduction.

Tailoring asymmetric RuCu dual-atom electrocatalyst toward ammonia synthesis from nitrate

Atomically dispersed Ru-Cu dual-atom catalysts (DACs) with asymmetric coordination are critical for sustainable ammonia production via electrochemical nitrate reduction (NO3RR), but their rational synthesis remains challenging. Here, we report a pulsed discharge strategy that injects a microsecond pulse current into ruthenium (Ru) and copper (Cu) precursors supported by nitrogen-doped graphene aerogels (NGA). The atomically dispersed Ru and Cu dual atoms anchor onto nanopore defects of NGA (RuCu DAs/NGA) through explosive decomposition of the metal salt nanocrystals. The catalyst achieves 95.7% Faraday efficiency and 3.1 mg h-1 cm-2 NH3 yield at -0.4 V vs. RHE. In situ studies reveal an asymmetric RuN2-CuN3 active-site dynamic evolution during NO3RR. Density functional theory calculations demonstrate that asymmetric RuN2CuN3/C structure synergistically optimizes intermediate adsorption and reduces energy barriers of key steps. The pulsed discharge enables ultrafast synthesis of various DACs (e.g., PtCu, AgCu, PdCu, FeCu, CoCu, NiCu) with tailored coordination environments, offering a general-purpose strategy for the precise preparation of atomically dispersed dual-atom catalysts, which are traditionally challenging to synthesize.

Oxidized Carbon Nanoparticles Enhance Cellular Energetics With Application to Injured Brain

Pro-energetic effects of functionalized, oxidized carbon nanozymes (OCNs) are reported. OCNs, derived from harsh acid oxidation of single-wall carbon nanotubes or activated charcoal are previously shown to possess multiple nanozymatic activities including mimicking superoxide dismutase and catalyzing the oxidation of reduced nicotinamide adenine dinucleotide (NADH) to NAD+. These actions are predicted to generate a glycolytic shift and enhance mitochondrial energetics under impaired conditions. Impaired mitochondrial energy metabolism is increasingly recognized as an important facet of traumatic brain injury (TBI) pathophysiology and decreases the efficiency of electron transport chain (ETC)-coupled adenosine triphosphate (ATP) and NAD+ regeneration. In vitro, OCNs promote a pro-aerobic shift in energy metabolism that persists through ETC inhibition and enhances glycolytic flux, glycolytic ATP production, and cellular generation of lactate, a crucial auxiliary substrate for energy metabolism. To address specific mechanisms of iron injury from hemorrhage, OCNs with the iron chelator, deferoxamine (DEF), covalently-linked were synthesized. DEF-linked OCNs induce a glycolytic shift in-vitro and in-vivo in tissue sections from a rat model of TBI complicated by hemorrhagic contusion. OCNs further reduced hemorrhage volumes 3 days following TBI. These results suggest OCNs are promising as pleiotropic mediators of cell and tissue resilience to injury.

Cathode Design Based on Nitrogen Redox and Linear Coordination of Cu Center for All-Solid-State Fluoride-Ion Batteries

All-solid-state fluoride-ion batteries (FIBs) have attracted extensive attention as candidates for next-generation energy storage devices; however, promising cathodes with high energy density are still lacking. In this study, Cu3N is investigated as a cathode material for all-solid-state fluoride-ion batteries, which offers enough anionic vacancies around the 2-fold coordinated Cu center for F- intercalation, thereby enabling a multielectron-transferred fluorination process. The contribution of both cationic and anionic redox to charge compensation, in particular, the generation of molecular nitrogen species in highly charged states, has been proved by several synchrotron-radiation-based spectroscopic technologies. As a result, Cu3N exhibits a high reversible capacity of ∼550 mAh g-1, exceeding many conventional fluoride-ion cathodes. It is believed that the new charge compensation chemistry as well as the unique intercalation behaviors of novel mixed-anion Cu-N/F local structures could bring new insights into energy storage materials.

Planar chlorination engineering induced symmetry-broken single-atom site catalyst for enhanced CO2 electroreduction

Breaking the geometric symmetry of traditional metal-N4 sites and further boosting catalytic activity are significant but challenging. Herein, planar chlorination engineering is proposed for successfully converting the traditional Zn-N4 site with low activity and selectivity for CO2 reduction reaction (CO2RR) into highly active Zn-N3 site with broken symmetry. The optimal catalyst Zn-SA/CNCl-1000 displays a highest faradaic efficiency for CO (FECO) around 97 ± 3% and good stability during 50 h test at high current density of 200 mA/cm2 in zero-gap membrane electrode assembly (MEA) electrolyzer, with promising application in industrial catalysis. At -0.93 V vs. RHE, the partial current density of CO (JCO) and the turnover frequency (TOF) value catalyzed by Zn-SA/CNCl-1000 are 271.7 ± 1.4 mA/cm2 and 29325 ± 151 h-1, as high as 29 times and 83 times those of Zn-SA/CN-1000 without planar chlorination engineering. The in-situ extended X-ray absorption fine structure (EXAFS) measurements and density functional theory (DFT) calculation reveal the adjacent C-Cl bond induces the self-reconstruction of Zn-N4 site into the highly active Zn-N3 sites with broken symmetry, strengthening the adsorption of *COOH intermediate, and thus remarkably improving CO2RR activity.

Oxygen Reduction Reaction Catalysts for Zinc-Air Batteries Featuring Single Cobalt Atoms in a Nitrogen-Doped 3D-Interconnected Porous Graphene Framework

Single-atom catalysts (SACs) with high activity and efficient atom utilization for oxygen reduction reactions (ORRs) are imperative for rechargeable Zinc-air batteries (ZABs). However, it is still a prominent challenge to construct a noble-metal-free SAC with low cost but high efficiency. Herein, a novel nitrogen-doped graphene (NrGO) based SAC, immobilized with atomically dispersed single cobalt (Co) atoms (Co-NrGO-SAC), is reported for ORRs. In this 3D NrGO, the Co-N4 sites endow high-efficiency ORR activity, and the 3D-interconnected porous architectures of NrGOs guarantee numberous active sites accessibility. Compared to commercial Pt/C catalyst (≈5.8 mA cm-2), as-prepared Co-NrGO-SACs presents considerable limiting current density of ≈5.9 mA cm-2, prominent half-wave potential of ≈0.84 V, onset potential of ≈1.05 V, and as well as superior methanol resistance. Particularly, ZABs with Co-NrGO-SACs deliver remarkable power density (≈240 mW cm-2), super durability of over 233 h at 5 mA cm-2, outperforming noble-metal-based benchmarks. This work provides an effective noble-metal free carbon-based SAC nano-engineering for superdurable ZABs.

MOF-derived Carbon-Based Materials for Energy-Related Applications

New carbon-based materials (CMs) are recommended as attractively active materials due to their diverse nanostructures and unique electron transport pathways, demonstrating great potential for highly efficient energy storage applications, electrocatalysis, and beyond. Among these newly reported CMs, metal-organic framework (MOF)-derived CMs have achieved impressive development momentum based on their high specific surface areas, tunable porosity, and flexible structural-functional integration. However, obstacles regarding the integrity of porous structures, the complexity of preparation processes, and the precise control of active components hinder the regulation of precise interface engineering in CMs. In this context, this review systematically summarizes the latest advances in tailored types, processing strategies, and energy-related applications of MOF-derived CMs and focuses on the structure-activity relationship of metal-free carbon, metal-doped carbon, and metallide-doped carbon. Particularly, the intrinsic correlation and evolutionary behavior between the synergistic interaction of micro/nanostructures and active species with electrochemical performances are emphasized. Finally, unique insights and perspectives on the latest relevant research are presented, and the future development prospects and challenges of MOF-derived CMs are discussed, providing valuable guidance to boost high-performance electrochemical electrodes for a broader range of application fields.

Transforming Plastics to Single Atom Catalysts for Peroxymonosulfate Activation: Axial Chloride Coordination Intensified Electron Transfer Pathway

Transforming plastics into single-atom catalysts is a promising strategy for upcycling waste plastics into value-added functional materials. Herein, a graphene-based single-atom catalyst with atomically dispersed FeN4Cl sites (Fe─N/Cl─C) is produced from high-density polyethylene wastes via one-pot catalytic pyrolysis. The Fe─N/Cl─C catalyst exhibited much higher turnover frequency and surface area normalized activity (Kac) compared with the Fe─N─C catalyst without axial Cl modulation. Both experiments and density functional theory (DFT) computations demonstrated that the axial incorporation of chloride fine-tuned the coordination environment of FeN4 sites and enhanced peroxymonosulfate (PMS) activation because of improved conductivity and modulated spin state. In situ, Raman, and infrared spectroscopic techniques revealed that PMS is activated by the Fe─N/Cl─C catalyst through an electron transfer process. The formation of a key PMS* intermediate at the Fe site effectively elevated the redox capacity of the catalyst surface to realize a fast degradation of diverse pollutants. The non-radical oxidation manner secures high selectivity toward target pollutants and high chemical utilization efficiency. A continuous operation in a column reactor also demonstrated the high efficiency and stability of the (Fe─N/Cl─C + PMS) system for practical water treatment.

Transient pulsed discharge preparation of graphene aerogel supports asymmetric Cu cluster catalysts promote CO2 electroreduction

Designing asymmetrical structures is an effective strategy to optimize metallic catalysts for electrochemical carbon dioxide reduction reactions. Herein, we demonstrate a transient pulsed discharge method for instantaneously constructing graphene-aerogel supports asymmetric copper nanocluster catalysts. This process induces the convergence of copper atoms decomposed by copper chloride onto graphene originating from the intense current pulse and high temperature. The catalysts exhibit asymmetrical atomic and electronic structures due to lattice distortion and oxygen doping of copper clusters. In carbon dioxide reduction reaction, the selectivity and activity for ethanol production are enhanced by the asymmetric structure and abundance of active sites on catalysts, achieving a Faradaic efficiency of 75.3% for ethanol and 90.5% for multicarbon products at -1.1 V vs. reversible hydrogen electrode. Moreover, the strong interactions between copper nanoclusters and graphene-aerogel support confer notable long-term stability. We elucidate the key reaction intermediates and mechanisms on Cu4O-Cu/C2O1 moieties through in situ testing and density functional theory calculations. This study provides an innovative approach to balancing activity and stability in asymmetric-structure catalysts for energy conversion.

Substance migration in the synthesis of single-atom catalysts

Substance migration is universal and crucial in the synthesis of catalysts, which directly affects their existing form and the micro-structure of their active sites. Realizing migration during the synthesis of single-atom catalysts (SACs) is beneficial for not only increasing their metal loading capacity but also manipulating the electronic structures (coordination structure, long-range interactions, etc.) of their metal sites. This review summarizes the thermodynamics and kinetic processes involved in the synthesis of SACs to unveil the fundamental principles involved in their synthesis. For a better understanding of the effect of migration, the migration of both metal (including ions, atoms, and molecules) and nonmetal species is outlined. Moreover, we propose the research directions to guide the rational design of SACs in the future and deepen the fundamental understanding in the formation of catalysts.

Nonprecious Triple-Atom Catalysts with Ultrahigh Activity for Electrochemical Reduction of Nitrate to Ammonia: A DFT Screening

Electrochemical nitrate reduction to ammonia (NO3RR) is promising to not only tackle environmental issues caused by nitrate but also produce ammonia at room temperatures. However, two critical challenges are the lack of effective electrocatalysts and the understanding of related reaction mechanisms. To overcome these challenges, we employed first-principles calculations to thoroughly study the performance and mechanisms of triple-atom catalysts (TACs) composed of transition metals (including 27 homonuclear TACs and 4 non-noble bimetallic TACs) anchored on N-doped carbon (NC). We found five promising candidates possessing not only thermodynamic and electrochemical stability, but also high activity and selectivity for ammonia production. Among them, non-noble homonuclear Ni3@NC TAC show high activity with low theoretical limiting potential of -0.31 VRHE. Surprisingly, bimetallic Co2Ni@NC, Co2Cu@NC, and Fe2Ni@NC TACs show ultrahigh activity with theoretical limiting potentials of 0.00 VRHE, without a potential determining step in the whole reaction pathways, representing the best theoretical activity been reported up to date. These promising candidates are facilitated by circumventing the limit of scaling relationships, a well-known obstacle for single-atom catalysts. This study indicates that designing suitable TACs can be a promising strategy for efficiently electro-catalyzing NO3RR and breaking the limit of the scaling relationship.

Enhancing Oxygen Reduction Reaction of Single-Atom Catalysts by Structure Tuning

Deciphering the fine structure has always been a crucial approach to unlocking the distinct advantages of high activity, selectivity, and stability in single-atom catalysts (SACs). However, the complex system and unclear catalytic mechanism have obscured the significance of exploring the fine structure. Therefore, we endeavored to develop a three-component strategy to enhance oxygen reduction reaction (ORR), delving deep into the profound implications of the fine structure, focusing on central atoms, coordinating atoms, and environmental atoms. Firstly, the mechanism by which the chemical state and element type of central atoms influence catalytic performance is discussed. Secondly, the significance of coordinating atoms in SACs is analyzed, considering both the number and type. Lastly, the impact of environmental atoms in SACs is reviewed, encompassing existence state and atomic structure. Thorough analysis and summarization of how the fine structure of SACs influences the ORR have the potential to offer valuable insights for the accurate design and construction of SACs.

Single-Atom Mo Supported by TiO2 for Photocatalytic Nitrogen Fixation

The challenge of achieving efficient photocatalysts for the fixation of ambient nitrogen to ammonia persists. The utilization efficiency of single-metal-atom catalysts leads to an increased number of active sites, while their distinctive geometrical and electronic characteristics contribute to enhancing the intrinsic activity of each individual site. In this study, we present a method using an organic molecule to assist in loading TiO2 with Mo single atoms for the purpose of photocatalytic nitrogen fixation. By adjusting the number of Mo single atoms loaded, we were able to regulate the microenvironment surrounding the catalytic center. Our results demonstrate that TiO2-Mo10 achieved a remarkable photocatalytic nitrogen fixation performance of 42.05 μmol·g-1·h-1 at room temperature while maintaining excellent structural stability and cycle life. The incorporation of Mo single atoms effectively enhanced electron separation and migration within TiO2, leading to a significant weakening of the N≡N bond. This research highlights the potential for predesigning TiO2-based single-atom photocatalysts with tailored structures for efficient nitrogen fixation through photocatalysis. These findings offer valuable insights for the future development and rational design of single-atom photocatalysts.

Unveiling the Proton-Electron Transfer Pathway in Zn-Embedded N-Doped Carbon Catalyst for Enhanced CO2 Electroreduction

Proton-electron transfer (PET) processes play a pivotal role in numerous electrochemical reactions; yet, effectively harnessing them remains a formidable challenge. Consequently, unveiling the PET pathway is imperative to elucidate the factors influencing the efficiency and selectivity of small molecule electrochemical conversion. In this study, a Zn-NC model catalyst with N and C vacancies was synthesized using a hydriding method to investigate the universal impact of PET on CO2 electroreduction. The introduction of N vacancies induced the formation of a distinctive Zn-N3 topological structure and atomically populated Znδ+ sites with lower valence states, thereby facilitating the cleavage of the C═O bonds. Conversely, C vacancies led to the formation of stable C-H bonds and tuned the rate of dissociation of H2O to H*. In comparison to sequential proton-electron transfer, concerted proton-electron transfer significantly enhanced the formation of *COOH species, a critical step in the CO2 reduction process on a Zn-enhanced N-doped carbon catalyst. The catalyst exhibited a remarkable 96% CO Faradaic efficiency at -0.36 V vs RHE. This research contributes to the ongoing endeavors to unlock the full potential of concerted proton-electron transfer in electrochemical synthesis and its application in sustainable energy and environmental solutions.

Precisely designing asymmetrical selenium-based dual-atom sites for efficient oxygen reduction

Owing to their synergistic interactions, dual-atom catalysts (DACs) with well-defined active sites are attracting increasing attention. However, more experimental research and theoretical investigations are needed to further construct explicit dual-atom sites and understand the synergy that facilitates multistep catalytic reactions. Herein, we precisely design a series of asymmetric selenium-based dual-atom catalysts that comprise heteronuclear SeN2-MN2 (M = Fe, Mn, Co, Ni, Cu, Mo, etc.) active sites for the efficient oxygen reduction reaction (ORR). Spectroscopic characterisation and theoretical calculations revealed that heteronuclear selenium atoms can efficiently polarise the charge distribution of other metal atoms through short-range regulation. In addition, compared with the Se or Fe single-atom sites, the SeFe dual-atom sites facilitate a reduction in the conversion energy barrier from *O to *OH via the coadsorption of *O intermediates. Among these designed selenium-based dual-atom catalysts, selenium-iron dual-atom catalysts achieves superior alkaline ORR performance, with a half-wave potential of 0.926 V vs. a reversible hydrogen electrode. In addition, the SeN2-FeN2-based Zn-air battery has a high specific capacity (764.8 mAh g-1) and a maximum power density (287.2 mW cm-2). This work may provide a good perspective for designing heteronuclear DACs to improve ORR efficiency.

Optimizing surface active sites via burying single atom into subsurface lattice for boosted methanol electrooxidation

The precise fabrication and regulation of the stable catalysts with desired performance still challengeable for single atom catalysts. Here, the Ru single atoms with different coordination environment in Ni3FeN lattice are synthesized and studied as a typical case over alkaline methanol electrooxidation. The Ni3FeN with buried Ru atoms in subsurface lattice (Ni3FeN-Ruburied) exhibits high selectivity and Faradaic efficiency of methanol to formate conversion. Meanwhile, operando spectroscopies reveal that the Ni3FeN-Ruburied exhibits an optimized adsorption of reactants along with an inhibited surface structural reconstruction. Additional theoretical simulations demonstrate that the Ni3FeN-Ruburied displays a regulated local electronic states of surface metal atoms with an optimized adsorption of reactants and reduced energy barrier of potential determining step. This work not only reports a high-efficient catalyst for methanol to formate conversion in alkaline condition, but also offers the insight into the rational design of single atom catalysts with more accessible surficial active sites.

General synthesis of neighboring dual-atomic sites with a specific pre-designed distance via an interfacial-fixing strategy

A potential non-precious metal catalyst for oxygen reduction reaction should contain metal-N4 moieties. However, most of the current strategies to regulate the distances between neighboring metal sites are not pre-designed but depend on the probability by tuning the metal loading or the support. Herein, we report a general method for the synthesis of neighboring metal-Nx moieties (metal = Fe, Cu, Co, Ni, Zn, and Mn) via an interfacial-fixing strategy. Specifically, polydopamine is used to coat nanotemplates made of metal oxides, followed by pyrolysis to form a metal-oxide skeleton coated by rich nitrogen-doped carbon shells. After chemically etching the skeleton, only interfacial metal atoms strongly bonded with the support via nitrogen atoms are retained. The high purity (>95%) of dual Fe sites was confirmed by both the direct visualization of local regions and the indirect evidence of the averaged information. When these neighboring metal-Nx moieties are applied for oxygen reduction reaction, Fe-Nx moieties exhibit the superior activity, even outperforming commercial Pt/C in the aspects of the half-wave potential, methanol tolerance, carbon monoxide tolerance, and robustness.

Two-dimensional Cu-phenylalanine nanoflakes for efficient and robust CO2 electroreduction to C2+ products

The electrocatalytic reduction of CO2 to multicarbon (C2+) products is of great importance but still faces challenges. The moderate oxidation state of Cu (Cuδ+) plays a critical role in promoting the C-C coupling, thereby enhancing the Faraday efficiency (FE) for C2+ products. However, Cuδ+ active species are unstable during the reaction. In this work, two-dimensional (2D) Cu-phenylalanine (Cu-phe) nanoflakes by assembling Cu ions and phenylalanine are prepared. X-ray absorption spectroscopy (XAS) is performed to confirm the moderate oxidation state and Cu-O/N coordination of Cu-phe nanoflakes. Owing to the carboxylic ligand and more stable Cu-N coordination, Cu-phe nanoflakes maintain a moderate oxidation state and exhibit high FE for C2+ products (88.1% at -0.8 V) in a flow cell, along with excellent stability. This work offers valuable insights for designing stable and efficient catalysts for the electro-conversion of CO2 into high-value chemical stocks.

Prussian Blue-Derived Atomic Fe/Fe3C@N-Doped C Catalysts Supported by Carbon Cloth as Integrated Air Cathode for Flexible Zn-Air Batteries

The development of an integrated air cathode with superior oxygen reduction reaction (ORR) performance is fundamental to flexible zinc-air batteries (ZABs) for wearable electronics. Herein, a self-assembled metal-organic framework (MOF)-derived strategy is proposed to prepare a atomic Fe/Fe3C@N-doped C catalysts supported by carbon cloth (CC) catalyst for use as an air cathode of flexible ZABs. The Prussian Blue precursor, which self-assembles on the surface of the carbon cloth due to electrostatic attraction, is critical in achieving the uniform dispersion of catalysts with high density loading on carbon cloth substrates. The hollow cubic structure, N-doped carbon layer coating, and the integrated electrode design can provide more accessible active sites and facilitate a rapid electron transfer and mass transport. Density functional theory (DFT) calculation reveals that the electronic interactions between the Fe-N4 and Fe3C dual active sites can optimize the adsorption-desorption behavior of oxygen intermediates formed during the ORR. Consequently, the Fe/Fe3C@N-doped C/CC exhibits an excellent half wave potential (E1/2 = 0.903 V) and superior long-term cycling stability in alkaline environments. With excellent ORR performance, ZABs and flexible ZABs based on Fe/Fe3C@N-doped C/CC air cathode demonstrate excellent overall electrochemical performance in terms of open circuit voltage, maximum power density, flexibility, and cycling stability.

Modulating Spin of Atomic Manganese Center for High-Performance Oxygen Reduction Reaction

Single atom catalysts (SACs) are promising non-precious catalysts for oxygen reduction reaction (ORR). Unfortunately, the ORR SACs usually suffer from unsatisfactory activity and in particular poor stability. Herein, we report atomically dispersed manganese (Mn) embedded on nitrogen and sulfur co-doped graphene as an efficient and robust electrocatalyst for ORR in alkaline electrolyte, realizing a half-wave potential (E1/2) of 0.883 V vs. reversible hydrogen electrode (RHE) with negligible activity degradation after 40,000 cyclic voltammetry (CV) cycles in 0.1 M KOH. Introducing sulfur (S) to form Mn-S coordination changes the spin state of single Mn atom from high-spin to low-spin, verified by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements as well as density functional theory (DFT) calculations, which effectively optimizes the oxygen intermediates adsorption over the single Mn atomic sites and thus greatly improves the ORR activity.

Progress and challenges in structural, in situ and operando characterization of single-atom catalysts by X-ray based synchrotron radiation techniques

Single-atom catalysts (SACs) represent the ultimate size limit of nanoscale catalysts, combining the advantages of homogeneous and heterogeneous catalysts. SACs have isolated single-atom active sites that exhibit high atomic utilization efficiency, unique catalytic activity, and selectivity. Over the past few decades, synchrotron radiation techniques have played a crucial role in studying single-atom catalysis by identifying catalyst structures and enabling the understanding of reaction mechanisms. The profound comprehension of spectroscopic techniques and characteristics pertaining to SACs is important for exploring their catalytic activity origins and devising high-performance and stable SACs for industrial applications. In this review, we provide a comprehensive overview of the recent advances in X-ray based synchrotron radiation techniques for structural characterization and in situ/operando observation of SACs under reaction conditions. We emphasize the correlation between spectral fine features and structural characteristics of SACs, along with their analytical limitations. The development of IMST with spatial and temporal resolution is also discussed along with their significance in revealing the structural characteristics and reaction mechanisms of SACs. Additionally, this review explores the study of active center states using spectral fine characteristics combined with theoretical simulations, as well as spectroscopic analysis strategies utilizing machine learning methods to address challenges posed by atomic distribution inhomogeneity in SACs while envisaging potential applications integrating artificial intelligence seamlessly with experiments for real-time monitoring of single-atom catalytic processes.

Atomic Printing Strategy Achieves Precise Anchoring of Dual-Copper Atoms on C2N Structure for Efficient CO2 Reduction to Ethylene

Isolated metal sites catalysts (IMSCs) play crucial role in electrochemical CO2 reduction, with potential industrial applications. However, tunable synthesis strategies for IMSCs are limited. Herein, we present an atomic printing strategy that draws inspiration from the ancient Chinese "movable-type printing technology". Selecting customizable combinations of metal atoms as metal precursors from an extensive binuclear metal library. A series of dual-atom catalysts were prepared by utilizing the edge nitrogen atoms in the C2N cavity as anchoring "pincers" to capture metal atoms. To prove utility, the dual atom catalyst Cu2-C2N is investigated as electrocatalytic CO2RR catalyst. The synergistic interaction of dual Cu atoms promotes C-C coupling and guarantees FEC2+ (90.8 %) and FEC2H4. (71.7 %) at -1.10 V vs RHE. DFT calculations revealed the Cu2 site would be subtly flipped during CO2RR for enhancing *CO adsorption and dimerization. We validate that atomic printing strategies are applicable to wide range of metal combinations, representing a significant advancement in the development of IMSCs.

Well-defined asymmetric nitrogen/carbon-coordinated single metal sites for carbon dioxide conversion

Asymmetric nitrogen/carbon-coordinated single metal sites (M-NxC4-x) outperform symmetric M-N4 sites in carbon dioxide (CO2) electroreduction. However, the challenge of crafting well-defined M-NxC4-x sites complicates the understanding of their structure-catalytic performance relationship. In this study, we employ metallized N-confused tetraphenylporphyrin (M-NCTPP) to investigate CO2 conversion on M-N3C1 sites using both density functional theory and experimental methods. The optimal cobalt (Co)-N3C1 site (Co-NCTPP) achieves a current density of 500 mA cm-2 and a carbon monoxide Faraday efficiency exceeding 90 % at -1.25 V vs. the reversible hydrogen electrode, surpassing the performance of Co-N4 (Co-TPP). This research introduces a novel approach for designing and synthesizing high-activity heteroatom-anchored single metal sites, advancing fundamental understanding in the field.