Single-atom Sites Research Articles

Superhydrophobic Co/Fe sulfide nanoparticles and single-atoms doped carbon nanosheets composite air cathode for high-performance zinc-air batteries

Development of a high-performance bifunctional catalyst is essential for the actual implementation of zinc-air batteries in practical applications. Herein, a bifunctional cathode of Co3S4/FeS heterogeneous nanoparticles embedded in Co/Fe single-atom-loaded nitrogen-doped carbon nanosheets is designed. Cobalt-iron sulfides and single atomic sites with Co-N4/Fe-N4 configurations are confirmed to coexist on the carbon matrix by EXAFS spectroscopy. 3D self-supported super-hydrophobic multiphase composite cathode provides abundant active sites and facilitates gas–liquid-solid three-phase interface reactions, resulting in excellent electrocatalytic activity and batteries performance, i.e., an OER overpotential (η10) of 260 mV, a half-wave potential (E1/2) of 0.872 V for ORR, a ΔE of 0.618 V, and a discharge power density of 170 mW cm−2, a specific capacity of 816.3 mAh g−1. DFT analysis shows multiphase coupling of sulfide heterojunction through single-atomic metal doped carbon nanosheets reduces offset on center of electronic density of states before and after oxygen adsorption, and spin density of adsorbed oxygen with same spin orientation, leading to weakened charge/spin interactions between adsorbed oxygen and substrate, and a lowered oxygen adsorption energy to accelerate OER/ORR.

Fully exposed copper single-atom sites on mesoporous N/S-codoped graphene for efficient zinc-air battery

Transition metal single-atom catalysts are recently emerging as the most potential candidates for the oxygen reduction reaction due to their remarkable activity and durability, yet subjected to limited availability proportion of active sites to reactant in practice due to the lack of favorable morphology. Herein, the ultrathin mesoporous N/S-codoped graphene is fabricated by a potassium thiocyanate (KSCN) assisted pyrolysis of metal-organic framework (ZIF-8) as the robust substrate for anchoring copper single-atom sites. The KSCN-assisted pyrolysis can not only create N and S coordination atoms but also regulate the fully exposed morphology. The graphene-supported copper single-atom catalysts (g-Cu-SACs) show typical mesoporous structure with larger surface area of 1612 m2 g–1. Spectral and microscopy results reveal highly isolated Cu single-atom sites on mesoporous graphene with unsymmetrical Cu-S1N3 structure. Theoretical analysis demonstrated that the asymmetric coordination environment effectively enhanced O2 adsorption and facilitated the ORR performance. The g-Cu-SACs show excellent catalytic activity in alkaline oxygen reduction reaction with a half-wave potential of 0.920 VRHE and good cycling stability, which are superior to that of three-dimensional copper single-atom catalysts (Cu-SACs, supported by N/S-codoped carbon framework directly derived from ZIF-8). Furthermore, the zinc-air battery assembled with g-Cu-SACs also exhibits high specific capacity and remarkable cycling lifetime. This work provides a novel strategy to construct highly exposed single-atom catalysts for energy-related applications.

Dual single atomic Ni sites constructing Janus hollow graphene for boosting electrochemical sensing of glucose.

Single atom catalysts (SACs) have attracted attention due to their excellent catalysis activity under specific reactions and conditions. However, the low density of SACs greatly limits catalytic performance. The three-dimensional graphene hollow nanospheres (GHSs) with very thin shell structure can be used as excellent carrier materials. Not only can its outer surface be used to anchor metal single atoms, but its inner surface can also provide rich sites. Here, a novel step-by-step assembly strategy is reported to anchor nickel single atoms (Ni SAs) on the inner and outer surfaces of GHSs (Ni SAs/GHSs/Ni SAs), which significantly increases the loading capacity of Ni SAs (4.8 wt%). Compared to conventional materials that only anchor Ni SAs to the outer surface of the carrier (Ni SAs/GHSs), Ni SAs/GHSs/Ni SAs exhibits significantly higher electrocatalytic activity toward glucose oxidation in alkaline media. The sensitivity of Ni SAs/GHSs/Ni SAs/GCE is nearly five times higher than that of Ni SAs/GHSs/GCE. Moreover, the sensor based on Ni SAs/GHSs/Ni SAs can detect glucose in a wide concentrationrange of 0.8µM-1.1244mM with a low detection limit of 0.19µM (S/N = 3). This study not only provides an effective sensing material for glucose detection, but also opens a new avenue to construct high-density metal SACs.

Precise Modulation of the Coordination Environment of Single Cu Site Catalysts to Regulate the Peroxymonosulfate Activation Pathway for Water Remediation.

Single atom site catalysts (SACs) with atomically dispersed active sites can be expected to be potential ideal catalysts for accurately modulating the persulfate activation pathway during the water remediation process because of their well-defined structure and the maximum metallic atom utilization. In this paper, a series of Cu SACs with different coordination environments were synthesized to elaborately regulate the peroxymonosulfate activation pathway in AOPs to clarify active species generation and transformation in water remediation. The degradation rate constants (kobs) of Cu-N2, Cu-N3, and Cu-N4 were 0.028, 0.021, and 0.015 min-1, respectively. Cu-N2 SACs exhibited a noticeable enhanced performance for bisphenol A (BPA) removal from water compared to that of the Cu-Nx SACs (x = 3, 4), accompanied by peroxymonosulfate (PMS) activation pathway variation. As shown by experimental and theoretical results, the PMS activation pathway was transformed from ROS to electron transfer with nitrogen coordination numbers decreasing from 4 to 2, which can be ascribed to the uneven charge distribution of Cu sites as well as upshifts in the d-band center, and thereby optimized electron transfer for PMS activation. Furthermore, the increasing nitrogen vacancies of single Cu site catalysts can also result in more unoccupied 3d orbitals of Cu atoms in SACs, thereby improving the intermediates' (PMS and BPA) adsorption-desorption process and BPA removal performance. These findings provided a beneficial approach for the coordination number regulation of SACs in water remediation.

Constructing Ru single-atomic sites through potential-induced self-reconstruction to accelerate electrocatalytic nitrate reduction for ammonia production

Conversion of NO3−-to-NH3 via the electrocatalytic nitrate reduction reaction (NO3-RR) is an emerging strategy for ammonia production and storage of “green hydrogen”, but is limited by the dissatisfactory activity and selectivity. In this study, we discovered that cobalt carbonate hydroxide (Co2(OH)2CO3) underwent a potential-induced self-reconstruction to cobalt hydroxide (Co(OH)2) during NO3-RR. The incorporation of Ru into Co2(OH)2CO3 expedited the aforementioned self-reconstruction process and resulted in the formation of Ru single-atomic sites (Ru SASs) anchored on Co(OH)2 nanosheets. This structure is reported as a highly efficient electrocatalyst for NO3−-to-NH3 conversion and exhibits exceptional electrochemical performance in zinc-NO3− batteries. Theoretical analysis revealed that the conversion of NO3−-to-NH3 occurred on Ru SASs through an N-end pathway with *NO as a characteristic intermediate. Furthermore, Ru SASs facilitated the thermodynamic-determining step of *NH2-to-*NH3, thus promoting the overall NO3−-to-NH3 conversion process.

Controlled dispersion of Ni catalyst on N-doped carbon support for stable and selective hydrogen production from formic acid

Formic acid is a liquid organic hydrogen carrier from which hydrogen can be released together with CO2 by catalytic decomposition. The development of supported Ni catalysts for H2 production is important. Here, the effects of Ni state/dispersion are considered. For this purpose, three samples were prepared with about 3 wt% Ni deposited on porous N-doped carbon. The first sample contained predominantly Ni nanoparticles (∼2 nm), the second contained Ni clusters (<1 nm), and the third – single-atom Ni sites. The catalysts showed close activity in the gas-phase reaction. However, a minimum apparent activation energy of 105 kJ/mol and a maximum selectivity towards H2 production of 99% were achieved for the single-atom Ni catalyst. The nature of its single-atom sites was established to correspond to Ni-N4 and Ni-O4, which showed greater stability under the conditions of the catalytic reaction.

Precisely constructing pentagon trapped single-atomic iron sites in defective carbon for efficient oxygen electroreduction

Precisely constructing pentagon trapped single-atomic iron sites in defective carbon for efficient oxygen electroreduction

Neighbouring Synergy in High-Density Single Ir Atoms on CoGaOOH for Efficient Alkaline Electrocatalytic Oxygen Evolution.

The catalytic performance of single-atom catalysts was strictly limited by isolated single-atom sites. Fabricating high-density single atoms to realize the synergetic interaction in neighbouring single atoms could optimize the adsorption behaviors of reaction intermediates, which exhibited great potential to break performance limitations and deepen mechanistic understanding of electrocatalysis. However, the catalytic behavior governed by neighbouring single atoms is particularly elusive and has yet to be understood. Herein, we revealed that the synergetic interaction in neighbouring single atoms contributes to superior performance for oxygen evolution relative to isolated Ir single atoms. Neighbouring single atoms was achieved by fabricating high-density single atoms to narrow the distance between single atoms. Electrochemical measurements demonstrated that the Nei-Ir1/CoGaOOH with neighbouring Ir single atoms exhibited a low overpotential of 170 mV at a current density of 10 mA cm-2, and long-durable stability over 2000 h for oxygen evolution. Mechanistic studies revealed that neighbouring single atoms synergetic stabilized the *OOH intermediates via extra hydrogen bonding interactions, thus significantly reducing the reaction energy barriers, as compared to isolated Ir single atoms. The discovery of the synergetic interaction in neighbouring single atoms could offer guidance for the development of efficient electrocatalysts, thus accelerating the world's transition to sustainable energy.

Insights on the activity-selectivity trade-off in iron-containing nitrogen-doped carbon catalyst via cobalt addition for oxygen reduction reaction in alkaline medium

Iron-based noble-metal-free electrocatalysts exhibit impressive performance and stability for the Oxygen reduction reaction (ORR) in alkaline media, but face challenges. This study investigates the impact of Co addition to Fe in nitrogen(N)-doped carbon (Fe/NC) catalysts prepared via one-pot synthesis involving direct pyrolysis of the metal (M) and 2,4,6-tris(2-pyridyl)-s-triazine complexes (M-TPTZ) on carbon. Comprehensive characterization reveals N-doped carbon structures with single-atom sites and metal oxides, with M-Nx centers mainly in carbon pores and metal oxides on the carbon surface. N2 adsorption/desorption experiments and electrochemical surface area (ECSA) reveals that Co introduction enhances the catalyst surface area. Moreover, Co addition alters nitrogenated species distribution, affecting catalytic activity. Electrochemical studies rank catalytic activity as Fe/NC < Co/NC < CoFe/NC, while rotating ring-disk electrode (RRDE) investigations show mixed 2 and 4 electrons pathways. Fe/NC follows a 4e- pathway with minimal HO2− production, while Co-containing catalysts suggest a mixed (2e- + 2e-) pathway with an average of 3.75 electrons involved. This divergence highlights nuanced electrochemical characteristics of Fe- and Co-based materials, emphasizing the need for in-depth characterization.

High-Efficiency Electrocatalytic Reduction of N2O with Single-Atom Cu Supported on Nitrogen-Doped Carbon.

Nitrous oxide (N2O) is a potent greenhouse gas with a high global warming potential, emphasizing the critical need to develop efficient elimination methods. Electrocatalytic N2O reduction reaction (N2ORR) stands out as a promising approach, offering room temperature conversion of N2O to N2 without the production of NOx byproducts. In this study, we present the synthesis of a copper-based single-atom catalyst featuring atomic Cu on nitrogen-doped carbon black (Cu1-NCB). Attributed to the highly dispersed single-atom Cu sites and the effective suppression of the hydrogen evolution reaction, Cu1-NCB demonstrated an optimal N2 faradaic efficiency (82.1%) and yield rate (3.53 mmol h-1 mgmetal-1) at -0.2 and -0.5 V vs RHE, respectively, outperforming previously reported N2ORR electrocatalysts. Further, a gas diffusion electrode cell was employed to improve mass transfer and achieved a 28.6% conversion rate of 30% N2O with only a 14 s residence time, demonstrating the potential for practical application. Density functional theory calculations identified Cu-N4 as the crucial active site for N2ORR, highlighting the significance of the unsaturated coordination and metal-support electronic structure. O-terminal adsorption of N2O was favored, and the dissociative adsorption (*ON2 → *O + N2) was the rate-determining step. These findings reveal the broad prospects of N2O decomposition via electrocatalysis.

Near-range modulation of single-atomic Fe sites by simultaneously integrating heteroatom and nanocluster for efficient oxygen reduction

Modulation strategies are widely developed to regulate electronic state of single-atom catalysts (SACs) to reinforce the catalytic activity of oxygen reduction reaction (ORR). However, the modulation effect using only single coordination regulation is often insufficient to optimize the electronic and geometric structure of metal active centers. Herein, a general strategy to modify the activity of single-atomic Fe site is achieved by dual decoration of Fe centers with contiguous sulfur atoms and metal nanoclusters via an aggregation-redispersion route. Under near-range engagement, the adjacent S atoms and Fe nanoclusters can break the symmetric electronic interface of Fe-N moiety, and act as the modulators to synergistically tune the electronic configurations of Fe centers, leading to less electron transfer to *OH, and subsequent favorable desorption. In situ spectroscopic characterization and theoretical results reinforces the significant roles of S atoms and metal clusters in tandem by correlating their induced electron redistribution with ORR activity, which ultimately accelerates the adsorption/desorption of oxygenated intermediates for robust catalytic performance. Due to the improvement of graphitization degree, carbon supports possess efficient active sites and exhibit superior anti-corrosion. The resultant FeNC-2 M demonstrates outstanding ORR activity with high power density, maintaining remarkable durability in Zn-air batteries and microbial fuel cells. This work provides effective and universal way to modulate microenvironment of single metal sites, facilitating the open up of potential application spaces for various SACs.

Ruthenium Single Atomic Sites Surrounding the Support Pit with Exceptional Photocatalytic Activity.

Single-metal atomic sites and vacancies can accelerate the transfer of photogenerated electrons and enhance photocatalytic performance in photocatalysis. In this study, a series of nickel hydroxide nanoboards (Ni(OH)x NBs) with different loadings of single-atomic Ru sites (w-SA-Ru/Ni(OH)x) were synthesized via a photoreduction strategy. In such catalysts, single-atomic Ru sites are anchored to the vacancies surrounding the pits. Notably, the SA-Ru/Ni(OH)x with 0.60 wt % Ru loading (0.60-SA-Ru/Ni(OH)x) exhibits the highest catalytic performance (27.6 mmol g-1 h-1) during the photocatalytic reduction of CO2 (CO2RR). Either superfluous (0.64 wt %, 18.9 mmol g-1 h-1; 3.35 wt %, 9.4 mmol-1 h-1) or scarce (0.06 wt %, 15.8 mmol g-1 h-1; 0.29 wt %, 21.95 mmol g-1 h-1; 0.58 wt %, 23.4 mmol g-1 h-1) of Ru sites have negative effect on its catalytic properties. Density functional theory (DFT) calculations combined with experimental results revealed that CO2 can be adsorbed in the pits; single-atomic Ru sites can help with the conversion of as-adsorbed CO2 and lower the energy of *COOH formation accelerating the reaction; the excessive single-atomic Ru sites occupy vacancies that retard the completion of CO2RR.

Atomically Dispersed Ga Synergy Lewis Acid‐Base Pairs in F‐doped Mesoporous Cu2O for Efficient Eletroreduction of CO2 to C2+ Products

AbstractElectroreduction of CO2 into high‐value chemicals and fuels driven is an effective way to alleviate the environmental crisis, but it suffers from poor activity and low selectivity of the catalyst. Single‐atom catalysts have excellent selectivity and the highest atomic efficiency, and are widely used in the 2‐electron transfer to produce CO. However, electroreduction of CO2 to C2+ products involves complex processes such as multi‐electron reaction and competitive adsorption, so single‐atom catalysis is often powerless. Herein, a single‐atom Ga‐anchored F‐doped Cu2O catalyst with dual active sites is reported. The Lewis acid‐base pairs and Ga single atom sites promote the adsorption/activation of CO2 and the dissociation of water molecules, respectively, enhance the coverage of *CO and *H, and their synergy optimizes the reaction path. At a high current density of 600 mA cm−2, the FEC2+ reached 72.8 ± 3.2% with remarkable stability. Experiments and theory calculations demonstrate that the dual sites increase the coverage of *CO and *H, and the key intermediate *CO is transformed into *CHO through protonation reaction, which changes the reaction path from the C─C coupling (*OCCO) to the protonation followed by C─C coupling (*OCCHO) with low energy barrier, greatly improving the selectivity for C2+ products.

Ruthenium Single Atomic Sites Surrounding the Support Pit with Exceptional Photocatalytic Activity

AbstractSingle‐metal atomic sites and vacancies can accelerate the transfer of photogenerated electrons and enhance photocatalytic performance in photocatalysis. In this study, a series of nickel hydroxide nanoboards (Ni(OH)x NBs) with different loadings of single‐atomic Ru sites (w‐SA‐Ru/Ni(OH)x) were synthesized via a photoreduction strategy. In such catalysts, single‐atomic Ru sites are anchored to the vacancies surrounding the pits. Notably, the SA‐Ru/Ni(OH)x with 0.60 wt % Ru loading (0.60‐SA‐Ru/Ni(OH)x) exhibits the highest catalytic performance (27.6 mmol g−1 h−1) during the photocatalytic reduction of CO2 (CO2RR). Either superfluous (0.64 wt %, 18.9 mmol g−1 h−1; 3.35 wt %, 9.4 mmol−1 h−1) or scarce (0.06 wt %, 15.8 mmol g−1 h−1; 0.29 wt %, 21.95 mmol g−1 h−1; 0.58 wt %, 23.4 mmol g−1 h−1) of Ru sites have negative effect on its catalytic properties. Density functional theory (DFT) calculations combined with experimental results revealed that CO2 can be adsorbed in the pits; single‐atomic Ru sites can help with the conversion of as‐adsorbed CO2 and lower the energy of *COOH formation accelerating the reaction; the excessive single‐atomic Ru sites occupy vacancies that retard the completion of CO2RR.

Regulating local charge distribution of single Ni sites in covalent organic frameworks for enhanced photocatalytic CO2 reduction

Covalent organic frameworks (COFs) engineered by single-atom sites have attracted significant attention for CO2 photoreduction. However, precisely manipulating the chemical environment of active sites on the COFs is a grand challenge. Herein, we synthesized a series of isostructural COFs for photocatalytic CO2 reduction, where the strong coordination conformation guides atomically dispersed metal sites to chelate spontaneously in the predesigned imine-pyridine position of COFs. Experimental and theoretical results revealed the crucial influence of the single-Ni site engineering and electronic structures of COF configuration on improving extended π-conjugation, exciton dissociation, charge separation efficiency, and charge carrier migration. Benefiting from the synergistic effect, the optimal Ni-TAPT-COF exhibited a record-high CO production rate of 25.5 mmol g-1h-1 and a selectivity of 98.8%, even natural-sunlight-driven diluted CO2 (10%). This work paves the way for the rational design of high-performance COF-based photocatalysts at the molecular level, highlighting their practical potential for CO2 photoreduction.

Synergy of Ni Nanoclusters and Single Atom Site: Size Effect on the Performance of Electrochemical CO2 Reduction Reaction and Rechargeable Zn−CO2 Batteries

AbstractThe design of bifunctional electrocatalysts toward reduction reaction of carbon dioxide (ECO2RR) and oxygen evolution reaction (OER) in aqueous rechargeable Zn─CO2 batteries (ZABs) still poses a significant challenge. Herein, Ni clusters (Nix) of 0.5 and 0.8 nm in diameter coupled with single Ni site (Ni−N4−C), denoted as Ni−N4/Ni5 and Ni−N4/Ni8, respectively, are synthesized and the size effect of Ni nanoclusters are studied. Ni−N4/Ni5 exhibits an ≈100% Faradaic efficiency (FECO) toward ECO2RR for CO from −0.4 to −0.8 V versus the reversible hydrogen electrode, superior to that of Ni−N4−C (FECO = 55.0%) and Ni−N4/Ni8 (FECO = 80.0%). The OER performance of Ni−N4/Ni5 and Ni−N4/Ni8 are superior or comparable to that of commercial RuO2 but outperform that of Ni−N4−C. Theoretical calculation indicates that *COOH of ECO2RR intermediates bond synergistically with Nix clusters and Ni−N4−C single atom site, promoting the activation of CO2 and reducing the energy barrier of the potential determining step of ECO2RR. Such effect is strongly size‐dependent and larger Nix nanoclusters result in too strong binding of *COOH intermediates, impede the formation of *CO. As a bifunctional cathode electrocatalyst of rechargeable alkaline aqueous ZABs, Ni−N4/Ni5 exhibits a peak power density of 11.7 mW cm−2 and cycling durability over 1200 cycles and 420 h.

A flexible self-supported electrochemical sensor Co-NC/PS@CC for real-time detection of cell-released H2O2

BackgroundHydrogen peroxide (H2O2) is an important reactive oxygen species (ROS) molecule involved in cell metabolism regulation, transcriptional regulation, and cytoskeleton remodeling. Real-time monitoring of H2O2 levels in live cells is of great significance for disease prevention and diagnosis. ResultsWe utilized carbon cloth (CC) as the substrate material and employed a single-atom catalysis strategy to prepare a flexible self-supported sensing platform for the real-time detection of H2O2 secreted by live cells. By adjusting the coordination structure of single-atom sites through P and S doping, a cobalt single-atom nanoenzyme Co-NC/PS with excellent peroxidase-like activity was obtained. Furthermore, we explored the enzyme kinetics and possible catalytic mechanism of Co-NC/PS. Due to the excellent flexibility, high conductivity, strong adsorption performance of carbon cloth, and the introduction of non-metallic atom-doped active sites, the developed Co-NC/PS@CC exhibited ideal sensing performance. Experimental results showed that the linear response range for H2O2 was 1–17328 μM, with a detection limit (LOD) of 0.1687 μM. Additionally, the sensor demonstrated good reproducibility, repeatability, anti-interference, and stability. SignificanceThe Co-NC/PS@CC prepared in this study has been successfully applied for detecting H2O2 secreted by MCF-7 live cells, expanding the application of single-atom nanoenzymes in live cell biosensing, with significant implications for health monitoring and clinical diagnostics.

Breaking Continuously Packed Bimetallic Sites to Singly Dispersed on Nonmetallic Support for Efficient Hydrogen Production.

We have synthesized Pt1Zn3/ZnO, also termed 0.01 wt %Pt/ZnO-O2-H2, as a catalyst containing singly dispersed single-atom bimetallic sites, also called a catalyst of singly dispersed bimetallic sites or a catalyst of isolated single-atom bimetallic sites. Its catalytic activity in partial oxidation of methanol to hydrogen at 290 °C is found to be 2-3 orders of magnitude higher than that of Pt-Zn bimetallic nanoparticles supported on ZnO, 5.0 wt %Pt/ZnO-N2-H2. Selectivity for H2 on Pt1Zn3/ZnO reaches 96%-100% at 290-330 °C, arising from the uniform coordination environment of single-atom Pt1 in singly dispersed single-atom bimetallic sites, Pt1Zn3 on 0.01 wt %Pt/ZnO-O2-H2, which is sharply different from various coordination environments of Pt atoms in coexisting PtxZny (x ≥ 0, y ≥ 0) sites on Pt-Zn bimetallic nanoparticles. Computational simulations attribute the extraordinary catalytic performance of Pt1Zn3/ZnO to the stronger adsorption of methanol and the lower activation barriers in O-H dissociation of CH3OH, C-H dissociations of CH2O to CO, and coupling of intermediate CO with atomic oxygen to form CO2 on Pt1Zn3/ZnO as compared to those on Pt-Zn bimetallic nanoparticles. It demonstrates that anchoring uniform, isolated single-atom bimetallic sites, also called singly dispersed bimetallic sites on a nonmetallic support can create new catalysts for certain types of reactions with much higher activity and selectivity in contrast to bimetallic nanoparticle catalysts with coexisting, various metallic sites MxAy (x ≥ 0, y ≥ 0). As these single-atom bimetallic sites are cationic and anchored on a nonmetallic support, the catalyst of singly dispersed single-atom bimetallic sites is different from a single-atom alloy nanoparticle catalyst. The critical role of the 0.01 wt %Pt in the extraordinary catalytic performance calls on fundamental studies of the profound role of a trace amount of a metal in heterogeneous catalysis.

Co-N-C axially coordination regulated H2O2 selectivity via water medicated recombination of solute •OH: A new route

The cobalt, earth abundant transition metal, embedded in nitrogen doped carbon material as single atom site (Co-N-C) has been manifested as promising electrochemical oxygen reduction reaction (ORR) catalyst, however the unsatisfying production selectivity has hampered its widespread applications. Herein, the H2O2 selectivity of Co-N-C catalyst has been tailored with Co axial functional groups. Thermodynamically, the selectivity is regulated due to the fine-tuning of the adsorption of the key reaction intermediates (ΔG*OOH), and five functional groups, including −O, –OH, –CN, −CH3 and −SO3, endow the Co-N-C catalyst with superior H2O2 selectivity. Importantly, we unravel a new water medicated recombination of solute •OH reaction pathway for H2O2 production, which was the result of dissociation of *HOOH in explicit water environment. That is, two •OH species reaction in the liquid environment which originated from the creaking of *OOH intermediates due to the weakened O-O bond by the interaction with surrounding water. This study provides foundational understanding for the ORR catalytic mechanism at the electrochemical interface and opens up new avenues for rational design of targeted high efficiency electrocatalysts.

Electron redistribution and proton transfer induced by atomically fully exposed Cu-O-Fe clusters coupled with single-atom sites for efficient oxygen electrocatalysis

Single-atom catalysts have garnered significant attention by showing sparkling performance in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the air cathode side of energy devices such as metal-air batteries and fuel cells. This work presents a novel catalyst, AC-CuFe-NC, that incorporates Fe-doped CuO atomic clusters (CuOFe) synergistically with single-atom sites. The AC-CuFe-NC demonstrates outstanding ORR performance (half-wave potential of 0.92 V) and an oxygen overpotential gap between ORR and OER as low as 0.61 V, which is among the top reported performances. Combined with in situ ATR-SEIRAS and DFT calculations, it is shown that the synergistic CuOFe atomic clusters are effective in inducing the electronic structure redistribution of the Fe single-atom site, modulating oxygen adsorption energy, and lowering ORR barriers. More importantly, it is revealed that the synergistic adsorption of clusters and single-atom sites establishes hydrogen bonds between the oxygenated intermediates and the electrolyte H2O molecules. The constructed hydrogen bond can provide a pathway for efficient proton transport as supported by kinetic isotope experiments, leading to a substantial enhancement in reaction kinetics. Additionally, the oxygenated intermediates are stabilized, and the Fe-O bond is elongated during the final step of ORR, thereby facilitating the desorption of OH*. The excellent bifunctional electrocatalytic performance of AC-CuFe-NC enable it to show promising application in rechargeable Zn-air batteries. The innovative catalyst structure and synergistic mechanism demonstrated in this study shed light on the development of high-performance catalysts in energy devices.