Multiple Electron Transfer Research Articles

Multiple Electron Transfers Enable High-Capacity Cathode Through Stable Anionic Redox.

Single-electron transfer, low alkali metal contents, and large-molecular masses limit the capacity of cathodes. This study uses a cost-effective and light-molecular-mass orthosilicate material, K2FeSiO4, with a high initial potassium content, as a cathode for potassium-ion batteries to enable the transfer of more than one electron. Despite the limited valence change of Fe ions during cycling, K2FeSiO4 can undergo multiple electron transfers via successive oxygen anionic redox reactions to generate a high reversible capacity. Although the formation of O‒O dimers in K2FeSiO4 occur upon removing large amounts of potassium, the strong binding effect of Si on O mitigates irreversible oxygen release and voltage degradation during cycling. K2FeSiO4 achieves 236 mAh g-1 at 50mA g-1, with an energy density of 520Wh kg-1, which can be comparable with commercial LiFePO4 materials. Moreover, it also exhibits 1400 stable cycles under high-current conditions. These findings enhance the potential commercialization prospects for potassium-ion batteries.

Feδ+ diaspora titanium dioxide and graphene: A study of conductive powder materials and coating applications.

Developing new conductive primers to ensure electrostatic spraying is crucial in response to the call for lightweight production of new energy vehicles. We report a stabilized material, Fe-T/G, of Fe-doped TiO2 composite graphene synthesized by a simple hydrothermal and electrostatic self-assembly method. The resistivity decreases from 0.9165Ω·cm to 0.0943Ω·cm for T/G. XPS and EPR confirm that Fe3+ is doped into the TiO2 lattice to generate OVs, and Feδ+ is introduced to activate the surrounding Fe-Ti active sites to break the obstruction of the Ti-O bond and build the Ti-O-C and Feδ+-O-C bonds between TiO2 and graphene to connect the two tightly. Multiple electron transfer channels promote Feδ+ impurity energy levels in the TiO2 valence and conduction bands to build electron leaping pathways, enhancing the electron transport ability. Based on this, Fe-T/G can be used as a conductive coating material to develop various insulator surfaces. With Fe-T/G powder material and PVDF, a conductive primer coating can be made and overlaid on a plastic plate to simulate actual applications. The resistance can still be maintained below 25Ω·cm. Through contact angle experiments, it has been confirmed that the superhydrophobic surface has a water contact angle of 142.8°, with self-cleaning potential.

Subtle Tuning of Catalytic Well Effect in Phthalocyanine Covalent Organic Frameworks for Selective CO2 Electroreduction into C2H4.

In the electrocatalytic CO2 reduction reaction (CO2RR), the strategic design of a catalytic well capable of regulating the overall confinement effects of catalytic sites holds significant promise for enhancing multiple-electron transfer and C─C coupling efficiency, particularly for the generation of C2+ products. Here, a series of Cu-salphen-based covalent organic frameworks (COFs) featuring hydroxyl-induced catalytic well are synthesized, which demonstrate successful application in electrocatalytic CO2RR to yield multiple-electron transferred products. The meticulously engineered catalytic well, facilitated by multi-hydroxyl groups, manifests robust confinement effects, facilitating selective adsorption, enrichment, and activation of CO2, intermediate stabilization, and reduction of energy barriers for electrocatalytic CO2RR. Specifically, product selectivity can be finely tuned from CH4 to C2H4 by modulating the levels of catalytic well, with CuPc-DFP-4OH-Cu exhibiting the most pronounced catalytic well effect, yielding a high 56.86% faradaic efficiency (FE) for C2H4 at -0.7 V, while CuPc-DFP-Cu, with the weakest catalytic well effect, achieves a 75.24% FE for CH4 at -1.0 V. Notably, the attained FE for C2H4 (56.86%) surpasses that of all reported COFs to date. Complemented by theoretical calculations and in situ tests, this study delves deeply into the pivotal roles of hydroxyl-induced catalytic well with confinement effects.

Amphi-Funtional Mediator for Proton-Coupled Electron Transfer in Low-Voltage Electrocatalytic-Hydrogenation

Within renewable energy systems, proton exchange membrane (PEM) electrolyzer relies on multiple proton-coupled electron transfer (PCET) reaction on heterogeneous catalyst surface. In PEM electrolyzer, the catalytic process of hydrogen adsorption through Volmer reaction, involving the combination of a proton and an electron on surface, holds significance. Recent attention has been focused on optimizing the proton and an electron coupling by lowering the activation barrier and driving force of the hydrogen adsorption reaction. This focus is primarily on the cathodic part, involving hydrogen evolution reaction (HER) and organic electro-hydrogenation systems, initiating the formation of a surface-adsorbed hydrogen atom (H*) as first step. Among them, hydrogen spillover has emerged as a new method to reduce the activation barrier in HER and hydrogenation systems. This mechanism contains the diffusion of adsorbed H+ from hydrogen-rich to deficient surface. An optimal catalyst for hydrogen spillover is characterized by strong dissociation abilities and weak binding to dissociated hydrogen atoms. Palladium (Pd) exhibits commendable equilibrium of these features, suggesting the potential for performance improvement through alloying with other metals. However, hydrogen spillover is specific to the cathodic part, where the reactant is the surface-adsorbed hydrogen atom, and do not extend to the anodic part, which involves reactants unrelated to the adsorbed hydrogen atom.Generally, in the anodic part of the electrolyzer system, water-based reactants (H2O in acid/ OH- in based) or organic-based reactants (such as hydrazine, ethanol, and formic acid) are utilized. Nowadays, organic-based reactants are preferred in low-voltage electrolysis due to the sluggish kinetics of electro-decomposition in water-based reactants. Among them, formic acid emerges as a promising organic molecule for achieving high efficiency. Formic acid electrooxidation reaction (FAOR) theoretically exhibits a negative oxidation potential compared to both hydrogen oxidation reaction (HOR) and oxygen evolution reaction (OER): Eo = -0.17 VSHE for HCOOH/CO2 < +0 VSHE for H2/H+ < +1.23 VSHE for H2O/O2. Platinum (Pt)-based catalysts are utilized in FAOR. Unfortunately, since HCOOH oxidation occurs under more positive potential than H* desorption (0.05 V < E < 0.35 VRHE), the FAOR encounters a limitation of overpotential that exceeds the potential of H* desorption. In other words, acceleration of H* desorption on active site could be necessary for the anodic reaction. To facilitate the movement of H* in both anodic and cathodic reactions, it is essential to consider accelerating both H* adsorption and desorption on the active site to ensure the efficiency. Despite the emphasis on activating the target reaction by controlling PCET, there are limited studies on dual mechanisms of H* adsorption and desorption in catalytic system.Biological energy conversion involves a diverse array of ion-coupled electron transfer reaction. Many organisms in electron transport chain facilitate the movement of electrons from electron donors to acceptors through redox reactions, linking this electron transfer with H+ ions. Here, we report Amphi-functional mediator (AFM) molecules, as a hydrogen atom modulator. Through the electrodeposition method onto Pt and Pd, we facilitate distinct movements of H*, resulting in low overpotential and enhanced catalytic efficiency. Depending on the migration energy of H*, AFM can function as both an acceptor and donor of H* to Pt and Pd, respectively. In a hydrogen-producing electrolyzer employing FAOR as the anodic process (FAOR||HER), AFC reduced the cell potential by 1.15 V at 10 mA cm-2, improving the faradaic efficiency from 87% to 100%. In an electrochemical hydrogen-carrier-producing reactor to hydrogenate toluene to methylcyclohexane (MCH), AFM successfully generated MCH, which cannot be produced without AFM. (Figure 1) Figure 1

(Invited) Evaluation of Oxygen Evolution Reaction Electrodes through Machine-Learning Analysis and in-Situ Electrochemical Spectroscopy

To enhance the catalysis of the oxygen evolution reaction (OER) at water electrolysis electrodes, it is imperative to eliminate the energy-consuming processes involved in multiple electron and proton transfer reactions. We propose employing a combination of machine-learning analysis of electrochemical activity and in-situ electrochemical Raman observation for the OER electrodes. The OER behavior can be categorized based on the contributions of Ni-OH and Ni-OOH, which serve as key OER intermediates. This information is utilized to elucidate the OER behavior through energetic and intermediate analyses. The presented study provides the direction for designing active OER catalysis in the future.

(Invited) Recent Insights on Conversion Materials for Lithium Batteries

The use of conversion materials as negative electrodes for lithium based batteries holds appeal due to the opportunity for high electrochemical capacity as the reactions of these materials typically involve multiple electron transfers per active center. However, the material phase changes often accompanied by large volume expansion can negatively impact cycle life due to a variety of degradation methods. Significant insights have been gained in recent years in the understanding of conversion materials and their electrochemistry through the use of multiple characterization methods over various length scales that have allowed investigation at the crystallite, particle, electrode, and systems scales. These insights have motivated deliberate manipulation of the materials and their environment including chemical composition, nanosizing, modification of surface chemistry, controlled aggregation, and electrode design. This presentation will discuss recent findings in the context of the field.

Engineering Delocalized Polarizations in Metal Oxide Electrodes with Conducting Polymers for Efficient and Durable Water-Splitting.

Oxygen evolution reaction is a pivotal anodic reaction for electrolysis, however, it remains the obstacle from its sluggish reaction kinetics originating from multiple electron transfer pathways at electrochemical interfaces. Especially, it remains a challenge to achieve stable operation at elevated current densities as electrodes suffer oxidative environment in corrosive conditions. Herein, we report that the conducting polymer polypyrrole electrodeposited Pr0.7Sr0.3CoO3 perovskite oxides for durable oxygen evolution electrodes. We found that the conducting polymer electrodeposited oxides exhibited a highly durable electrochemical oxygen evolution performance maintaining >99 % of initial activities during the accelerated durability test. Meanwhile, bare metal oxides presented significant performance drops (<6 % of initial activities) over the consecutive 20,000 accelerated durability test. High-resolution transmission electron microscope images identified the maintenance of high crystallinity of the heterostructure, suggesting that the electrodeposited pPy clusters can effectively delocalize highly polarized electrodes preventing material corrosion. The overall water electrolysis experiments further demonstrated that the heterostructure showed excellent stability at the high current density of 100 mA cm-2 over 700 hours. This marks the first report of the delocalized polarization benefiting from conducting polymers for durable oxygen evolution for perovskite oxides, suggesting great potential for scalable water electrolysis.

Surface and morphology modulated adsorption-activation of trace concentration hydrogen peroxide with multiple electron transfer pathways and sustained Fenton reactions

To promote mass transfer and activation of hydrogen peroxide (H2O2) in Fenton-like reactions, a novel MOFs-derived Fe2O3 was tailor-designed through surface sulfur modification and morphology tuning for degrading a group of persistent micropollutants, i.e., sulfamethoxazole, enrofloxacin, and ofloxacin. The introduction of Ca2+ and Mg2+ modulated the growth of crystal clusters to prevent aggregation of Fe2O3 nanoparticles and provide more reaction sites. Likewise, the abundant acid sites (–SO3H) promote the chemisorption of even trace-concentration H2O2 (S–O bonding), whereas the S–Fe bonding accelerates electron transfer to promote the Fe3+/Fe2+ cycle and thus the H2O2 utilization. More interestingly, surface-adsorbed H2O is found to be activated to form •OH, due to electron-poor Fe sites formed after detachment of –SO3H, demonstrating a sustained radical yield for the micropollutant degradation. This study opens new perspectives in catalyst design to ultimately realize the utilization of trace-concentration H2O2 and even H2O in Fenton-like systems.

Plasmon enhanced oxygen evolution reaction on Au decorated Ni(OH)2 nanostructures: The role of alkaline cations solvation

Water electrolysis is widely acknowledged to be kinetically hindered by the oxygen evolution reaction (OER), which involves multiple electron transfer steps. A critical yet often overlooked factor ruling the OER rate is the intricate interplay between alkaline cations of electrolyte, reaction intermediates, and the electrocatalyst surface. This study investigates the impact of plasmonic excitation on the OER using hexagonal hybrid Ni(OH)2-Au nanoplates in different alkaline electrolytes. While CsOH electrolyte exhibited the highest overall OER electroactivity, LiOH presented a remarkable enhancement under plasmonic excitation. Furthermore, FTIR-RAS and calculations analysis revealed that plasmonic relaxation mechanisms accelerate the Li+ environment modification process, mimicking the electrostatic configuration of Cs+, which facilitates a stabilized interaction between the active site (Ni3+) and OER intermediates, promoting rapid O−O bond formation. Our findings suggest that manipulating the cation’s vicinity through plasmonic heating is a promising strategy for enhancing OER efficiency.

Targeted Electrocatalysis for High‐Performance Lithium–Sulfur Batteries

The intricate sulfur redox chemistry involves multiple electron transfers and complicated phase changes. Catalysts have been previously explored to overcome the kinetic barrier in lithium–sulfur batteries (LSBs). This work contributes to closing the knowledge gap and examines electrocatalysis for enhancing LSB kinetics. With a strong chemical affinity for polysulfides, the electrocatalyst enables efficient adsorption and accelerated electron transfer reactions. Resulting cells with catalyzed cathodes exhibit improved rate capability and excellent stability over 500 cycles with 91.9% capacity retention at C/3. In addition, cells were shown to perform at high rates up to 2C and at high sulfur loadings up to 6 mg cm−2. Various electrochemical, spectroscopic, and microscopic analyses provide insights into the mechanism for retaining high activity, coulombic efficiency, and capacity. This work delves into crucial processes identifying pivotal reaction steps during the cycling process at commercially relevant areal capacities and rates.

Enhancing Compatibility of Two-Step Tandem Catalytic Nitrate Reduction to Ammonia Over P-Cu/Co(OH)2.

Electrochemical nitrate reduction reaction (NO3RR) is a promising approach to realize ammonia generation and wastewater treatment. However, the transformation from NO3 - to NH3 involves multiple proton-coupled electron transfer processes and by-products (NO2 -, H2, etc.), making high ammonia selectivity a challenge. Herein, a two-phase nanoflower P-Cu/Co(OH)2 electrocatalyst consisting of P-Cu clusters and P-Co(OH)2 nanosheets is designed to match the two-step tandem process (NO3 - to NO2 - and NO2 - to NH3) more compatible, avoiding excessive NO2 - accumulation and optimizing the whole tandem reaction. Focusing on the initial 2e- process, the inhibited *NO2 desorption on Cu sites in P-Cu gives rise to the more appropriate NO2 - released in electrolyte. Subsequently, P-Co(OH)2 exhibits a superior capacity for trapping and transforming the desorbed NO2 - during the latter 6e- process due to the thermodynamic advantage and contributions of active hydrogen. In 1m KOH + 0.1m NO3 -, P-Cu/Co(OH)2 leads to superior NH3 yield rate of 42.63mgh- 1cm- 2 and NH3 Faradaic efficiency of 97.04% at -0.4V versus the reversible hydrogen electrode. Such a well-matched two-step process achieves remarkable NH3 synthesis performance from the perspective of optimizing the tandem catalytic reaction, offering a novel guideline for the design of NO3RR electrocatalysts.

Bulk Alloy Anodes for Sodium‐Ion Batteries

AbstractSodium‐ion batteries (SIBs) are considered a promising candidate for next‐generation energy storage systems due to the abundance of available sodium resources. The practical application of SIBs critically depends on developing durable electrode materials with high capacity and long lifespan, particularly when it comes to finding suitable anode materials. Alloy‐type anodes are appealing for their high capacities owing to the multiple electron transfer alloying reaction mechanism, making them ideal for high‐energy‐density SIBs. However, the huge volume change during charge/discharge process can cause the active material pulverization to detach from the current collector, leading to poor cycling performance, especially for bulk alloy anodes. Despite this challenge, recent progress in bulk or micro‐sized alloy anodes for SIBs have shown promise. This review highlights the up‐to‐date advancements and research on bulk alloy‐based anode materials for SIBs, including synthetic strategies and electrochemical performance. The crucial role of bulk alloy anodes in advancing SIB technology is discussed, along with a summary of research on bulk alloy‐type anodes and their compounds for sodium storage. Strategies to improve the electrochemical performance of bulk alloy‐based anode materials are also explored. Additionally, the potential of multi‐component alloys and high‐entropy alloys as future research directions for alloy‐based anodes is proposed.

Preventing Nitrite Desorption via Switching Hydrogenation Position: A Dual-Site Approach for Selective Nitrate Reduction to Ammonia.

The electrochemical nitrate reduction reaction (NO3RR), which converts harmful nitrates into valuable ammonia (NH3) with zero carbon emission, is one of the most promising alternatives to the Haber-Bosch process. However, the NO3RR process is complex and involves multiple proton-coupled electron transfers that generate intermediates or byproducts, such as NO2 -, resulting in low ammonia yields and faradaic efficiency (FE). Herein, by constructing a FeCu bimetallic catalyst (FeCu-NC), the hydrogenation position of *NO3 is switched at the FeCu dual-atom site, preventing the desorption of *NO2 intermediate. Furthermore, electron transfer from Cu to Fe sites mimics the electron flow direction in natural nitrite reductase enzymes and accelerates the reduction of *NO2 to NH3, achieving efficient conversion of NO3 - to NH3. A 24-hour electrocatalytic experiment with FeCu-NC demonstrates negligible NO2 - formation throughout the NO3RR process, with an ammonia production rate of 6.13mgh-1mgcat -1 and an impressive FE of 95%, which are remarkably superior in comparison to most of the NO3RR electrocatalysts. This work opens new avenues for the fundamental understanding of catalytic mechanisms and the development of next-generation catalysts for sustainable ammonia production.

Valence switching of bismuth in ferricyanide as cathode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) are considered potential alternatives to lithium-ion batteries, and the key to their widespread use lies in finding efficient and cost-effective cathode materials. Ferricyanides have emerged as promising candidates for SIBs cathodes due to their low cost and open channel structure allowing for favorable ion and electron transport. However, traditional ferricyanides such as Prussian blue (PB) and its analogs (PBAs) have a limited two-electron transfer capacity, which hampers their practical application. Bi-based ferricyanide materials with multiple valence states, low toxicity and abundant resources are attractive for electrochemical reactions and enable multiple electron transfers to develop high-capacity cathode materials. In this study, we synthesized a rod-like BiHCF·4H2O sample using a simple coprecipitation method. After dehydration, the rod-like BiHCF compounds with a robust framework and reduced lattice water defects demonstrated good electrochemical performance in SIBs. The rod-like BiHCF electrode exhibited a specific capacity of 221 mAh g−1 at 20 mA g−1 based on a three-electron transfer of Bi3+/Bi0. A full SIBs composed of a BiHCF cathode and Bi anode demonstrated acceptable performance, indicating potential for practical applications. This work provides valuable insights into the development of redox-active site substitution strategies for high performance positive electrode materials in SIBs.

Probing the Molecular Interactions of Electrochemically Reduced Vitamin B2 with CO2.

The electrochemical reduction of riboflavin (vitamin B2) in a dimethyl sulfoxide solvent was examined under a CO2 atmosphere and compared with results under an argon atmosphere. Variable-scan-rate cyclic voltammetry combined with controlled potential electrolysis (CPE) and analysis by UV-vis and EPR spectroscopies provided insights into the nature of interactions of reduced flavins with dissolved CO2. Reductive exhaustive CPE experiments under CO2 indicated an overall two-electron stoichiometry, compared to one-electron reduction under an argon atmosphere, due to the lowering of the formal one-electron reduction potential of the flavin radical anion to form the dianion, which can be rationalized by riboflavin-CO2 molecular interactions. UV-vis spectroscopic measurements confirmed complete chemical reversibility of the redox transformations over extended time scales. Digital simulation modeling of the voltammetric data enabled extraction of thermodynamic and kinetic parameters for the proposed mechanism, comprising multiple proton-coupled electron transfer steps, diamagnetic anions, radical anions, and neutral radical intermediates enroute to the fully reduced state, as well as evidence of a long-lived solution phase complex of the reduced riboflavin with CO2.

A proton-coupled electron transfer process from functionalized carbon dots to molecular substrates: the role of pH.

Multiple electron and proton transfers in nanomaterials pose significant demands and challenges across the various fields such as renewable energy, chemical processes, biological applications, and photophysics. In this context, pH-responsive functional group-enriched carbon dots (C-Dots) emerge as superior proton-coupled electron transfer (PCET) agents owing to the presence of multiple functional groups (-COOH, -NH2, and -OH) on the surface and redox-active sites in the core. Here, we elucidate the 2e-/2H+ transfer ability of carboxyl-enriched C-Dots (C-Dot-COOH) and amine-enriched C-Dots (C-Dot-NH2) with molecular 2e-/2H+ acceptor (benzoquinone, BQ) as a function of pKa, facilitated by the formation of new O-H bonds. The ground state and excited state pKa values of different functional groups on the surface of C-Dots are determined using steady-state absorbance and photoluminescence (PL) spectroscopy. The optical spectroscopy and electrochemical studies are employed to comprehend the influence of the surface and core of C-Dots on the proton and electron transfer processes as a function of pH. The cyclic voltammetry analysis reveals a standard Nernstian shift in E1/2 per pH unit of 30 mV, indicating that the functionalized C-Dots hold promise as candidates for the 2e-/2H+ transfer process. The calculated bond dissociation free energy (BDFE) of the electroactive O-H/N-H bonds provides a more nuanced and detailed understanding of PCET thermodynamic landscapes. These findings underscore the potential of nanoscale functionalized C-Dots for facilitating multiple PCET reactions in future energy technologies.

High‐performance vanadium oxide‐based aqueous zinc batteries: Organic molecule modification, challenges, and future prospects

AbstractAqueous Zn‐vanadium batteries have been attracting significant interest due to the high theoretical capacity, diverse crystalline structures, and cost‐effectiveness of vanadium oxide cathodes. Despite these advantages, challenges such as low redox potential, sluggish reaction kinetics, and vanadium dissolution lead to inferior energy density and unsatisfactory lifespan of vanadium oxide cathodes. Addressing these issues, given the abundant redox groups and flexible structures in organic compounds, this study comprehensively reviews the latest developments of organic‐modified vanadium‐based oxide strategies, especially organic interfacial modification, and pre‐intercalation. The review presents detailed analyses of the energy storage mechanism and multiple electron transfer reactions that contribute to enhanced battery performance, including boosted redox kinetics, higher energy density, and broadened lifespan. Furthermore, the review emphasizes the necessity of in situ characterization and theoretical calculation techniques for the further investigation of appropriate organic “guest” materials and matched redox couples in the organic‐vanadium oxide hybrids with muti‐energy storage mechanisms. The review also highlights strategies for Zn anode protection and electrolyte solvation regulation, which are critical for developing advanced Zn‐vanadium battery systems suitable for large‐scale energy storage applications.

In-situ formation of V and Mg2Co/Mg2CoH5 for boosting the hydrogen storage properties of MgH2

Among the potential candidates for solid-state hydrogen storage, magnesium hydride (MgH2) exhibits high storage capacity of 7.6 wt%. However, its commercial application is hindered by the unsatisfactory kinetics properties and stable thermodynamics. In this study, we synthesized porous spherical CoV₂O₆ and incorporated it into MgH2, reducing the initial dehydrogenation temperature of MgH2 to 190 °C. Additionally, rapid hydrogen uptake was also observed, approaching 6.5 wt% H2 within 1000 s at 190 °C. A notable decrease of 45.78 kJ/mol in the apparent activation energy (Ea) for dehydrogenation signifies an improved dehydrogenation kinetic. The formation of Mg2Co/Mg2CoH5, along with the presence of single-valence and multi-valence vanadium, facilitated multiple electron transfer pathways. In particular, vanadium elongated the Mg–H bond is responsible for the high catalytic activity in boosting the hydrogen storage performance of MgH2. These findings provide new intuitions for further research to enhance the kinetic properties of hydrogen adsorption and desorption in magnesium hydride.

Construction of Ag/AgCl@MIL-53(Fe): Achieving Efficient Photocatalytic Water Oxidation via the Plasma-Phase Silver and Heterojunction Synergistic Effect

The development of highly efficient water oxidation catalysts is a bottleneck in achieving artificial photosynthesis, as water oxidation is a complex process involving multiple electron and proton transfers. To further improve the photocatalytic water oxidation performance of MIL-53(Fe), a series of Ag/AgCl@MIL-53(Fe) samples with different Fe:Ag ratios were synthesized by hydrothermal methods and used in the photocatalytic water oxidation reactions. XRD characterization showed the successful preparation of Ag/AgCl@MIL-53(Fe) heterostructure catalysts. The reaction results showed that sample AAM-2 (Fe:Ag=5:1) had the best photocatalytic water oxidation performance, with the highest TOF value of 0.14 mmol/(g·s) and quantum efficiency of 39.0 % under the conditions of catalyst mass of 1 mg and pH=9.0 for boric acid-borax buffer solution. Measurements of photocurrent indicated that the AAM-2 samples doped with Ag/AgCl had higher photocurrent densities, thus improving the photocatalytic performance. This provides new insights for constructing highly efficient porous MOFs catalysts.

A Metal-Sulfur-Carbon Catalyst Mimicking the Two-Component Architecture of Nitrogenase.

The production of ammonia (NH3) from nitrogen sources involves competitive adsorption of different intermediates and multiple electron and proton transfers, presenting grand challenges in catalyst design. In nature nitrogenases reduce dinitrogen to NH3 using two component proteins, in which electrons and protons are delivered from Fe protein to the active site in MoFe protein for transfer to the bound N2. We draw inspiration from this structural enzymology, and design a two-component metal-sulfur-carbon (M-S-C) catalyst composed of sulfur-doped carbon-supported ruthenium (Ru) single atoms (SAs) and nanoparticles (NPs) for the electrochemical reduction of nitrate (NO3 -) to NH3. The catalyst demonstrates a remarkable NH3 yield rate of ~37 mg L-1 h-1 and a Faradaic efficiency of ~97 % for over 200 hours, outperforming those consisting solely of SAs or NPs, and even surpassing most reported electrocatalysts. Our experimental and theoretical investigations reveal the critical role of Ru SAs with the coordination of S in promoting the formation of the HONO intermediate and the subsequent reduction reaction over the NP-surface nearby. Such process results in a more energetically accessible pathway for NO3 - reduction on Ru NPs co-existing with SAs. This study proves a better understanding of how M-S-Cs act as a synthetic nitrogenase mimic during ammonia synthesis, and contributes to the future mechanism-based catalyst design.