Constructing Co4(SO4)4 Clusters within Metal-Organic Frameworks for Efficient Oxygen Electrocatalysis.

Multinuclear metal clusters are ideal candidates to catalyze small molecule activation reactions involving the transfer of multiple electrons. However, synthesizing active metal clusters is a big challenge. Herein, on constructing an unparalleled Co4(SO4)4 cluster within porphyrin-based metal-organic frameworks (MOFs) and the electrocatalytic features of such Co4(SO4)4 clusters for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is reported. The reaction of CoII sulfate and metal complexes of tetrakis(4-pyridyl)porphyrin under solvothermal conditions afforded Co4-M-MOFs (M═Co, Cu, and Zn). Crystallographic studies revealed that these Co4-M-MOFs have the same framework structure, having the Co4(SO4)4 clusters connected by metalloporphyrin units through Co─Npyridyl bonds. In the Co4(SO4)4 cluster, the four CoII ions are chemically and symmetrically equivalent and are each coordinated with four sulfate O atoms to give a distorted cube-like structure. Electrocatalytic studies showed that these Co4-M-MOFs are all active for electrocatalytic OER and ORR. Importantly, by regulating the activity of the metalloporphyrin units, it is confirmed that the Co4(SO4)4 cluster is active for oxygen electrocatalysis. With the use of Co porphyrins as connecting units, Co4-Co-MOF displays the highest electrocatalytic activity in this series of MOFs by showing a 10 mA cm-2 OER current density at 357 mV overpotential and an ORR half-wave potential at 0.83 V versus reversible hydrogen electrode (RHE). Theoretical studies revealed the synergistic effect of two proximal Co atoms in the Co4(SO4)4 cluster in OER by facilitating the formation of O─O bonds. This work is of fundamental significance to present the construction of Co4(SO4)4 clusters in framework structures for oxygen electrocatalysis and to demonstrate the cooperation between two proximal Co atoms in such clusters during the O─O bond formation process.

Piezo-catalysis Mechanism Elucidation by Tracking Oxygen Reduction to Hydrogen Peroxide with In-situ EPR Spectroscopy.

For piezoelectric catalysis, the catalytic mechanism is a topic of great controversy, with debates centered around whether it belongs to the energy band theory of photocatalysis or the screening charge effect of electrochemical catalysis. Due to the formation of different intermediate active-species during two-electron oxygen reduction reaction (ORR) via electro- and photo-catalysis, the key to solving this problem is precisely monitoring the active species involved in ORR during electro-, photo-, and piezo-catalysis under identical condition. Here, a semiconductor material, BiOBr with abundant oxygen vacancies (BOB-OV) was found remarkable catalytic activity in H2O2 production by all three catalytic methods. By employing in-situ electron paramagnetic resonance (EPR) spectroscopy, the H2O2 evolution pathway through piezo-catalysis over BOB-OV was monitored, which showed a similar reaction pathway to that observed in photo-catalytic process. This finding represents solid evidence supporting the notion that piezo-catalytic mechanism of ORR is more inclined towards photo-catalysis rather than electro-catalysis. Significantly, this exploratory conclusion provides insight to deepen our understanding of piezo-catalysis.

Chemical Vapor Deposition Toward Efficient Bimetallic Atomically Dispersed Oxygen Reduction Catalysts.

Non-precious metal-based nitrogen-doped carbon (M-Nx/C) shows great potential as a substitute for precious metal Pt-based catalysts. However, the conventional pyrolytic methods for forming M-Nx/C active sites are prone to issues such as the lack of synergistic interactions among bimetallic atoms and the potential encasement of active sites, leading to compromised catalytic efficiency and hindered mass transfer. In this work, a highly active FeCo-N-C@U-AC electrocatalyst is developed with a high density of active sites, adequate exposure of catalytic sites, and robust mass transfer capability using the chemical vapor-phase deposition (CVD) technique. The resulting catalyst demonstrates impressive oxygen reduction reaction (ORR) catalytic performance and stability, with half-wave potentials of 0.820 V (0.1 M HClO4) and 0.911 V (0.1 M KOH), respectively. It also exhibits significantly enhanced stability, retaining 93.25% and 98.38% of current after continuous 50 000 s of durability testing, surpassing the retention rates of Pt/C (80.31% in HClO4 and 84.96% in KOH electrolytes). Notably, when employed as a cathode catalyst in proton exchange membrane fuel cells (PEMFCs) and zinc-air flow batteries (ZAFBs), the FeCo-N-C@U-AC catalyst delivers peak power densities of 859 and 162 mW·cm-2, respectively, showcasing competitive performance comparable to benchmark Pt/C.

Metal Atom-Support Interaction in Single Atom Catalysts toward Hydrogen Peroxide Electrosynthesis.

Single metal atom catalysts (SACs) have garnered considerable attention as promising agents for catalyzing important industrial reactions, particularly the electrochemical synthesis of hydrogen peroxide (H2O2) through the two-electron oxygen reduction reaction (ORR). Within this field, the metal atom-support interaction (MASI) assumes a decisive role, profoundly influencing the catalytic activity and selectivity exhibited by SACs, and triggers a decade-long surge dedicated to unraveling the modulation of MASI as a means to enhance the catalytic performance of SACs. In this comprehensive review, we present a systematic summary and categorization of recent advancements pertaining to MASI modulation for achieving efficient electrochemical H2O2 synthesis. We start by introducing the fundamental concept of the MASI, followed by a detailed and comprehensive analysis of the correlation between the MASI and catalytic performance. We describe how this knowledge can be harnessed to design SACs with optimized MASI to increase the efficiency of H2O2 electrosynthesis. Finally, we distill the challenges that lay ahead in this field and provide a forward-looking perspective on the future research directions that can be pursued.

Synergy of oxygen reduction for H2O2 production and electro-fenton induced by atomic hydrogen over a bifunctional cathode towards water purification.

In the Electro-Fenton (EF) process, hydrogen peroxide (H2O2) is produced in situ by a two-electron oxygen reduction reaction (2e ORR), which is further activated by electrocatalysts to generate reactive oxygen specieces (ROS). However, the selectivity of 2e transfer from catalysts to O2 is still unsatisfactory, resulting in the insufficient H2O2 availability. Carbon based materials with abundant oxygen-containing functional groups have been used as excellent 2e ORR electrocatalysts, and atomic hydrogen (H*) can quickly transfer one electron to H2O2 in a wide pH range and avoiding the restrict of traditional Fenton reaction. Herein, nickel nanoparticles growth on oxidized carbon deposited on modified carbon felt (Ni/Co@CFAO) was prepared as a bifunctional catalytic electrode coupling 2e ORR to form H2O2 with H* reducing H2O2 to produce ROS for highly efficient degradation of antibiotics. Electrochemical oxidation and thermal treatment were used to modulate the structure of carbon substrates for increasing the electro-generation of H2O2, while H* was produced over Ni sites through H2O/H+ reduction constructing an in-situ EF system. The experimental results indicated that 2e ORR and H* induced EF processes could promote each other mutually. The optimized Ni/Co@CFAO with a Ni:C mass ratio of 1:9 exhibited a high 2e selectivity and H2O2 yield of 49 mg L-1. As a result, the designed Ni/Co@CFAO exhibited excellent electrocatalytic ability to degrade tetracycline (TC) under different aqueous environmental conditions, and achieved 98.5% TC removal efficiency within 60 min H2O2 and H* were generated simultaneously at the bifunctional cathode and react to form strong oxidizing free radicals •OH. At the same time, O2 gained an electron to form •O2-, which could react with •OH and H2O to form 1O2, which had relatively long life (10-6∼10-3 s), further promoting the efficient removal of antibiotics in water.

Bifunctional Oxygen-Defect Bismuth Catalyst toward Concerted Production of H2O2 with over 150% Cell Faradaic Efficiency in Continuously Flowing Paired-Electrosynthesis System.

The electrosynthesis of hydrogen peroxide (H2O2) from O2 or H2O via the two-electron (2e-) oxygen reduction (2e- ORR) or water oxidation (2e- WOR) reaction provides a green and sustainable alternative to the traditional anthraquinone process. Herein, a paired-electrosynthesis tactic is reported for concerted H2O2 production at a high rate by coupling the 2e- ORR and 2e- WOR, in which the bifunctional oxygen-vacancy-enriched Bi2O3 nanorods (Ov-Bi2O3-EO), obtained through electrochemically oxidative reconstruction of Bi-based metal-organic framework (Bi-MOF) nanorod precursor, are used as both efficient anodic and cathodic electrocatalysts, achieving concurrent H2O2 production at both electrodes with high Faradaic efficiencies. Specifically, the coupled 2e- ORR//2e- WOR electrolysis system based on such distinctive oxygen-defect Bi catalyst displays excellent performance for the paired-electrosynthesis of H2O2, delivering a remarkable cell Faradaic efficiency of 154.8% and an ultrahigh H2O2 production rate of 4.3 mmol h-1 cm-2. Experiments combined with theoretical analysis reveal the crucial role of oxygen vacancies in optimizing the adsorption of intermediates associated with the selective two-electron reaction pathways, thereby improving the activity and selectivity of the 2e- reaction processes at both electrodes. This work establishes a new paradigm for developing advanced electrocatalysts and designing novel paired-electrolysis systems for scalable and sustainable H2O2 electrosynthesis.

Advanced Nanocarbons Toward two-Electron Oxygen Electrode Reactions for H2O2 Production and Integrated Energy Conversion.

Hydrogen peroxide (H2O2) plays a pivotal role in advancing sustainable technologies due to its eco-friendly oxidizing capability. The electrochemical two-electron (2e-) oxygen reduction reaction and water oxidation reaction present an environmentally green method for H2O2 production. Over the past three years, significant progress is made in the field of carbon-based metal-free electrochemical catalysts (C-MFECs) for low-cost and efficient production of H2O2 (H2O2EP). This article offers a focused and comprehensive review of designing C-MFECs for H2O2EP, exploring the construction of dual-doping configurations, heteroatom-defect coupling sites, and strategic dopant positioning to enhance H2O2EP efficiency; innovative structural tuning that improves interfacial reactant concentration and promote the timely release of H2O2; modulation of electrolyte and electrode interfaces to support the 2e- pathways; and the application of C-MFECs in reactors and integrated energy systems. Finally, the current challenges and future directions in this burgeoning field are discussed.

Proton-Enriched Alginate-Graphene Hydrogel Microreactor for Enhanced Hydrogen Peroxide Photosynthesis.

Efficient synthesis of H2O2 via photocatalytic oxygen reduction without sacrificial agents is challenging due to inadequate proton supply from water and difficulty in maintaining O-O bond during O2 activation. Herein, we developed a straightforward strategy involving a proton-rich hydrogel cross-linked by metal ions [M(n)], which is designed to facilitate the selective production of H2O2 through proton relay and metal ion-assisted detachment of crucial intermediates. The hydrogel comprises CdS/graphene and alginate cross-linked by metal ions via O=C-O-M(n) bonds. Efficient O2 reduction and hydrogenation occurred, benefitting from the collaboration between proton-rich alginate and the photocatalytically active CdS/graphene. Meanwhile, the O=C-O-M(n) bonds enhance the electron density of α-carbon sites on graphene, crucial for O2 activation and *OOH intermediate detachment, preventing deeper O-O bond cleavage. The role of metal ions in promoting *OOH desorption was evident through Lewis acidity-dependent activity, with Y(III) demonstrating the highest activity followed by Lu(III), La(III), and Ca(II).

Compressively Strained Fe3O4 in Core-Shell Oxygen Reduction Electrocatalyst Boosts Zinc-Air Battery Performance.

Fe3O4 is barely taken into account as an electrocatalyst for oxygen reduction reaction (ORR), an important reaction for metal-air batteries and fuel cells, due to its sluggish catalytic kinetics and poor electron conductivity. Herein, how strain engineering can be employed to regulate the local electronic structure of Fe3O4 for high ORR activity is reported. Compressively strained Fe3O4 shells with 2.0% shortened Fe─O bond are gained on the Fe/Fe4N cores as a result of lattice mismatch at the interface. A downshift of the d-band center occurs for compressed Fe3O4, leading to weakened chemisorption energy of oxygenated intermediates, and lower reaction overpotential. The compressed Fe3O4 exhibits greatly enhanced electrocatalytic ORR activity with a kinetic current density of 27 times higher than that of pristine one at 0.80 V (vs reversible hydrogen electrode), as well as potential application in zinc-air batteries. The findings provide a new strategy for tuning electronic structures and improving the catalytic activity of other metal catalysts.

Ultra-Small High-Entropy Alloy as Multi-Functional Catalyst for Ammonia Based Fuel Cells.

Ammonia fuel cells using carbon-neutral ammonia as fuel are regarded as a fast, furious, and flexible next-generation carbon-free energy conversion technology, but it is limited by the kinetically sluggish ammonia oxidation reaction (AOR), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER). Platinum can efficiently drive these three types of reactions, but its scale-up application is limited by its susceptibility to poisoning and high cost. In order to reduce the cost and alleviate poisoning, incorporating Pt with various metals proves to be an efficient and feasible strategy. Herein, PtFeCoNiIr/C trifunctional high-entropy alloy (HEA) catalysts are prepared with uniform mixing and ultra-small size of 2 ± 0.5 nm by Joule heating method. PtFeCoNiIr/C exhibits efficient performance in AOR (Jpeak = 139.8 A g-1 PGM), ORR (E1/2 = 0.87 V), and HER (E10 = 20.3 mV), outperforming the benchmark Pt/C, and no loss in HER performance at 100 mA cm-2 for 200 h. The almost unchanged E1/2 in the anti-poisoning test indicates its promising application in real fuel cells powered by ammonia. This work opens up a new path for the development of multi-functional electrocatalysts and also makes a big leap toward the exploration of cost-effective device configurations for novel fuel cells.

Design of Atomically Dispersed CoN4 Sites and Co Clusters for Synergistically Enhanced Oxygen Reduction Electrocatalysis.

Constructing dual-site catalysts consisting of atomically dispersed metal single atoms and metal atomic clusters (MACs) is a promising approach to further boost the catalytic activity for oxygen reduction reaction (ORR). Herein, a porous CoSA-AC@SNC featuring the coexistence of Co single-atom sites (CoN4) and S-coordinated Co atomic clusters (SCo6) in S, N co-doped carbon substrate is successfully synthesized by using porphyrinic metal-organic framework (Co-TPyP MOF) as the precursor. The introduction of the sulfur source creates abundant microstructural defects to anchor Co metal clusters, thus modulating the electronic structure of its surrounding carbon substrate. The synergistic effect between the two types of active sites and structural advantages, in turn, results in high ORR performance of CoSA-AC@SNC with half-wave potential (E1/2) of 0.86 V and Tafel slope of 50.17 mV dec-1. Density functional theory (DFT) calculations also support the synergistic effect between CoN4 and SCo6 by detailing the catalytic mechanism for the improved ORR performance. The as-fabricated Zn-air battery (ZAB) using CoSA-AC@SNC demonstrates impressive peak power density of 174.1 mW cm-2 and charge/discharge durability for 148 h. This work provides a facile synthesis route for dual-site catalysts and can be extended to the development of other efficient atomically dispersed metal-based electrocatalysts.

Cascade Synthesis of Fe-N2-Fe Dual-Atom Catalysts for Superior Oxygen Catalysis.

Dual-atom catalysts (DACs) have been proposed to break the limitation of single-atom catalysts (SACs) in the synergistic activation of multiple molecules and intermediates, offering an additional degree of freedom for catalytic regulation. However, it remains a challenge to synthesize DACs with high uniformity, atomic accuracy, and satisfactory loadings. Herein, we report a facile cascade synthetic strategy for DAC via precise electrostatic interaction control and neighboring vacancy construction. We synthesized well-defined, uniformly dispersed dual Fe sites which were connected by two nitrogen bonds (denoted as Fe-N2-Fe). The as-synthesized DAC exhibited superior catalytic performances towards oxygen reduction reaction, including good half-wave potential (0.91 V), high kinetic current density (21.66 mA cm-2), and perfect durability. Theoretical calculation revealed that the DAC structure effectively tunes the oxygen adsorption configuration and decreases the cleavage barrier, thereby improving the catalytic kinetics. The DAC-based zinc-air batteries exhibited impressive power densities of 169.8 and 52.18 mW cm-2 at 25 oC and -40 oC, which is 1.7 and 2.0 times higher than those based on Pt/C+Ir/C, respectively. We also demonstrated the universality of our strategy in synthesizing other M-N2-M DACs (M= Co, Cu, Ru, Pd, Pt, and Au), facilitating the construction of a DAC library for different catalytic applications.

Synergistic enhancement of Zn-air battery performance via integration of Ni-doped cobalt sulfide nanoparticles within N, S-doped carbon matrix.

Exploring precious metal-free bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is essential for the practical application of rechargeable Zn-air battery (ZAB). Herein, Ni-doped Co9S8 nanoparticles embedded in a defect-rich N, S co-doped carbon matrix (d-NixCo9-xS8@NSC) are synthesized via a facile pyrolysis and acid treatment process. The introduction of abundant defects in both the carbon matrix and metal sulfide provides numerous active sites and significantly enhances the electrocatalytic performances for both the ORR and OER. d-NixCo9-xS8@NSC exhibits a superior half-wave potential of 0.841 V vs. RHE for the ORR and delivers a low overpotential of 0.329 V at 10 mA cm-2 for the OER. Additionally, Zn-air secondary battery using d-NixCo9-xS8@NSC as the air cathode displays a higher specific capacity of 734 mAh gZn-1 and a peak power density of 148.03 mW cm-2 compared to those of state-of-the-art Pt/C-RuO2 (673 mAh gZn-1 and 136.9 mW cm-2, respectively). These findings underscore the potential of d-NixCo9-xS8@NSC as a high-performance electrocatalyst for secondary ZABs, offering new perspectives on the design of efficient noble metal-free electrocatalysts for future energy storage and conversion applications.

S-Block Metal Mg-Mediated Co─N─C as Efficient Oxygen Electrocatalyst for Durable and Temperature-Adapted Zn-Air Batteries.

In the quest to enhance Zn-air batteries (ZABs) for operating across a wide spectrum of temperatures, synthesizing robust oxygen electrocatalysts is paramount. Conventional strategies focusing on orbital hybridization of d-d and p-d aim to moderate the excessive interaction between the d-band of the transition metal active site and oxygen intermediate, yet often yield suboptimal performance. Herein, an innovative s-block metal modulation is reported to refine the electronic structure and catalytic behavior of Co─NC catalysts. Employing density functional theory (DFT) calculations, it is revealed that incorporating Mg markedly depresses the d-band center of Co sites, thereby fine-tuning the adsorption energy of the oxygen reduction reaction (ORR) intermediate. Consequently, the Mg-modified Co─NC catalyst (MgCo─NC) unveils remarkable intrinsic ORR activity with a significantly reduced activation energy (Ea) of 10.0 kJ mol-1, outstripping the performance of both Co─NC (17.6 kJ mol-1), benchmark Pt/C (15.9 kJ mol-1), and many recent reports. Moreover, ZABs outfitted with the finely tuned Mg0.1Co0.9─NC realize a formidable power density of 157.0 mW cm-2, paired with an extremely long cycle life of 1700 h, and an exceptionally minimal voltage gap decay rate of 0.006 mV h-1. Further, the Mg0.1Co0.9─NC-based flexible ZAB presents a mere 2% specific capacity degradation when the temperature fluctuates from 25 to -20 °C, underscoring its robustness and suitability for practical deployment in diverse environmental conditions.

Enhancing electrokinetics and desalination efficiency through catalysts and electrode modifications in microbial desalination cells.

Microbial desalination cells (MDCs) are considered as a sustainable technology for water desalination, wastewater treatment, and power generation. However, this neoteric technology suffers from different challenges, including sluggish oxygen reduction reaction and poor electron transfer from microbes to electrodes, ultimately leading to less power generation and desalination efficiency. This review delves into the intricate roles of both abiotic and biocatalysts in enhancing performance of MDCs through ion removal and charge transfer mechanisms. Detailed discussions highlight the comparative advantages and limitations of different catalyst types and insights into electrode modifications to optimise catalytic activity and biofilm formation. Further, recent advancements in electrode engineering, including surface coatings and integration of nanomaterial, geared towards enhancing efficiency of MDC and performance stability are discussed. Finally, future recommendations are provided, focusing on innovative catalyst designs, material integration, and considerations for scale-up and commercialisation, thereby offering a comprehensive roadmap for the continued advancement of MDC.

Microwave heating-assisted synthesis of ultrathin platinum-based trimetallic nanosheets as highly stable catalysts towards oxygen reduction reaction in acidic medium.

There are currently almost no ternary platinum-based nanosheets used for acidic oxygen reduction reactions (ORR) due to the difficulty in synthesizing ternary nanosheets with high Pt content. In this work, several ultrathin platinum-palladium-copper nanosheets (PtPdCu NSs) with a thickness of around 1.90 nm were prepared via a microwave heating-assisted method. Microwave heating allows a large number of Pt atoms to deposit into PdCu nanosheets, forming Pt-based ternary nanosheets with high Pt content. Among them, Pt38Pd50Cu12 NSs catalyst displays the highest mass activity (MA) measured in 0.1 M HClO4 of 0.932 A/mgPt+Pd which is 8.6 times of that Pt/C. Besides, Pt38Pd50Cu12 NSs catalyst also exhibits excellent stability with an extremely low MA attenuation after 80,000 cycles accelerated durability testing (ADT) tests. In the single cell tests, the Pt38Pd50Cu12 NSs catalyst manifests higher maximum power density of 796 mW cm-2 than Pt/C of 606 mW cm-2. Density functional theory (DFT) calculations indicate the weaker adsorption between Pt and O-species in Pt38Pd50Cu12 NSs leads to a significant enhancement of ORR activity. This study provides a new strategy to design and prepare ultrathin Pt-based trimetallic nanosheets as efficient and durable ORR catalysts.

Spin Polarization Enhances the Catalytic Activity of Monolayer MoSe2 for Oxygen Reduction Reaction.

The key factors in achieving high energy efficiency for proton exchange membrane fuel cells are reducing overpotential and increasing the oxygen reduction rate. Based on first-principles calculations, we induce H atom adsorption on 4 × 4 × 1 monolayer MoSe2 to induce spin polarization, thereby improving the catalytic performance. In the calculation of supercells, the band unfolding method is used to address the band folding effect in doped systems. Furthermore, it is evident from analyzing the unique energy band configuration of MoSe2 that a higher valley splitting value has better catalytic effects on the oxygen reduction reaction. We believe that the symmetries of the distinct adsorption site result in different overpotentials. In addition, when an even number of hydrogen atoms is adsorbed, the monolayer MoSe2 has no spin polarization. The spin can affect the electron transfer process and alter the hybrid energy with the reaction products, thereby regulating its catalytic performance.

Multilayer porous Co-Fe bimetallic electrocatalyst based on multi-walled carbon nanotubes for rechargeable zinc-air batteries.

The rational design of efficient, stable, low-cost non-precious metal-based electrocatalysts with enhanced oxygen reduction reaction (ORR) activity has attracted widespread attention. In this study, a novel electrocatalyst, Fe/Co-N-MWCNT, was prepared by in-situ growth of ZIF-8 and Fe/Co-Phen on multi-walled carbon nanotubes (MWCNTs), then pyrolysis under different temperature to obtain optimal one. During the pyrolysis process, the incorporation of Fe and Co facilitated the formation of metal active sites and Fe-Co alloy, thereby promoting electron transfer and enhancing the ORR activity. Compared to Pt/C (E1/2 = 0.854V, JL = 4.90 mA cm-2), Fe/Co-N-MWCNT demonstrated a comparable half-wave potential (E1/2 = 0.812V) and an enhanced limiting current density (JL = 5.37 mA cm-2). Furthermore, Fe/Co-N-MWCNT was stable and showed no significant change after 2000 cycles, with only a negative shift of 7 mV in E1/2. Ampere response testing revealed that the current decay of Fe/Co-N-MWCNT after 10000 s was only about 7.8%, while that of Pt/C was about 18.4%. Due to its excellent catalytic stability, Fe/Co-N-MWCNT was demonstrated to be an excellent candidate for rechargeable zinc-air batteries. The outstanding electrocatalytic performance of Fe/Co-N-MWCNT can be attributed to its high pyridinic nitrogen content, the unique structure and abundant metal active sites.

Promoting Proton Donation through Hydrogen Bond Breaking on Carbon Nitride for Enhanced H2O2 Photosynthesis.

Photocatalytic H2O2 production has attracted much attention as an alternative way to the industrial anthraquinone oxidation process but is limited by the weak interaction between the catalysts and reactants as well as inefficient proton transfer. Herein, we report on a hydrogen-bond-broken strategy in carbon nitride for the enhancement of H2O2 photosynthesis without any sacrificial agent. The H2O2 photosynthesis is promoted by the hydrogen bond formation between the exposed N atoms on hydrogen-bond-broken carbon nitride and H2O molecules, which enhances proton-coupled electron transfer and therefore the photocatalytic activity. The exposed N atoms serve as proton buffering sites for the proton transfer from H2O molecules to carbon nitride. The H2O2 photosynthesis is also enhanced through the enhanced adsorption and reduction of O2 gas toward H2O2 on hydrogen-bond-broken carbon nitride because of the formation of nitrogen vacancies (NVs) and cyano groups after the intralayer hydrogen bond breaking on carbon nitride. A high light-to-chemical conversion efficiency (LCCE) value of 3.85% is achieved. O2 and H2O molecules are found to undergo a one-step two-electron reduction pathway by photogenerated hot electrons and a four-electron oxidation process to produce O2 gas, respectively. Density functional theory (DFT) calculations validate the O2 adsorption and reaction pathways. This study elucidates the significance of the hydrogen bond formation between the catalyst and reactants, which greatly increases the proton tunneling dynamics.

Oxygen-bridging Fe, Co dual-metal dimers boost reversible oxygen electrocatalysis for rechargeable Zn-air batteries.

Rechargeable zinc-air batteries (ZABs) are regarded as a remarkably promising alternative to current lithium-ion batteries, addressing the requirements for large-scale high-energy storage. Nevertheless, the sluggish kinetics involving oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) hamper the widespread application of ZABs, necessitating the development of high-efficiency and durable bifunctional electrocatalysts. Here, we report oxygen atom-bridged Fe, Co dual-metal dimers (FeOCo-SAD), in which the active site Fe-O-Co-N6 moiety boosts exceptional reversible activity toward ORR and OER in alkaline electrolytes. Specifically, FeOCo-SAD achieves a half-wave potential (E1/2) of 0.87 V for ORR and an overpotential of 310 mV at a current density of 10 mA cm-2 for OER, with a potential gap (ΔE) of only 0.67 V. Meanwhile, FeOCo-SAD manifests high performance with a peak power density of 241.24 mW cm-2 in realistic rechargeable ZABs. Theoretical calculations demonstrate that the introduction of an oxygen bridge in the Fe, Co dimer induced charge spatial redistribution around Fe and Co atoms. This enhances the activation of oxygen and optimizes the adsorption/desorption dynamics of reaction intermediates. Consequently, energy barriers are effectively reduced, leading to a strong promotion of intrinsic activity toward ORR and OER. This work suggests that oxygen-bridging dual-metal dimers offer promising prospects for significantly enhancing the performance of reversible oxygen electrocatalysis and for creating innovative catalysts that exhibit synergistic effects and electronic states.