Boosting Neutral Water Oxidation through Surface Oxygen Modulation

Topological Synthesis of 2D High-Entropy Multimetallic (Oxy)hydroxide for Enhanced Lattice Oxygen Oxidation Mechanism

Owing to sluggish reaction kinetics and high potential, oxygen evolution reaction (OER) electrocatalysts face a trade-off between activity and stability. Herein, an innovative topological strategy is presented for preparing 2D multimetallic (oxy)hydroxide, including ternary CoFeZn, quaternary CoFeMnZn, and high-entropy CoFeMnCuZn. The key to the synthesis lies in using Ca-rich brownmillerite oxide as a precursor, which possesses inherent structural flexibility enabling tailored elemental adjustments and topologically transforms from a point-shared structure of metal-oxygen octahedrons into an edge-shared structure under alkaline conditions. The presence of Zn in the catalysts causes a shift in the center of the O2p band toward the Fermi level, resulting in more Co4+ species, which drive holes into oxygen ligands to promote intramolecular oxygen coupling. The triggered lattice oxidation mechanism is identified by detecting peroxo-like (O2 2-) negative species using tetramethylammonium chemical probe, along with 18O isotope labeling experiments. As a result, the catalyst demonstrates an overpotential of 267 mV at 10 mA cm-2, ranking it among the top-performing non-Ni-based catalysts. Importantly, the catalysts also show high Fe-leaching resistance during OER compared to conventional NiFe and CoFe hydroxides/(oxy)hydroxides. The assembled zinc-air battery enables stable operation for over 225 h at a low charging voltage of 1.93 V.

Scalable Low-Temperature CO2 Electrolysis: Current Status and Outlook

The electrochemical CO2 reduction (eCO2R) in membrane electrode assemblies (MEAs) has brought e-chemical production one step closer to commercialization because of its advantages of minimized ohmic resistance and stackability. However, the current performance of reported eCO2R in MEAs is still far below the threshold for economic feasibility where low overall cell voltage (<2 V) and extensive stability (>5 years) are required. Furthermore, while the production cost of e-chemicals heavily relies on the carbon capture and product separation processes, these areas have received much less attention compared to CO2 electrolysis, itself. In this perspective, we examine the current status of eCO2R technologies from both academic and industrial points of view. We highlight the gap between current capabilities and commercialization standards and offer future research directions for eCO2R technologies with the hope of achieving industrially viable e-chemical production.

High-Dimensional Nb2O5 with NbO6 Octahedra for Efficient Electrocatalytic Upgrading of Methanol to Formate

Facilitating the selective electrochemical oxidation of methanol into value-added formate is essential for electrochemical refining. Here we propose a high-dimensional Nb2O5 on Ni foam (Nb2O5-HD@NF) composite as anode for methanol oxidation reaction (MOR) for efficient production of formate. In an electrolyte containing 3 M methanol aqueous solution, the Nb2O5-HD@NF anode requires only 240 mV overpotential to deliver an industrial-level current density of 100 mA cm-2 with a formate Faraday efficiency of 100%. In situ Raman and electrochemical kinetic analyses reveal that the origin of the excellent activity in 3 M methanol electrolyte can be ascribed to the NbO6 octahedra as active sites and the Lewis acid sites on the surface of Nb2O5-HD. This work may pave a way for the design of non-noble metal electrocatalysts with surface acidity engineering for the effective electrocatalytic upgrading of biomass molecules.

Atomically Dispersed Iridium on Polyimide Support for Acidic Oxygen Evolution

Designing a high-performing iridium (Ir) single-atom catalyst is desired for acidic water electrolysis, which shows enormous potential given its high catalytic activity toward acidic oxygen evolution reaction (OER) with minimum usage of precious Ir metal. However, it still remains a substantial challenge to stabilize the Ir single atoms during the OER operation without sacrificing the activity. Here, we report a high-performing OER catalyst by immobilizing Ir single atoms on a polyimide support, which exhibits a high mass activity on a carbon paper electrode while simultaneously achieving outstanding stability with negligible decay for 360 h. The resulting electrode (denoted as Ir1-PI@CP) reaches a 49.7-fold improvement in mass activity compared to the counterpart electrode prepared without polyimide support. Both our experimental and theoretical results suggest that, owing to the strong metal-support interactions, the polyimide support can enhance the Ir 5d states of Ir single atoms in Ir1-PI@CP, which can tailor the adsorption energies of intermediates and decrease the thermodynamic barrier at the rate-determining step of the OER, but also facilitate the proton-electron-transfer process and improve the reaction kinetics. This work offers an alternative avenue for developing single-atom catalysts with superior activity and durability toward various catalytic systems and beyond.

Toward Realistic Models of the Electrocatalytic Oxygen Evolution Reaction

The electrocatalytic oxygen evolution reaction (OER) supplies the protons and electrons needed to transform renewable electricity into chemicals and fuels. However, the OER is kinetically sluggish; it operates at significant rates only when the applied potential far exceeds the reversible voltage. The origin of this overpotential is hidden in a complex mechanism involving multiple electron transfers and chemical bond making/breaking steps. Our desire to improve catalytic performance has then made mechanistic studies of the OER an area of major scientific inquiry, though the complexity of the reaction has made understanding difficult. While historically, mechanistic studies have relied solely on experiment and phenomenological models, over the past twenty years ab initio simulation has been playing an increasingly important role in developing our understanding of the electrocatalytic OER and its reaction mechanisms. In this Review we cover advances in our mechanistic understanding of the OER, organized by increasing complexity in the way through which the OER is modeled. We begin with phenomenological models built using experimental data before reviewing early efforts to incorporate ab initio methods into mechanistic studies. We go on to cover how the assumptions in these early ab initio simulations─no electric field, electrolyte, or explicit kinetics─have been relaxed. Through comparison with experimental literature, we explore the veracity of these different assumptions. We summarize by discussing the most critical open challenges in developing models to understand the mechanisms of the OER.

Single-atom catalysts for electrocatalytic nitrate reduction into ammonia

Ammonia (NH3) is a versatile and important compound with a wide range of uses, which is currently produced through the demanding Haber-Bosch process. Electrocatalytic nitrate reduction into ammonia (NRA) has recently emerged as a sustainable approach for NH3synthesis under ambient conditions. However, the NRA catalysis is a complex multistep electrochemical process with competitive hydrogen evolution reaction that usually results in poor selectivity and low yield rate for NH3synthesis. With maximum atom utilization and well-defined catalytic sites, single atom catalysts (SACs) display high activity, selectivity and stability toward various catalytic reactions. Very recently, a number of SACs have been developed as promising NRA electrocatalysts, but systematical discussion about the key factors that affect their NRA performance is not yet to be summarized to date. This review focuses on the latest breakthroughs of SACs toward NRA catalysis, including catalyst preparation, catalyst characterization and theoretical insights. Moreover, the challenges and opportunities for improving the NRA performance of SACs are discussed, with an aim to achieve further advancement in developing high-performance SACs for efficient NH3synthesis.

High-Entropy Perovskite Oxides as a Family of Electrocatalysts for Efficient and Selective Nitrogen Oxidation

Electrocatalytic nitrogen oxidation reaction (NOR) can convert nitrogen (N2) into nitrate (NO3-) under ambient conditions, providing an attractive approach for synthesis of NO3-, alternative to the current approach involving the harsh Haber-Bosch and Ostwald oxidation processes that necessitate high temperature, high pressure, and substantial carbon emission. Developing efficient NOR catalysts is a prerequisite, which remains a formidable challenge, owing to the weak activation/dissociation of N2. A variety of NOR electrocatalysts have been developed, but their NOR kinetics are still extremely sluggish, resulting in inferior Faradaic Efficiencies. Here, we report a high-entropy Ru-based perovskite oxide (denoted as Ru-HEP) that can function as a high-performance NOR catalyst and exhibit a high NO3- yield rate of 39.0 μmol mg-1 h-1 with a Faradaic Efficiency of 32.8%. Both our experimental results and theoretical calculations suggest that the high-entropy configuration of Ru-HEP perovskite oxide can markedly enhance the oxygen-vacancy concentration, where the Ru sites and their neighboring oxygen vacancies can serve as unsaturated centers and decrease the overall energy barrier for N2 electrooxidation, thereby leading to promoted NOR kinetics. This work presents an alternative avenue for promoting NOR catalysis on perovskite oxides through the high-entropy engineering strategy.

Engineering high-valence metal-enriched cobalt oxyhydroxide catalysts for an enhanced OER under near-neutral pH conditions

Understanding water splitting in pH-neutral media has important implications for hydrogen production from seawater. Despite their significance, electrochemical water oxidation and reduction in neutral electrolytes still face great challenges. This study focuses on designing efficient electrocatalysts capable of promoting the oxygen evolution reaction (OER) in neutral media by incorporating high-valence elements into transition-metal hydroxides. The as-prepared and optimized two-dimensional Mo-Co(OH)2 nanosheets, which undergo operando transformation into oxyhydroxide active species, demonstrated an overpotential of 550 mV at 10 mA cm-2 with a Tafel slope of 110.1 mV dec-1 in 0.5 M KHCO3. In situ X-ray absorption spectroscopy revealed that the incorporation of high-valence elements facilitates the generation of CoOOH active sites at low potential and enhances electron transfer kinetics by altering the electronic environment of the Co center. This study offers new insights for developing more efficient OER electrocatalysts and provides fresh ideas for seawater utilization through the study of the reaction mechanism of the near-neutral-pH OER.

Surface charge modulation boosts electrocatalytic water splitting over iridium catalysts on a polyimide support

Developing high-performance iridium (Ir)-based catalysts with minimal precious Ir metal is a significant but challenging step towards the acidic oxygen evolution reaction (OER). Here, we report a high-performance OER catalyst with Ir nanoparticles on a polyimide support, where the polyimide support can effectively modulate the electronic structures of the Ir active sites for decreased thermodynamic barriers, but also enrich the local proton concentration near the Ir active sites, enhancing the OER rates.

Lewis Acid Driving Asymmetric Interfacial Electron Distribution to Stabilize Active Species for Efficient Neutral Water Oxidation

Neutral oxygen evolution reaction (OER) with unique reactive environments exhibits extremely slow reaction kinetics, posing significant challenges in the design of catalysts. Herein, a built-in electric field between the tungstate (Ni-FeWO4 ) with adjustable work function and Lewis acid WO3 is elaborately constructed to regulate asymmetric interfacial electron distribution, which promotes electron accumulation of Fe sites in the tungstate. This decelerates the rapid dissolution of Fe under the OER potentials, thereby retaining the active hydroxyl oxide with the optimized OER reaction pathway. Meanwhile, Lewis acid WO3 enhances hydroxyl adsorption near the electrode surface to improve mass transfer. As expected, the optimized Ni-FeWO4 @WO3 /NF self-supporting electrode achieves a low overpotential of 235 mV at 10 mA cm-2 in neutral media and maintains stable operation for 200 h. Furthermore, the membrane electrode assembly constructed by such self-supporting electrode exhibits robust stability for 250 h during neutral seawater electrolysis. This work deepens the understanding of the reconstruction of OER catalysts in neutral environments and paves the way for development of the energy conversion technologies.

Perovskite Oxide as A New Platform for Efficient Electrocatalytic Nitrogen Oxidation

Electrocatalytic nitrogen oxidation reaction (NOR) offers an efficient and sustainable approach for conversion of widespread nitrogen (N2 ) into high-value-added nitrate (NO3 - ) under mild conditions, representing a promising alternative to the traditional approach that involves harsh Haber-Bosch and Ostwald oxidation processes. Unfortunately, due to the weak absorption/activation of N2 and the competitive oxygen evolution reaction, the kinetics of NOR process is extremely sluggish accompanied with low Faradaic efficiencies and NO3 - yield rates. In this work, an oxygen-vacancy-enriched perovskite oxide with nonstoichiometric ratio of strontium and ruthenium (denoted as Sr0.9 RuO3 ) was synthesized and explored as NOR electrocatalyst, which can exhibit a high Faradaic efficiency (38.6 %) with a high NO3 - yield rate (17.9 μmol mg-1  h-1 ). The experimental results show that the amount of oxygen vacancies in Sr0.9 RuO3 is greatly higher than that of SrRuO3 , following the same trend as their NOR performance. Theoretical simulations unravel that the presence of oxygen vacancies in the Sr0.9 RuO3 can render a decreased thermodynamic barrier toward the oxidation of *N2 to *N2 OH at the rate-determining step, leading to its enhanced NOR performance.

Electrode/Electrolyte Synergy for Concerted Promotion of Electron and Proton Transfers toward Efficient Neutral Water Oxidation

Neutral water oxidation is a crucial half-reaction for various electrochemical applications requiring pH-benign conditions. However, its sluggish kinetics with limited proton and electron transfer rates greatly impacts the overall energy efficiency. In this work, we created an electrode/electrolyte synergy strategy for simultaneously enhancing the proton and electron transfers at the interface toward highly efficient neutral water oxidation. The charge transfer was accelerated between the iridium oxide and in situ formed nickel oxyhydroxide on the electrode end. The proton transfer was expedited by the compact borate environment that originated from hierarchical fluoride/borate anions on the electrolyte end. These concerted promotions facilitated the proton-coupled electron transfer (PCET) events. Due to the electrode/electrolyte synergy, Ir-O and Ir-OO- intermediates could be directly detected by in situ Raman spectroscopy, and the rate-limiting step of Ir-O oxidation was determined. This synergy strategy can extend the scope of optimizing electrocatalytic activities toward more electrode/electrolyte combinations.

Self-Decoupled Oxygen Electrocatalysis for Ultrastable Rechargeable Zn-Air Batteries with Mild-Acidic Electrolyte

Rechargeable zinc-air batteries (ZABs) have been considered promising as next-generation sustainable energy storage devices; however, their large-scale deployment is hampered by the unsatisfactory cyclic lifespan. Employing neutral and mild-acidic electrolytes is effective in extending the cyclability, but the rapid performance degradation of the bifunctional catalysts owing to different microenvironmental requirements of the alternative oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a serious limitation of their cyclic life. Herein, we propose a "self-decoupling" strategy to significantly improve the stability of the bifunctional catalysts by constructing a smart interface in the bifunctional air electrode. This smart interface, containing a resistance-switchable sulfonic acid doped polyaniline nanoarray interlayer, is nonconductive at high potential but conductive at low potential, which enables spontaneous electrochemical decoupling of the bifunctional catalyst for the ORR and OER, respectively, and thus protects it from degradation. The resulting self-decoupled mild-acidic ZAB delivers stable cyclic performances in terms of a negligible energy efficiency loss of 0.015% cycle-1 and 3 times longer cycle life (∼1400 h) compared with the conventional mild-acidic ZAB using a normal bifunctional air electrode and the same low-cost ZnCo phosphide/nitrogen-doped carbon bifunctional catalyst. This work provides an effective strategy for tolerating alternative oxidation-reduction reactions and emphasizes the importance of smart nanostructure design for more sustainable batteries.

Stable and oxidative charged Ru enhance the acidic oxygen evolution reaction activity in two-dimensional ruthenium-iridium oxide

The oxygen evolution reactions in acid play an important role in multiple energy storage devices. The practical promising Ru-Ir based catalysts need both the stable high oxidation state of the Ru centers and the high stability of these Ru species. Here, we report stable and oxidative charged Ru in two-dimensional ruthenium-iridium oxide enhances the activity. The Ru0.5Ir0.5O2 catalyst shows high activity in acid with a low overpotential of 151 mV at 10 mA cm-2, a high turnover frequency of 6.84 s-1 at 1.44 V versus reversible hydrogen electrode and good stability (618.3 h operation). Ru0.5Ir0.5O2 catalysts can form more Ru active sites with high oxidation states at lower applied voltages after Ir incorporation, which is confirmed by the pulse voltage induced current method. Also, The X-ray absorption spectroscopy data shows that the Ru-O-Ir local structure in two-dimensional Ru0.5Ir0.5O2 solid solution improved the stability of these Ru centers.

Reconstructed Ir‒O‒Mo species with strong Brønsted acidity for acidic water oxidation

Surface reconstruction generates real active species in electrochemical conditions; rational regulating reconstruction in a targeted manner is the key for constructing highly active catalyst. Herein, we use the high-valence Mo modulated orthorhombic Pr₃Ir_1-xMo_xO₇ as model to activate lattice oxygen and cations, achieving directional and accelerated surface reconstruction to produce self-terminated Ir‒O_bri‒Mo (O_bri represents the bridge oxygen) active species that is highly active for acidic water oxidation. The doped Mo not only contributes to accelerated surface reconstruction due to optimized Ir‒O covalency and more prone dissolution of Pr, but also affords the improved durability resulted from Mo-buffered charge compensation, thereby preventing fierce Ir dissolution and excessive lattice oxygen loss. As such, Ir‒O_bri‒Mo species could be directionally generated, in which the strong Brønsted acidity of O_bri induced by remaining Mo assists with the facilitated deprotonation of oxo intermediates, following bridging-oxygen-assisted deprotonation pathway. Consequently, the optimal catalyst exhibits the best activity with an overpotential of 259 mV to reach 10 mA cm_geo^-2, 50 mV lower than undoped counterpart, and shows improved stability for over 200 h. This work provides a strategy of directional surface reconstruction to constructing strong Brønsted acid sites in IrO_x species, demonstrating the perspective of targeted electrocatalyst fabrication under in situ realistic reaction conditions.

Proposal of spin crossover as a reversible switch of catalytic activity for the oxygen evolution reaction in two dimensional metal-organic frameworks

The development of oxygen evolution reaction (OER) catalysts with high activity and controllability is crucial for clean energy conversion and storage but remains a challenge. Here, based on first-principles calculations, we propose to utilize spin crossover (SCO) in two-dimensional (2D) metal-organic frameworks (MOFs) to achieve reversible control of OER catalytic activity. The theoretical design of a 2D square lattice MOF with Co as nodes and tetrakis-substituted cyanimino squaric acid (TCSA) as ligands, which transforms between the high spin (HS) and the low spin (LS) state by applying an external strain (∼2%), confirms our proposal. In particular, the HS-LS spin state transition of Co(TCSA) considerably regulates the adsorption strength of the key intermediate HO* in the OER process, resulting in a significant reduction of the overpotential from 0.62 V in the HS state to 0.32 V in the LS state, thus realizing a reversible switch for the activity of the OER. Moreover, the high activity of the LS state is confirmed by microkinetic and constant potential method simulations.

Electrochemical Oxidation Encapsulated Ru Clusters Enable Robust Durability for Efficient Oxygen Evolution

Electrochemical oxidization and thermodynamic instability agglomeration are a primary challenge in triggering metal-support interactions (MSIs) by immobilizing metal atoms on a carrier to achieve efficient oxygen evolution reactions (OER). Herein, Ru clusters anchored to the VS₂ surface and the VS₂ nanosheets embedded vertically in carbon cloth (Ru-VS₂ @CC) are deliberately designed to realize high reactivity and exceptional durability. In situ Raman spectroscopy reveals that the Ru clusters are preferentially electro-oxidized to form RuO₂ chainmail, both affording sufficient catalytic sites and protecting the internal Ru core with VS₂ substrates for consistent MSIs. Theoretical calculations elucidate that electrons across the Ru/VS₂ interface aggregate toward the electro-oxidized Ru clusters, while the electronic coupling of Ru 3p and O 2p orbitals boosts a positive shift in the Fermi energy level of Ru, optimizing the adsorption capacity of the intermediates and diminishing the migration barriers of the rate-determining steps. Therefore, the Ru-VS₂ @CC catalyst demonstrated ultra-low overpotentials of 245 mV at 50 mA cm^-2 , while the zinc-air battery maintained a narrow gap (0.62 V) after 470 h of reversible operation. This work has transformed the corrupt into the miraculous and paved a new way for the development of efficient electrocatalysts.

Perovskites with Enriched Oxygen Vacancies as a Family of Electrocatalysts for Efficient Nitrate Reduction to Ammonia

Electrochemical nitrate reduction to ammonia (NRA) provides an efficient, sustainable approach to convert the nitrate pollutants into value-added products, which is regarded as a promising alternative to the industrial Haber-Bosch process. Recent studies have shown that oxygen vacancies of oxide catalysts can adjust the adsorption energies of intermediates and affect their catalytic performance. Compared with other metal oxides, perovskite oxides can allow their metal cations to exist in abnormal or mixed valence states, thereby resulting in enriched oxygen vacancies in their crystal structures. Here, the catalytic activities of perovskite oxides toward NRA catalysis with respect to the amount of oxygen vacancies are explored, where four perovskite oxides with different crystal structures (including cubic LaCrO₃ , orthorhombic LaMnO₃ and LaFeO₃ , hexagonal LaCoO₃ ) are chosen and investigated. By combining X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy and electrochemical measurements, it is found that the amount of oxygen vacancies in these perovskite oxides surprisingly follow the same order as their activities toward NRA catalysis (LaCrO₃  < LaMnO₃  < LaFeO₃  < LaCoO₃ ). Further theoretical studies reveal that the existence of oxygen vacancies in LaCoO₃ perovskite can decrease the energy barriers for reduction of *HNO₃ to *NO₂ , leading to its superior NRA performance.

Balancing Activity and Stability in Spinel Cobalt Oxides through Geometrical Sites Occupation towards Efficient Electrocatalytic Oxygen Evolution

Designing active and stable oxygen evolution reaction (OER) catalysts are vitally important to various energy conversion devices. Herein, we introduce elements Ni and Mn into (Co)_tet (Co₂ )_oct O₄ nanosheets (NSs) at fixed geometrical sites, including Mn_oct , Ni_oct , and Ni_tet , to optimize the initial geometrical structure and modulate the CoCo₂ O₄ surface from oxygen-excess to oxygen-deficiency. The pristine (Ni,Mn)-(Co)_tet (Co₂ )_oct O₄ NSs shows excellent OER activity with an overpotential of 281.6 mV at a current density of 10 mA cm^-2 . Moreover, without damaging their initial activity, the activated (Act)-(Ni,Mn)-(Co)_tet (Co₂ )_oct O₄ NSs after surface reconstruction exhibit long-term stability of 100 h under 10 mA cm^-2 , 50 mA cm^-2 , or even 100 mA cm^-2 . The optimal balance between electroactivity and stability leads to remarkable OER performances, providing a pivotal guideline for designing ideal electrocatalysts and inspiring more works to focus on the dynamic change of each occupation site component.

Interface engineering breaks both stability and activity limits of RuO2 for sustainable water oxidation

Designing catalytic materials with enhanced stability and activity is crucial for sustainable electrochemical energy technologies. RuO2 is the most active material for oxygen evolution reaction (OER) in electrolysers aiming at producing 'green' hydrogen, however it encounters critical electrochemical oxidation and dissolution issues during reaction. It remains a grand challenge to achieve stable and active RuO2 electrocatalyst as the current strategies usually enhance one of the two properties at the expense of the other. Here, we report breaking the stability and activity limits of RuO2 in neutral and alkaline environments by constructing a RuO2/CoOx interface. We demonstrate that RuO2 can be greatly stabilized on the CoOx substrate to exceed the Pourbaix stability limit of bulk RuO2. This is realized by the preferential oxidation of CoOx during OER and the electron gain of RuO2 through the interface. Besides, a highly active Ru/Co dual-atom site can be generated around the RuO2/CoOx interface to synergistically adsorb the oxygen intermediates, leading to a favourable reaction path. The as-designed RuO2/CoOx catalyst provides an avenue to achieve stable and active materials for sustainable electrochemical energy technologies.

Emerging Electrocatalysts for Water Oxidation under Near-Neutral CO2 Reduction Conditions

Electrocatalytic CO₂ reduction reaction (CO₂ RR), which produces valuable fuels and chemicals under near-neutral conditions, offers a renewable approach to alleviate the global energy crisis as well as the increasing concerns on climate change. However, to implement this strategy, one of the major challenges, the sluggish kinetics of the paired oxygen evolution reaction (OER) at anode, needs to be surmounted. It is therefore highly desirable to explore high-performance and cost-effective OER electrocatalysts suitable for CO₂ RR conditions, which is very different from those widely investigated under acidic or alkaline conditions. In this review, the ongoing development of OER electrocatalysts under near pH-neutral CO₂ -saturated (bi)carbonate solutions are highlighted and the future opportunities are discussed. It is started with a brief introduction on OER paired with CO₂ RR, the relevant theoretical tools such as density functional theory (DFT) and particularly machine learning (ML), and the operando characterization techniques. Then, there are some detailed discussions of recent progress on the rational design of OER electrocatalysts under CO₂ RR conditions ranging from noble-metal oxides to nonprecious metal phosphides, carbonates, (hydro)oxides, and so on. Finally, a perspective for developing OER electrocatalysts integrated with CO₂ electroreduction is proposed.

Regulation of electrocatalytic activity by local microstructure: focusing on catalytic active zone

Traditional regulation methods of active sites have been successfully optimized the performance of electrocatalysts, but seem unable to achieve further breakthrough in the catalytic activity. Unlike the conventional viewpoint of focusing on single active site, the concept of local microstructure active zone is more comprehensive and new suits of methods to regulate reaction zone for electrocatalytic reactions are developed accordingly. The local microstructure active zone refers to the zone with high catalytic activity formed by the interaction between active atoms and neighboring coordination atoms as well as the surrounding environment. Instead of the traditional single active atom site, the active zone is more suitable for the actual electrochemical reaction process. According to this concept, the activity of the electrocatalysts can be coordinated by multiple active atoms. This strategy is beneficial to understand the relationship between material, structure and catalysis, which realizes the scientific design and synthesis of high performance electrocatalysts. This review provides the research progress of this strategy in electrocatalytic reactions, with the emphasis on their important applications in oxygen evolution reaction, urea oxidation reaction and carbon dioxide reduction.

Self-supported Cu3P nanowire electrode as an efficient electrocatalyst for the oxygen evolution reaction

Hydrogen is an ideal energy carrier due to its abundant reserves and high energy density. Electrolyzing water is one of the carbon free technologies for hydrogen production, which is limited by the sluggish kinetics of the half reaction of the anode – the oxygen evolution reaction (OER). In this study, a self-supported Cu₃P nanowire (Cu₃P NWs/CF) electrode is prepared by electrodeposition of a Cu(OH)₂ nanowire precursor on conductive Cu foam (Cu(OH)₂ NWs/CF) with a subsequent phosphating procedure under a N₂ atmosphere. When used as an OER working electrode in 1.0 M KOH solution at room temperature, Cu₃P NWs/CF exhibits excellent catalytic performance with an overpotential of 327 mV that delivers a current density of 20 mA cm⁻². Notably, it can run stably for 22 h at a current density of 20 mA cm⁻² without obvious performance degradation. This highly efficient and stable OER catalytic performance is mainly attributed to the unique nanostructure and stable electrode construction. Interestingly, this synthesis strategy has been proved to be feasible to prepare large-area working electrodes (e.g. 40 cm⁻²) with unique nanowire structure. Therefore, this work has provided a good paradigm for the mass fabrication of self-supporting non-noble metal OER catalysts and effectively promoted the reaction kinetics of the anode of the electrolyzing water reaction.

We prepared Cu₃P nanowires via a simple two-step method and Cu(OH)₂ NWs/CF was converted to Cu₃P/NWs after a phosphating process. The prepared Cu₃P NWs/CF electrode shows high efficiency and excellent stability to OER in alkaline medium.

Heuristic Iron-Cobalt-Mediated Robust pH-Universal Oxygen Bifunctional Lusters for Reversible Aqueous and Flexible Solid-State Zn-Air Cells

Rechargeable aqueous zinc-air cells (ZACs) promise an extremely safe and high energy technology. However, they are still significantly limited by sluggish electrochemical kinetics and irreversibility originating from the parasitic reactions of the bifunctional catalysts and electrolytes. Here, we report the preferential in situ building of interfacial structures featuring the edge sites constituted by FeCo single/dual atoms with the integration of Co sites in the nitrogenized graphitic carbon frameworks (FeCo SAs@Co/N-GC) by electronic structure modulation approach. Compared to commercial Pt/C and RuO₂, FeCo SAs@Co/N-GC reveals exceptional electrochemical performance, reversible redox kinetics, and durability toward oxygen reduction and evolution reactions under universal pH environments, i.e., alkaline, neutral, and acidic, due to synergistic effect at interfaces and preferred charge/mass transfer. The aqueous (alkaline, nonalkaline, and acidic electrolytes) ZACs constructed with a FeCo SAs@Co/N-GC cathode tolerate stable operations, have significant reversibility, and have the highest energy densities, outperforming those of noble metal counterparts and state-of-the-art ZACs in the ambient atmosphere. Additionally, flexible solid-state ZACs demonstrate excellent mechanical and electrochemical performances with a highest power density of 186 mW cm^-2, specific capacity of 817 mAh g_Zn^-1, energy density of 1017 Wh kg_Zn^-1, and cycle life >680 cycles with extremely harsh operating conditions, which illustrates the great potential of triphasic catalyst for green energy storage technologies.

Polyaniline/Carbon Dots Composite as a Highly Efficient Metal-Free Dual-Functional Photoassisted Electrocatalyst for Overall Water Splitting

Photoassisted electrocatalytic (P-EC) water splitting for H₂ production has received much attention. Here, we report a metal-free bifunctional photoassisted catalyst of a polyaniline/carbon dots (PANI/CDs) composite for overall water splitting. In a neutral electrolyte, under visible light, the overpotentials of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) for PANI/CDs/NF are reduced by 150 and 65 mV to reach the current densities of 30 and 20 mA cm^-2, respectively. In a full water-splitting cell, under visible light, the current density is 13.27 mA cm^-2 at 2.0 V, which increases by 62.8% compared with that under the dark conditions (8.15 mA cm^-2). The in situ transient photovoltage (TPV) tests were used to study the light-induced effects on half-reactions of water splitting, as well as the charge-transfer kinetic characteristics at the catalyst interface.

Stabilizing Highly Active Ru Sites by Suppressing Lattice Oxygen Participation in Acidic Water Oxidation

In hydrogen production, the anodic oxygen evolution reaction (OER) limits the energy conversion efficiency and also impacts stability in proton-exchange membrane water electrolyzers. Widely used Ir-based catalysts suffer from insufficient activity, while more active Ru-based catalysts tend to dissolve under OER conditions. This has been associated with the participation of lattice oxygen (lattice oxygen oxidation mechanism (LOM)), which may lead to the collapse of the crystal structure and accelerate the leaching of active Ru species, leading to low operating stability. Here we develop Sr-Ru-Ir ternary oxide electrocatalysts that achieve high OER activity and stability in acidic electrolyte. The catalysts achieve an overpotential of 190 mV at 10 mA cm^-2 and the overpotential remains below 225 mV following 1,500 h of operation. X-ray absorption spectroscopy and ¹⁸O isotope-labeled online mass spectroscopy studies reveal that the participation of lattice oxygen during OER was suppressed by interactions in the Ru-O-Ir local structure, offering a picture of how stability was improved. The electronic structure of active Ru sites was modulated by Sr and Ir, optimizing the binding energetics of OER oxo-intermediates.

Self-Powered and Self-Sensing Energy Textile System for Flexible Wearable Applications

Intelligent textiles require flexible power sources that can be seemingly integrated with a variety of electronic devices to realize new smart wearable applications. However, current research mainly focuses on the design of the textile structures, often ignoring the importance of seamless configuration. This approach results in an uncomfortable experience when the device is worn and makes it difficult to smoothly connect each monofunctional device. The view of the yarn structure, a multifunctional yarn-based wearable system is fabricated through combining seamless strain sensors and energy storage devices. Yarn deposited with poly(3,4-ethylenedioxythiophene) (PEDOT) via in situ polymerization is then prepared as a highly conductive yarn sensor and a flexible yarn-shaped supercapacitor (SC). All-yarn-based SCs are incorporated with strain sensors within self-powered flexible devices designed to detect human motion. Multiple textile structures can be woven into garments including power supply to sensors, with promising application potential across wearable electronics and smart clothing.