Spin-Polarization Strategy for Enhanced Acidic Oxygen Evolution Activity

Asymmetric tacticity navigates the localized metal spin state for sustainable alkaline/sea water oxidation

Anodic oxygen evolution reaction (OER) that involves a spin-dependent singlet-to-triplet oxygen changeover largely restrains the water electrolysis efficiency for hydrogen production. However, the modulation of spin state is still challengeable for most OER catalysts, and there remains a debate on deciphering the active spin state in OER. Here, we pioneered an asymmetric Fe-incorporated NiPS3 tactic system to retune the metal localized spin for efficient OER electrocatalysis. It is unraveled that the synergistic effect of medium-spin FeIII site and P/S coordination can effectively boost OER activity and Cl resistance selectivity in alkaline/sea water. Resultantly, the Fe/NiPS3-based asymmetric electrodes exhibit low cell voltages of 1.50 volts/1.52 volts in alkaline/sea water at 10 milliamperes per square centimeter, together with a sustainable retention for 1000 hours. It also delivers the durable performance in anion exchange membrane water electrolyzers with a low operation voltage at 45°C. This research navigates the atomic localized spin state as the criterion in rationalizing efficient nonprecious alkaline/sea water oxidation electrocatalysts.

Single-Atom Ru-Triggered Lattice Oxygen Redox Mechanism for Enhanced Acidic Water Oxidation

Activating the oxygen anionic redox presents a promising avenue for developing highly active oxygen evolution reaction (OER) electrocatalysts for proton-exchange membrane water electrolyzers (PEMWE). Here, we engineered a lattice-confined Ru single atom dispersed on a lamellar manganese oxide (MnO2) cation site. The strong Ru-O bond induced an upward shift in the O 2p band, enhancing metal-oxygen covalency and reshaping the OER mechanism toward lattice oxygen oxidation pathway with increased activity. In situ spectral characterization combined with density functional theory (DFT) calculations revealed that electron transfer from Mn to Ru alleviates the Jahn-Teller effect within the MnO6 octahedral structure, stabilizing the lattice. The layered Ru/MnO2 architecture also promotes the rapid replenishment of oxygen vacancies, preventing structural collapse. As a result, the optimized Ru/MnO2 electrocatalyst achieves an OER overpotential of only 179 mV at 10 mA cm-2 in 0.5 M H2SO4, along with exceptional durability over 1000 h at 100 mA cm-2. Moreover, the Ru/MnO2-based PEM device requires only 1.71 V to reach 1 A cm-2 and shows a durability of 500 h at 500 mA cm-2.

Synergistic niobium and manganese co-doping into RuO2 nanocrystal enables PEM water splitting under high current

Low-cost ruthenium-based catalysts with high activity have emerged as promising alternatives to iridium-based counterparts for acidic oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE), but the poor stability under high current density remains as a key challenge. Here, we utilize the synergistic complementary strategy of introducing earth-abundant Mn and Nb dopants in ruthenium dioxide (RuO2) for Nb0.1Mn0.1Ru0.8O2 nanoparticle electrocatalyst that exhibits a low overpotential of 209 mV at 10 mA cm-2 and good stability of > 400 h at 0.2 A cm-2 in 0.5 M H2SO4. Significantly, a PEMWE device fabricated with Nb0.1Mn0.1Ru0.8O2 anode can operate continuously at least for 1000 h at 0.5 A cm-2 with 59 μV h-1 decay rate. Operando Raman spectroscopy analysis, differential electrochemical mass spectroscopy measurements, X-ray absorption spectroscopy analysis and theoretical calculations indicate that OER reaction on Nb0.1Mn0.1Ru0.8O2 primarily follows the adsorbate evolution mechanism with much favorable energy barrier accompanied by a locally passivated lattice oxygen mechanism (AEM-LPLOM) and the co-existed Nb and Mn in RuO2 crystal lattice could not only stabilize the lattice oxygen, but also relieve the valence state fluctuation of Ru site to stabilize the catalyst during the reaction.

Magnetic Effects in Electrocatalysis Studied with Electrochemical Impedance Spectroscopy: The Cases of Oxygen Reduction and Evolution Reactions on Cobalt Ferrite Electrodes

Recent years have witnessed an intense effort to unravel magnetic field effects in electrocatalysis, as they can enhance the performance of common electrocatalysts. Both experimental and theoretical studies have shown that magnetic fields may affect, among others, the macroscopic spin-orbital ordering, charge transport, bubble release, and electron transfer kinetics. This paper highlights Electrochemical Impedance Spectroscopy (EIS) as a tool to analyze and separate the effects of magnetic field on both the oxygen reduction and evolution reactions at cobalt iron oxide electrodes. The unequivocal existence of magnetic field effects is demonstrated through EIS, which provides additional information useful to individuate the magnetic field effects. In the almost superparamagnetic nanoparticles studied here, while the magnetic field impact is positive for oxygen reduction, it turns out to be negligible in the case of oxygen evolution. In addition, this study reveals new significant insights, including the exceptionally slow relaxation kinetics of the magnetic effects and the significance of magnetic-induced surface modifications. The fact that the effects virtually disappear in the presence of electrolyte cesium ions points to the key role of electrode surface states. This study showcases the potential of EIS to probe the effects of permanent magnetic fields in electrocatalysis.

A Magnetic Field-Assisted Lithium-Oxygen Batteries with Enhanced Reaction Kinetics by Spin-Polarization Strategy

Lithium-oxygen (Li-O2) batteries have attracted significant attention due to their ultrahigh theoretical energy density, but are obstructed by the sluggish reaction kinetics at the cathode and high overpotential. Our previous researches have proved that energy fields such as light, force, and heat are effective strategies to improve the reaction kinetics of Li-O2 batteries. Herein, we proposed a novel magnetic field-assisted Li-O2 batteries via a spin polarization strategy. By doping magnetic Mn2+ ions with spin polarization characteristics into CsPbBr3 (Mn-CsPbBr3) perovskite, a magnetic field-responsive cathode was designed and prepared. The incorporation of Mn2+ ions drives the charge redistribution and spin polarization of CsPbBr3, which remarkably improve the carrier separation efficiency and the oxygen species adsorption energy. The Increased spin-polarization of the magnetic elements by Zeeman effect in an external magnetic field results in the enhanced oxygen reduction and evolution reaction. In the magnetic field, a low overpotential of 0.40 V was obtained for Li-O2 batteries with Mn-CsPbBr3 cathodes, demonstrating an ultralow overpotential of 0.12 V and an ultrahigh energy efficiency of 96.3% with the further illumination. The introduction of magnetic fields into the Li-O2 battery system provides a new avenue for improving the reaction kinetics of rechargeable Li-O2 battery.

p-p Orbital Hybridization Stabilizing Lattice Oxygen in Two-Dimensional Amorphous RuOx for Efficient Acidic Oxygen Evolution

Developing efficient Ru-based catalysts is crucial in reducing reliance on costly Ir for the acidic oxygen evolution reaction (OER). However, these Ru-based catalysts face a fundamental stability challenge due to the highly reactive nature of lattice oxygen. In this work, we propose an effective strategy to stabilize lattice oxygen in 2D amorphous RuOx through p-p orbital hybridization by incorporating dopants such as Al, Ga, and In. Notably, Ga doping exhibits remarkable acidic OER performance, leading to a 137 mV reduction in overpotential at 10 mA cm-2 and a 125-fold improvement in stability compared to undoped RuOx. This also surpasses the performances of most reported Ru-based catalysts. In contrast, doping with other elements from the same period, such as Mn, Co, or Cu, shows negligible improvements in catalytic performance. In situ electrochemical spectroscopic analysis, couples with theoretical calculations, reveals that the p-p orbital hybridization in the Ga-O coordination within Ga-RuOx effectively reduces the reactivity of lattice oxygen, suppresses the overoxidation of Ru, and switches the reaction pathway from the lattice oxygen mechanism to the adsorbate evolution mechanism. This novel p-p orbital hybridization strategy holds great potential for the development of efficient and robust electrocatalysts for OER and beyond.

Sub-4 nm Ru-RuO2 Schottky Nanojunction as a Catalyst for Durable Acidic Water Oxidation

RuO2 with high intrinsic activity for water oxidation is a promising alternative to IrO2 in proton exchange membrane (PEM) electrolyzer, but it suffers from long-term stability issues due to overoxidation. Here, we report a sub-4 nm Ru-RuO2 Schottky nanojunction (Ru-RuO2-SN) prepared by a microwave reaction that exhibits high activity and long-term stability in both three-electrode systems and PEM devices. The lattice strain and charge transfer induced by the metal-oxide SN increase the work function of the Ru-RuO2-SN, optimize the local electronic structure, and reduce the desorption energy of the metal site to the oxygen-containing intermediates; as a result, it leads to the oxide path mechanism (OPM) and inhibits the excessive oxidation of surface ruthenium. The Ru-RuO2-SN requires only 165 mV overpotential to obtain 10 mA·cm-2 with 1400 h stability without obvious activity degradation, achieving a stability number (6.7 × 106) matching iridium-based catalysts. In a PEM electrolyzer with Ru-RuO2-SN as an anode catalyst, only 1.6 V is needed to reach 1.0 A·cm-2 and it shows long-term stability at 100 mA·cm-2 for 1100 h and at 500 mA·cm-2 for 100 h. The reaction mechanism for the high stability of Ru-RuO2-SN was analyzed by density functional theory calculations. This work reports a durable, pure Ru-based water-oxidation catalyst and provides a new perspective for the development of efficient Ru-based catalysts.

Anode Alchemy on Multiscale: Engineering from Intrinsic Activity to Impedance Optimization for Efficient Water Electrolysis

The past decade has seen significant progress in proton exchange membrane water electrolyzers (PEMWE), but the growing demand for cost-effective electrolytic hydrogen pushes for higher efficiency at lower costs. As a complex system, the performance of PEMWE is governed by a combination of multiscale factors. This review summarizes the latest progress from quantum to macroscopic scales. At the quantum level, electron spin configurations can be optimized to enhance catalytic activity. At the nano and meso scales, advancements in atomic structure optimization, crystal phase engineering, and heterostructure design improve catalytic performance and mass transport. At the macro scale, innovative techniques in gas bubble management and internal resistance reduction drive further efficiency gains under ampere-level operating conditions. These modifications at the quantum level cascade through meso- and macro-scales, affecting charge transfer, reaction kinetics, and gas evolution management. Unlike conventional approaches that focus solely on one scale-either at the catalyst level (e.g., atomic, or crystal modifications) or at the device level (e.g., porous transport layers design)-combining multiscale optimizations unlocks greater performance improvements. Finally, a perspective on future opportunities for multiscale engineering in PEMWE anode design toward commercial viability is offered.

Recent achievements in noble metal-based oxide electrocatalysts for water splitting

The search for sustainable energy sources has accelerated the exploration of water decomposition as a clean H2 production method. Among the methods proposed, H2 production via water electrolysis has garnered considerable attention. However, the process of H2 production from water electrolysis is severely limited by the slow kinetics of the anodic oxygen evolution reaction and large intrinsic overpotentials at the anode; therefore, suitable catalysts need to be found to accelerate the reaction rate. Noble metal-based oxide electrocatalysts retain the advantages of abundant active sites, high electrical conductivity of noble metals, and low cost, which make them promising electrocatalysts; however, they suffer from the challenge of an imbalance between catalytic activity and stability. This review presents recent research progress in noble metals and their oxides as electrocatalysts. In this review, two half-reactions (the hydrogen evolution reaction and the oxygen evolution reaction) of water electrolysis are described. Recently reported methods for the synthesis of noble metal-based oxide electrocatalysts, improvement strategies, and sources of enhanced activity and stability for these types of catalysts are presented. Finally, the challenges and future perspectives in the field are summarised. This review is expected to help improve the understanding of noble metal-based oxide electrocatalysts.

Spin Effects in Optimizing Electrochemical Applications

Efficient electrocatalyst development is crucial for addressing global energy challenges, and recent advances have highlighted the significant role of electron spin-a fundamental property of electrons-in influencing catalytic processes. Regulating the spin states of active sites has emerged as a powerful strategy to enhance catalytic performance. In response to growing interest in spin-induced electrocatalysis, this review offers a comprehensive examination of the impact of spin states on electrocatalytic activity. We explore various strategies for modulating spin states, review state-of-the-art techniques for spin state characterization, and elucidate the mechanisms by which spin effects enhance catalytic efficiency. Additionally, we discuss future research directions, emphasizing the potential of spin regulation to drive innovation in electrocatalyst design and application. This review aims to provide a foundational understanding of spin effects in electrocatalysis, guiding future efforts in the rational design of high-performance catalysts.

Chloride Residues in RuO2 Catalysts Enhance Its Stability and Efficiency for Acidic Oxygen Evolution Reaction

. Ruthenium dioxide (RuO2) is a benchmark electrocatalyst for proton exchange membrane water electrolyzers (PEMWE), but its stability during the oxygen evolution reaction (OER) is often compromised by lattice oxygen involvement and metal dissolution. Despite that the typical synthesis of RuO2 produces chloride residues, the underlying function of chloride have not well investigated. In this study, we synthesized chlorine-containing RuO2 (RuO2-Cl) and pure RuO2 catalysts with similar morphology and crystallinity. RuO2-Cl demonstrated superior stability, three times greater than that of pure RuO2, and a lower overpotential of 176 mV at 10 mA cm-2. Furthermore, the RuO2-Cl catalysts that were in situ synthesized on a platinum-coated titanium felt could maintain high performance for up to 1200 hours at 100 mA cm-2. Computational and experimental analyses show that chloride stabilizes RuO2 by substituting the bridging oxygen atoms, which subsequently inhibits lattice oxygen evolution and Ru demetallation. Notably, this substitution also lowers the energy barrier of the rate-determining step by strengthening the binding of *OOH intermediates. These findings offer new insights into the previously unknown role of chloride residues and how to improve RuO2 stability.

A perspective on field-effect in energy and environmental catalysis

The development of catalytic technologies for sustainable energy conversion is a critical step toward addressing fossil fuel depletion and associated environmental challenges. High-efficiency catalysts are fundamental to advancing these technologies. Recently, field-effect facilitated catalytic processes have emerged as a promising approach in energy and environmental applications, including water splitting, CO2 reduction, nitrogen reduction, organic electrosynthesis, and biomass recycling. Field-effect catalysis offers multiple advantages, such as enhancing localized reactant concentration, facilitating mass transfer, improving reactant adsorption, modifying electronic excitation and work functions, and enabling efficient charge transfer and separation. This review begins by defining and classifying field effects in catalysis, followed by an in-depth discussion on their roles and potential to guide further exploration of field-effect catalysis. To elucidate the theory-structure-activity relationship, we explore corresponding reaction mechanisms, modification strategies, and catalytic properties, highlighting their relevance to sustainable energy and environmental catalysis applications. Lastly, we offer perspectives on potential challenges that field-effect catalysis may face, aiming to provide a comprehensive understanding and future direction for this emerging area.

Electron-phonon coupling and coherent energy superposition induce spin-sensitive orbital degeneracy for enhanced acidic water oxidation

The development of acid-stable water oxidation electrocatalysts is crucial for high-performance energy conversion devices. Different from traditional nanostructuring, here we employ an innovative microwave-mediated electron-phonon coupling technique to assemble specific Ru atomic patterns (instead of random Ru-particle depositions) on Mn0.99Cr0.01O2 surfaces (RuMW-Mn1-xCrxO2) in RuCl3 solution because hydrated Ru-ion complexes can be uniformly activated to replace some Mn sites at nearby Cr-dopants through microwave-triggered energy coherent superposition with molecular rotations and collisions. This selective rearrangement in RuMW-Mn1-xCrxO2 with particular spin-differentiated polarizations can induce localized spin domain inversion from reversed to parallel direction, which makes RuMW-Mn1-xCrxO2 demonstrate a high current density of 1.0 A cm-2 at 1.88 V and over 300 h of stability in a proton exchange membrane water electrolyzer. The cost per gallon of gasoline equivalent of the hydrogen produced is only 43% of the 2026 target set by the U.S. Department of Energy, underscoring the economic significance of this nanotechnology.

Unveiling the Structure and Dissociation of Interfacial Water on RuO2 for Efficient Acidic Oxygen Evolution Reaction

Understanding the structure and dynamic process of interfacial water molecules at the catalyst-electrolyte interface on acidic oxygen evolution reaction (OER) kinetics is highly desirable for the development of proton exchange membrane water electrolyzers. Herein, we construct a series of p-block metal elements (Ga, In, Sn) doped RuO2 catalysts with manipulated electronic structure and Ru-O covalency to investigate the effect of electrochemical interfacial engineering on the improvement of acidic OER activity. Associated with operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy measurements and theoretical analysis, we uncover the free-H2O enriched local environment and dynamic evolution from 4-coordinated hydrogen-bonded water and 2-coordinated hydrogen-bonded water to free-H2O on the surface of Ga-RuO2, are responsible for the optimized connectivity of hydrogen bonding network in the electrical double layer by promoting solvent reorganization. In addition, the structurally ordered interfacial water molecules facilitate high-efficiency proton-coupled electron transfer across the interface, leading to reduced energy barrier of the follow-up dissociation process and enhanced acidic OER performance. This work highlights the key role of structure and dynamic process of interfacial water for acidic OER, and demonstrates the electrochemical interfacial engineering as an efficient strategy to design high-performance electrocatalysts.

Doping Ti into RuO2 to Accelerate Bridged-Oxygen-Assisted Deprotonation for Acidic Oxygen Evolution Reaction

The development of efficient and durable electrocatalysts for the acidic oxygen evolution reaction (OER) is essential for advancing renewable hydrogen energy technology. However, the slow deprotonation kinetics of oxo-intermediates, involving the four proton-coupled electron steps, hinder the acidic OER progress. Herein, a RuTiOx solid solution electrocatalyst is investigated, which features bridged oxygen (Obri) sites that act as proton acceptors, accelerating the deprotonation of oxo-intermediates. Electrochemical tests, infrared spectroscopy, and density functional theory results reveal that the moderate proton adsorption energy on Obri sites facilitates fast deprotonation kinetics through the adsorbate evolution mechanism. This process effectively prevents the over-oxidation and deactivation of Ru sites caused by the lattice oxygen mechanism. Consequently, RuTiOx shows a low overpotential of 198 mV at 10 mA cm-2 geo and performance exceeding 1400 h at 50 mA cm-2 geo with negligible deactivation. These insights into the OER mechanism and the structure-function relationship are crucial for the advancement of catalytic systems.

Integrating Interactive Ir Atoms into Titanium Oxide Lattice for Proton Exchange Membrane Electrolysis

Iridium (Ir)-based oxide is the state-of-the-art electrocatalyst for acidic water oxidation, yet it is restricted to a few Ir-O octahedral packing modes with limited structural flexibility. Herein, the geometric structure diversification of Ir is achieved by integrating spatially correlated Ir atoms into the surface lattice of TiO2 and its booting effect on oxygen evolution reaction (OER) is investigated. Notably, the resultant i-Ir/TiO2 catalyst exhibits much higher electrocatalytic activity, with an overpotential of 240 mV at 10 mA cm-2 and excellent stability of 315 h at 100 mA cm-2 in acidic electrolyte. Both experimental and theoretical findings reveal that flexible Ir─O─Ir coordination with varied geometric structure plays a crucial role in enhancing OER activity, which optimize the intermediate adsorption by adjusting the d-band center of active Ir sites. Operando characterizations demonstrate that the interactive Ir─O─Ir units can suppress over-oxidation of Ir, effectively widening the stable region of Ir species during the catalytic process. The proton exchange membrane (PEM) electrolyzer, equipped with i-Ir/TiO2 as an anode, gives a low driving voltage of 1.63 V at 2 A cm-2 and maintains stable performance for over 440 h. This work presents a general strategy to eliminate the inherent geometric limitations of IrOx species, thereby inspiring further development of advanced catalyst designs.

Atomically Dispersed Mn-Doped Ru@RuO2 Core/Shell Nanostructure with High Acidic Water Oxidation Performance Arising from Multiple Synergies

The high overpotential and unsatisfactory stability of RuO2-based catalysts seriously hinder their application in acidic oxygen evolution reaction (OER). Herein, a Ru@RuO2 core/shell catalyst doped with atomically dispersed Mn species, denoted as Ru@Mn-RuO2, is reported, which is prepared by a facile one-pot method. Detailed structural characterizations confirm that Mn is homogeneously and atomically distributed in RuO2 shell, which causes lattice contraction of RuO2. The as-prepared Ru@Mn-RuO2 exhibits a very low overpotential of 190 mV at the current density of 10 mA cm-2 and an excellent stability of 360 h, far surpassing the control samples Ru@RuO2 without atomically dispersed Mn dopants and home-made RuO2 nanoparticles without metallic Ru core. With the further assistance of density functional theory calculations, the enhanced OER activity of Ru@Mn-RuO2 is attributed to multiple synergistic effects, including the MnOx-Ru (oxide shell) synergy, MnOx-Ru (metal core) synergy, and the Ru (core)-RuO2 (shell) synergy. Besides, the atomically dispersed Mn doping can increase the formation energy of soluble Ru cations, thus leading to the excellent stability of the Ru@Mn-RuO2 catalyst. This work shines light on the design of electrocatalysts with multiple synergistic effects towards efficient acid water splitting.

Diatomic Catalysts for Aqueous Zinc-Iodine Batteries: Mechanistic Insights and Design Strategies

There has been a growing interest in developing catalysts to enable the reversible iodine conversion reaction for high-performance aqueous zinc-iodine batteries (AZIBs). While diatomic catalysts (DACs) have demonstrated superior performance in various catalytic reactions due to their ability to facilitate synergistic charge interactions, their application in AZIBs remains unexplored. Herein, we present, for the first time, a DAC comprising Mn-Zn dual atoms anchored on a nitrogen-doped carbon matrix (MnZn-NC) for iodine loading, resulting in a high-performance AZIB with a capacity of 224 mAh g-1 at 1 A g-1 and remarkable cycling stability over 320,000 cycles. The electron hopping along the Mn-N-Zn bridge is stimulated via a spin exchange mechanism. This process broadens the Mn 3dxy band width and enhances the metallic character of the catalyst, thus facilitating charge transfer between the catalysts and reaction intermediates. Additionally, the increased electron occupancy within the d-orbital of Zn elevates Zn's d-band center, thereby enhancing chemical interactions between MnZn-NC and I-based species. Furthermore, our mechanism demonstrates potential applicability to other Metal-Zn-NC DACs with spin-polarized atoms. Our work elucidates a clear mechanistic understanding of diatomic catalysts and provides new insights into catalyst design for AZIBs.

Magnetically Enhanced Oxygen Evolution Reaction in Mild Alkaline Electrolytes by Building Catalysts on Magnetic Frame

Under large current densities, the excessive hydroxide ion (OH) consumption hampers alkaline water splitting involving the oxygen evolution reaction (OER). High OH concentration (≈30 wt.%) is often used to enhance the catalytic activity of OER, but it also leads to higher corrosion in practical systems. To achieve higher catalytic activity in low OH concentration, catalysts on magnetic frame (CMF) are built to utilize the local magnetic convection induced from the host frame's magnetic field distributions. This way, a higher reaction rate can be achieved in relatively lower OH concentrations. A CMF model system with catalytically active CoFeOx nanograins grown on the magnetic Ni foam is demonstrated. The OER current of CoFeOx@NF receives ≈90% enhancement under 400 mT (900 mA cm-2 at 1.65 V) compared to that in zero field, and exhibits remarkable durability over 120 h. As a demonstration, the water-splitting performance sees a maximum 45% magnetic enhancement under 400 mT in 1 m KOH (700 mA cm-2 at 2.4 V), equivalent to the concentration enhancement of the same electrode in a more corrosive 2 m KOH electrolyte. Therefore, the catalyst-on-magnetic-frame strategy can make efficient use of the catalysts and achieve higher catalytic activity in low OH concentration by harvesting local magnetic convection.

Spin Manipulation of Heterogeneous Molecular Electrocatalysts by an Integrated Magnetic Field for Efficient Oxygen Redox Reactions

Understanding the spin-dependent activity of nitrogen-coordinated single metal atom (M-N-C) electrocatalysts for oxygen reduction and evolution reactions (ORR and OER) remains challenging due to the lack of structure-defined catalysts and effective spin manipulation tools. Herein, both challenges using a magnetic field integrated heterogeneous molecular electrocatalyst prepared by anchoring cobalt phthalocyanine (CoPc) deposited carbon black on polymer-protected magnet nanoparticles, are addressed. The built-in magnetic field can shift the Co center from low- to high-spin (HS) state without atomic structure modification, affording one-order higher turnover frequency, a 50% increased H2O2 selectivity for ORR, and a ≈4000% magnetocurrent enhancement for OER. This catalyst can significantly minimize magnet usage, enabling safe and continuous production of a pure H2O2 solution for 100 h from a 100 cm2 electrolyzer. The new strategy demonstrated here also applies to other metal phthalocyanine-based catalysts, offering a universal platform for studying spin-related electrochemical processes.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Spontaneous-Spin-Polarized 2D π-d Conjugated Frameworks Towards Enhanced Oxygen Evolution Kinetics

Alternative strategies to design sustainable-element-based electrocatalysts enhancing oxygen evolution reaction (OER) kinetics are demanded to develop affordable yet high-performance water-electrolyzers for green hydrogen production. Here, it is demonstrated that the spontaneous-spin-polarized 2D π-d conjugated framework comprising abundant elements of nickel and iron with a ratio of Ni:Fe = 1:4 with benzenehexathiol linker (BHT) can improve OER kinetics by its unique electronic property. Among the bimetallic NiFex:y-BHTs with various ratios with Ni:Fe = x:y, the NiFe1:4-BHT exhibits the highest OER activity. The NiFe1:4-BHT shows a specific current density of 140 A g-1 at the overpotential of 350 mV. This performance is one of the best activities among state-of-the-art non-precious OER electrocatalysts and even comparable to that of the platinum-group-metals of RuO2 and IrO2. The density functional theory calculations uncover that introducing Ni into the homometallic Fe-BHT (e.g., Ni:Fe = 0:1) can emerge a spontaneous-spin-polarized state. Thus, this material can achieve improved OER kinetics with spin-polarization which previously required external magnetic fields. This work shows that a rational design of 2D π-d conjugated frameworks can be a powerful strategy to synthesize promising electrocatalysts with abundant elements for a wide spectrum of next-generation energy devices.

Deciphering the work function induced local charge regulation towards activating an octamolybdate cluster-based solid for acidic water oxidation

The advancement of highly robust and efficient electrocatalysts for the oxygen evolution reaction (OER) under acidic conditions is imperative for the sustainable production of green hydrogen. In accomplishing sustainable and sturdy electrocatalysts for oxygen evolution at low pH, the challenge is tough for non-iridium/ruthenium-based electrocatalysts. This study elaborates on the intrinsic alterations in electronic arrangements and structural disorder upon the precise activation of an octamolybdate cluster-based solid [{Cu(pz)4}2Mo8O26]·2H2O through room temperature grinding with rGO (reduced graphene oxide), resulting in enhanced conductivity, stability, and activity of the electrocatalyst towards the acidic OER without employing any benchmark metal ion (Ru or Ir). Additionally, the work function of the composites was found to be low compared to that of pristine polyoxometalates (POMs), indicative of the improved conducive behavior, which is lacking in the POM structure. The catalyst displays a notably reduced overpotential of 185 mV to achieve a current density of 10 mA cm-2, coupled with significant stability lasting 24 hours at a higher current density of 100 mA cm-2. These findings propose the manipulation of crystalline POMs with highly conductive non-metallic elements to facilitate superior water oxidation at lower pH levels which can help in the production of green hydrogen.

Fluorinated Organic Cations Derived Chiral 2D Perovskite Enabling Enhanced Spin-Dependent Oxygen Evolution Reaction

Chirality-induced spin selectivity observed in chiral 2D organic-inorganic hybrid perovskite holds promise to achieve spin-dependent electrochemistry. However, conventional chiral 2D perovskites suffer from low conductivity and hygroscopicity, limiting electrochemical performance and operational stability. Here, a cutting-edge material design is introduced to develop a stable and efficient chiral perovskite-based spin polarizer by employing fluorinated chiral cation. The fluorination approach effectively promotes the charge carrier transport along the out-of-plane direction by mitigating the dielectric confinement effect within the multi-quantum well-structured 2D perovskite. Integrating the fluorinated cation incorporated spin polarizer with BiVO4 photoanode considerably boosts the photocurrent density while reducing overpotential through a spin-dependent oxygen evolution reaction. Furthermore, the hydrophobic nature of fluorine in spin polarizer endows operational stability to the photoanode, extending the durability by 280% as compared to the device with non-fluorinated spin polarizer.

Spin-dependent electrocatalysis

The shift towards sustainable energy requires efficient electrochemical conversion technologies, emphasizing the crucial need for robust electrocatalyst design. Recent findings reveal that the efficiency of some electrocatalytic reactions is spin-dependent, with spin configuration dictating performance. Consequently, understanding the spin's role and controlling it in electrocatalysts is important. This review succinctly outlines recent investigations into spin-dependent electrocatalysis, stressing its importance in energy conversion. It begins with an introduction to spin-related features, discusses characterization techniques for identifying spin configurations, and explores strategies for fine-tuning them. At the end, the article provides insights into future research directions, aiming to reveal more unknown fundamentals of spin-dependent electrocatalysis and encourage further exploration in spin-related research and applications.

Accelerated Proton Transfer in Asymmetric Active Units for Sustainable Acidic Oxygen Evolution Reaction

The poor durability of Ru-based catalysts limits the practical application in proton exchange membrane water electrolysis (PEMWE). Here, we report that the asymmetric active units in Ru1-xMxO2 (M = Sb, In, and Sn) binary solid solution oxides are constructed by introducing acid-resistant p-block metal sites, breaking the activity and stability limitations of RuO2 in acidic oxygen evolution reaction (OER). Constructing highly asymmetric Ru-O-Sb units with a strong electron delocalization effect significantly shortens the spatial distance between Ru and Sb sites, improving the bonding strength of the overall structure. The unique two-electron redox couples at Sb sites in asymmetric active units trigger additional chemical steps at different OER stages, facilitating continuous proton transfer. The optimized Ru0.8Sb0.2O2 solid solution requires a superlow overpotential of 160 mV at 10 mA cm-2 and a record-breaking stability of 1100 h in an acidic electrolyte. Notably, the scale-prepared Ru0.8Sb0.2O2 achieves efficient PEMWE performance under industrial conditions. General mechanism analysis shows that the enhanced proton transport in the asymmetric Ru-O-M unit provides a new working pathway for acidic OER, breaking the scaling relationship without sacrificing stability.

Recent Advancements on Spin Engineering Strategies for Highly Efficient Electrocatalytic Oxygen Evolution Reactions

Oxygen evolution reaction (OER) is a widely employed half-electrode reaction in oxygen electrochemistry, in applications such as hydrogen evolution, carbon dioxide reduction, ammonia synthesis, and electrocatalytic hydrogenation. Unfortunately, its slow kinetics limits the commercialization of such applications. It is therefore highly imperative to develop highly robust electrocatalysts with high activity, long-term durability, and low noble-metal contents. Previously intensive efforts have been made to introduce the advancements on developing non-precious transition metal electrocatalysts and their OER mechanisms. Electronic structure tuning is one of the most effective and interesting ways to boost OER activity and spin angular momentum is an intrinsic property of the electron. Therefore, modulation on the spin states and the magnetic properties of the electrocatalyst enables the changes on energy associated with interacting electron clouds with radical absorbance, affecting the OER activity and stability. Given that few review efforts have been made on this topic, in this review, the-state-of-the-art research progress on spin-dependent effects in OER will be briefed. Spin engineering strategies, such as strain, crystal surface engineering, crystal doping, etc., will be introduced. The related mechanism for spin manipulation to boost OER activity will also be discussed. Finally, the challenges and prospects for the development of spin catalysis are presented. This review aims to highlight the significance of spin engineering in breaking the bottleneck of electrocatalysis and promoting the practical application of high-efficiency electrocatalysts.

Chirality-Induced Spin Selectivity Enables New Breakthrough in Electrochemical and Photoelectrochemical Reactions

To facilitate the transition from a carbon-energy-dependent society to a sustainable society, conventional engineering strategies, which encounter limitations associated with intrinsic material properties, should undergo the paradigm shift. From a theoretical viewpoint, the spin-dependent feature of oxygen evolution reaction (OER) reveals the potential of a spin-polarization strategy in enhancing the performance of electrochemical (EC) reactions. The chirality-induced spin selectivity (CISS) phenomenon attracts unprecedented attention owing to its potential utility in achieving novel breakthroughs. This paper starts with the experimental results aimed at enhancing the efficiency of the spin-dependent OER focusing on the EC system based on the CISS phenomenon. The applicability of spin-polarization to EC system is verified through various analytical methodologies to clarify the theoretical groundwork and mechanisms underlying the spin-dependent reaction pathway. The discussion is then extended to effective spin-control strategies in photoelectrochemical system based on the CISS effect. Exploring the influence of spin-state control on the kinetic and thermodynamic aspects, this perspective also discusses the effect of spin polarization induced by the CISS phenomenon on spin-dependent OER. Lastly, future directions for enhancing the performance of spin-dependent redox systems are discussed, including expansion to various chemical reactions and the development of materials with spin-control capabilities.

The spin polarization strategy regulates heterogeneous catalytic activity performance: from fundamentals to applications

In recent years, there has been significant attention towards the development of catalysts that exhibit superior performance and environmentally friendly attributes. This surge in interest is driven by the growing demands for energy utilization and storage as well as environmental preservation. Spin polarization plays a crucial role in catalyst design, comprehension of catalytic mechanisms, and reaction control, offering novel insights for the design of highly efficient catalysts. However, there are still some significant research gaps in the current study of spin catalysis. Therefore, it is urgent to understand how spin polarization impacts catalytic reactions to develop superior performance catalysts. Herein, we present a comprehensive summary of the application of spin polarization in catalysis. Firstly, we summarize the fundamental mechanism of spin polarization in catalytic reactions from two aspects of kinetics and thermodynamics. Additionally, we review the regulation mechanism of spin polarization in various catalytic applications and several approaches to modulate spin polarization. Moreover, we discuss the future development of spin polarization in catalysis and propose several potential avenues for further progress. We aim to improve current catalytic systems through implementing a novel and distinctive spin engineering strategy.

Rapid Conversion from Alloy Nanoparticles to Oxide Nanowires: Strain Wave-Driven Ru-O-Mn Collaborative Catalysis for Durable Oxygen Evolution Reaction

Metal-doped ruthenium oxides with low prices have gained widespread attention due to their editable compositions, distorted structures, and diverse morphologies for electrocatalysis. However, the mainstream challenge lies in breaking the so-called seesaw relationship between activity and stability during acidic oxygen evolution reaction (OER). Herein, strain wave-featured Mn-RuO2 nanowires (NWs) with asymmetric Ru-O-Mn bonds are first fabricated by thermally driven rapid solid phase conversion from RuMn alloy nanoparticles (NPs) at moderate temperature (450 °C). In 0.5 M H2SO4, the resultant NWs display a surprisingly ultralow overpotential of 168 mV at 10 mA cm-2 and run at a stable cell voltage (1.67 V) for 150 h at 50 mA cm-2 in PEMWE, far exceeding IrO2||Pt/C assemble. The simultaneous enhancement of both activity and stability stems from the presence of dense strain waves composed of alternating compressive and tensile ones in the distorted NWs, which collaboratively activate the Ru-O-Mn sites for faster OER. More importantly, the atomic strain waves trigger dynamic Ru-O-Mn regeneration via the refilling of oxygen vacancies by oxyanions adsorbed on adjacent Mn and Ru sites, achieving long-term stability. This work opens a door to designing non-precious metal-assisted ruthenium oxides with unique strains for practical application in commercial PEMWE.

Lanthanide-regulating Ru-O covalency optimizes acidic oxygen evolution electrocatalysis

Precisely modulating the Ru-O covalency in RuOx for enhanced stability in proton exchange membrane water electrolysis is highly desired. However, transition metals with d-valence electrons, which were doped into or alloyed with RuOx, are inherently susceptible to the influence of coordination environment, making it challenging to modulate the Ru-O covalency in a precise and continuous manner. Here, we first deduce that the introduction of lanthanide with gradually changing electronic configurations can continuously modulate the Ru-O covalency owing to the shielding effect of 5s/5p orbitals. Theoretical calculations confirm that the durability of Ln-RuOx following a volcanic trend as a function of Ru-O covalency. Among various Ln-RuOx, Er-RuOx is identified as the optimal catalyst and possesses a stability 35.5 times higher than that of RuO2. Particularly, the Er-RuOx-based device requires only 1.837 V to reach 3 A cm-2 and shows a long-term stability at 500 mA cm-2 for 100 h with a degradation rate of mere 37 μV h-1.

A dual spin-controlled chiral two-/three-dimensional perovskite artificial leaf for efficient overall photoelectrochemical water splitting

The oxygen evolution reaction, which involves high overpotential and slow charge-transport kinetics, plays a critical role in determining the efficiency of solar-driven water splitting. The chiral-induced spin selectivity phenomenon has been utilized to reduce by-product production and hinder charge recombination. To fully exploit the spin polarization effect, we herein propose a dual spin-controlled perovskite photoelectrode. The three-dimensional (3D) perovskite serves as a light absorber while the two-dimensional (2D) chiral perovskite functions as a spin polarizer to align the spin states of charge carriers. Compared to other investigated chiral organic cations, R-/S-naphthyl ethylamine enable strong spin-orbital coupling due to strengthened π-π stacking interactions. The resulting naphthyl ethylamine-based chiral 2D/3D perovskite photoelectrodes achieved a high spin polarizability of 75%. Moreover, spin relaxation was prevented by employing a chiral spin-selective L-NiFeOOH catalyst, which enables the secondary spin alignment to promote the generation of triplet oxygen. This dual spin-controlled 2D/3D perovskite photoanode achieves a 13.17% of applied-bias photon-to-current efficiency. Here, after connecting the perovskite photocathode with L-NiFeOOH/S-naphthyl ethylamine 2D/3D photoanode in series, the resulting co-planar water-splitting device exhibited a solar-to-hydrogen efficiency of 12.55%.

Sulfurized NiFe2O4 Electrocatalyst with In Situ Formed Fe-NiOOH Nanoparticles to Realize Industrial-Level Oxygen Evolution

Constructing composite catalysts with refined geometric control and optimal electronic structure provides a promising route to enhance electrocatalytic performance toward the oxygen evolution reaction (OER). Herein, a composite catalyst is prepared with multiple components using chemical vapour deposition method to transform crystalline NiFe2O4 into crystalline NiFe2O4@amorphous S-NiFe2O4 with core-shell structure (C-NiFe2O4@A-S-NiFe2O4), and Fe-NiOOH nanoparticles are subsequently in situ generated on its surface during the process of electrocatalytic OER. The C-NiFe2O4@A-S-NiFe2O4 catalyst exhibits a low overpotential of 275 mV while possessing an excellent stability for 500 h at 10 mA cm-2. The anion exchange membrane water electrolyzer with C-NiFe2O4@A-S-NiFe2O4 anode catalyst obtains a current density of 4270 mA cm- 2 at 2.0 V. Further, in situ Raman spectroscopy result demonstrates that in situ generated Fe-NiOOH nanoparticles are revealed to act as the catalytic active phase for catalyzing the OER. Besides, introducing A-S-NiFe2O4 in C-NiFe2O4@A-S-NiFe2O4 facilitates the formation of Fe-NiOOH nanoparticles with high-valency Ni, thus increasing the proportion of lattice oxygen-participated OER. This work not only provides an alternative strategy for the design of high-performance catalysts, but also lays a foundation for the exploration of catalytic mechanisms.

Magnetic Field Enhanced Cobalt Iridium Alloy Catalyst for Acidic Oxygen Evolution Reaction

Magnetic field mediated magnetic catalysts provide a powerful pathway for accelerating their sluggish kinetics toward the oxygen evolution reaction (OER) but remain great challenges in acidic media. The key obstacle comes from the production of an ordered magnetic domain catalyst in the harsh acidic OER. In this work, we form an induced local magnetic moment in the metallic Ir catalyst via the significant 3d-5d hybridization by introducing cobalt dopants. Interestingly, CoIr nanoclusters (NCs) exhibit an excellent magnetic field enhanced acidic OER activity, with the lowest overpotential of 220 mV at 10 mA cm-2 and s long-term stability of 120 h under a constant magnetic field (vs 260 mV/20 h without a magnetic field). The turnover frequency reaches 7.4 s-1 at 1.5 V (vs RHE), which is 3.0 times higher than that without magnetization. Density functional theory results show that CoIr NCs have a pronounced spin polarization intensity, which is preferable for OER enhancement.

Spin-Magnetic Effect of d-π Conjugation Polymer Enhanced O-H Cleavage in Water Oxidation

A deep understanding of the mechanism for the spin-magnetic effect on O-H cleavage is crucial for the development of new catalysts for water oxidation. Herein, we designed and synthesized the crystalline Fe-DABDT and Co-DABDT (DABDT = 2,5-diaminobenzene-1,4-dithiol) and optimized an effective magnetic moment to explore the role of the spin-magnetic effect in the regulation of water oxidation activity. It can be found that the OER activity of the catalyst is positively correlated with its effective magnetic moment. Under the external magnetic field, Fe-DABDT with more spin single electrons has a stronger spin-magnetic response to water oxidation than Fe/Co-DABDT and Co-DABDT. The increase in OER current of Fe-DABDT is nearly 2 times higher than that of Co-DABDT. Experimental and density functional theory studies show that magnetized Fe sites could realize nucleophilic reaction, accelerate the polarization of electron spin states, and promote the polar decomposition of O-H and the formation of the O-O bond. This study provides mechanistic insight into the spin-magnetic effect of oxygen evolution reaction and further understanding of the spin origin of catalytic activity, which is expected to improve the energy efficiency of hydrogen production.

Highly Active and Stable Alkaline Hydrogen Evolution Electrocatalyst Based on Ir-Incorporated Partially Oxidized Ru Aerogel under Industrial-Level Current Density

The realization of large-scale industrial application of alkaline water electrolysis for hydrogen generation is severely hampered by the cost of electricity. Therefore, it is currently necessary to synthesize highly efficient electrocatalysts with excellent stability and low overpotential under an industrial-level current density. Herein, Ir-incorporated in partially oxidized Ru aerogel has been designed and synthesized via a simple in situ reduction strategy and subsequent oxidation process. The electrochemical measurements demonstrate that the optimized Ru98 Ir2 -350 electrocatalyst exhibits outstanding hydrogen evolution reaction (HER) performance in an alkaline environment (1 M KOH). Especially, at the large current density of 1000 mA cm-2 , the overpotential is as low as 121 mV, far exceeding the benchmark Pt/C catalyst. Moreover, the Ru98 Ir2 -350 catalyst also displays excellent stability over 1500 h at 1000 mA cm-2 , denoting its industrial applicability. This work provides an efficient route for developing highly active and ultra-stable electrocatalysts for hydrogen generation under industrial-level current density.