Regulating the Spin State of FeIII Enhances the Magnetic Effect of the Molecular Catalysis Mechanism

The Role of Lattice Distortion in Catalysis: Functionality and Distinctions from Strain

Achieving high-performance catalysts is imperative for clean energy and environmental applications. In this context, an expanding body of research underscores the critical significance of structural modifications, with lattice distortion emerging as an intrinsic reconfiguration of atomic arrangements that profoundly influences catalytic processes. By contrast, strain typically arises from interfacial mismatches or external forces. Building on these distinctions, this review systematically compares these concepts, examining their definitions, origins, criteria, characterization methods, and impacts on catalytic activity. Special emphasis is placed on the mechanistic roles of lattice distortion in catalysis, particularly its ability to enhance function through intrinsic structure modification, carrier migration dynamics modulation, surface chemistry modulation, and enhanced catalyst stability. Furthermore, the impact of lattice distortion on enhancing catalytic reactivity is elucidated by influencing molecular adsorption and activation, optimizing reaction pathways, tailoring active sites, and coupling with spin polarization effects to promote efficient catalytic performance. Finally, the remaining challenges and future outlook in the synergistic regulation of local distortion and strain, multi-scale dynamic in-situ characterization, and sustainable strategies for practical applications are discussed, offering valuable insights for advancing efficient and scalable chemical and energy transformation technologies.

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.

Enhancing C─C Bond Cleavage of Glycerol Electrooxidation Through Spin-Selective Electron Donation in Pd-PdS2-Cox Heterostructural Nanosheets

As a 4d transition metal, the spin state of Pd is extremely difficult to directly regulate for the optimized d orbital states owing to the strong spin-orbit coupling effect and further extended d orbital. Herein, we devise a "spin-selective electron donation" strategy to tune specific d orbital electrons of Pd inspired by the Dewar-Chatt-Duncanson model theory. Co-S-Pd bridges with different spin-states of CoIII have been constructed in a series of Pd-PdS2-Cox HNSs with tunable Co content. Experiments and theoretical calculations indicate that low-spin CoIII (t2g 6eg 0) with fully occupied t2g orbitals and emptyd z 2 $d_{{z^2}}$ orbitals can accurately alter thed z 2 $d_{{z^2}}$ electron of Pd by σ-donation via the Co-S-Pd bridge. In contrast, the unfilled dxy orbital of high-spin CoIII (t2g 5eg 1) is essential for controlling the dxy electron of Pd via π-donation. Benefiting fromd z 2 $d_{{z^2}}$ state optimization by σ-donation, Pd-PdS2-Co4.0 delivers superior performance toward various bio-alcohols (ethanol, ethylene glycol, and glycerol) with enhanced C─C bond cleavage. Furthermore, coupling the glycerol oxidation reaction with the CO2 reduction reaction (GOR||CO2RR), the electricity consumption of GOR||CO2RR drops 46.4% compared to the state-of-art system (OER||CO2RR). Moreover, anodic Faraday efficiency (FE) of formic acid can be attainable at more than 90% at low voltage regions.

Electron Donor-Acceptor Activated Anti-Fenton Property for the Ultradurable Oxygen Reduction Reaction

Iron-nitrogen-carbon (Fe-N-C) materials are recognized as an effective category of catalysts that do not contain platinum (Pt) for the oxygen reduction reaction (ORR). Nonetheless, the long-term stability and effectiveness of these materials are significantly hindered by the dissolution and oxidation of Fe atoms. Microstructural engineering of Fe-N-C is a viable approach to enhancing ORR activity and stability. Herein, CuN5-single-atom nanozymes (SAzyme)-assisted Fe-N5 catalysts (SA-Fe-N5) were developed by introducing single-atom Cu to enhance Fe-N-C catalyst ORR performance. Electrochemical assessments indicated that SA-Fe-N5 exhibited excellent ORR activity in alkaline solutions, with a half-wave potential and a diffusion-limited current density similar to that of commercial Pt/C. Calculations based on density functional theory indicated that a single copper atom can function as an electron donor, enhancing the electron density at the iron sites. This modification improves the adsorption and desorption energies for intermediates involved in the ORR process, ultimately boosting the ORR performance of the single-atom Fe-N5 catalyst. Moreover, the introduction of the Cu site can be regarded as a catalase single-atom nanozyme (CAT-SAzyme), facilitating the decomposition of the byproduct H2O2 to H2O and thereby enhancing the anti-Fenton activity during the ORR process. Notably, as a cathode catalyst in a zinc-air battery, SA-Fe-N5 demonstrated an impressive power density of 217.8 mW cm-2 alongside a current density of 257.3 mA cm-2.

Asymmetry Spin-Orbit of Single Iron Active Site Enhance Oxygen Reduction Reaction

Asymmetric electron distribution of single-atom catalysts (SAC) is an important means of regulating intrinsic catalytic activity. However, limited by synthetic preparation methods, understanding of the mechanism of asymmetrically coordinated single-atom catalysis is restricted. In this study, leveraging the micropore confinement effect, nitrogen and phosphorus-doped microporous carbon is used as a substrate to successfully anchor singly dispersed Fe atoms, constructing the asymmetrically coordinated single-atom Fe site coordinated with N and P atoms (Fe-SAs/NPC). The existence of the Fe-N3P1 site structure breaks the symmetry Fe-N4 in Fe-SAs/NC, which would optimize the adsorption strength of intermediates. The resulting Fe-SAs/NPC exhibits excellent ORR activity with a half-wave potential of 0.91 V (0.1 m KOH), which is 40 mV higher than that of Fe-SAs/NC (0.87 V). Combined with theoretical calculations, an in-depth understanding of the asymmetric electronic configuration from the perspective of spin orbitals can enhance the electronic activity near the Fermi level and strengthen the adsorption of oxygen-containing intermediates. This work provides new perspectives and ideas for understanding spin-electronic behavior in catalytic processes. Furthermore, the Zn-air battery constructed using Fe-SAs/NPC exhibits a high power density of 187.7 mW cm-2 and a specific capacity of 819.6 mAh gZn -1 at 10 mA cm-2.

Isolated Metal Centers Activate Small Molecule Electrooxidation: Mechanisms and Applications

Electrochemical oxidation of small molecules shows great promise to substitute oxygen evolution reaction (OER) or hydrogen oxidation reaction (HOR) to enhance reaction kinetics and reduce energy consumption, as well as produce high-valued chemicals or serve as fuels. For these oxidation reactions, high-valence metal sites generated at oxidative potentials are typically considered as active sites to trigger the oxidation process of small molecules. Isolated atom site catalysts (IASCs) have been developed as an ideal system to precisely regulate the oxidation state and coordination environment of single-metal centers, and thus optimize their catalytic property. The isolated metal sites in IASCs inherently possess a positive oxidation state, and can be more readily produce homogeneous high-valence active sites under oxidative potentials than their nanoparticle counterparts. Meanwhile, IASCs merely possess the isolated metal centers but lack ensemble metal sites, which can alter the adsorption configurations of small molecules as compared with nanoparticle counterparts, and thus induce various reaction pathways and mechanisms to change product selectivity. More importantly, the construction of isolated metal centers is discovered to limit metal d-electron back donation to CO 2p* orbital and reduce the overly strong adsorption of CO on ensemble metal sites, which resolve the CO poisoning problems in most small molecules electro-oxidation reactions and thus improve catalytic stability. Based on these advantages of IASCs in the fields of electrochemical oxidation of small molecules, this review summarizes recent developments and advancements in IASCs in small molecules electro-oxidation reactions, focusing on anodic HOR in fuel cells and OER in electrolytic cells as well as their alternative reactions, such as formic acid/methanol/ethanol/glycerol/urea/5-hydroxymethylfurfural (HMF) oxidation reactions as key reactions. The catalytic merits of different oxidation reactions and the decoding of structure-activity relationships are specifically discussed to guide the precise design and structural regulation of IASCs from the perspective of a comprehensive reaction mechanism. Finally, future prospects and challenges are put forward, aiming to motivate more application possibilities for diverse functional IASCs.

Regulating the spin state of a single Fe atom in BiOBr to enhance photocatalytic nitrogen reduction: insights from theoretical studies

Herein, we investigated the effects of the spin state of a single Fe atom on the nitrogen reduction reaction (NRR) in BiOBr using density functional theory. Our simulations revealed that P doping can reduce the spin state of the single Fe atom. This leads to an overlap of orbitals between N2 and the Fe atom at the Fermi energy level, thereby promoting the activation of N2. The investigation of NRR mechanisms revealed that the enzymatic mechanism is more favorable compared to the distal and alternating mechanisms. The formation of NNH with an energy barrier of 2.32 eV is identified as the rate-determining step for the NRR process in the Fe-doped BiOBr system. Furthermore, P doping dramatically reduces the energy barrier of the rate-determining step, which involves releasing the second NH3 molecule, by a factor of 2.37. This study elucidates the influence mechanism of the Fe spin state on the performance of the NRR, providing valuable theoretical guidance for designing highly efficient photocatalysts.

Conductive Metal-Organic Frameworks and Their Electrocatalysis Applications

Recently, electrically conductive metal-organic frameworks (EC-MOFs) have emerged as a wealthy library of porous frameworks with unique properties, allowing their use in diverse applications of energy conversion, including electrocatalysis. In this review, the electron conduction mechanisms in EC-MOFs are examined, while their electrical conductivities are considered. There have been various strategies to enhance the conductivities of MOFs including ligand modification, the incorporation of conducting materials, and the construction of multidimensional architectures. With sufficient conductivities being established for EC-MOFs, there have been extensive pursuits in their electrocatalysis applications, such as in the hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, N2 reduction reaction, and CO2 reduction reaction. In addition, computational modeling of EC-MOFs also exerts an important impact on revealing the synthesis-structure-performance relationships. Finally, the prospects and current challenges are discussed to provide guidelines for designing promising framework materials.

Spin Magnetic Effect Activate Dual Site Intramolecular O─O Bridging for Nickel-Iron Hydroxide Enhanced Oxygen Evolution Catalysis

The oxygen evolution reaction (OER) involves the recombination of diamagnetic hydroxyl (OH) or water (H2O) into the paramagnetic triplet state of oxygen (O2). The spin conservation of oxygen intermediates plays a crucial role in OER, however, research on spin dynamics during the catalytic process remains in its early stages. Herein, β-Ni(OH)2 and Fe-doped β-Ni(OH)2 (Ni5Fe1(OH)2) are utilized as model catalysts to understand the mechanism of spin magnetic effects at iron (III) sites during OER. Combined with magnetic characterization, it is founded that the introduction of Fe transforms the antiferromagnetic Ni(OH)2 into a ferromagnetic material. Testing the magnetic response of the catalyst under an external magnetic field, the OER activity of Ni5Fe1(OH)2 is significantly enhanced in comparison to Ni(OH)2. This improvement is likely due to the introduction of iron sites, which promote spin magnetic effects and enhance reaction kinetics, thereby increasing catalytic efficiency. Combining experimental and theoretical characterization, it is discovered that the iron sites accelerate the formation of heterogeneous dual-site O─O bridging, represented as ─Ni─O─O─Fe─, thereby effectively enhancing the kinetics of the OER reaction. This study provides a magnetic perspective on the structure-function relationship of magnetic iron-based catalysts and has significant implications for the design of new catalysts.

Spin State Modulation with Oxygen Vacancy Orientates C/N Intermediates for Urea Electrosynthesis of Ultrahigh Efficiency

The co-electrolysis of CO2 and NO3 - to synthesize urea has become an effective pathway to alternate the conventional Bosch-Meiser process, while the complexity of C-/N-containing intermediates for C-N coupling results in the urea electrosynthesis of unsatisfactory efficiency. In this work, an electronic spin state modulation maneuver with oxygen vacancies (Ov) is unveiled to effectively meliorate the oriented generation of key intermediates *NH2 and *CO for C-N coupling, furnishing urea in ultrahigh yield of 2175.47 µg mg-1 h-1 and Faraday efficiency of 70.1%. Mechanistic studies expound that Ov can induce the conversion of the high-spin state Ni2+ (t2g 6eg 2) of Ni@CeO2-x to the low-spin state Ni3+ (t2g 6eg 1), which markedly enhances the hybridization degree of the Ni 3d and the N 2p orbitals of *NO, facilitating the selective formation of *NH2. Notably, the in situ generated *NH2 intermediates can serve as a localized proton donor to promote the electroreduction of CO2 on the adjacent site Ce3+-O to exclusively afford *CO, followed by C-N coupling of each other to efficiently synthesize urea. The strategy of tailored switching of the active site spin state provides a reliable reference to rectify the electronic structure of electrocatalysts for directional CO2 valorization.

Oxygen evolution reaction on NiFe-LDH/(Ni,Fe)OOH: theoretical insights into the effects of electronic structure and spin-state evolution

NiFe-layered double hydroxides (NiFe-LDH) have emerged as promising oxygen evolution reaction (OER) catalysts in alkaline medium, but their commercial applications are limited due to the decrease in their activity as the electrolyte becomes less alkaline. Thus, a comprehensive understanding of the OER mechanism of NiFe-LDH in alkaline medium is desirable for the rational design of new catalysts with improved performances. Especially, their spin-related factors have rarely been systematically investigated during the OER (diamagnetic H2O → paramagnetic O2). Herein, we simulated the OER performance of NiFe-LDH and (Ni,Fe)OOH as NiFe-LDH underwent surface-reconstruction and formed (Ni,Fe)OOH under alkaline conditions. Results demonstrated an enhanced OER performance on (Ni,Fe)OOH, and the Fe active site of NiFe-LDH on losing 3H (namely, NiFe(OH)2 - 3H) showed the lowest overpotential for OER because the d-orbital electron of the Fe atom shifted up to the Fermi level. Notably, the electronic interaction between Fe and OOH induced a change in the spin state of Fe, which further decreased the overpotential for the OER. Thus, the overpotential of the Fe site on NiFe(OH)2 - 3H decreased from 0.55 eV to 0.46 eV. The density of states (DOS) analysis revealed that the spin flip of Fe promoted the formation of bonding states between Fe and OOH, endowing the catalyst with a better OER performance. Our findings can help pave the way for the development of high-performance OER catalysts at the spintronic level.

Optimized Ni(II)-doping in Co(III)-based layered double hydroxides towards electrochemical oxygen evolution catalysis

An OER catalyst showing both high activity and stability in promoting oxygen evolution is important for its practical application in electrochemical water-splitting. Here, we report the screening of such a catalyst by optimizing the Ni(II)-doping in Co(III)-based layered double hydroxides (LDHs). Such LDH samples tailored with Ni(II)-doping are prepared by an oxidative intercalation reaction where brucite-like Ni(II)xCo(II)1-x(OH)2 (0 ≤ x ≤ 0.50) is reacted with Br2 in acetonitrile. These samples exhibit a volcano-like trend in OER activity related to the fraction of the dopant. At the optimized doping level (x = 0.20), the activity of the catalyst exceeds that of Ni(II)-Fe(III) LDHs at overpotentials higher than 375 mV. In situ Raman spectroscopy and Fourier-transformed alternating current voltammetry reveal that Ni cations can promote the formation of Co(IV)-oxo intermediates, thereby accelerating the kinetics of the OER. The volcano-like activity trend manifests the underlying synergistic communication between Ni and Co cations.

Reconstructed Hydroxyl Coordination Field Enhances Mass Transfer for Efficient Electrocatalytic Water Oxidation

Mass transfer factor plays an indispensable role in high current density to accelerate the oxygen evolution reaction (OER) process, yet research on modulating reactant mass transport remains limited. Herein, by leveraging the dual acid-base properties of aluminum sites, both the activation of the electronic activity of the layer for layered double hydroxides (LDH) and construction of the interlayer hydroxide coordination field (IHCF) have been achieved through in situ electrochemical reconstruction. It not only facilitates charge transfer and the surface catalytic transformation of reaction intermediates but, most notably, the presence of the IHCF significantly enhances the mass transport of reactants. As a result, the overpotential of LDHs with IHCF is only 164 mV, significantly better than the reported Ni-based catalysts. Deuterium kinetic isotope effect experiments and pH-dependence measurements demonstrate that the IHCF effectively enhances substrate mass transport capability and structural stability, thereby accelerating the proton-coupled electron transfer process. To further validate the high mass transport characteristics, stability tests of the alkaline flow electrolyzer show that catalysts maintain over 1000 h of stability at a high current density. This work suggests that the IHCF effect can be utilized for further design and synthesis of efficient water oxidation catalysts for practical application.

Modulating Electronic Spin State of Perovskite Fluoride by Ni─F─Mn Bond Activating the Dynamic Site of Oxygen Reduction Reaction

Establishing the relationship between catalytic performance and material structure is crucial for developing design principles for highly active catalysts. Herein, a type of perovskite fluoride, NH4MnF3, which owns strong-field coordination including fluorine and ammonia, is in situ grown on carbon nanotubes (CNTs) and used as a model structure to study and improve the intrinsic catalytic activity through heteroatom doping strategies. This approach optimizes spin-dependent orbital interactions to alter the charge transfer between the catalyst and reactants. As a result, the oxygen reduction reaction (ORR) activity of NH4MnF3 on CNTs is significantly enhanced by partial substitution of Mn sites with Ni, such as a half-wave potential (E1/2) of 0.86 V and a limiting current density of 5.26 mA cm-2, which are comparable to those of the commercial Pt/C catalysts. Experimental and theoretical calculations reveal that the introduction of Ni promotes lattice distortion, adjusts the electronic states of the active Mn centers, facilitates the transition from low-spin to intermediate-spin states, and shifts the d-band center closer to the Fermi level. This study establishes a novel approach for designing high-performance perovskite-based fluoride electrocatalysts by modulating spin states.

Advanced Ir-Based Alloy Electrocatalysts for Proton Exchange Membrane Water Electrolyzers

Proton exchange membrane water electrolyzer (PEMWE) coupled with renewable energy to produce hydrogen is an important part of clean energy acquisition in the future. However, the slow kinetics of the oxygen evolution reaction (OER) hinder the large-scale application of PEM water electrolysis technology. To deal with the problems existing in the PEM electrolyzer and improve the electrolysis efficiency, substantial efforts are invested in the development of cost-effective and stable electrocatalysts. Within this scenario, the different OER reaction mechanisms are first discussed here. Based on the in-depth understanding of the reaction mechanism, the research progress of low-iridium noble metal alloys is reviewed from the aspects of special effects, design strategies, reaction mechanisms, and synthesis methods. Finally, the challenges and prospects of the future development of high-efficiency and low-precious metal OER electrocatalysts are presented.

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.

Structurally Asymmetric Ni-O-Mn Node in Metal-Organic Layers on Carbon Nitride Support for CO2 Photoreduction

The Jahn-Teller (J-T) effect-induced lattice distortion presents an advantageous approach to tailor the electronic structure and CO2 adsorption properties of catalytic centers, consequently conferring desirable photocatalytic CO2 reduction activity and selectivity. Nevertheless, achieving precise J-T distortion control over catalytic sites to enhance CO2 adsorption/activation and target-product desorption remains a formidable challenge. In this work, we successfully induced J-T lattice distortion in neighboring Ni sites by exchanging high-spin Mn2+ into Ni-O-Ni nodes. EXAFS results and DFT simulations revealed that the highly asymmetric Ni-O-Mn nodes induced structural contraction (shortened Ni-O bonds) in the adjacent Ni-O lattice. The magnetic hysteresis loop (M-H) confirmed that the introduction of Mn2+ increased the number of spin electrons, thereby increasing the magnetization intensity. The spin mismatch between photogenerated electrons and holes suppressed charge recombination. Significantly, the d orbitals of the Ni sites in the Ni-O-Mn nodes exhibited strong orbital hybridization with the p orbitals of CO2, as evidenced by the enhanced d-p orbital overlap, facilitating rapid CO2 adsorption and activation. Consequently, the sample featuring lattice-mismatched Ni-O-Mn nodes exhibited an 8.79-fold enhancement in CO production rate compared to the Ni-O-Ni nodes, in the absence of cocatalysts and sacrificial reagents.

Engineering Lattice Oxygen Regeneration of NiFe Layered Double Hydroxide Enhances Oxygen Evolution Catalysis Durability

The lattice oxygen mechanism (LOM) endows NiFe layered double hydroxide (NiFe-LDH) with superior oxygen evolution reaction (OER) activity, yet the frequent evolution and sluggish regeneration of lattice oxygen intensify the dissolution of active species. Herein, we overcome this challenge by constructing the NiFe hydroxide/Ni4Mo alloy (NiFe-LDH/Ni4Mo) heterojunction electrocatalyst, featuring the Ni4Mo alloy as the oxygen pump to provide oxygenous intermediates and electrons for NiFe-LDH. The released lattice oxygen can be timely offset by the oxygenous species during the LOM process, balancing the regeneration of lattice oxygen and assuring the enhancement of the durability. In consequence, the durability of NiFe-LDH is significantly enhanced after the modification of Ni4Mo with an impressive durability for over 60 h, much longer than that of NiFe-LDH counterpart with only 10 h. In situ spectra and first-principle simulations reveal that the adsorption of OH- is significantly strengthened owing to the introduction of Ni4Mo, ensuring the rapid regeneration of lattice oxygen. Moreover, NiFe-LDH/Ni4Mo-based anion exchange membrane water electrolyzer (AEMWE) presents an impressive durability for over 150 h at 100 mA cm-2. The oxygen pump strategy opens opportunities to balance the evolution and regeneration of lattice oxygen, enhancing the durability of efficient OER catalysts.

Edge-Induced Synergy of Ni-Ni Defects in NiFe Layered-Double-Hydroxide for Electrocatalytic Water Oxidation Reaction

Defect engineering is widely regarded as a promising strategy to enhance the performance of electrocatalysts for water splitting. In this work, defective NiFe layered double hydroxide (NiFe LDH) with a high density of edge sites (edge-rich NiFe LDH) is synthesized via a simple reduction process during the early stages of nucleation. The introduction of edges into oxygen evolution reaction (OER) catalysts modulates the electronic structure of the active sites. X-ray absorption spectroscopy (XAS) analyses revealed that the edges facilitated the formation of unsaturated Ni-Ni coordination, which is crucial for promoting the deprotonation of the OH* intermediate. Consequently, the edge-rich NiFe LDH exhibited a significantly lower overpotential of 228 mV to achieve a current density of 10 mA cm⁻2, compared to 275 mV for pristine NiFe LDH. The assembled membrane electrode can reach a current density of 1000 mA cm⁻2 at a cell voltage of 2.5 V. This study highlights the role of edge effects in defect engineering to enhance OER activity and provides valuable theoretical insights for the design of efficient electrocatalysts.

Low-Spin Fe3+ Evoked by Multiple Defects with Optimal Intermediate Adsorption Attaining Unparalleled Performance in Water Oxidation

Electrocatalytic water splitting is long constrained by the sluggish kinetics of anodic oxygen evolution reaction (OER), and rational spin-state manipulation holds great promise to break through this bottleneck. Low-spin Fe3+ (LS, t2g 5eg 0) species are identified as highly active sites for OER in theory, whereas it is still a formidable challenge to construct experimentally. Herein, a new strategy is demonstrated for the effective construction of LS Fe3+ in NiFe-layered double hydroxide (NiFe-LDH) by introducing multiple defects, which induce coordination unsaturation over Fe sites and thus enlarge their d orbital splitting energy. The as-obtained catalyst exhibits extraordinary OER performance with an ultra-low overpotential of 244 mV at the industrially required current density of 500 mA cm-2, which is 110 mV lower than that of the conventional NiFe-LDH with high-spin Fe3+ (HS, t2g 3eg 2) and superior to most previously reported NiFe-based catalysts. Comprehensive experimental and theoretical studies reveal that LS Fe3+ configuration effectively reduces the adsorption strength of the O* intermediate compared with that of the HS case, thereby altering the rate-determining step from (O* → OOH*) to (OH* → O*) of OER and lowering its reaction energy barrier. This work paves a new avenue for developing efficient spin-dependent electrocatalysts for OER and beyond.

Understanding the Role of Spin State in Cobalt Oxyhydroxides for Water Oxidation

Although the electronic state of catalysts is strongly corrected with their oxygen evolution reaction (OER) performances, understanding the role of spin state in dynamic electronic structure evolution during OER process is still challenging. Herein, we developed a spin state regulation strategy to boost the OER performance of CoOOH through elemental doping (CoMOOH, M=V, Cr, Mn, Co and Cu). Experimental results including magnetic characterization, in situ X-ray absorption spectroscopy, in situ Raman and density functional theory calculations unveil that Mn doping could successfully increase the Co sites from low spin state to intermediate spin state, leading to the largest lattice distortion and smallest energy gap between dxy and dz 2 orbitals among the obtained CoMOOH electrocatalysts. Benefiting from the promoted electron transfer from dxy to dz 2 orbital, facilitated formation of active high-valent *O-Co(IV) species at applied potential, and reduced energy barrier of rate-determining step, the CoMnOOH exhibits the highest OER performance. Our work provides significant insight into the correction between dynamic electronic structure evolution and OER performance by understanding the role of spin state regulation in metal oxyhydroxides, paving a new avenue for rational design of high-activity electrocatalysts.

Electrodeposition of Ni/Cu Bimetallic Conductive Metal-Organic Frameworks Electrocatalysts with Boosted Oxygen Reduction Activity for Zinc-Air Batteries

Zinc-air batteries employing non-Pt cathodes hold significant promise for advancing cathodic oxygen reduction reaction (ORR). However, poor intrinsic electrical conductivity and aggregation tendency hinder the application of metal-organic frameworks (MOFs) as active ORR cathodes. Conductive MOFs possess various atomically dispersed metal centers and well-aligned inherent topologies, eliminating the additional carbonization processes for achieving high conductivity. Here, a novel room-temperature electrochemical cathodic electrodeposition method is introduced for fabricating uniform and continuous layered 2D bimetallic conductive MOF films cathodes without polymeric binders, employing the organic ligand 2,3,6,7,10,11-hexaiminotriphenylene (HITP) and varying the Ni/Cu ratio. The influence of metal centers on modulating the ORR performance is investigated by density functional theory (DFT), demonstrating the performance of bimetallic conductive MOFs can be effectively tuned by the unpaired 3d electrons and the Jahn-Teller effect in the doped Cu. The resulting bimetallic Ni2.1Cu0.9(HITP)2 exhibits superior ORR performance, boasting a high onset potential of 0.93 V. Moreover, the assembled aqueous zinc-air battery demonstrates high specific capacity of 706.2 mA h g-1, and exceptional long-term charge/discharge stability exceeding 1250 cycles.

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.

Unveiling the Enhancement of Electrocatalytic Oxygen Evolution Activity in Ru-Fe2O3/CoS Heterojunction Catalysts

The development of highly efficient electrocatalysts for the sluggish anodic oxygen evolution reaction (OER) is crucial to meet the practical demand for water splitting. In this study, an effective approach is proposed that simultaneously enhances interfacial interaction and catalytic activity by modifying Fe2O3/CoS heterojunction using Ru doping strategy to construct an efficient electrocatalytic oxygen evolution catalyst. The unique morphology of Ru doped Fe2O3 (Ru-Fe2O3) nanoring decorated by CoS nanoparticles ensures a large active surface area and a high number of active sites. The designed Ru-Fe2O3/CoS catalyst achieves a low OER overpotential (264 mV) at 10 mA cm-2 and demonstrates exceptional stability even at high current density of 100 mA cm-2, maintaining its performance for an impressive duration of 90 h. The catalytic performance of this Ru-Fe2O3/CoS catalyst surpasses that of other iron-based oxide catalysts and even outperforms the state-of-the-art RuO2. Density functional theory (DFT) calculation as well as experimental in situ characterization confirm that the introduction of Ru atoms can enhance the interfacial electron interaction, accelerating the electron transfer, and serve as highly active sites reducing the energy barrier for rate determination step. This work provides an efficient strategy to reveal the enhancement of electrocatalytic oxygen evolution activity of heterojunction catalysts by doping engineering.

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.

Manipulation of d-Orbital Electron Configurations in Nonplanar Fe-Based Electrocatalysts for Efficient Oxygen Reduction

Manipulation of the spin state holds great promise to improve the electrochemical activity of transition metal-based catalysts. However, the underlying relationship between the nonplanar metal coordination environment and spin states remains to be explored. Herein, we report the precise regulation of nonplanar Fe atomic d-orbital energy level into an irregular tetrahedral crystal field configuration by introducing P atoms. With the increase of P coordination number, the spin magnetic moment decreases linearly from 3.8 μB to 0.2 μB, and the high spin content decreases linearly from 31% to 5%. Significantly, a volcanic curve between the spin states of Fe-based catalysts (Fe-NxPy) and oxygen reduction reaction (ORR) activity has been unequivocally established based on the thermodynamic results. Thus, the Fe-N3P1 catalyst with a 19% medium spin state experimentally exhibits the optimal reaction activity with a high half-wave potential of 0.92 V. These findings indicate that regulating electron spin moments through coordination engineering is a promising catalyst design strategy, providing important insights into spin catalysis.

Rigidly Axial O Coordination-Induced Spin Polarization on Single Ni-N4-C Site by MXene Coupling for Boosting Electrochemical CO2 Reduction to CO

Regulating the spin states in transition-metal (TM)-based single-atom catalysts (SACs), such as the TM-Nx-C configurations, is crucial for improving the catalytic activity. However, the role of spin in single Ni atoms facilitating the electrochemical CO2 reduction reaction (CO2RR) has been largely overlooked. Using first-principles simulations, we investigated the electrocatalytic performance of Ni-N4-C SACs vertically stacked on the O-terminated MXene nanosheets for the CO2RR. The terminated O atoms on MXene axially interact with the Ni atom due to significant charge transfer between them. Unlike the pure Ni-N4 site, which lacks spin polarization, the newly formed Ni-N4O configuration breaks the spin degeneracy of Ni d orbitals, dramatically lifting the energy level of spin-down d orbitals relative to that of spin-up d orbitals. As a result, the d electrons of Ni in the two spin channels are rearranged, leading to large net spin moments of 1.4 μB. Compared to the Ni-N4 site, the partially filled minority-spin dz2 orbitals of Ni on Ni-N4O weaken the occupied d-π* orbitals between Ni and *COOH, significantly stabilizing the key intermediate. The detailed reaction mechanisms and energetics show that four MXenes, namely, Hf3C2, Zr3C2, Hf2C, and Zr2C, can induce a large spin on the Ni site, thereby improving catalytic activity for CO2 reduction to CO, with a lower onset potential of about -0.75 V vs SHE compared to pure Ni SACs (-1.17 V) according to the potential-constant model with an explicit solvent environment.

Factorial Optimization of CoCuFe-LDH/Graphene Ternary Composites as Electrocatalysts for Water Splitting

The layered double hydroxides (LDHs) have demonstrated significant potential as non-noble-metal electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Their unique compositional and structural properties contribute to their efficiency and stability as catalysts. In this study, CoCuFe-LDH composites were grown on graphene (G) via a cost-effective and straightforward one-step hydrothermal process. A 2-level full-factorial model was employed to determine the impact of Co (1.5, 3, and 4.5 mmol) and graphene (10, 30, and 50 mg) concentrations on the onset potential of OER and HER, which were the chosen response variables. OER and HER activity variabilities were assessed in triplicate using Co[3]Cu[3]Fe[3]-LDH/G[30] (central point), which were determined at 0.01% and 0.02%, respectively. Statistical analyses demonstrated that Co[4.5]Cu[3]Fe[3]-LDH/G[10] and Co[1.5]Cu[3]Fe[3]-LDH/G[10] showed the lowest onset potential at 1.52 V and -0.32 V (V vs RHE) for the OER and HER, respectively, suggesting that a high cobalt concentration enhances OER performance, while optimal HER catalysis was achieved with lower cobalt concentrations. Moreover, the trimetallic composites exhibited good stability with negligible loss of catalytic activity over 24 h.

From Charge to Spin: An In-Depth Exploration of Electron Transfer in Energy Electrocatalysis

Catalytic materials play crucial roles in various energy-related processes, ranging from large-scale chemical production to advancements in renewable energy technologies. Despite a century of dedicated research, major enduring challenges associated with enhancing catalyst efficiency and durability, particularly in green energy-related electrochemical reactions, remain. Focusing only on either the crystal structure or electronic structure of a catalyst is deemed insufficient to break the linear scaling relationship (LSR), which is the golden rule for the design of advanced catalysts. The discourse in this review intricately outlines the essence of heterogeneous catalysis reactions by highlighting the vital roles played by electron properties. The physical and electrochemical properties of electron charge and spin that govern catalysis efficiencies are analyzed. Emphasis is placed on the pronounced influence of external fields in perturbing the LSR, underscoring the vital role that electron spin plays in advancing high-performance catalyst design. The review culminates by proffering insights into the potential applications of spin catalysis, concluding with a discussion of extant challenges and inherent limitations.

Amorphous P-CoOX Promotes the Formation of Hypervalent Ni Species in NiFe LDHs by Amorphous/Crystalline Interfaces for Excellent Catalytic Performance of Oxygen Evolution Reaction

Water electrolysis has become an attractive hydrogen production method. Oxygen evolution reaction (OER) is a bottleneck of water splitting as its four-electron transfer procedure presents sluggish reaction kinetics. Designing composite catalysts with high performance for efficient OER still remains a huge challenge. Here, the P-doped cobalt oxide/NiFe layered double hydroxides (P-CoOX/NiFe LDHs) composite catalysts with amorphous/crystalline interfaces are successfully prepared for OER by hydrothermal-electrodeposition combined method. The results of electrochemical characterizations, operando Raman spectra, and DFT theoretical calculations have demonstrated the electrons in the P-CoOX/NiFe LDHs heterointerfaces are easily transferred from Ni2+ to Co3+ because that the amorphous configuration of P-CoOX can well induce Ni-O-Co orbital coupling. The electron transfer of Ni2+ to the surrounding Fe3+ and Co3+ will lead to the unoccupied eg orbitals of Ni3+ that can promote water dissociation and accelerate *OOH migration to improve OER catalytic performance. The optimized P-CoOX/NiFe LDHs exhibit superior catalytic performance for OER with a very low overpotential of 265 mV at 300 mA cm-2 and excellent long-term stability of 500 h with almost no attenuation at 100 mA cm-2. This work will provide a new method to design high-performance NiFe LDHs-based catalysts for OER.

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.

Highly Active CoNi-CoN3 Composite Sites Synergistically Accelerate Oxygen Electrode Reactions in Rechargeable Zinc-Air Batteries

Reaching rapid reaction kinetics of oxygen reduction (ORR) and oxygen evolution reactions (OER) is critical for realizing efficient rechargeable zinc-air batteries (ZABs). Herein, a novel CoNi-CoN3 composite site containing CoNi alloyed nanoparticles and CoN3 moieties is first constructed in N-doped carbon nanosheet matrix (CoNi-CoN3/C). Benefiting from the high electroactivity of CoNi-CoN3 composite sites and large surface area, CoNi-CoN3/C shows a superior half-wave potential (0.88 V versus RHE) for ORR and a small overpotential (360 mV) for OER at 10 mA cm-2. Theoretical calculations have demonstrated that the introduction of CoNi alloys has modulated the electronic distributions near the CoN3 moiety, inducing the d-band center of CoNi-CoN3 composite site to shift down, thus stabilizing the valence state of Co active sites and balancing the adsorption of OER/ORR intermediates. Accordingly, the reaction energy trends exhibit optimized overpotentials for OER/ORR, leading to superior battery performances. For aqueous and flexible quasi-solid-state rechargeable ZABs with CoNi-CoN3/C as catalyst, a large power density (250 mW cm-2) and high specific capacity (804 mAh g-1) are achieved. The in-depth understanding of the electroactivity enhancement mechanism of interactive metal nanoparticles and metal coordinated with nitrogen (MNx) moieties is crucial for designing novel high-performance metal/nitrogen-doped carbon (M─N─C) catalysts.

Spin Effect to Regulate the Electronic Structure of Ir─Fe Aerogels for Efficient Acidic Water Oxidation

"Spin" has been recently reported as an important degree of electronic freedom to promote catalysis, yet how it influences electronic structure remains unexplored. This work reports the spin-induced orbital hybridization in Ir─Fe bimetallic aerogels, where the electronic structure of Ir sites is effectively regulated by tuning the spin property of Fe atoms. The spin-optimized electronic structure boosts oxygen evolution reaction (OER) electrocatalysis in acidic media, resulting in a largely improved catalytic performance with an overpotential of as low as 236 mV at 10 mA cm-2. Furthermore, the gelation kinetics for the aerogel synthesis is improved by an order of magnitude based on the introduction of a magnetic field. Density functional theory calculation reveals that the increased magnetic moment of Fe (3d orbital) changes the d-band structure (i.e., the d-band center and bandwidth) of Ir (5d orbital) via orbital hybridization, resulting in optimized binding of reaction intermediates. This strategy builds the bridge between the electron spin theory with the d-band theory and provides a new way for the design of high-performance electrocatalysts by using spin-induced orbital interaction.

Simultaneous Interface Engineering and Phase Tuning of CeO2-Decorated Catalysts for Boosted Oxygen Evolution Reaction

Heterogeneous catalysts have attracted extensive attention among various emerging catalysts for their exceptional oxygen evolution reaction (OER) capabilities, outperforming their single-component counterparts. Nonetheless, the synthesis of heterogeneous materials with predictable, precise, and facile control remains a formidable challenge. Herein, a novel strategy involving the decoration of catalysts with CeO2 is introduced to concurrently engineer heterogeneous interfaces and adjust phase composition, thereby enhancing OER performance. Theoretical calculations suggest that the presence of ceria reduces the free energy barrier for the conversion of nitrides into metals. Supporting this, the experimental findings reveal that the incorporation of rare earth oxides enables the controlled phase transition from nitride into metal, with the proportion adjustable by varying the amount of added rare earth. Thanks to the role of CeO2 decoration in promoting the reaction kinetics and fostering the formation of the genuine active phase, the optimized Ni3FeN/Ni3Fe/CeO2-5% nanoparticles heterostructure catalyst exhibits outstanding OER activity, achieving an overpotential of just 249 mV at 10 mA cm-2. This approach offers fresh perspectives for the conception of highly efficient heterogeneous OER catalysts, contributing a strategic avenue for advanced catalytic design in the field of energy conversion.

Electron Accumulation Induced by Electron Injection-Incomplete Discharge on NiFe LDH for Enhanced Oxygen Evolution Reaction

Optimizing the local electronic structure of electrocatalysts can effectively lower the energy barrier of electrochemical reactions, thus enhancing the electrocatalytic activity. However, the intrinsic contribution of the electronic effect is still experimentally unclear. In this work, the electron injection-incomplete discharge approach to achieve the electron accumulation (EA) degree on the nickel-iron layered double hydroxide (NiFe LDH) is proposed, to reveal the intrinsic contribution of EA toward oxygen evolution reaction (OER). Such NiFe LDH with EA effect results in only 262 mV overpotential to reach 50 mA cm-2, which is 51 mV-lower compared with pristine NiFe LDH (313 mV), and reduced Tafel slope of 54.8 mV dec-1 than NiFe LDH (107.5 mV dec-1). Spectroscopy characterizations combined with theoretical calculations confirm that the EA near concomitant Vo can induce a narrower energy gap and lower thermodynamic barrier to enhance OER performance. This study clarifies the mechanism of the EA effect on OER activity, providing a direct electronic structure modulation guideline for effective electrocatalyst design.

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.

Regulating Spin Density using TEMPOL Molecules for Enhanced CO2-to-Ethylene Conversion by HKUST-1 Framework Derived Electrocatalysts

The selectivity of multicarbon products in the CO2 reduction reaction (CO2RR) depends on the spin alignment of neighboring active sites, which requires a spin catalyst that facilitates electron transfer with antiparallel spins for enhanced C-C coupling. Here, we design a radical-contained spin catalyst (TEMPOL@HKUST-1) to enhance CO2-to-ethylene conversion, in which spin-disordered (SDO) and spin-ordered (SO) phases co-exist to construct an asymmetric spin configuration of neighboring active sites. The replacement of axially coordinated H2O molecules with TEMPOL radicals introduces spin-spin interactions among the Cu(II) centers to form localized SO phases within the original H2O-mediated SDO phases. Therefore, TEMPOL@HKUST-1 derived catalyst exhibited an approximately two-fold enhancement in ethylene selectivity during the CO2RR at -1.8 V versus Ag/AgCl compared to pristine HKUST-1. In situ ATR-SEIRAS spectra indicate that the spin configuration at asymmetric SO/SDO sites significantly reduces the kinetic barrier for *CO intermediate dimerization toward the ethylene product. The performance of the spin catalyst is further improved by spin alignment under a magnetic field, resulting in a maximum ethylene selectivity of more than 50 %. The exploration of the spin-polarized kinetics of the CO2RR provides a promising path for the development of novel spin electrocatalysts with superior performance.

Construction of Ferric-Oxide-Doped Nickel-Iron Hydroxide Electrocatalysts by Magnetic-Field-Assisted Chemical Corrosion toward Boosted Oxygen Evolution Reaction

Transition-metal-based oxygen evolution reaction (OER) catalysts have attracted widespread attention due to their inexpensive prices, unique layered structures, and rich active sites. Currently, designing low-cost, sustainable, and simple synthesis methods is essential for the application of transition-metal-based catalysts. Here, magnetic field (MF)-assisted chemical corrosion, as a novel technology, is adopted to construct superior OER electrocatalysts. The produced Ni(Fe)(OH)2-Fe2O3 electrode exhibits an overpotential of 272 mV at a current density of 100 mA cm-2, presenting a 64 mV reduction compared to the electrode without an MF. The experimental results indicate that an MF can induce the directional growth of Fe2O3 rods and reduce their accumulation. In addition, an external MF is beneficial for the lattice dislocation of the obtained catalysts, which can increase the surface free energy, thus reducing the activation energy and accelerating the electrochemical reaction kinetics. This work effectively combines a magnetic field with chemical corrosion and electrochemical energy, which offers a novel strategy for the large-scale development of environmentally friendly and superior electrocatalysts.

Magnetic Order Transition of a Two-Dimensional Square-Lattice Electrocatalyst Assembled by Fe-N4 Units: Crucial Role on Oxygen Reduction

Herein, we theoretically investigate the effect of magnetic orders on electrocatalytic oxygen reduction reaction (ORR) properties on the Fe-N4 site-embedded two-dimensional (2D) covalent organic framework (Fe-N4@COF-C3N2) under realistic environments. The Fe-N4@COF-C3N2 shows a 2D square-lattice (sql) topology with three magnetic order states: one ferromagnetic state (FM) and two antiferromagnetic states (AFM1 and AFM2). Specially, the electrocatalyst in the AFM2 state shows a remarkable onset potential of 0.80 V/reversible hydrogen electrode (RHE) at pH 1, superior to the existing most excellent noble-metal catalysts. Thermodynamically, the onset potential for the 4e- ORR is 0.64 V/RHE at pH 1, with a magnetic state transition process of FM → AFM1 → FM → FM → FM, while at pH 13, the onset potential for the 4e- ORR is 0.54 V/RHE, with the magnetic transition process of FM → FM → AFM1 → FM → FM. Generally, this finding will provide new avenues to rationally design the Fe-N4 electrocatalyst.

Unlocking Spin Gates of Transition Metal Oxides via Strain Stimuli to Augment Potassium Ion Storage

Transition metal oxides (TMOs) are key in electrochemical energy storage, offering cost-effectiveness and a broad potential window. However, their full potential is limited by poor understanding of their slow reaction kinetics and stability issues. This study diverges from conventional complex nano-structuring, concentrating instead on spin-related charge transfer and orbital interactions to enhance the reaction dynamics and stability of TMOs during energy storage processes. We successfully reconfigured the orbital degeneracy and spin-dependent electronic occupancy by disrupting the symmetry of magnetic cobalt (Co) sites through straightforward strain stimuli. The key to this approach lies in the unfilled Co 3d shell, which serves as a spin-dependent regulator for carrier transfer and orbital interactions within the reaction. We observed that the opening of these 'spin gates' occurs during a transition from a symmetric low-spin state to an asymmetric high-spin state, resulting in enhanced reaction kinetics and maintained structural stability. Specifically, the spin-rearranged Al-Co3O4 exhibited a specific capacitance of 1371 F g-1, which is 38 % higher than that of unaltered Co3O4. These results not only shed light on the spin effects in magnetic TMOs but also establish a new paradigm for designing electrochemical energy storage materials with improved efficiency.

Rearranging Spin Electrons by Axial-Ligand-Induced Orbital Splitting to Regulate Enzymatic Activity of Single-Atom Nanozyme with Destructive d-π Conjugation

Most of the nanozymes have been obtained based on trial and error, for which the application is usually compromised by enzymatic activity regulation due to a vague catalytic mechanism. Herein, a hollow axial Mo-Pt single-atom nanozyme (H-MoN5@PtN4/C) is constructed by a two-tier template capture strategy. The axial ligand can induce Mo 4d orbital splitting, leading to a rearrangement of spin electrons (↑ ↑ → ↑↓) to regulate enzymatic activity. This creates catalase-like activity and enhances oxidase-like activity to catalyze cascade enzymatic reactions (H2O2 → O2 → O2•-), which can overcome tumor hypoxia and accumulate cytotoxic superoxide radicals (O2•-). Significantly, H-MoN5@PtN4/C displays destructive d-π conjugation between the metal and substrate to attenuate the restriction of orbitals and electrons. This markedly improves enzymatic performance (catalase-like and oxidase-like activity) of a Mo single atom and peroxidase-like properties of a Pt single atom. Furthermore, the H-MoN5@PtN4/C can deplete overexpressed glutathione (GSH) through a redox reaction, which can avoid consumption of ROS (O2•- and •OH). As a result, H-MoN5@PtN4/C can overcome limitations of a complex tumor microenvironment (TME) for tumor-specific therapy based on TME-activated catalytic activity.

The Rational Design of Atomically Dispersed Catalysts via Spin Manipulation

The catalytic activity of transition-metal-based atomically dispersed catalysts is closely related to the spin states. Manipulating the spin state of metal active centers could directly adjust the d orbital occupancy and optimize the adsorption behavior and electron transfer of the intermediates and transition metals, which would enhance the catalytic activity. We summarize the means of manipulating spin states and the spin-related catalytic descriptors. In future work, we will build a quantifiable and accurate prediction intelligent model through artificial intelligence (AI) and machine learning tools. Furthermore, we will develop new spin regulation methods to carry out the directional regulation of atomically dispersed catalysts through this model, providing new insight into the rational design of transition-metal-based atomically dispersed catalysts through spin manipulation.

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.

Magnetic-Field-Induced Spin Regulation in Electrocatalytic Reactions

The utilization of a magnetic field to manipulate spin states has emerged as a novel approach to enhance efficiency in electrocatalytic reactions, distinguishing from traditional strategies that focus on tuning activation energy barriers. Currently, this approach is specifically tailored to reactions where spin states change during the catalytic process, such as the oxidation of singlet H2O to triplet O2. In the magnetically enhanced oxygen evolution reaction (OER) procedure, the parallel spin alignment on the ferromagnetic catalyst was induced by the external magnetic field, facilitating the triplet O-O bonding, which is the rate limiting step in OER. This review centers on recent advancements in harnessing external magnetic fields to enhance OER performance, delving into mechanistic approaches for this magnetic promotion. Additionally, we provide a summary of magnetic field application in other electrocatalytic reactions, including oxygen reduction, methanol oxidation, and CO2 reduction.

Fe,Co co-implanted dendritic CeO2/CeF3 heterostructure@MXene nanocomposites as structurally stable electrocatalysts with ultralow overpotential for the alkaline oxygen evolution reaction

Exploring low-cost, high-activity, and structurally stable nonprecious metal electrocatalysts for sluggish oxygen evolution reaction (OER) is paramount for water electrolysis. Herein, we successfully prepare a novel Fe,Co-CeO2/CeF3@MXene heterostructure with Fe-Co dual active sites and oxygen vacancies for alkaline OER using an energy-free consumption co-deposition method. Impressively, Fe,Co-CeO2/CeF3@MXene achieves an ultralow overpotential of 192 mV and a long-term stability of 110 h at 10 mA cm-2 without structural changes, thereby outperforming the commercial IrO2 (345 mV). In addition, Fe,Co-CeO2/CeF3@MXene exhibits much superior activity (271 mV) and durability to IrO2 (385 mV) in the real seawater OER. Wind- and solar energy-assisted water electrolysis devices show their promising prospects for sustainable green hydrogen production. Characterization techniques and theoretical calculations reveal that the Fe,Co co-implanted CeO2/CeF3 heterostructure effectively degrades the energy barrier of the OER and optimizes the adsorption strength of *OH, *O, and *OOH intermediates. It exhibits the dual coupling mechanism of the adsorbed evolution and lattice oxygen mechanisms, which synergistically improves the OER performance. This work provides a facile and efficacious strategy for synthesizing a new class of heterostructures to achieve significant enhancement in the activity and stability of OER catalysts.

Intercalated and Surface-Adsorbed Phosphate Anions in NiFe Layered Double-Hydroxide Catalysts Synergistically Enhancing Oxygen Evolution Reaction Activity

The oxygen evolution reaction (OER), a crucial semireaction in water electrolysis and rechargeable metal-air batteries, is vital for carbon neutrality. Hindered by a slow proton-coupled electron transfer, an efficient catalyst activating the formation of an O-H bond is essential. Here, we proposed a straightforward one-step hydrothermal procedure for fabricating PO43--modified NiFe layered double-hydroxide (NiFe LDH) catalysts and investigated the role of PO43- anions in enhancing OER. Phosphate amounts can efficiently regulate LDH morphology, crystallinity, composition, and electronic configuration. The optimized sample showed a low overpotential of 267 mV at 10 mA cm-2. Density functional theory calculations revealed that intercalated and surface-adsorbed PO43- anions in NiFe LDH reduced the Gibbs free energy in the rate-determining step of *OOH formation, balancing oxygen-containing intermediate adsorption/dissociation and promoting the OER. Intercalated phosphate ions accelerated precatalyst dehydrogenation kinetics, leading to a rapid reconstruction into active NiFe oxyhydroxide species. Surface-adsorbed PO43- interacted favorably with adsorbed *OOH on the active Ni sites, stabilizing *OOH. Overall, the synergistic effects of intercalated and surface-adsorbed PO43- anions significantly contributed to enhanced OER activity. Achieving optimal catalytic activity requires a delicate equilibrium between thermodynamic and kinetic factors by meticulously regulating the quantity of introduced PO43- ions. This endeavor will facilitate a deeper comprehension of the influence of anions in electrocatalysis for OER.

Study on Water Splitting of the 214-Type Perovskite Oxides LnSrCoO4 (Ln = La, Pr, Sm, Eu, and Ga)

We present a study on the electrocatalysis of 214-type perovskite oxides LnSrCoO4 (Ln = La, Pr, Sm, Eu, and Ga) with semiconducting-like behavior synthesized using the sol-gel method. Among these five catalysts, PrSrCoO4 exhibits the optimal electrochemical performance in both the oxygen evolution reaction and the hydrogen evolution reaction, mainly due to its larger electrical conductivity, mass activity, and turnover frequency. Importantly, the weak dependency of LSV curves in a KOH solution with different pH values, revealing the adsorbate evolving mechanism in PrSrCoO4, and the density functional theory (DFT) calculations indicate that PrSrCoO4 has a smaller Gibbs free energy and a higher density of states near the Fermi level, which accelerates the electrochemical water splitting. The mutual substitution of different rare-earth elements will change the unit-cell parameters, regulate the electronic states of catalytic active site Co ions, and further affect their catalytic performance. Furthermore, the magnetic results indicate strong spin-orbit coupling in the electroactive sites of Co ions in SmSrCoO4 and EuSrCoO4, whereas the magnetic moments of Co ions in the other three catalysts mainly arise from the spin itself. Our experimental results expand the electrochemical applications of 214-type perovskite oxides and provide a good platform for a deeper understanding of their catalytic mechanisms.

Mechanistic Studies of Stimulus-Response Integrated Catalysis of Single-Atom Alloys under Electric Fields for Electrochemical Nitrogen Reduction

The present work introduces a novel catalytic strategy to promote the nitrogen reduction reaction (NRR) by employing a cooperative Cu-based single-atom alloy (SAA) and oriented external electric fields (OEEFs) as catalysts. The field strength (F)-dependent reaction pathways are investigated by means of first-principles calculations. Different dipole-induced responses of intermediates to electric fields break the original scaling relationships and effectively tune not only the activity but also the product selectivity of the NRR. When the most active Os1Cu SAA is taken as an example, in the absence of an OEEF, the overpotential (η) of the NRR is 0.62 V, which is even larger than that of the competitive hydrogen evolution reaction (HER). A negative field not only reduces η but switches the preference to the NRR over the HER. In particular, η at F = -1.14 V/Å reaches the bottom of 0.18 V, which is 70% lower than that in the field-free state.

Constructing FeNiPt@C Trifunctional Catalyst by High Spin-Induced Water Oxidation Activity for Zn-Air Battery and Anion Exchange Membrane Water Electrolyzer

Developing cost-efficient trifunctional catalysts capable of facilitating hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) activity is essential for the progression of energy devices. Engineering these catalysts to optimize their active sites and integrate them into a cohesive system presents a significant challenge. This study introduces a nanoflower (NFs)-like carbon-encapsulated FeNiPt nanoalloy catalyst (FeNiPt@C NFs), synthesized by substituting Co2+ ions with high-spin Fe2+ ions in Hofmann-type metal-organic framework, followed by carbonization and pickling processes. The FeNiPt@C NFs catalyst, characterized by its nitrogen-doped carbon-encapsulated metal alloy structure and phase-segregated FeNiPt alloy with slight surface oxidization, exhibits excellent trifunctional catalytic performance. This is evidenced by its activities in HER (-25 mV at 10 mA cm-2), ORR (half-wave potential of 0.93 V), and OER (294 mV at 10 mA cm-2), with the enhanced water oxidation activity attributed to the high-spin state of the Fe element. Consequently, the Zn-air battery and anion exchange membrane water electrolyzer assembled by FeNiPt@C NFs catalyst demonstrate remarkable power density (168 mW cm-2) and industrial-scale current density (698 mA cm-2 at 1.85 V), respectively. This innovative integration of multifunctional catalytic sites paves the way for the advancement of sustainable energy systems.

Single-Atom Mn Catalysts via Integration with Mn Sub Nano-Clusters Synergistically Enhance Oxygen Reduction Reaction

Integrating single atoms and clusters into one system represents a novel strategy for achieving the desired catalytic performance. In comparison to single-atom catalysts, catalysts combining single atoms and clusters harness the advantages of both, thus displaying greater potential. Nevertheless, constructing single-atom-cluster systems remains challenging, and the fundamental mechanism for enhancing catalytic activity remains elusive. In this study, a directly confined preparation of a 3D hollow sea urchin-like carbon structure (MnSA/MnAC-SSCNR) is developed. Mn single atoms synergistically interact with Mn clusters, optimizing and reducing energy barriers in the reaction pathway, thus enhancing reaction kinetics. Consequently, in contrast to Mn single-atom catalysts (MnSA-SSCNR), MnSA/MnAC-SSCNR exhibits significantly improved oxygen reduction activity, with a half-wave potential (E1/2) of 0.90 V in 0.1 m KOH, surpassing that of MnSA-SSCNR and Pt/C. This work demonstrates a strategy of remote synergy between heterogeneous single atoms and clusters, which not only contributes to electrocatalytic reactions but also holds potential for reactions involving more complex products.