Orbital Occupancy and Spin Polarization: From Mechanistic Study to Rational Design of Transition Metal-Based Electrocatalysts toward Energy Applications

Rhombohedrally stacked layered transition metal dichalcogenides and their electrocatalytic applications

Layered transition metal dichalcogenides (TMDCs) are extensively investigated as catalyst materials for a wide range of electrochemical applications due to their high surface area and versatile electronic and chemical properties. Bulk TMDCs are van der Waals solids that possess strong in-plane bonding and weak inter-layer interactions. In the few-layer 2D TMDCs, several polymorphic structures have been reported as each individual layer can either retain octahedral or trigonal prismatic coordination. Among them, 1T (tetragonal), 2H (hexagonal) and 3R (rhombohedral) phases are very common. These polymorphs can display discrepancies in their catalytic activity as their electronic structure diverges due to different d orbital filling states. The broken inversion symmetry and large exposed edge sites of some of the 3R-phase TMDCS such as MoS2, NbS2 and TaS2 appear to be advantageous for electrocatalytic water reduction and battery applications. We describe recent studies in phase engineering of 2D TMDCs, particularly aiming at the 3R polytype and their electrocatalytic properties. Redox ability primarily depends on a distinct polymorphic phase in which TMDCs are isolated, and hence, with rich polymorphic structures being reported, numerous new catalytic applications can be realized. Phase conversion from 2H to 3R phase in some TMDCs enhances structural integrity and establishes robustness under harsh chemical conditions.

P-Bridging Asymmetry Diatomic Catalysts Sites Drive Efficient Bifunctional Oxygen Electrocatalysis for Zinc-Air Batteries

Rechargeable zinc-air batteries (ZABs) rely on the development of high-performance bifunctional oxygen electrocatalysts to facilitate efficient oxygen reduction/evolution reactions (ORR/OER). Single-atom catalysts (SACs), characterized by their precisely defined active sites, have great potential for applications in ZABs. However, the design and architecture of atomic site electrocatalysts with both high activity and durability present significant challenges, owing to their spatial confinement and electronic states. In this study, a strategy is proposed to fabricate structurally uniform dual single-atom electrocatalyst (denoted as P-FeCo/NC) consisting of P-bridging Fe and Co bimetal atom (i.e., Fe-P-Co) decorated on N, P-co-doped carbon framework as an efficient and durable bifunctional electrocatalyst for ZABs. Experimental investigations and theoretical calculations reveal that the Fe-P-Co bridge-coupling structure enables a facile adsorption/desorption of oxygen intermediates and low activation barrier. The resultant P-FeCo/NC exhibits ultralow overpotential of 340 mV at 10 mA cm-2 for OER and high half-wave potential of 0.95 V for ORR. In addition, the application of P-FeCo/NC in rechargeable ZABs demonstrates enhanced performance with maximum power density of 115 mW cm-2 and long cyclic stability, which surpass Pt/C and RuO2 catalysts. This study provides valuable insights into the design and mechanism of atomically dispersed catalysts for energy conversion applications.

Drivers and Pathways for the Recovery of Critical Metals from Waste-Printed Circuit Boards

The ever-increasing importance of critical metals (CMs) in modern society underscores their resource security and circularity. Waste-printed circuit boards (WPCBs) are particularly attractive reservoirs of CMs due to their gamut CM embedding and ubiquitous presence. However, the recovery of most CMs is out of reach from current metal-centric recycling industries, resulting in a flood loss of refined CMs. Here, 41 types of such spent CMs are identified. To deliver a higher level of CM sustainability, this work provides an insightful overview of paradigm-shifting pathways for CM recovery from WPCBs that have been developed in recent years. As a crucial starting entropy-decreasing step, various strategies of metal enrichment are compared, and the deployment of artificial intelligence (AI) and hyperspectral sensing is highlighted. Then, tailored metal recycling schemes are presented for the platinum group, rare earth, and refractory metals, with emphasis on greener metallurgical methods contributing to transforming CMs into marketable products. In addition, due to the vital nexus of CMs between the environment and energy sectors, the upcycling of CMs into electro-/photo-chemical catalysts for green fuel synthesis is proposed to extend the recycling chain. Finally, the challenges and outlook on this all-round upgrading of WPCB recycling are outlined.

Advancing overall water splitting via phase-engineered amorphous/crystalline interface: A novel strategy to accelerate proton-coupled electron transfer

Traditional phase engineering enhances conductivity or activity by fully converting electrocatalytic materials into either a crystalline or an amorphous state, but this approach often faces limitations. Thus, a practical solution entails balancing the dynamic attributes of both phases to maximize an electrocatalyst's functionality is urgently needed. Herein, in this work, Co/Co2C crystals have been assembled on the amorphous N, S co-doped porous carbon (NSPC) through hydrothermal and calcination processes. The stable biphase structure and amorphous/crystalline (A/C) interface enhance conductivity and intrinsic activity. Moreover, the adsorption ability of water molecules and intermediates is improved significantly attributed to the rich oxygen-containing groups, unsaturated bonds, and defect sites of NSPC, which accelerates proton-coupled electron transfer (PCET) and overall water splitting. Consequently, A/C-Co/Co2C/NSPC (Co/Co2C/NSPC with amorphous/crystalline interface) exhibits outstanding behavior for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), requiring the overpotential of 240.0 mV and 70.0 mV to achieve 10 mA cm-2. Moreover, an electrolyzer assembled by A/C-Co/Co2C/NSPC-3 (anode) and A/C-Co/Co2C/NSPC-2 (cathode) demonstrates a low drive voltage of 1.54 V during overall water splitting process. Overall, this work has pioneered the coexistence of crystalline/amorphous phases in electrocatalysts and provided new insights into phase engineering.

Regulating the electronic structure of Pt SAs-Ni2P for enhanced hydrogen evolution reaction

The single atom catalysts (SACs) show immense promise as catalytic materials. By doping the single atoms (SAs) of precious metals onto substrates, the atomic utilization of these metals can be maximized, thereby reducing catalyst costs. The electronic structure of precious metal SAs is significantly influenced by compositions of doped substrates. Therefore, optimizing the electronic structure through appropriate doping of substrates can further enhance catalytic activity. Here, Pt single atoms (Pt SAs) are doped onto transition metal sulfide substrate NiS2 (Pt SAs-NiS2) and phosphide substrate Ni2P (Pt SAs-Ni2P) to design and prepare catalysts. Compared to the Pt SAs-NiS2 catalyst, the Pt SAs-Ni2P catalyst exhibits better hydrogen evolution catalytic performance and stability. Under 1 M KOH conditions, the hydrogen evolution mass activity current density of the Pt SAs-Ni2P catalyst reaches 0.225 A mgPt-1 at 50 mV, which is 33 times higher than that of commercial Pt/C catalysts. It requires only 44.9 mV to achieve a current density of 10 mA cm-2. In contrast, for the Pt SAs-NiS2 catalyst, the hydrogen evolution mass activity current density is 0.178 A mgPt-1, requiring 77.8 mV to achieve a current density of 10 mA cm-2. Theoretical calculations indicate that in Pt SAs-Ni2P, the interaction between Pt SAs and the Ni2P substrate causes the Pt d-band center to shift downward, enhancing the H2O desorption and providing optimal H binding sites. Additionally, the hollow octahedral morphology of Ni2P provides a larger surface area, exposing more reactive sites and improving reaction kinetics. This study presents an effective pathway for preparing high-performance hydrogen evolution electrocatalysts by selecting appropriate doped substrates to control the electronic structure of Pt SAs.

Ultrafine Nanoclusters Unlocked 3d-4f Electronic Ladders for Efficient Electrocatalytic Water Oxidation

The vast extensional planes of two-dimensional (2D) nanomaterials are recognized as desirable ground for electrocatalytic reactions. However, they tend to exhibit catalytic inertia due to their surface-ordered coordination configurations. Herein, an in situ autoxidation strategy enables high-density grafting of ultrafine CeO2 nanoclusters on 2D Co(OH)2. Affluent active units were activated at the inert interface of Co(OH)2 via the formation of Co-O-Ce units. The optimized catalyst exhibits oxygen evolution reaction activity with an overpotential of 83 mV lower than that of Co(OH)2 at 10 mA cm-2. The cascade orbital coupling between Co (3d) and Ce (4f) in Co-O-Ce units drives electron transfer by unlocking a "d-f electron ladder". Meanwhile, the bond-order theorem analyses and the d-band center show that the occupancy of Co-3d-eg is optimized to balance the adsorption-desorption process of active sites to the key reaction intermediate *OOH, thereby making it easier to release oxygen. This work will drive the development of wider area electron modulation methods and provide guidance for the surface engineering of 2D nanomaterials.

Promoting Polysulfide Redox Reactions through Electronic Spin Manipulation

Catalytic additives able to accelerate the lithium-sulfur redox reaction are a key component of sulfur cathodes in lithium-sulfur batteries (LSBs). Their design focuses on optimizing the charge distribution within the energy spectra, which involves refinement of the distribution and occupancy of the electronic density of states. Herein, beyond charge distribution, we explore the role of the electronic spin configuration on the polysulfide adsorption properties and catalytic activity of the additive. We showcase the importance of this electronic parameter by generating spin polarization through a defect engineering approach based on the introduction of Co vacancies on the surface of CoSe nanosheets. We show vacancies change the electron spin state distribution, increasing the number of unpaired electrons with aligned spins. This local electronic rearrangement enhances the polysulfide adsorption, reducing the activation energy of the Li-S redox reactions. As a result, more uniform nucleation and growth of Li2S and an accelerated liquid-solid conversion in LSB cathodes are obtained. These translate into LSB cathodes exhibiting capacities up to 1089 mA h g-1 at 1 C with 0.017% average capacity loss after 1500 cycles, and up to 5.2 mA h cm-2, with 0.16% decay per cycle after 200 cycles in high sulfur loading cells.

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.

Semi-Ionic F Modified N-Doped Porous Carbon Implanted with Ruthenium Nanoclusters toward Highly Efficient pH-Universal Hydrogen Generation

Developing high electroactivity ruthenium (Ru)-based electrocatalysts for pH-universal hydrogen evolution reaction (HER) is challenging due to the strong bonding strengths of key Ru─H/Ru─OH intermediates and sluggish water dissociation rates on active Ru sites. Herein, a semi-ionic F-modified N-doped porous carbon implanted with ruthenium nanoclusters (Ru/FNPC) is introduced by a hydrogel sealing-pyrolying-etching strategy toward highly efficient pH-universal hydrogen generation. Benefiting from the synergistic effects between Ru nanoclusters (Ru NCs) and hierarchically F, N-codoped porous carbon support, such synthesized catalyst displays exceptional HER reactivity and durability at all pH levels. The optimal 8Ru/FNPC affords ultralow overpotentials of 17.8, 71.2, and 53.8 mV at the current density of 10 mA cm-2 in alkaline, neutral, and acidic media, respectively. Density functional theory (DFT) calculations elucidate that the F-doped substrate to support Ru NCs weakens the adsorption energies of H and OH on Ru sites and reduces the energy barriers of elementary steps for HER, thus enhancing the intrinsic activity of Ru sites and accelerating the HER kinetics. This work provides new perspectives for the design of advanced electrocatalysts by porous carbon substrate implanted with ultrafine metal NCs for energy conversion applications.

Relay-Type Catalysis by a Dual-Metal Single-Atom System in a Waste Biomass Derivative Host for High-Rate and Durable Li-S Batteries

An environmental-friendly and sustainable carbon-based host is one of the most competitive strategies for achieving high loading and practicality of Li-S batteries. However, the polysulfide conversion reaction kinetics is still limited by the nonuniform or monofunctional catalyst configuration in the carbon host. In this work, we propose a catalysis mode based on "relay-type" co-operation by adjacent dual-metal single atoms for high-rate and durable Li-S batteries. A discarded sericin fabric-derived porous N-doped carbon with a stacked schistose structure is prepared as the high-loading sulfur (84 wt %) host by a facile ionothermal method, which further enables the uniform anchoring of Fe/Co dual-metal single atoms. This multifunctional host enables superior lithiophilic-sulfiphilic and electrocatalytic capabilities contributed by the "relay-type" single-atom modulation effects on different conversion stages of liquid polysulfides and solid Li2S2/Li2S, leading to the suppression of the "shuttle effect", alleviation of nucleation and decomposition barriers of Li2Sx, and acceleration of polysulfide conversion kinetics. The corresponding Li-S batteries exhibit a high specific capacity of 1399.0 mA h g-1, high-rate performance up to 10 C, and excellent cycling stability over 1000 cycles. They can also endure the high sulfur loading of 8.5 mg cm-2 and the lean electrolyte condition and yield an areal capacity as high as 8.6 mA h cm-2. This work evidentially demonstrates the potential of waste biomass reutilization coupled with the design of a single-atom system for practical Li-S batteries with high energy density.

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.

Self-Assembly Strategy for Constructing Porous Boron and Nitrogen Co-Doped Carbon as an Efficient ORR Electrocatalyst toward Zinc-Air Battery

Carbon nanomaterials doped with N and B could activate nearby carbon atoms to promote charge polarization through the synergistic coupling effect between N and B atoms, thus facilitating adsorption of O2 and weakening O-O bond to enhance oxygen reduction reaction. Herein, a simple and controllable self-assembly strategy is applied to synthesize porous B, N co-doped carbon-based catalysts (BCN-P), which employs the macrocyclic molecule cucurbit[7]uril (CB7) as nitrogen source, and 3D aromatic-like closo-[B12H12]2- as boron source. In addition, polystyrene microspheres are added to help introduce porous structure to expose more active sites. Benefitting from porous structures and the synergistic coupling effect between N and B atoms, BCN-P has a high onset potential (Eonset=0.846 V) and half-wave potential (E1/2=0.74 V) in alkaline media. The zinc-air battery assembled with BCN-P shows high operating voltage (1.42 V), peak power density (128.7 mW cm-2) and stable charge/discharge cycles, which is even comparable with Pt/C.

High-Energy Facet Engineering for Electrocatalytic Applications

The design of high-energy facets in electrocatalysts has attracted significant attention due to their potential to enhance electrocatalytic activity. In this review, the significance of high-energy facets in various electrochemical reactions are highlighted, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CRR). Their importance in various electrochemical reactions and present strategies for constructing high-energy facets are discussed, including alloying, heterostructure formation, selective etching, capping agents, and coupling with substrates. These strategies enable control over crystallographic orientation and surface morphology, fine-tuning electrocatalytic properties. This study also addresses future directions and challenges, emphasizing the need to better understand fundamental mechanisms. Overall, high-energy facets offer exciting opportunities for advancing electrocatalysis.

Modulating Electronic Structure and Atomic Insights into the Novel Hierarchically Porous PdCuFe Trimetallic Alloy Aerogel for Efficient Oxygen Reduction

The high cost of noble Pd/Pt required for the oxygen reduction reaction (ORR) in the cathode restricts the wide applications of fuel cells. In this study, the synthesis of a novel Pd3CuFe0.5 aerogel electrocatalyst is successfully demonstrated using self-assembly and lyophilization techniques, employing a mild reducing agent. The resulting aerogel electrocatalyst exhibits a distinctive 3D network structure, possessing a substantial BET-specific surface area of 75.19 m2 g-1. It is worth noting that the optimized Pd3CuFe0.5 aerogel demonstrates exceptional ORR performance with a high half-wave potential of 0.92 V versus RHE, a significant limiting current density of 7.6 mA cm-2, and the excellent electrocatalytic stability, superior to the reported noble metal electrocatalysts, with the ORR activity decays only 4.9% after 16 000 s. In addition, the Pd3CuFe0.5 aerogel electrocatalyst shows superior cycling stability for ≈120 h at a charge/discharge current density of 10 mA cm-2, indicating its promising application in fuel cells. Furthermore, the resulting composite aerogel possesses excellent hydrogen evolution reaction and ethanol oxidation reaction activity. The density functional theory calculations show that the partial oxidation of Pd3CuFe0.5 aerogel leads to a negative shift of the d-band center, which energetically optimizes the binding strength of *O intermediates, therefore accelerating the ORR activity.

Demagnetizing Ferromagnetic Catalysts to the Sabatier Optimal of Haber-Bosch Process

Achieving the Sabatier optimal of a chemical reaction has been the central topic in heterogeneous catalysis for a century. However, this ultimate goal was greatly hindered in previous catalyst design strategies since the active sites indeed changed. Fortunately, the magneto-catalytic effect (MCE) provides a promising solution to this long-standing challenge. Recent research suggests that the performance of ferromagnetic catalysts is capable to be promoted without changing its chemical structure. Herein, we use time-dependent density functional perturbation theory (TDDFPT) calculations to elucidate that a partially demagnetized (DM) ferromagnet could be a Sabatier optimal catalyst. Using ammonia synthesis as the model reaction, we determined the activity of Cobalt at each DM state by including the magnetic thermal excitations via magnon analysis, making the 55% DM Co to the genuine Sabatier optimal. As an essential but underexcavated phenomenon in heterogeneous catalysis, the MCE will open a new avenue to design high-performance catalysts.

A chiral metal cluster triggers enantiospecific electronic transport

Chirality is a geometric property of matter that can be present at different scales, especially at the nanoscale. Here, we investigate the manifestation of chirality in electronic transport through a molecular junction. Spinless electronic transport through a chiral molecular junction is not enantiospecific. However, when a chiral metal cluster, C3-Au34, is attached to the source electrode, a different response is obtained in spinless electronic transport between R and L systems: this indicates the crucial role of chiral clusters in triggering enantiospecific spinless electronic transport. In contrast, when an achiral metal cluster, C3v-Au34, is attached, no change in conductance occurs between enantiomeric systems. Using the non-equilibrium green's function method, we characterized this phenomenon by calculating the transmission and conductance of spin-unpolarized electrons. Our theoretical results highlight the importance of metal clusters with specific sizes and chiral structures in electronic transport and support previously published experimental results that exhibited enantiospecific scanning tunneling measurements with intrinsically chiral tips.

Subnanometric Osmium Clusters Confined on Palladium Metallenes for Enhanced Hydrogen Evolution and Oxygen Reduction Catalysis

Highly efficient, cost-effective, and durable electrocatalysts, capable of accelerating sluggish reaction kinetics and attaining high performance, are essential for developing sustainable energy technologies but remain a great challenge. Here, we leverage a facile heterostructure design strategy to construct atomically thin Os@Pd metallenes, with atomic-scale Os nanoclusters of varying geometries confined on the surface layer of the Pd lattice, which exhibit excellent bifunctional properties for catalyzing both hydrogen evolution (HER) and oxygen reduction reactions (ORR). Importantly, Os5%@Pd metallenes manifest a low η10 overpotential of only 11 mV in 1.0 M KOH electrolyte (HER) as well as a highly positive E1/2 potential of 0.92 V in 0.1 M KOH (ORR), along with superior mass activities and electrochemical durability. Theoretical investigations reveal that the strong electron redistribution between Os and Pd elements renders a precise fine-tuning of respective d-band centers, thereby guiding adsorption of hydrogen and oxygen intermediates with an appropriate binding energy for the optimal HER and ORR.

Efficient and Stable pH-Universal Water Electrolysis Catalyzed by N-Doped Hollow Carbon Confined RuIrOx Nanocrystals

A facile strategy is developed to fabricate 3 nm RuIrOx nanocrystals anchored onto N-doped hollow carbon for highly efficient and pH-universal overall water splitting and alkaline seawater electrolysis. The designed catalyst exhibits much lower overpotential and superior stability than most previously reported Ru- and Ir-based electrocatalysts for hydrogen/oxygen evolution reactions. It also manifests excellent overall water splitting activities and maintains ≈100% Faradic efficiency with a cell voltage of 1.53, 1.51, and 1.54 V at 10 mA cm-2 for 140, 255, and 200 h in acid, alkaline, and alkaline seawater electrolytes, respectively. The excellent electrocatalytic performance can be attributed to solid bonding between RuIrOx and the hollow carbon skeleton, and effective electronic coupling between Ru and Ir, thus inducing its remarkable electrocatalytic activities and long-lasting stability.

Biomimetic Design of a Dynamic M-O-V Pyramid Electron Bridge for Enhanced Nitrogen Electroreduction

Electrochemical nitrogen reduction reaction (eNRR) offers a sustainable route for ammonia synthesis; however, current electrocatalysts are limited in achieving optimal performance within narrow potential windows. Herein, inspired by the heliotropism of sunflowers, we present a biomimetic design of Ru-VOH electrocatalyst, featuring a dynamic Ru-O-V pyramid electron bridge for eNRR within a wide potential range. In situ spectroscopy and theoretical investigations unravel the fact that the electrons are donated from Ru to V at lower overpotentials and retrieved at higher overpotentials, maintaining a delicate balance between N2 activation and proton hydrogenation. Moreover, N2 adsorption and activation were found to be enhanced by the Ru-O-V moiety. The catalyst showcases an outstanding Faradaic efficiency of 51.48% at -0.2 V (vs RHE) with an NH3 yield rate exceeding 115 μg h-1 mg-1 across the range of -0.2 to -0.4 V (vs RHE), along with impressive durability of over 100 cycles. This dynamic M-O-V pyramid electron bridge is also applicable to other metals (M = Pt, Rh, and Pd).

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.

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.

Enhancing Photocatalytic CO2 Conversion through Oxygen-Vacancy-Mediated Topological Phase Transition

Weak adsorption of gas reactants and strong binding of intermediates present a significant challenge for most transition metal oxides, particularly in the realm of CO2 photoreduction. Herein, we demonstrate that the adsorption can be fine-tuned by phase engineering of oxide catalysts. An oxygen vacancy mediated topological phase transition in Ni-Co oxide nanowires, supported on a hierarchical graphene aerogel (GA), is observed from a spinel phase to a rock-salt phase. Such in situ phase transition empowers the Ni-Co oxide catalyst with a strong internal electric field and the attainment of abundant oxygen vacancies. Among a series of catalysts, the in situ transformed spinel/rock-salt heterojunction supported on GA stands out for an exceptional photocatalytic CO2 reduction activity and selectivity, yielding an impressive CO production rate of 12.5 mmol g-1  h-1 and high selectivity of 96.5 %. This remarkable performance is a result of the robust interfacial coupling between two topological phases that optimizes the electronic structures through directional charge transfer across interfaces. The phase transition process induces more Co2+ in octahedral site, which can effectively enhance the Co-O covalency. This synergistic effect balances the surface activation of CO2 molecules and desorption of reaction intermediates, thereby lowering the energetic barrier of the rate-limiting step.

Current Status and Perspectives of Dual-Atom Catalysts Towards Sustainable Energy Utilization

The exploration of sustainable energy utilization requires the implementation of advanced electrochemical devices for efficient energy conversion and storage, which are enabled by the usage of cost-effective, high-performance electrocatalysts. Currently, heterogeneous atomically dispersed catalysts are considered as potential candidates for a wide range of applications. Compared to conventional catalysts, atomically dispersed metal atoms in carbon-based catalysts have more unsaturated coordination sites, quantum size effect, and strong metal-support interactions, resulting in exceptional catalytic activity. Of these, dual-atomic catalysts (DACs) have attracted extensive attention due to the additional synergistic effect between two adjacent metal atoms. DACs have the advantages of full active site exposure, high selectivity, theoretical 100% atom utilization, and the ability to break the scaling relationship of adsorption free energy on active sites. In this review, we summarize recent research advancement of DACs, which includes (1) the comprehensive understanding of the synergy between atomic pairs; (2) the synthesis of DACs; (3) characterization methods, especially aberration-corrected scanning transmission electron microscopy and synchrotron spectroscopy; and (4) electrochemical energy-related applications. The last part focuses on great potential for the electrochemical catalysis of energy-related small molecules, such as oxygen reduction reaction, CO2 reduction reaction, hydrogen evolution reaction, and N2 reduction reaction. The future research challenges and opportunities are also raised in prospective section.

How spin state and oxidation number of transition metal atoms determine molecular adsorption: a first-principles case study for NH3

Understanding how the electronic state of transition metal atoms can influence molecular adsorption on a substrate is of great importance for many applications. Choosing NH3 as a model molecule, its adsorption behavior on defected SnS2 monolayers is investigated. The number of valence electrons n is controlled by decorating the monolayer with different transition metal atoms, ranging from Sc to Zn. Density-Functional Theory based calculations show that the adsorption energy of NH3 molecules oscillates with n and shows a clear odd-even pattern. There is also a mirror symmetry of the adsorption energies for large and low electron numbers. This unique behavior is mainly governed by the oxidation state of the TM ions. We trace back the observed trends of the adsorption energy to the orbital symmetries and ligand effects which affect the interaction between the 3σ orbitals (NH3) and the 3d orbitals of the transition metals. This result unravels the role which the spin state of TM ions plays in different crystal fields for the adsorption behavior of molecules. This new understanding of the role of the electronic structure on molecular adsorption can be useful for the design of high efficiency nanodevices in areas such as sensing and photocatalysis.

Pd 4d Orbital Overlapping Modulation on Au@Pd Nanowires for Efficient H2O2 Production

Isolating Pd atoms has been shown to be crucial for the design of a Pd-based electrocatalyst toward 2e- oxygen reduction reaction (ORR). However, there are limited studies focusing on the systematic compositional design that leads to an optimal balance between activity and selectivity. Herein, we design a series of Au@Pd core@shell structures to investigate the influence of the Pd 4d orbital overlapping degree on 2e- ORR performance. Density functional theory (DFT) calculations indicate that enhanced H2O2 selectivity and activity are achieved at Pdn clusters with n ≤ 3, and Pd clusters larger than Pd3 should be active for 4e- ORR. However, experimental results show that Au@Pd nanowires (NWs) with Pd4 as the primary structure exhibit the optimal H2O2 performance in an acidic electrolyte with a high mass activity (7.05 A mg-1 at 0.4 V) and H2O2 selectivity (nearly 95%). Thus, we report that Pd4, instead of Pd3, is the upper threshold of Pd cluster size for an ideal 2e- ORR. It results from the oxygen coverage on the catalyst surface during the ORR process, and such an oxygen coverage phenomenon causes electron redistribution and weakened *OOH binding strength on active sites, leading to enhanced activity of Pd4 with only 0.06 V overpotential in acidic media.

N-Coordinated Iridium-Molybdenum Dual-Atom Catalysts Enabling Efficient Bifunctional Hydrogen Electrocatalysis

Achieving effective hydrogen evolution/oxidation reaction (HER/HOR) across a wide pH span is of critical importance in unlocking the full potential of hydrogen energy but remains intrinsically challenging. Here, we engineer the N-coordinated Ir-Mo dual atoms on a carbon matrix by ultrafast high-temperature sintering, creating an efficient bifunctional electrocatalyst for both HER and HOR in both acidic and alkaline electrolytes. The optimized catalyst, Ir-Mo DAC/NC, demonstrates exceptional performance, with a significantly reduced HER overpotential of 11.3 mV at 10 mA/cm2 and a HOR exchange current (i0,m) of 3972 mA/mgIr in acidic conditions, surpassing the performance of Pt/C and Ir/C catalysts. In alkaline conditions, Ir-Mo DAC/NC also outperforms Pt/C, as evidenced by its low HER overpotential of 23 mV at 10 mA/cm2 and a high i0,m of 1308 mA/mgIr. Furthermore, our catalyst exhibits remarkable stability in both acidic and alkaline environments. DFT calculations results reveal that the superior electrochemical performance of Ir-Mo DAC/NC arises from the electronic synergy between Ir and Mo pairs, which regulates the interaction between the intermediates and active sites. These findings present a promising strategy for the development of dual-atom catalysts (DACs), with potential applications in the polymer fuel cells and water electrolyzers.

Manipulation of Electron Spins with Oxygen Vacancy on Amorphous/Crystalline Composite-Type Catalyst

By substituting the oxygen evolution reaction (OER) with the anodic urea oxidation reaction (UOR), it not only reduces energy consumption for green hydrogen generation but also allows purification of urea-rich wastewater. Spin engineering of the d orbital and oxygen-containing adsorbates has been recognized as an effective pathway for enhancing the performance of electrocatalysts. In this work, we report the fabrication of a bifunctional electrocatalyst composed of amorphous RuO2-coated NiO ultrathin nanosheets (a-RuO2/NiO) with abundant amorphous/crystalline interfaces for hydrogen evolution reaction (HER) and UOR. Impressively, only 1.372 V of voltage is required to attain a current density of 10 mA cm-2 over a urea electrolyzer. The increased oxygen vacancies in a-RuO2/NiO by incorporation of amorphous RuO2 enhance the total magnetization and entail numerous spin-polarized electrons during the reaction, which speeds up the UOR reaction kinetics. The density functional theory study reveals that the amorphous/crystalline interfaces promote charge-carrier transfer, and the tailored d-band center endows the optimized adsorption of oxygen-generated intermediates. This kind of oxygen vacancy induced spin-polarized electrons toward boosting HER and UOR kinetics and provides a reliable reference for exploration of advanced electrocatalysts.

Spin polarized Fe1-Ti pairs for highly efficient electroreduction nitrate to ammonia

Electrochemical nitrate reduction to ammonia offers an attractive solution to environmental sustainability and clean energy production but suffers from the sluggish *NO hydrogenation with the spin-state transitions. Herein, we report that the manipulation of oxygen vacancies can contrive spin-polarized Fe1-Ti pairs on monolithic titanium electrode that exhibits an attractive NH3 yield rate of 272,000 μg h-1 mgFe-1 and a high NH3 Faradic efficiency of 95.2% at -0.4 V vs. RHE, far superior to the counterpart with spin-depressed Fe1-Ti pairs (51000 μg h-1 mgFe-1) and the mostly reported electrocatalysts. The unpaired spin electrons of Fe and Ti atoms can effectively interact with the key intermediates, facilitating the *NO hydrogenation. Coupling a flow-through electrolyzer with a membrane-based NH3 recovery unit, the simultaneous nitrate reduction and NH3 recovery was realized. This work offers a pioneering strategy for manipulating spin polarization of electrocatalysts within pair sites for nitrate wastewater treatment.

Bifunctional CoxP-FeP@C for overall water splitting realized by manipulating the electronic states of Co via phosphorization

The electronic properties and structural characteristics of transition metal materials have a significant impact on their electrocatalytic performance. Therefore, precisely controlling the electronic states of core metals and fabricating catalysts with advanced structures are conducive to facilitating electrolysis process. Herein, we manipulate the electronic properties of the electroactive sites of catalysts by controlling the degree of phosphorization during the phosphorization process. The CoxP-FeP@C electrocatalysts, characterized by their sea-urchin morphology, were synthesized by subjecting CoFc-metal organic framework (MOF) precursors to phosphorization for specific time intervals. The optimized Co2P-FeP@C-5 electrocatalyst showed the optimum performance towards the oxygen evolution reaction (OER) catalytic efficiency with 239 mV overpotential and the hydrogen evolution reaction (HER) activity with 169 mV overpotential to reach 10 mA·cm-2 in 1.0 M KOH (PH = 13.8). For comparison, the extended duration of phosphorization resulted in the formation of CoP-FeP@C-15 and CoP-FeP@C-30 electrocatalysts, which exhibited compromised electrocatalytic performance due to the transformation of the electroactive core Co2P to CoP during subsequent phosphorization processes. The improved interfacial properties between Co2P and FeP play a crucial role in enhancing the efficiency of water decomposition, attributed to the higher density of states (DOS) at the Fermi Level and the increased availability of electroactive sites for the adsorption of intermediates and electrolysis. These findings are substantiated by density functional theory (DFT) calculations. This approach offers a highly effective means of manipulating the electronic properties of the electroactive transition metal core by controlling the degree of phosphorization, with the ultimate goal of achieving efficient water splitting.

High Flux and Stability of Cationic Intercalation in Transition-Metal Oxides: Unleashing the Potential of Mn t2g Orbital via Enhanced π-Donation

Transition-metal oxides (TMOs) often struggle with challenges related to low electronic conductivity and unsatisfactory cyclic stability toward cationic intercalation. In this work, we tackle these issues by exploring an innovative strategy: leveraging heightened π-donation to activate the t2g orbital, thereby enhancing both electron/ion conductivity and structural stability of TMOs. We engineered Ni-doped layered manganese dioxide (Ni-MnO2), which is characterized by a distinctive Ni-O-Mn bridging configuration. Remarkably, Ni-MnO2 presents an impressive capacitance of 317 F g-1 and exhibits a robust cyclic stability, maintaining 81.58% of its original capacity even after 20,000 cycles. Mechanism investigations reveal that the incorporation of Ni-O-Mn configurations stimulates a heightened π-donation effect, which is beneficial to the π-type orbital hybridization involving the O 2p and the t2g orbital of Mn, thereby accelerating charge-transfer kinetics and activating the redox capacity of the t2g orbital. Additionally, the charge redistribution from Ni to the t2g orbital of Mn effectively elevates the low-energy orbital level of Mn, thus mitigating the undesirable Jahn-Teller distortion. This results in a subsequent decrease in the electron occupancy of the π*-antibonding orbital, which promotes an overall enhancement in structural stability. Our findings pave the way for an innovative paradigm in the development of fast and stable electrode materials for intercalation energy storage by activating the low orbitals of the TM center from a molecular orbital perspective.

Controllable atoms implantation for inducing high valency nickel towards optimizing electronic structure for enhanced overall water splitting

Adjusting the electronic structure and intrinsic activity of the active site of the catalyst based on atomic implantation is the crucial to realizing efficient electrochemical water splitting in alkaline media. Thus, we introduce vanadium (V) atoms with abundant vacant d orbitals as dopants into nickel selenides (NiSe), which has abundant variable valence states, and successfully synthesise three-dimensional bi-functional catalysts self-supported on Ni foam (NF). The electron structure characterisation reveals that, compared with the pure NiSe phase, the oxidation states of Ni cations and electron concentration at the Se site in V-NiSe increase due to the V doping. These changes are accompanied by changes in the electronic structure and active sites in V-NiSe. The as-generated V-NiSe nanorods exhibit an optimised electronic structure, high number of active sites and highly rough nanorod array structure with large electrochemically active surface area and in situ growth characteristics of conductive NF. Thus, the as-generated V-NiSe nanorods catalysts exhibit excellent bi-functional catalytic activity, with 50 mA⋅cm-2 at an overpotential of 270.2 and 251.2 mV for oxygen evolution reactions (OER) and hydrogen evolution reactions (HER), respectively, in KOH (1 M). Water electrolysis using V-NiSe as both the anode and cathode requires a cell voltage of 1.76 V to drive 50 mA⋅cm-2, continuously operating for 80 h. This study provides a systematic understanding of the design of transition-metal catalysts using heteroatomic doping to control their electronic structure and catalytic activity.

Spin-Selective Oxygen Evolution Reaction in Chiral Iron Oxide Nanoparticles: Synergistic Impact of Inherent Magnetic Moment and Chirality

Electron spin polarization is identified as a promising avenue for enhancing the oxygen evolution reaction (OER), which is the bottleneck that limits the energy efficiency of water-splitting. Here, we report that both ferrimagnetic (f-Fe3O4) and superparamagnetic iron oxide (s-Fe3O4) catalysts can exhibit external magnetic field (Hext)-induced OER enhancement, and the activity is proportional to their intrinsic magnetic moment. Additionally, the chirality-induced spin selectivity (CISS) effect was utilized in synergy with Hext to get a maximum enhancement of up to 89% improvement in current density (at 1.8 V vs RHE) with a low onset potential of 270 mV in s-Fe3O4 catalysts. Spin polarization and the resultant spin selectivity suppress the production of H2O2 and promote the formation of ground state triplet O2 during the OER. Furthermore, the design of chiral s-Fe3O4 with synergistic spin potential effect demonstrates a high spin polarization of ∼42%, as measured using conductive atomic force microscopy (c-AFM).

Photocatalytic Oxidative Coupling of Ethane to n-Butane Using CO2 as a Soft Oxidant over NiTi-Layered Double Hydroxide

Selective conversion of ethane (C2 H6 ) to high-value-added chemicals is a very important chemical process, yet it remains challenging owing to the difficulty of ethane activation. Here, a NiTi-layered double hydroxide (NiTi-LDH) photocatalyst is reported for oxidative coupling of ethane to n-butane (n-C4 H10 ) by using CO2 as an oxidant. Remarkably, the as-prepared NiTi-LDH exhibits a high selectivity for n-C4 H10 (92.35%) with a production rate of 62.06 µmol g-1 h-1 when the feed gas (CO2 /C2 H6 ) ratio is 2:8. The X-ray absorption fine structure (XAFS) and photoelectron characterizations demonstrate that NiTi-LDH possesses rich vacancies and high electron-hole separation efficiency, which can promote the coupling of C2 H6 to n-C4 H10 . More importantly, density functional theory (DFT) calculations reveal that ethane is first activated on the oxygen vacancies of the catalyst surface, and the C─C coupling pathway is more favorable than the C─H cleavage to C2 H4 or CH4 , resulting in the high production rate and selectivity for n-C4 H10 .

Phosphorus-Doped PdSn Nanocatalyst with Abundant Defective Atoms for Enhanced Methanol Oxidation

The design of the nanostructure of palladium-based nanocatalysts is considered to be a very effective way to improve the performance of nanocatalysts. Recent studies have shown that multiphase nanostructures can increase the active sites of palladium catalysts, thus effectively improving the catalytic efficiency of palladium atoms. However, it is difficult to regulate the phase structure of Pd nanocatalysts to form a compound phase structure. In this work, PdSnP nanocatalysts with different compositions were synthesized by fine-regulating the doping amount of phosphorus atoms. The results show that the doping of phosphorus atoms not only changes the composition of PdSn nanocatalysts but also changes the microstructure, forming amorphous and crystalline multiphase structures. This multiphase nanostructure contains abundant interfacial defects, which effectively promotes the electrocatalytic oxidation efficiency of Pd atoms in small-molecule alcohols. Compared with the undoped PdSn nanocatalyst (480 mA mg_Pd^-1 and 2.28 mA cm^-2) and the commercial Pd/C catalyst (397 mA mg_Pd^-1 and 1.15 mA cm^-2), the mass (1746 mA mg_Pd^-1) and specific activities (8.56 mA cm^-2) of PdSn_0.38P_0.05 nanocatalysts in the methanol oxidation reaction were increased by 3.6 and 3.8 times and 4.4 and 7.4 times, respectively. This study provides a new synthesis strategy for the design and synthesis of efficient palladium-based nanocatalysts for the oxidation of small-molecule alcohols.

Selective activation of peroxymonosulfate govern by B-site metal in delafossite for efficient pollutants degradation: Pivotal role of d orbital electronic configuration

Radical and non-radical oxidation pathways have been universally validated in transition metals (TMs) oxides activated peroxymonosulfate (PMS) processes. However, achieving high efficiency and selectivity of PMS activation remains challenging due to the ambiguous tuning mechanism of TMs sites on PMS activation in thermodynamic scope. Herein, we demonstrated that the exclusive PMS oxidation pathways were regulated by d orbital electronic configuration of B-sites in delafossites (CuBO₂) for Orange I degradation (Co^III 3d⁶ for reactive oxygen species (ROSs) vs. Cr^III 3d³ for electron transfer pathway). The d orbital electronic configuration was identified to affect the orbital overlap extent between 3d of B-sites and O 2p of PMS, which induced B-sites offering different types of hybrid orbital to coordinate with O 2p of PMS, thereby forming the high-spin complex (CuCoO₂@PMS) or the low-spin complex (CuCrO₂@PMS), on which basis PMS was selectively dissociated to form ROSs or achieve electron transfer pathway. As indicated by thermodynamic analysis, a general rule was proposed that B-sites of less than half-filled 3d orbital tended to act as electron shuttle, i.e., Cr^III (3d³), Mn^III (3d⁴), interacting with PMS to execute an electron transfer pathway for degrading Orange I, while B-sites of between half-filled and full-filled 3d orbital preferred to be electron donator, i.e., Co^III (3d⁶), Fe^III (3d⁵), activating PMS to generate ROSs. These findings lay a foundation for the oriented design of TMs-based catalysts from the atomic level according to d orbital electronic configuration optimization, as so to facilitate the achievement of PMS-AOPs with highly selective and efficient remediation of contaminants in water purification practice.

Oxygen-Bridged Stabilization of Single Atomic W on Rh Metallenes for Robust and Efficient pH-Universal Hydrogen Evolution

Highly efficient and durable electrocatalysts are of the utmost importance for the sustainable generation of clean hydrogen by water electrolysis. Here, we present a report of an atomically thin rhodium metallene incorporated with oxygen-bridged single atomic tungsten (Rh-O-W) as a high-performance electrocatalyst for pH-universal hydrogen evolution reaction. The Rh-O-W metallene delivers ascendant electrocatalytic HER performance, characterized by exceptionally low overpotentials, ultrahigh mass activities, excellent turnover frequencies, and robust stability with negligible deactivation, in pH-universal electrolytes, outperforming that of benchmark Pt/C, Rh/C and numerous other reported precious-metal HER catalysts. Interestingly, the promoting feature of -O-W single atomic sites is understood via operando X-ray absorption spectroscopy characterization and theoretical calculations. On account of electron transfer and equilibration processes take place between the binary components of Rh-O-W metallenes, fine-tuning of the density of states and electron localization at Rh active sites is attained, hence promoting HER via a near-optimal hydrogen adsorption.

Pd-PdO Nanodomains on Amorphous Ru Metallene Oxide for High-Performance Multifunctional Electrocatalysis

Developing highly efficient multifunctional electrocatalysts is crucial for future sustainable energy  pursuits, but remains a great challenge. Herein, a facile synthetic strategy is used to confine atomically thin Pd-PdO nanodomains to amorphous Ru metallene oxide (RuO₂ ). The as-synthesized electrocatalyst (Pd₂ RuOx-0.5 h) exhibits excellent catalytic activity toward the pH-universal hydrogen evolution reaction (η₁₀  = 14 mV in 1 m KOH, η₁₀  = 12 mV in 0.5 m H₂ SO₄ , and η₁₀  = 22 mV in 1 m PBS), alkaline oxygen evolution reaction (η₁₀  = 225 mV), and overall water splitting (E₁₀  = 1.49 V) with high mass activity and operational stability. Further reduction endows the material (Pd₂ RuOx-2 h) with a promising alkaline oxygen reduction activity, evidenced by high halfway potential, four-electron selectivity, and excellent poison tolerance. The enhanced catalytic activity is attributed to the rational integration of favorable nanostructures, including 1) the atomically thin nanosheet morphology, 2) the coexisting amorphous and defective crystalline phases, and 3) the multi-component heterostructural features. These structural factors effectively regulate the material's electronic configuration and the adsorption of intermediates at the active sites for favorable reaction energetics.

Heterointerface and Tensile Strain Effects Synergistically Enhances Overall Water-Splitting in Ru/RuO2 Aerogels

Designing robust electrocatalysts for water-splitting is essential for sustainable hydrogen generation, yet difficult to accomplish. In this study, a fast and facile two-step technique to synthesize Ru/RuO₂ aerogels for catalyzing overall water-splitting under alkaline conditions is reported. Benefiting from the synergistic combination of high porosity, heterointerface, and tensile strain effects, the Ru/RuO₂ aerogel exhibits low overpotential for oxygen evolution reaction (189 mV) and hydrogen evolution reaction (34 mV) at 10 mA cm^-2 , surpassing RuO₂ (338 mV) and Pt/C (53 mV), respectively. Notably, when the Ru/RuO₂ aerogels are applied at the anode and cathode, the resultant water-splitting cell reflected a low potential of 1.47 V at 10 mA cm^-2 , exceeding the commercial Pt/C||RuO₂ standard (1.63 V). X-ray adsorption spectroscopy and theoretical studies demonstrate that the heterointerface of Ru/RuO₂ optimizes charge redistribution, which reduces the energy barriers for hydrogen and oxygen intermediates, thereby enhancing oxygen and hydrogen evolution reaction kinetics.