Coupling Magnetic Single‐Crystal Co 2 Mo 3 O 8 with Ultrathin Nitrogen‐Rich Carbon Layer for Oxygen Evolution Reaction

Activating Lattice Oxygen in Layered Lithium Oxides through Cation Vacancies for Enhanced Urea Electrolysis

Despite the fact that high-valent nickel-based oxides exhibit promising catalytic activity for the urea oxidation reaction (UOR), the fundamental questions concerning the origin of the high performance and the structure-activity correlations remain to be elucidated. Here, we unveil the underlying enhanced mechanism of UOR by employing a series of prepared cation-vacancy controllable LiNiO₂ (LNO) model catalysts. Impressively, the optimized layered LNO-2 exhibits an extremely low overpotential at 10 mA cm^-2 along with excellent stability after the 160 h test. Operando characterisations combined with the theoretical analysis reveal the activated lattice oxygen in layered LiNiO₂ with moderate cation vacancies triggers charge disproportion of the Ni site to form Ni⁴⁺ species, facilitating deprotonation in a lattice oxygen involved catalytic process.

Guided Synthesis of a Mo/Zn Dual Single-Atom Nanozyme with Synergistic Effect and Peroxidase-like Activity

We present a facile route towards a dual single-atom nanozyme composed of Zn and Mo, which utilizes the non-covalent nano-assembly of polyoxometalates, supramolecular coordination complexes as the metal-atom precursor, and a macroscopic amphiphilic aerogel as the supporting substrate. The dual single-atoms of Zn and Mo have a high content (1.5 and 7.3 wt%, respectively) and exhibit a synergistic effect and a peroxidase-like activity. The Zn/Mo site was identified as the main active center by X-ray absorption fine structure spectroscopy and density functional theory calculation. The detection of versatile analytes, including intracellular H₂ O₂ , glucose in serum, cholesterol, and ascorbic acid in commercial beverages was achieved. The nanozyme has an outstanding stability and maintained its performance after one year's storage. This study develops a new peroxidase-like nanozyme and provides a robust synthetic strategy for single-atom catalysts by utilizing an aerogel as a facile substrate that is capable of stabilizing various metal atoms.

Vanadium-Incorporated CoP2 with Lattice Expansion for Highly Efficient Acidic Overall Water Splitting

A proton exchange membrane water electrolyzer (PEMWE) in acidic medium is a hopeful scenario for hydrogen production using renewable energy, but the grand challenge lies in substituting noble-metal catalysts. Herein, a robust electrocatalyst of V-CoP₂ porous nanowires arranged on a carbon cloth is successfully fabricated by incorporating vanadium into the CoP₂ lattice. Structural characterizations and theoretical analysis indicate that lattice expansion of CoP₂ caused by V incorporation results in the upshift of the d-band center, which is conducive to hydrogen adsorption for boosting the hydrogen evolution reaction (HER). Besides, V promotes surface reconstruction to generate a thicker Co₃ O₄ layer with an oxygen vacancy that enhances acid-corrosion resistance and optimizes the adsorption of water and oxygen-containing species, thus improving activity and stability toward the oxygen evolution reaction (OER). Accordingly, it presents a superior acidic overall water splitting activity (1.47 V@10 mA cm^-2 ) to Pt-C/CC||RuO₂ /CC (1.59 V@10 mA cm^-2 ), and remarkable stability. This work proposes a new route to design efficient non-noble metal electrocatalysts for PEMWE.

Engineering Lattice Oxygen Activation of Iridium Clusters Stabilized on Amorphous Bimetal Borides Array for Oxygen Evolution Reaction

Developing robust oxygen evolution reaction (OER) catalysts requires significant advances in material design and in-depth understanding for water electrolysis. Herein, we report iridium clusters stabilized surface reconstructed oxyhydroxides on amorphous metal borides array, achieving an ultralow overpotential of 178 mV at 10 mA cm^-2 for OER in alkaline medium. The coupling of iridium clusters induced the formation of high valence cobalt species and Ir-O-Co bridge between iridium and oxyhydroxides at the atomic scale, engineering lattice oxygen activation and non-concerted proton-electron transfer to trigger multiple active sites for intrinsic pH-dependent OER activity. The lattice oxygen oxidation mechanism (LOM) was confirmed by in situ ¹⁸ O isotope labeling mass spectrometry and chemical recognition of negative peroxo-like species. Theoretical simulations reveal that the OER performance on this catalyst is intrinsically dominated by LOM pathway, facilitating the reaction kinetics. This work not only paves an avenue for the rational design of electrocatalysts, but also serves the fundamental insights into the lattice oxygen participation for promising OER application.

Epitaxially Grown Heterostructured SrMn3 O6-x -SrMnO3 with High-Valence Mn3+/4+ for Improved Oxygen Reduction Catalysis

Heterostructured catalysts show outstanding performance in electrochemical reactions owing to their beneficial interfacial properties. However, the rational design of heterostructured catalysts with the desired interfacial properties and charge-transfer characteristics is challenging. Herein, we developed a SrMn₃ O_6-x -SrMnO₃ (SMO_x -SMO) heterostructure through epitaxial growth, which demonstrated excellent electrocatalyst performance for the oxygen reduction reaction (ORR). The formation of high-valence Mn^3+/4+ is beneficial for promoting a positive shift in the position of the d-band center, thereby optimizing the adsorption and desorption of ORR intermediates on the heterojunction surface and resulting in improved catalytic activity. When SMO_x -SMO was applied as an air-electrode catalyst in a rechargeable zinc-air battery, a high output voltage and power density was achieved, with performance comparable to a battery prepared with Pt/C-IrO₂ air-electrode catalysts, albeit with much better cycling stability.

Iodide-Induced Fragmentation of Polymerized Hydrophilic Carbon Nitride for High-Performance Quasi-Homogeneous Photocatalytic H2 O2 Production

Polymeric carbon nitride (PCN) as a class of two-electron oxygen reduction reaction (2 e^- ORR) photocatalyst has attracted much attention for H₂ O₂ production. However, the low activity and inferior selectivity of 2 e^- ORR greatly restrict the H₂ O₂ production efficiency. Herein, we develop a new strategy to synthesize hydrophilic, fragmented PCN photocatalyst by the terminating polymerization (TP-PCN) effect of iodide ions. The obtained TP-PCN with abundant edge active sites (AEASs), which can form quasi-homogeneous photocatalytic system, exhibits superior H₂ O₂ generation rate (3265.4 μM h^-1 ), far surpassing PCN and other PCN-based photocatalysts. DFT calculations further indicate that TP-PCN is more favorable for electron transiting from β spin-orbital to the π* orbitals of O₂ , which optimizes O₂ activation and reduces the energy barrier of H₂ O₂ formation. This work provides a new concept for designing functional photocatalysts and understanding the mechanism of O₂ activation in ORR for H₂ O₂ production.

Insight into Structural Evolution, Active Site and Stability of Heterogeneous Electrocatalysts

The structure-activity correlation study of electrocatalysts is essential for improving conversion from electrical to chemical energy. Recently, increasing evidences obtained by operando characterization techniques reveal that the structural evolution of catalysts caused by the interplay with electric fields, electrolytes or reactants/intermediates brings about the formation of real active sites. Hence, it is time to summarize the structural evolution-related research advances and envisage their future developments. In this minireview, we first introduce the fundamental concepts associated with structural evolution ( e.g., catalyst, active site/center and stability/lifetime) and their relevance. Then, the multiple inducements of structural evolution and advanced operando characterizations are discussed. Lastly, a brief overview of structural evolution and its reversibility in heterogeneous electrocatalysis, especially for representative electrocatalytic oxygen evolution reaction (OER) and CO 2 reduction reaction (CO 2 RR), along with key challenges and opportunities, is highlighted.

Synergetic Metal Defect and Surface Chemical Reconstruction into NiCo2 S4 /ZnS Heterojunction to Achieve Outstanding Oxygen Evolution Performance

Defect and interface engineering are recognized as effective strategies to regulate electronic structure and improve activity of metal sulfide. However, the practical application of sulfide is restricted by their low conductivity and rapid decline in activity derived from large volume fluctuation during electrocatalysis process. More importantly, the determination of exact active site of sulfide is complicated due to the inevitable electrochemical reconstruction. Herein, ZnS nanoparticles with Zn defect are anchored onto the surface of NiCo₂ S₄ nanosheet to construct NiCo₂ S₄ /ZnS hybrids, which exhibit outstanding oxygen evolution performance with an ultralow overpotential of 140 mV. The anchoring of defective ZnS nanoparticles inhibit the volume expansion of NiCo₂ S₄ nanosheet during the cycling process. Density-functional theory reveals that the build-in interfacial potential and Zn defect can facilitate the thermodynamic formation of *O to *OOH, thus improve their intrinsic activity.

Atomic Sulfur Filling Oxygen Vacancies Optimizes H Absorption and Boosts the Hydrogen Evolution Reaction in Alkaline Media

The hydrogen evolution reaction (HER) usually has sluggish kinetics in alkaline solution due to the difficulty in forming binding protons. Herein we report an electrocatalyst in which sulfur atoms are doping in the oxygen vacancies (V_O ) of inverse spinel NiFe₂ O₄ (S-NiFe₂ O₄ ) to create active sites with enhanced electron transfer capability. This electrocatalyst has an ultralow overpotential of 61 mV at the current density of 10 mA cm^-2 and long-term stability of 60 h at 1.0 Acm^-2 in 1.0 M KOH media. In situ Raman spectroscopy revealed that S sites adsorb hydrogen adatom (H*) and in situ form S-H*, which favor the production of hydrogen and boosts HER in alkaline solution. DFT calculations further verified that S introduction lowered the energy barrier of H₂ O dissociation. Both experimental and theoretical investigations confirmed S atoms are active sites of the S-NiFe₂ O₄ .

Controlled Synthesis and Structure Engineering of Transition Metal-based Nanomaterials for Oxygen and Hydrogen Electrocatalysis in Zinc-Air Battery and Water-Splitting Devices

Electrocatalytic energy conversion plays a crucial role in realizing energy storage and utilization. Clean energy technologies such as water electrolysis, fuel cells, and metal-air batteries heavily depend on a series of electrochemical redox reactions occurring on the catalysts surface. Therefore, developing efficient electrocatalysts is conducive to remarkably improved performance of these devices. Among numerous studies, transition metal-based nanomaterials (TMNs) have been considered as promising catalysts by virtue of their abundant reserves, low cost, and well-designed active sites. This Minireview is focused on the typical clean electrochemical reactions: hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. Recent efforts to optimize the external morphology and the internal electronic structure of TMNs are described, and beginning with single-component TMNs, the active sites are clarified, and strategies for exposing more active sites are discussed. The summary about multi-component TMNs demonstrates the complementary advantages of integrating functional compositions. A general introduction of single-atom TMNs is provided to deepen the understanding of the catalytic process at an atomic scale. Finally, current challenges and development trends of TMNs in clean energy devices are summarized.

Interface Engineering of Needle-Like P-Doped MoS2 /CoP Arrays as Highly Active and Durable Bifunctional Electrocatalyst for Overall Water Splitting

Developing a bifunctional water splitting catalyst with high efficiency and low cost are crucial in the electrolysis water industry. Here, we report a rational design and simple preparation method of MoS₂ -based bifunctional electrocatalyst on carbon cloth (CC). The optimized P-doped MoS₂ @CoP/CC catalyst presents low overpotentials for the hydrogen (HER) and oxygen evolution reactions (OER) of 64 and 282 mV in alkaline solution as well as 72 mV HER overpotential in H₂ SO₄ at a current density of 10 mA cm^-2 . Furthermore, P-MoS₂ @CoP/CC as a bifunctional catalyst delivered relatively low cell voltages of 1.83 and 1.97 V at high current densities of 500 and mA cm^-2 in 30 % KOH. The two-electrode system showed a remarkable stability for 30 h, even outperformed the benchmark RuO₂ ||Pt/C catalyst. The excellent electrochemical performance can be credited to the unique microstructure, high surface area, and the synergy between metal species. This study presents a possible alternative for noble metal-based catalysts to overcome the challenges of industrial applications.

N-Doped Graphene-Decorated NiCo Alloy Coupled with Mesoporous NiCoMoO Nano-sheet Heterojunction for Enhanced Water Electrolysis Activity at High Current Density

Developing highly effective and stable non-noble metal-based bifunctional catalyst working at high current density is an urgent issue for water electrolysis (WE). Herein, we prepare the N-doped graphene-decorated NiCo alloy coupled with mesoporous NiCoMoO nano-sheet grown on 3D nickel foam (NiCo@C-NiCoMoO/NF) for water splitting. NiCo@C-NiCoMoO/NF exhibits outstanding activity with low overpotentials for hydrogen and oxygen evolution reaction (HER: 39/266 mV; OER: 260/390 mV) at ± 10 and ± 1000 mA cm-2. More importantly, in 6.0 M KOH solution at 60 °C for WE, it only requires 1.90 V to reach 1000 mA cm-2 and shows excellent stability for 43 h, exhibiting the potential for actual application. The good performance can be assigned to N-doped graphene-decorated NiCo alloy and mesoporous NiCoMoO nano-sheet, which not only increase the intrinsic activity and expose abundant catalytic activity sites, but also enhance its chemical and mechanical stability. This work thus could provide a promising material for industrial hydrogen production.