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Electrocatalytic water splitting has been identified as a potential candidate for producing clean hydrogen energy with zero carbon emission. However, the sluggish kinetics of oxygen evolution reaction on the anode side of the water‐splitting device significantly hinders its practical applications. Generally, the efficiency of oxygen evolution processes depends greatly on the availability of cost‐effective catalysts with high activity and selectivity. In recent years, extensive theoretical and experimental studies have demonstrated that cobalt (Co)‐based nanomaterials, especially low‐dimensional Co‐based nanomaterials with a huge specific surface area and abundant unsaturated active sites, have emerged as versatile electrocatalysts for oxygen evolution reactions, and thus, great progress has been made in the rational design and synthesis of Co‐based nanomaterials for electrocatalytic oxygen evolution reactions. Considering the remarkable progress in this area, in this timely review, we highlight the most recent developments in Co‐based nanomaterials relating to their dimensional control, defect regulation (conductivity), electronic structure regulation, and so forth. Furthermore, a brief conclusion about recent progress achieved in oxygen evolution on Co‐based nanomaterials, as well as an outlook on future research challenges, is given. Cobalt‐based nanomaterials have been widely designed as efficient electrocatalysts for oxygen evolution reactions due to their electron orbitals. We summarize the recent development of cobalt‐based nanomaterials relating to dimensional control, defect regulation (conductivity), electronic structure regulation, and so forth for electrocatalytic oxygen evolution reactions.

The precise structural integration of single-atom and high-entropy-alloy features for energy electrocatalysis is highly appealing for energy conversion, yet remains a grand challenge. Herein, we report a class of single-atom Mo-tailored PdPtNiCuZn high-entropy-alloy nanosheets with dilute Pt-Pt ensembles and intrinsic tensile strain (Mo 1 -PdPtNiCuZn) as efficient electrocatalysts for enhancing the methanol oxidation reaction catalysis. The as-made Mo 1 -PdPtNiCuZn delivers an extraordinary mass activity of 24.55 A mg Pt −1 and 11.62 A mg Pd+Pt −1 , along with impressive long-term durability. The planted oxophilic Mo single atoms as promoters modify the electronic structure of isolated Pt sites in the high-entropy-alloy host, suppressing the formation of CO adsorbates and steering the reaction towards the formate pathway. Meanwhile, Mo promoters and tensile strain synergistically optimize the adsorption behaviour of intermediates to achieve a more energetically favourable pathway and minimize the methanol oxidation reaction barrier. This work advances the design of atomically precise catalytic sites by creating a new paradigm of single atom-tailored high-entropy alloys, opening an encouraging pathway to the design of CO-tolerance electrocatalysts. Atomically precise modification of high-entropy alloys is highly appealing for electrocatalysis. Here, the authors design single-atom Mo-tailored high-entropy alloy nanosheets with dilute Pt-Pt ensembles and intrinsic tensile strain for promoting methanol electro-oxidation towards formate.

The development of cost-effective, robust, and durable electrocatalysts to replace the expensive Pt-based catalysts towards oxygen reduction reaction (ORR) is the trending frontier research topic in renewable energy and electrocatalysis. Particular attention has been paid to metal-nitrogen-carbon (M-N-C) single atom catalysts (SACs) due to their maximized atom utilization efficiency, biomimetic active site, and distinct electronic structure. More importantly, their catalytic properties can be further tailored by rationally regulating the microenvironment of active sites (i.e., M–N coordination number, heteroatom doping and substitution. Herein, we present a comprehensive summary of the recent advancement in the microenvironment regulation of M-N-C SACs towards improved ORR performance. The coordination environment manipulation regarding central metal and coordinated atoms is first discussed, focusing on the structure—function relationship. Apart from the near-range coordination, long-range substrate modulation including heteroatom doping, defect engineering is discussed as well. Besides, the synergy mechanism of nanoparticles and single atom sites to tune the electron cloud density at the active sites is summarized. Finally, we provide the challenges and outlook of the development of M-N-C SACs.

Selective production of valuable glycerol chemicals, such as glycerate (which serves as an important chemical intermediate), poses a significant challenge due to the facile cleavage of C–C bonds and the presence of multiple reaction pathways. This challenge is more severe in the electro-oxidation of glycerol, which requires the development of desirable electrocatalysts. To facilitate the glycerol electro-oxidation reaction to glycerate, here we present an approach utilizing a high-entropy PtCuCoNiMn nanosurface. It exhibits exceptional activity (~200 mA cm −2 at 0.75 V versus a reversible hydrogen electrode) and selectivity (75.2%). In situ vibrational measurements and theoretical calculations reveal that the exceptional glycerol electro-oxidation selectivity and activity can be attributed to the unique characteristics of the high-entropy surface, which effectively modifies the electronic structure of the exposed Pt sites. The catalyst is successfully applied in an electrolyser for long-term glycerol electro-oxidation reaction, demonstrating excellent performance (~200 mA cm −2 at 1.2 V cell ) over 210 h. The present study highlights that tailoring the catalytic sites at the catalyst–electrolyte interface by constructing a high-entropy surface is an effective strategy for electrochemical catalysis. A high-entropy nanosurface is engineered for selective glycerol electro-oxidation to a high-value-added glycerate at an industrial current density, demonstrating the effectiveness of tailoring catalytic sites by the construction of high-entropy surfaces for electrochemical catalysis.

Single-atom catalysts (SACs) are promising candidates to catalyze electrochemical CO 2 reduction (ECR) due to maximized atomic utilization. However, products are usually limited to CO instead of hydrocarbons or oxygenates due to unfavorable high energy barrier for further electron transfer on synthesized single atom catalytic sites. Here we report a novel partial-carbonization strategy to modify the electronic structures of center atoms on SACs for lowering the overall endothermic energy of key intermediates. A carbon-dots-based SAC margined with unique CuN 2 O 2 sites was synthesized for the first time. The introduction of oxygen ligands brings remarkably high Faradaic efficiency (78%) and selectivity (99% of ECR products) for electrochemical converting CO 2 to CH 4 with current density of 40 mA·cm -2 in aqueous electrolytes, surpassing most reported SACs which stop at two-electron reduction. Theoretical calculations further revealed that the high selectivity and activity on CuN 2 O 2 active sites are due to the proper elevated CH 4 and H 2 energy barrier and fine-tuned electronic structure of Cu active sites. Single-atom catalysts (SACs) are promising candidates to catalyze CO 2 reduction for the formation of high value hydrocarbons but most of the reactions yield CO. Here, the authors show a low-temperature calcining process to fabricate a carbon-dots-based SAC to efficiently convert CO 2 to methane.

The introduction of single-atom catalysts (SACs) into Fenton-like oxidation promises ultrafast water pollutant elimination, but the limited access to pollutants and oxidant by surface catalytic sites and the intensive oxidant consumption still severely restrict the decontamination performance. While nanoconfinement of SACs allows drastically enhanced decontamination reaction kinetics, the detailed regulatory mechanisms remain elusive. Here, we unveil that, apart from local enrichment of reactants, the catalytic pathway shift is also an important cause for the reactivity enhancement of nanoconfined SACs. The surface electronic structure of cobalt site is altered by confining it within the nanopores of mesostructured silica particles, which triggers a fundamental transition from singlet oxygen to electron transfer pathway for 4-chlorophenol oxidation. The changed pathway and accelerated interfacial mass transfer render the nanoconfined system up to 34.7-fold higher pollutant degradation rate and drastically raised peroxymonosulfate utilization efficiency (from 61.8% to 96.6%) relative to the unconfined control. It also demonstrates superior reactivity for the degradation of other electron-rich phenolic compounds, good environment robustness, and high stability for treating real lake water. Our findings deepen the knowledge of nanoconfined catalysis and may inspire innovations in low-carbon water purification technologies and other heterogeneous catalytic applications. Nanoconfining single metal atom catalysts leads to faster decontamination, primarily due to improved interfacial mass transfer. This study identifies a change in the catalytic pathway as an additional significant factor contributing to the enhanced performance.

Grain boundary controlling is an effective approach for manipulating the electronic structure of electrocatalysts to improve their hydrogen evolution reaction performance. However, probing the direct effect of grain boundaries as highly active catalytic hot spots is very challenging. Herein, we demonstrate a general water-assisted carbothermal reaction strategy for the construction of ultrathin Mo 2 C nanosheets with high-density grain boundaries supported on N-doped graphene. The polycrystalline Mo 2 C nanosheets are connected with N-doped graphene through Mo–C bonds, which affords an ultra-high density of active sites, giving excellent hydrogen evolution activity and superior electrocatalytic stability. Theoretical calculations reveal that the d z 2 orbital energy level of Mo atoms is controlled by the MoC 3 pyramid configuration, which plays a vital role in governing the hydrogen evolution activity. The d z 2 orbital energy level of metal atoms exhibits an intrinsic relationship with the catalyst activity and is regarded as a descriptor for predicting the hydrogen evolution activity. Probing the direct effect of grain boundaries as active catalytic sites is very challenging. Here, the authors reveal that the d z 2 orbital energy level of Mo atoms in grain boundaries exhibits an intrinsic relationship with the hydrogen evolution activity.

Exposing and stabilizing undercoordinated platinum (Pt) sites and therefore optimizing their adsorption to reactive intermediates offers a desirable strategy to develop highly efficient Pt-based electrocatalysts. However, preparation of atomically controllable Pt-based model catalysts to understand the correlation between electronic structure, adsorption energy, and catalytic properties of atomic Pt sites is still challenging. Herein we report the atomically thin two-dimensional PtTe 2 nanosheets with well-dispersed single atomic Te vacancies (Te-SAVs) and atomically well-defined undercoordinated Pt sites as a model electrocatalyst. A controlled thermal treatment drives the migration of the Te-SAVs to form thermodynamically stabilized, ordered Te-SAV clusters, which decreases both the density of states of undercoordinated Pt sites around the Fermi level and the interacting orbital volume of Pt sites. As a result, the binding strength of atomically defined Pt active sites to H intermediates is effectively reduced, which renders PtTe 2 nanosheets highly active and stable in hydrogen evolution reaction. Precisely regulating Pt catalytic sites is important and challenging. Herein the authors engineer the clustering of single atomic Te vacancies in atomically thin PtTe 2 to optimize the electronic structure, adsorption energy, and catalytic performance of atomically defined Pt sites.

The coexistence of multi-component active sites like single-atom sites, diatomic sites (DAS) and nanoclusters is shown to result in superior performances in the hydrogen evolution reaction (HER). Metal diatomic sites are more complex than single-atom sites but their unique electronic structures can lead to significant enhancement of the HER kinetics. Although the synthesis and identification of DAS is usually challenging, we report a simple access to a diatomic catalyst by anchoring Co-Ru DAS on nitrogen-doped carbon supports along with Ru nanoparticles (NPs). Experimental and theoretical results revealed the atomic-level characteristics of Co-Ru sites, their strong electronic coupling and their synergy with Ru NPs within the catalyst. The unique electronic structure of the catalyst resulted in an excellent HER activity and stability in alkaline media. This work provides a valuable insight into a widely applicable design of diatomic catalysts with multi-component active sites for highly efficient HER electrocatalysis.

Water electrolysis powered by renewable electricity can produce clean hydrogen, but the technology is limited by the slow anodic oxygen evolution reaction (OER). The most active monometallic OER catalyst is high-valence ruthenium, but it is thermodynamically unstable. Here we leverage the strong and tunable interaction between substrate and active site found in single atom catalysts, and discover a local electronic manipulation strategy for stabilizing high-valence Ru single sites (Ru SS) on a class of Ni-based phosphate porous hollow spheres (Ru SS MNiPi PHSs where M = Fe, Co, Mn, Cu) for efficient electrolysis. Both X-ray absorption fine structure and density functional theory calculation results verify the intrinsic stability of the catalyst, and suggest that this originates from the tailored valence state, coordination number and local electronic structure of the Ru SS. We formulate general guidelines for stabilizing high-valence catalytic sites and introduce a double-volcano plot to describe the superior electrocatalytic behaviours of high-valence Ru SS. The optimum Ru SS/FeNiPi achieves a low overpotential of 204 mV and 49 mV for the OER and hydrogen evolution reaction at 10 mA cm−2, respectively. Assembling Ru SS/FeNiPi in an industrial-level electrolyser with a low Ru loading of 0.081 mg cm−2 realizes a stable industrial current density of 2,000 mA cm−2 at 1.78 V, which is the highest reported value in alkaline electrolyte to the best of our knowledge, and exceeds that of commercial Pt//RuO2 by 5.7 times.Water electrolysis can produce clean hydrogen, but it is limited by the slow anodic oxygen evolution reaction. Now, a local electronic manipulation strategy for stabilizing high-valence Ru single site catalysts has been developed. The catalyst demonstrates efficient bifunctional activity for water electrolysis.