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nanoparticles (NPs) catalysts, SACs display unique features like their unsaturatedcoordination configuration, quantum size effect, and strong atom-support interaction, which induce the single-atom sites with excellent activity and stability in electrocatalysis. [1b,2] In 2011, Zhang and co-workers employed a coprecipitation method to prepare Pt SACs supported on iron oxide which demonstrated high activity and stability for CO oxidation. [3] Sun and co-workers reported the fabrication of Pt SACs on graphene by atomic layer deposition, and the as-prepared Pt SACs showed 10 times higher activity for methanol oxidation and superior CO tolerance compared to the benchmark Pt/C catalyst. [4] According to this research, it can be seen that "single atom catalysts" developed rapidly and have become a hot research topic in heterogeneous electrocatalysis. 1.1. Identification and Features of SACs SACs have isolated metal atoms that are anchored on a specific support and can behave as active centers for heterogeneous catalysis. The concept of single-atom catalysts can be traced back to the pioneering research reported by Zhang and co-workers in 2011. In their work, well-dispersed Pt single atoms were successfully prepared on the FeOx support, which opens the avenue of "single atom catalysts." The active single-atom sites generally consist of metal atoms and neighboring atoms from support materials. In addition, ion-exchanged metal atoms located on a porous support, as well as organometallic complexes anchored to the substrate, in principle, could also be viewed as SACs. The unique features of single atoms are significantly different from NPs, which endow SACs with exceptional catalytic activity, stability and selectivity. i) Decreasing the size of metal particles down to single atoms results in the maximum atom-utilization efficiency and metal dispersion. Owing to the low-coordination environment property and fully exposed active sites, SACs are capable to exhibit remarkable electrocatalytic activity toward diverse reactions. [5] ii) Single metal atoms can coordinate with support materials via strong interaction or charge transfer, which ensure the atomic dispersion and enhanced stability of SACs. [6] iii) The uniform active sites and geometric configuration of SACs enable similar electronic and spatial interactions with reactant molecules, thereby achieving Electrocatalysis plays a critical role in clean energy conversion, enabling great improvement for future sustainable technologies. Single atom catalysts (SACs) derived from metal-organic framework (MOF) are emerging extraordinary materials in electrochemical catalytic applications. Covering the merits of unique electronic structure, low-coordination environment, quantum size effect, and metal-support interaction, SACs promise enhanced electrocatalytic activity, stability, and selectivity in the field of clean energy conversion. In this article, MOF synthesis routes to afford well-dispersed SACs along with the respective synthesis mechanism are systematically reviewed first...

The sluggish kinetics of oxygen evolution reaction (OER) is the main bottleneck for the electrocatalytic water splitting to produce hydrogen (H2), and the by‐product is worthless O2. Therefore, designing a thermodynamically favorable oxidation reaction to replace OER and coupling with value‐added product generation on the anode is of significance for boosting H2 generation under low electrolysis voltage. Herein, cobalt hydroxide@hydroxysulfide nanosheets on carbon paper (Co(OH)2@HOS/CP) are synthesized as bifunctional electrocatalysts to facilitate H2 production and convert methanol to valuable formate simultaneously. Benefiting from the influences/changes on the composition, surface properties, electronic structure, and chemistry of Co(OH)2, the as‐obtained electrodes exhibit very high selectivity for methanol to value‐added formate oxidation (MFO) and boost electrocatalytic performance with low overpotential of 155 mV for MFO and 148 mV for hydrogen evolution reaction at a current density of 10 mA cm−2. Furthermore, the integrated two‐electrode electrolyzer drives 10 mA cm−2 at a cell voltage of 1.497 V with united 100% Faradaic efficiency for anodic and cathodic reaction and continuous 20 h of operation without obvious decay. The electrocatalytic hydrogen production with the assistance of alternative oxidation by the robust electrocatalyst can be further used to realize the upgrading of other organic molecules with less energy consumption.

Electrochemical nitrate reduction (NITRR) offers a promising alternative toward nitrogen recycling and ammonia production under ambient conditions, for which highly active and selective electrocatalyst is desired. In this study, metallic cobalt nanoarrays as facilely prepared from the electrochemical reduction of Co(OH)2 nanoarrays (NAs) are demonstrated to exhibit unprecedented NH3 producing capability from catalyzing NITRR. Benefitting from the high intrinsic activity of Co0, intimate contact between active species and conductive substrate and the nanostructure which exposes large number of active sites, the Co‐NAs electrode exhibits current density of −2.2 A cm−2 and NH3 production rate of 10.4 mmol h−1 cm−2 at −0.24 V versus RHE under alkaline condition and significantly surpasses reported counterparts. Moreover, the close‐to‐unity (≥96%) Faradaic efficiency (FE) toward NH3 is achieved over wide application range (potential, NO3− concentration and pH). Density function theory calculation reveals the optimized adsorption energy of NITRR intermediates on Co surface over Co(OH)2. Furthermore, it is proposed that despite the sluggish kinetics of Volmer step (H2O → *H + *OH) which provides protons in conventional hydrogenation mechanism, the proton‐supplying water dissociation process on Co surface is drastically facilitated following a concerted water dissociation–hydrogenation pathway.

Constructing monodispersed metal sites in heterocatalysis is an efficient strategy to boost their catalytic performance. Herein, a new strategy using monodispersed metal sites to tailor Pt-based nanocatalysts is addressed by engineering unconventional p-d orbital hybridization. Thus, monodispersed Ga on Pt 3 Mn nanocrystals (Ga-O-Pt 3 Mn) with high-indexed facets was constructed for the first time to drive ethanol electrooxidation reaction (EOR). Strikingly, the Ga-O-Pt 3 Mn nanocatalyst shows an enhanced EOR performance with achieving 8.41 times of specific activity than that of Pt/C. The electrochemical in situ Fourier transform infrared spectroscopy results and theoretical calculations disclose that the Ga-O-Pt 3 Mn nanocatalyst featuring an unconventional pd orbital hybridization not only promote the CÀ C bondbreaking and rapid oxidation of -OH of ethanol, but also inhibit the generation of poisonous CO intermediate species. This work discloses a promising strategy to construct a novel nanocatalysts tailored by monodispersed metal site as efficient fuel cell catalysts.

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Electro‐oxidative organic upgrading, as an ideal alternative to sluggish oxygen evolution reaction (OER) performance, can effectively decrease energy consumption to boost hydrogen evolution reaction (HER) performance. However, developing highly active electrocatalysts for long‐term durable organic upgrading with high selectivity at large and steady current density remains challenging. Herein, hollow NiSe nanocrystals heterogenized with carbon nanotubes (h‐NiSe/CNTs) are fabricated via a facile one‐pot approach. The highly dispersed h‐NiSe/CNTs 3D network can efficiently facilitate rapid mass/electron diffusion, thus achieving highly active and long‐term stable electrocatalysis for catalyzing methanol to value‐added formate at high and steady current density (≈345 mA cm−2) with high Faradaic efficiency (>95%). This reaction replaces sluggish OER performance to reduce the energy consumption for boosting H2 generation by six times. The critical active species and methanol activation mechanism are systematically studied using X‐ray photoelectron spectroscopy, X‐ray absorption fine structure analysis, in situ Raman, and density functional theory calculations, indicating that the non‐ignorable SeOx collaborated with in situ formed NiOOH species can synergistically modulate the d band center to achieve an optimal adsorption for methanol selective oxidation and suppress the further oxidation to CO2, thus leading to active and stable electrolysis for producing value‐added formate with high selectivity and co‐generating H2 with less energy consumption.

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