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.

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Developing high-efficiency and low-cost catalysts for the hydrogen evolution reaction (HER) and hydrogen generation from chemical hydrogen storage materials are both significant and critical for the exploitation and utilization of hydrogen energy. Herein, we reported a ruthenium−cobalt alloy (Ru, 1.8 wt %) enriched in hollow carbon spheres (denoted RuCo@HCSs) synthesized through a wet vacuum impregnation method followed by pyrolysis treatment. RuCo alloys are obtained by direct reduction of Ru and Co chloride precursors, avoiding hydrothermal and washing processes, and the Ru/Co ratio of the alloy can be precisely controlled. The RuCo@HCS catalyst not only displays outstanding HER performance with a low overpotential (η 10 ) and Tafel slope (21 mV and 32 mV dec −1 in 1.0 M KOH, 57 mV and 48 mV dec −1 in 0.5 M H 2 SO 4 , and 49 mV and 59 mV dec −1 in 1.0 M phosphate-buffered saline) within a wide pH range but also offers a high turnover frequency (TOF) value of 784 mol H2 min −1 mol cat −1 for the hydrolysis of ammonia borane under ambient conditions. The excellent catalytic performance of RuCo@HCSs is attributed to the special hollow embedded configuration and collaborative effect between carbon shells and RuCo alloys. Density functional theory calculations reveal that the excellent catalytic performance of RuCo@HCSs originates from the carbon shells activated by the electron transferred from the embedded metal nanoparticles. This work provides a convenient route for preparing highly active and inexpensive metal/carbon composite bifunctional catalysts.

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