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• V 8 C 7 /CoP were prepared through pyrolysis and a subsequent phosphidation. • V 8 C 7 /CoP exhibits a splendid electrocatalytic activity toward HER, OER and UOR. • A V 8 C 7 /CoP-AAAE was set up for energy-saving electrolytic hydrogen production. Hydrogen production via water electrolysis for large scale application is still limited majorly by the huge energy consumption and high cost of catalyst materials. In this work, with rationally designing V/Co metal-organic framework (V/Co-MOF) as a precursor, a series of V 8 C 7 decorating CoP nanosheets-assembled microspheres (V 8 C 7 /CoP) was synthesized via pyrolysis and a subsequent phosphidation. Thanks to the synergistic effect between V 8 C 7 and CoP, the optimized V 8 C 7 /CoP as trifunctional catalysts exhibit remarkable performance toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and urea oxidation reaction (UOR). More importantly, we propose an acid-alkaline asymmetric-electrolyte electrolyzer (AAAE) by using the optimized V 8 C 7 /CoP electrode as both acidic cathode for HER and alkaline anode UOR, respectively. The optimum AAAE system only needs an applied voltage of 0.8 V to reach an electrolytic current density of 10 mA cm−2 for hydrogen production, which significantly reduces the energy consumption for hydrogen production owing to the assistance of electrochemical neutralization energy (ENE) and electrochemical urea oxidation energy. [ABSTRACT FROM AUTHOR]

• RuCo@NG/N-GNs catalyst were fabricated via one-step annealing strategy. • RuCo@NG/N-GNs holds unique structure and plenty of active sites. • RuCo@NG/N-GNs exhibits a top-level acidic OER and alkaline HER performance. • DFT calculations reveals the critical role of Co in enhancing HER and OER. There remain certain critical issues for hydrogen production in both proton exchange membrane (PEM) and alkaline water electrolysis, the former of which faces daunting challenges in the development of high-activity and high-stability catalysts for acidic oxygen evolution reaction (OER), while the latter one strongly demands enhancing the sluggish kinetic of alkaline cathodic hydrogen evolution reaction (HER). Herein, we reported a facile one-step annealing strategy for fabricating hybrid electrocatalyst with RuCo alloy nanoparticles encapsulated by N-doped graphite loading on N-doped graphite nanosheets (RuCo@NG/N-GNs), which manifests highly desirable electrocatalytic features toward both acidic OER and alkaline HER with impressively high activity, fast kinetic and excellent stability. The optimized RuCo@NG/N-GNs requires a quite low overpotential of 209 mV at 10 mA cm−2 for acidic OER with a quite low Tafel slope of 56 mV dec−1, and demands a striking low overpotentials of 9 mV at 10 mA cm−2 toward alkaline HER with a Tafel slope of as low as 30 mV dec−1. Experiments combined with density functional theory (DFT) calculations reveal that the critical role of Co element in enhancing the HER and OER performance. For HER, the surface Co improves the oxophilicity of catalyst that indirectly aids the proton donation in alkaline; and for OER, surface Co itself acts as active sites to directly aid the reaction. The relatively low-cost electrocatalyst in this work is expected to inspire more innovative researches to step forward the large-scale commercial practice feasibility of PEM and alkaline water splitting. [ABSTRACT FROM AUTHOR]