V8C7 decorating CoP nanosheets-assembled microspheres as trifunctional catalysts toward energy-saving electrolytic hydrogen production.

• 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]