Hierarchical Ni/Ni4Mo nanosheets array on carbon fiber as a bifunctional electrocatalyst for urea-oxidation-assisted water splitting

Abstract

Designing and constructing hierarchical structures to enhance electron transfer, electrolyte transport and product release in electrocatalytic reactions can effectively improve electrocatalytic performance of transition metal-based catalysts. Herein, a novel nanostructured electrode consisting of hierarchical Ni/Ni4Mo nanosheets array grown on carbon fiber (CF@Ni/Ni4Mo) has been designed and synthesized. Smaller Ni4Mo nanonets are distributed on Ni nanosheet surface, and this hierarchical nanosheets array structure can expose abundant active sites (nickel oxide/hydroxide for urea oxidation reaction (UOR) and Ni4Mo for hydrogen evolution reaction (HER)) and ensure multi-channel transport of electrolyte and gaseous products in electrocatalytic reaction. Moreover, the Ni nanosheet skeleton facilitates speedy electron transmit to/from catalytic sites. The optimal CF@Ni/Ni4Mo-5 electrode exhibits remarkable catalytic activity with requiring only 1.396 V and −0.095 V to drive 100 mA cm−2 toward UOR and HER, respectively, in 1.0 M KOH with 0.5 M urea. Furthermore, the overall urea-electrolysis system based on CF@Ni/Ni4Mo-5 as bifunctional electrode can achieve 100 mA cm−2 by only need 1.579 V, which can easily be powered by a commercial mercury-flee alkaline battery.