Energy-saving hydrogen production coupling urea oxidation over a bifunctional nickel-molybdenum nanotube array

Hydrogen production via water electrolysis is promising but impeded by sluggish cathodic and anodic reactions. Consequently, highly-efficient and earth-abundant electrocatalysts are attracting considerable attention. Herein we report a bifunctional NiMo alloy nanotube for efficient hydrogen production coupled with anodic urea oxidation in a hybrid water electrolysis system. Specifically, ultralow potentials of −44 mV and 1.36 V (vs. RHE) are required to deliver 10 mA cm−2 current density for cathodic and anodic reactions, respectively. Density functional theory (DFT) calculation results show the Mo center is the main reaction site for the chemisorption and OH bond cleavage of H2O while Ni center is identified as the hydrogen-evolving site. Based on this bifunctional NiMo electrocatalyst, a hybrid water electrolysis cell is proposed and the overall cell voltage of ∼1.43 V is achieved for outputting 10 mA cm−2 current density during the 10 h operation. The understandings in alternative electrode reactions coupled with highly-efficient and earth-abundant electrocatalysts for hybrid water electrolysis in this work holds encouraging potential in future energy conversion technologies and urea-related water treatments.