Heterogeneous Ni-MoN nanosheet-assembled microspheres for urea-assisted hydrogen production.

Electrocatalytic water splitting is a promising technology for sustainable hydrogen (H) production; however, it is restricted by the kinetically sluggish anodic oxygen evolution reaction (OER). Replacing OER with urea oxidation reaction (UOR) with low thermodynamic potential can simultaneously improve the energy efficiency of H production and purify urea-containing wastewater. Here we report a facile assembly-calcination two-step method to synthesize heterogeneous Ni-MoN nanosheet-assembled microspheres (Ni-MoN NAMs). The nanosheet-assembled structure and the synergistic metallic Ni-MoN heterogeneous interface endow the Ni-MoN NAMs with good OER (1.52 V@10 mA cm), UOR (1.28 V@10 mA cm), and hydrogen evolution reaction (HER, 0.16 V@10 mA cm) activity. The two-electrode urea electrolysis cell with Ni-MoN NAMs as both the cathode and anode requires an extremely low cell voltage of 1.41 V to afford 20 mA cm, which is 0.3 V lower than that of the water electrolyzer, paving the way for energy-saving H production.