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

Electrocatalytic water splitting is a promising technology for sustainable hydrogen (H2) 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 H2 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-2), UOR (1.28 V@10 mA cm-2), and hydrogen evolution reaction (HER, 0.16 V@10 mA cm-2) 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-2, which is 0.3 V lower than that of the water electrolyzer, paving the way for energy-saving H2 production.