Electronic structure modulation of nickel hydroxide porous nanowire arrays via manganese doping for urea-assisted energy-efficient hydrogen generation

Abstract

Replacement of the sluggish anodic reaction in water electrocatalysis by a thermodynamically favorable urea oxidation reaction (UOR) offers the prospect of energy-saving H2 generation, additionally mitigating urea-rich wastewater pollution, whereas the lack of highly efficient and earth-abundant UOR catalysts severely restricts widespread use of this catalytic system. Herein, Mn-doped nickel hydroxide porous nanowire arrays (denoted Mn-Ni(OH)2 PNAs) are rationally developed and evaluated as efficient catalysts for the UOR in an alkaline solution via the in situ electrochemical conversion of NiMn-based metal–organic frameworks. Mn doping can modulate the electronic structural configuration of Ni(OH)2 to significantly increase the electron density and optimize the energy barriers of the CO*/NH2* intermediates of the UOR. Meanwhile, porous nanowire arrays will afford abundant spaces/channels to facilitate active site exposure and electron/mass transfer. As a result, the Mn-Ni(OH)2 PNAs delivered superior UOR performance with a small potential of 1.37 V vs. RHE at 50 mA cm−2, a Tafel slope of 31 mV dec-1, and robust stability. Notably, the overall urea electrolysis system coupled with a commercial Pt/C cathode demonstrated excellent activity (1.40 V at 20 mA cm−2) and durability operation (only 1.40% decay after 48 h).