Heterostructured Mn-doped NiSx/NiO/Ni3N nanoplate arrays as bifunctional electrocatalysts for energy-saving hydrogen production and urea degradation

Urea oxidation reaction (UOR) instead of sluggish oxygen evolution reaction (OER) is a desirable approach to hydrogen production with reduced energy consumption, but developing an efficient bifunctional electrocatalyst for both HER and UOR is still a challenge. Here we report a Mn-doped NiSx/NiO/Ni3N nanosheets arrays loaded on nickel foam (denoted by Mn-NiSx/NiO/Ni3N@NF) catalyst through a simple hydrothermal and thiourea-assisted solid reaction. Benefitting from the densely interlaced network structure and plentiful heterojunctions induced by Mn dopant, Mn-NiSx/NiO/Ni3N@NF displays a superior HER and UOR activity. In the alkaline urea electrolyte, a low potential of 93 mV (for HER) and 1.31 V (for UOR) are needed to achieve 10 mA cm−2. Assembled in a symmetrical two-electrode electrolyzer, Mn-NiSx/NiO/Ni3N@NF can require a cell voltage of 1.70 V to deliver 100 mA cm−2 in alkaline urea medium, reducing by 200 and 239 mV in contrast with the commercial Pt/C@NF||RuO2@NF couple and the conventional water splitting, respectively. Furthermore, Mn-NiSx/NiO/Ni3N@NF as UOR electrode can impel urea removal rate reach up 56% after a successive operation for 32 h. The work provides a green and sustainable strategy from sewage treatment to recycling accompanied by energy-saving hydrogen production and urea-rich wastewater degradation.