In situ growth of S-incorporated CoNiFe(oxy)hydroxide nanoarrays as efficient multifunctional electrocatalysts

Abstract

Ni-, Co-based (oxy)hydroxides have received considerable attentions as promising electrocatalysts for the oxygen evolution reaction (OER), urea oxidation reaction (UOR), and even overall urea/water splitting. Constructing catalysts with a special morphological and electronic structure is still an effective strategy to further enhance their electrocatalytic performances. Herein, we report a facile, versatile, and scalable method to grow S-incorporated CoNiFe(oxy)hydroxides (CoNiFeS–OH) nanosheets on needle-like CoNi(oxy)hydroxides (CoNi–OH) nanoarrays under hydrothermal conditions. The special morphology provided more active sites and facilitated mass transfer. In particular, Fe and S incorporation modified the electronic structure of CoNi–OH, boosts its electronic conductivity, provided metals in high valent states, and created a crystalline/amorphous phase interface, thus intrinsically improving the electrocatalytic performance toward OER, UOR, and even overall water splitting/urea electrolysis. The CoNiFeS–OH nanosheets therefore showed superior OER activity with a low overpotential of 192 and 272 mV to reach a current density of 10 and 100 mA cm⁻², respectively. For UOR, the potential was measured to be as low as 1.329 and 1.373 V at a current density of 10 and 100 mA cm⁻², respectively. Furthermore, a quite low cell voltages of 1.571 and 1.461 V for overall water splitting and overall urea electrolysis were respectively detected to reach a current density of 10 mA cm⁻², which were superior to the benchmark Pt/C//RuO₂ and other reported Ni, Co-based (oxy)hydroxides. More importantly, the voltage differences required for overall urea electrolysis and overall water splitting at a current density of 10 and 100 mA cm⁻² were 0.110 and 0.153 V. Additionally, the CoNiFeS–OH electrocatalysts also showed great stability during long-term (20 h) and cycling (1000 cycles) measurements.