Constructing Hierarchical Fluffy CoO–Co4N@NiFe-LDH Nanorod Arrays for Highly Effective Overall Water Splitting and Urea Electrolysis

Exploration of highly efficient bifunctional electrocatalysts for optimal hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been widely carried out, though it still remains a big challenge. Herein, a hierarchical CoO–Co4N@NiFe-LDH (layered-double-hydroxides) heterostructure electrode anchored on nickel foam (NF) is prepared via a developed three-step hydrothermal–nitridation–electrodeposition pathway. The fabricated CoO–Co4N@NiFe-LDH/NF electrode needs low overpotential values of 66 and 231 mV to supply a current density value of 10 mA cm–2 in aqueous solution of KOH (1 M) for HER and OER, respectively. The Tafel slopes and electrochemical impedance spectroscopy results display favorable reaction kinetics throughout the electrolysis process. Subsequently, an alkaline electrolyzer is assembled with CoO–Co4N@NiFe-LDH/NF, which serves both as the anode and cathode, yielding 10 mA cm–2 with a small voltage of 1.529 V and showing a robust stability for 28 h. Impressively, a urine-mediated electrolysis cell shows efficient catalytic activity as well, allowing to mount the sluggish OER during water splitting. To drive the urine-mediated electrolysis cell containing 0.33 M urea, a low voltage of 1.393 V is required, which is about 136 mV lower compared to the urea-free electrolysis cell. This work presents a solid step for the electrocatalytic generation of hydrogen through water splitting by harvesting low energy.