Constructing nanoporous crystalline/amorphous NiFe2O4/NiO electrocatalyst for high efficiency OER/UOR

Exploring highly efficient, stable and durable electrocatalysts for oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is a challenging task for energy-saving H2 generation during water electrolysis. Herein, a rose-like crystalline/amorphous heterostructure of NiFe2O4/NiO/NF grown on Ni-foam (NF) was synthesized via a simple two-step (i.e., hydrothermal-annealing) pathway. The as-synthesized NiFe2O4/NiO/NF catalyst presents outstanding electrocatalytic performance towards OER with small overpotentials of 122 and 145 mV to deliver 20 and 100 mA cm−2 current densities in 1.0 M KOH electrolyte, respectively. Further, the electrocatalyst revealed robust stability for over 168 h. For UOR, ultra-low potentials of 1.181 and 1.315 V (vs. the RHE) are required at current densities of 10 and 100 mA cm−2, relatively lower than those required for the OER process. Furthermore, employing the NiFe2O4/NiO/NF catalyst as an anode and Pt/C/NF as a cathode in 1 M KOH electrolyte, only 1.356 and 1.498 V is required to drive current densities of 10 mA cm-2 and 300 mA cm-2 during the overall water splitting reaction. Significantly, the urea electrolyzer presents ultra-low cell voltages of 1.218 and 1.490 V at 10 and 300 mA cm−2 current densities, respectively. The performance of the electrocatalyst is better than many of the reported transition-metal based electrocatalysts and even superior to most of the noble metal-based electrocatalysts. This work presents a solid step for the cost-effective and energy-saving hydrogen generation.