Fe, Co-induced hydrolysis to prepare α-Ni (OH)2/β-Ni(OH)2 interfaces for improved overall water splitting efficiency

The development of effective bifunctional electrode materials is necessary for worldwide adoption of large-scale hydrogen production by water electrolysis. Nickel hydroxide - based transition metal materials are among the most promising electrodes for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). While Ni(OH)2 exists in two crystalline states, namely α-Ni(OH)2 and β-Ni(OH)2, neither can meet requirements for effective bifunctional electrode materials on their own, due to relatively low catalytic activity. In this study, bifunctional catalysts with α-Ni(OH)2/β-Ni(OH)2 interfaces, prepared using Fe, Co-induced hydrolysis, have been successfully applied for electrolytic water splitting. According to physical characterization, Fe3+ and Co2+ are incorporated into Ni(OH)2 layers, where Fe doping leads to the formation of a regular flake structure, while Co doping facilitates surface electron transfer, enhancing electrocatalytic activity towards HER and OER. Overpotentials of the obtained catalysts at 100 mA·cm−2 are as low as 224 mV for HER and 324 mV for OER. Both HER and OER overpotentials remained almost unchanged after 24 h operation at a high current density of 1 A·cm−2, demonstrating excellent stability of the newly prepared materials during water electrolysis. The synthesis of α-Ni(OH)2/β-Ni(OH)2 interfaces is a new direction for the manufacturing of industrially applicable water splitting electrocatalysts suitable for high current density operation.