Low-temperature etch synthesis of Fe-doped Ni(OH)₂ for enhanced bifunctional water splitting

The development of electrocatalyst preparation methods that are straightforward, efficient, and energy-saving is crucial for the large-scale production and application of hydrogen energy. This study introduces a low-temperature etching-assisted synthesis approach to fabricate iron-doped nickel hydroxide (Fe-Ni(OH)₂) bifunctional electrocatalysts for overall water splitting. The catalysts synthesized using this low-temperature method tend to form a composite structure consisting of nanosheets and nanoflowers, along with a mixed phase of crystalline and amorphous materials. This unique combination significantly enhances electron transport and increases the number of active sites. Furthermore, iron doping promotes the formation of high-valent nickel species, resulting in the coexistence of NiFe bimetallic hydroxides (Ni(Fe)LDH) and NiFe oxyhydroxides (Ni(Fe)OOH) within the catalyst. This coexistence ensures exceptional performance in both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) under alkaline conditions. Notably, the overpotentials for the HER and OER at a current density of 10 mA cm⁻² in a 1.0 M KOH solution are as low as 92 mV and 232 mV, respectively. Moreover, the Fe-Ni(OH)₂/NF catalyst demonstrates superior overall water splitting performance, achieving a cell voltage of just 1.59 V at a current density of 10 mA cm⁻². This work not only explores the synthesis of nickel-iron-based electrocatalysts through low-temperature etching but also provides an in-depth discussion of the overall water splitting mechanism, offering insights for the design of highly efficient catalysts for overall water splitting.