Formamide-assisted synthesis of phosphate-intercalated Ni(OH)₂/NiOOH electrode for boosting oxygen evolution reaction

Electrochemical water splitting (EWS) represents a promising method for green hydrogen production. However, the commercial viability of this approach is significantly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Layered Ni(OH)₂/NiOOH serves as a low-cost and effective OER electrocatalyst, yet the activity and stability do not meet the requirements for commercial EWS, particularly in terms of operational stability under high current densities. Herein, we report a phosphate-intercalated (Pi) Ni(OH)₂/NiOOH synthesized with the assistance of formamide (FA), termed NiOH-Pi-FA, which demonstrates significantly-enhanced OER performance. Systematic investigations reveal that FA facilitates phosphate intercalation, which improves OER via lattice oxygen oxidation, interlayer proton transport, electrode conductivity, electrode surface wetting and O₂ bubbles release. More importantly, FA alters the catalyst's morphology, creating a porous structure and reducing catalyst particle size, which decreases the interlayer proton transport distance. FA also increases the surface roughness, promoting the release of O₂ bubbles. Consequently, the OER performance of NiOH-Pi-FA is much better than that of Ni(OH)₂/NiOOH prepared without FA (NiOH-Pi). It achieves overpotentials of 106 and 223 mV at current densities of 10 and 100 mA cm^-2, respectively, and maintains exceptional stability at 350-330 mA cm^-2 for over 400 h. Overall, the OER performance of NiOH-Pi-FA surpasses that of RuO₂ and other Ni-based hydroxide electrocatalysts, offering valuable insights for designing efficient and stable OER catalysts.