Solvent effect on facile in situ precipitation of nickel–iron hydroxide for enhanced overall water splitting

Abstract

Efficient and economical electrocatalysts are essential for addressing the high overpotential challenges of the oxygen evolution reaction (OER) in electrochemical water splitting. This study explores the synthesis of nickel–iron hydroxide (NiFeOH) catalysts via in situ precipitation, focusing on the impact of the solvent composition on the morphology and catalytic performance of the material. The volumetric ratio of H₂O to ethanol in the solvent mixture was systematically varied, revealing that higher proportions of H₂O promoted the formation of thicker and larger needle-like NiFeOH structures. In contrast with the common preference for thin needle-shaped morphologies, our findings reveal that these thicker structures exhibit superior electrocatalytic activity. This enhanced performance is attributed to the higher iron content and faster reaction kinetics promoted by the increased permittivity of water-rich environments. The optimized NiFeOH catalysts, particularly those with higher water content, exhibit excellent OER and hydrogen evolution reaction (HER) activities, achieving low overpotentials of 288 mV at 100 mA cm⁻² for OER and 131 mV at 10 mA cm⁻² for HER. Furthermore, long-term stability tests confirmed the robustness of the catalysts, with minimal morphological degradation and consistent performance in overall water splitting. This work highlights the significance of solvent effects in tailoring the morphology and catalytic properties of NiFeOH, providing valuable insights for the design of effective water-splitting electrocatalysts.