Unveiling the transformation of CoNi hydroxides to CoNiFe layered double hydroxides with implications for electron modulation in one-step coprecipitation for efficient oxygen evolution electrocatalysis

It is a significant challenge to achieve state-of-the-art trimetallic layered double hydroxide (LDH) electrocatalysts with high activity and stability in the oxygen evolution reaction (OER) without compromising conductivity. This can be overcome by fine-tuning the local structure and electron modulation in the materials. Herein, we report the one-pot synthesis of CoNiFeLDH using a coprecipitation method under ambient conditions, and determine the metal ion substitution, crystal phase transformation and electronic rearrangement upon the introduction of relatively highly electronegative iron into CoNi hydroxides. CoNiFeLDH was evolved as a sheet-like structure, as shown by TEM analysis, and exhibited an increased surface area of 185 m² g^-1, around 2.85 times higher than that of CoNi hydroxide (65 m² g^-1). In OER electrolysis, the material exhibited a reduced overpotential of 280 mV at 10 mA cm^-2, 73 mV lower than that of CoNi hydroxides, and exhibited a high turnover frequency (TOF) of 2.6 s^-1. The superior activity of CoNiFeLDH was also assessed using the decreased Tafel slope of 60 mV dec^-1, impressive mass activity of 737 A g^-1 at a 350 mV overpotential and high stability in constant current electrolysis for 12 h. The facile electron delocalisation routes in Fe-O-Ni and Fe-O-Co and a high surface area of CoNiFeLDH are reasons for the enhanced OER activity.