Abstract
Trimetallic double hydroxide NiFeCo−OH is prepared by coprecipitation, from which three different catalysts are fabricated by different heat treatments, all at 350 °C maximum temperature. Among the prepared catalysts, the one prepared at a heating and cooling rate of 2 °C min−1 in N2 atmosphere (designated NiFeCo−N2‐2 °C) displays the best catalytic properties after stability testing, exhibiting a high current density (9.06 mA cm−2 at 320 mV), low Tafel slope (72.9 mV dec−1), good stability (over 20 h), high turnover frequency (0.304 s−1), and high mass activity (46.52 A g−1 at 320 mV). Stability tests reveal that the hydroxide phase is less suitable for long‐term use than catalysts with an oxide phase. Two causes are identified for the loss of stability in the hydroxide phase: a) Modeling of the distribution function of relaxation times (DFRT) reveals the increase in resistance contributed by various relaxation processes; b) density functional theory (DFT) surface energy calculations reveal that the higher surface energy of the hydroxide‐phase catalyst impairs the stability. These findings represent a new strategy to optimize catalysts for water splitting.