Phase segregation reversibility in mixed-metal hydroxide water oxidation catalysts

Achieving stable, low-cost electrocatalysts represents a daunting challenge towards practical water oxidation reactions. Here, we report that a degraded electrocatalyst can be revivified under catalytic operating conditions by manipulating reversible phase segregation. Under the oxygen evolution reaction conditions, Fe segregation develops in the Ni–Fe hydroxide host lattice, with the formation of FeOOH, resulting in an interface between the FeOOH and the host lattice. A dynamic metal dissolution–redeposition process accelerates the Fe segregation and formation of the FeOOH secondary phase, resulting in catalyst deactivation. Operando synchrotron spectroscopic and microscopic analyses suggest that the phase segregation is reversible between the water oxidation potential and the catalyst reduction potential. Therefore, we have developed an intermittent reduction methodology to revivify the catalytic activity under the operating conditions, enhancing catalyst durability. The present study highlights that tailoring phase segregation at the catalyst/electrolyte interface constitutes an important strategy for revivifying and stabilizing catalytic activity. Achieving long-term stability of water oxidation electrocatalysts remains a formidable challenge. Now, an in situ electrochemical reduction strategy to revivify mixed Ni–Fe hydroxide catalysts by reversible phase segregation is presented.