Molten Salt Assisted Ni‐Doped α‐FeOOH on Regulating Spin State for Efficient Oxygen Evolution Reactions

Abstract α‐FeOOH is a promising catalyst for oxygen evolution reaction (OER). However, owing to the high spin state (HS, t 2g 3 e g 2 ) of Fe 3+ in typical α‐FeOOH structure, the bonding strength of oxygen‐containing intermediates are usually too strong. In this work, the successful synthesis of intermediate spin state (IS) Fe 3+ in α‐FeOOH structure on iron foam (IF) by introducing Ni atom is reported. Refined structural analysis and theoretical calculations reveal that doped‐Ni atom enlarged the d orbital splitting energy, thus converting the crystal field stable HS Fe 3+ state to intermediate spin state. The IS Fe 3+ optimized the adsorption energy of oxygen‐containing intermediates and reduced the reaction energy barrier of rate‐determining step (RDS, O* to OOH*). Moreover, the doped Ni reduced the generation of Fe 4+ during OER, combined with the amorphous layer formed by the molten salt method, inhibiting the dissolution of Fe. The as‐obtained catalyst exhibited excellent OER activity with an overpotential of 178 mV at 10 mA cm −2 and a Tafel slope of 27 mV dec −1 , which outperforms those of the state‐of‐the‐art iron oxyhydroxides catalysts. In this paper, a fast and efficient method for the construction of a low‐cost and high‐activity iron‐based OER catalyst is provided.