In-situ identification and dynamic transformation of FeOOH with different phases for oxygen evolution reaction

Abstract

Iron(III) oxyhydroxide (FeOOH) is a highly promising non-precious metal oxygen evolution reaction (OER) catalyst due to its abundance, cost-effectiveness, and favorable electrochemical characteristics. Nevertheless, its low electrical conductivity and sluggish OER kinetics pose significant challenges for practical applications. OER typically occurs through the adsorbed evolution mechanism (AEM), involving multiple proton-coupled electron transfer steps with higher theoretical overpotential requirements. In contrast, the lattice oxygen mechanism (LOM) facilitates oxygen generation through direct coupling of the O−O bond, potentially circumventing the thermodynamic constraints inherent in AEM. In this study, an effective ion exchange between small-sized anions with large dipole moments and chloride ions residing within the tunnels of β-FeOOH was successfully achieved through phase-induced oxygen defect engineering. The experimental findings demonstrate that the synthesized α/β-FeOOH with high-density oxygen vacancy (O_V) exhibits enhanced lattice oxygen redox reactivity, expedited OER kinetics, and reduced thermodynamic barriers. Those improvements are ascribed to the activation of lattice oxygen within FeOOH, which has triggered a transition in its OER mechanism from AEM to LOM. Further investigations suggest that elevated reaction temperatures, within an appropriate range, foster ion exchange in β-FeOOH channels and actively encourage the creation of O_V in FeOOH. That dynamic behavior transition of FeOOH enables it to overcome the inherent thermodynamic limitations of the AEM, resulting in a remarkable enhancement of its intrinsic OER activity. Remarkably, this improvement is achieved without relying on additional co-catalysts, which is expected to promote the understanding of intrinsic kinetic alterations in FeOOH electrocatalysts.