Understanding the Phase-Induced Electrocatalytic Oxygen Evolution Reaction Activity on FeOOH Nanostructures

The crystalline phase plays a crucial, yet not well-understood, role in enhancing the oxygen evolution reaction (OER) performance of iron oxyhydroxide (FeOOH) materials. Herein, single-phase (α-, β-, and δ-) and mixed-phase (α/β-, α/δ-, and β/δ-) FeOOH nanostructures have been successfully synthesized through a controlled solvothermal route. Combined analyses of X-ray photoelectron spectroscopy and partial density of state calculation suggest that rich oxygen vacancies confined in the mixed-phase FeOOH samples (with optimized electronic structure) can effectively improve the OER activity. Notably, the mixed phase of β/δ-FeOOH displays an enhanced OER activity and stability in the alkaline media, with a very low overpotential of ∼180 mV vs a reversible hydrogen electrode at 10 mA cm^-2. Understanding of the phase-induced activity may also pave a pathway for the design and synthesis of highly efficient electrocatalysts.