Template Electro-Etching-Mediated FeOOH Nanotubes as Highly Efficient Photoactive Electrocatalysts for Oxygen Evolution Reaction

A fast, controlled, and low-cost technique for synthesis of catalysts with (photo)electrochemical oxygen evolution reaction (OER) activity is the key to developing (solar) electricity-driven water splitting. Here, we design a template electro-etching strategy to fabricate uniform FeOOH nanotubes (CC@FeOOH-NTs) as photoactive electrocatalysts, where the in situ conversion process of template etching and electrodeposition completes in less than 400 s. The structural stability of the nanotubes' morphology and phase transition from β-FeOOH to amorphous after thermal treatments are both determining factors to improve the activity and stability. The optimized CC@FeOOH-NTs-240 °C presents a low overpotential (η) of 328 mV, to achieve a current density of 10 mA cm^-2 with a small Tafel slope of 42 mV dec^-1, and maintains its structural integrity and catalytic activity after 15 h. Under visible light irradiation, the photon-excited charge carriers decrease the overpotential to 280 mV (onset) and increase the current density to 16 mA cm^-2 (η = 343 mV), 2.7 times higher than the value in the darkness.