Novel Cobalt Germanium Hydroxide for Electrochemical Water Oxidation

Developing efficient and stable oxygen evolution catalyst (OEC) is a critical step to overcome the sluggish kinetics of water oxidation. Here, we hydrothermally synthesized a novel OEC, cobalt germanium hydroxide, CoGeO₂(OH)₂. The inherent Co-bonded hydroxyl groups facilitate the formation of active oxygen evolution reaction intermediates. Meanwhile, the facile leaching of Ge at the OEC-electrolyte interface contributes to surface reconstruction, generating Co-based (oxy)hydroxides, which would weaken its lattice constraint and suppress the excessive corrosion in the OEC bulk. As a result, CoGeO₂(OH)₂ reveals good catalytic activity and stability. This CoGe-based OEC achieves the overpotential at 10 mA cm^-2 (η_@10mA) of ∼340 mV, and the turnover frequency of ∼0.08 s^-1. And the electrolysis kept at ∼10 mA cm^-2 could be sustained for over 350 h. In addition, this p-type CoGeO₂(OH)₂ is demonstrated to be an effective electrocatalytic overlayer on n-type Ta₃N₅ photoanode, remarkably decreasing the onset for nearly 400 mV and increasing the photocurrent density at 1.23 V_RHE about 3.8 times.