Electric-Field Assisted Hydrolysis-Oxidation of MOFs: Hierarchical Ternary (Oxy)hydroxide Micro-Flowers for Efficient...

Water oxidation is the key process of electrocatalytic water splitting owing to its inherently slow kinetics. The ingenious design of microstructures for oxygen evolution reaction (OER) catalysts is an important way to accelerate the kinetics of the water splitting reaction. In this work, a facile electric-field assisted alkaline hydrolysis-oxidation strategy is proposed to prepare 3D layered micro-flowers in situ constructed from ultra-thin CoNiFe (oxy)hydroxide (CoNiFe-OH) hexagonal plates by using Co/Ni/Fe metal-organic frameworks (MOFs) as sacrificial templates and metal sources. The growth of the ballflowers can be accurately controlled by matching the hydrolysis rate of MOFs templates and the coprecipitation rate of metal ions. More importantly, continuous oxidation voltage can drive transformation of some hydroxides into oxyhydroxide with abundant oxygen vacancies. Benefiting from the open structure with multiple electroactive sites and optimized chemical composition, the layered CoNiFe-OH micro-flowers show appealing OER electrocatalytic performance with a low overpotential of 207 mV@10 mA cm^-2 and robust durability over 60 h. This work provides a strategy to prepare non-noble hierarchical nanostructured electrocatalysts for electrochemical energy conversion.