Electrochemical evolution of cobalt-carboxylate framework for efficient water oxidation

Abstract The overall water splitting is severely limited by the sluggish oxygen evolution reaction (OER), which further restricts the large-scale production of hydrogen for sustainable energy. These transition metal-based (oxy)hydroxides (TM(O)OH) are recognized as the most efficient non-noble electrocatalysts for OER, but the rational design and fabrication of TM(O)OH species remain a big challenge. Here we have synthesized a porous metal-organic framework (MOF, CoHKUST-1), and the rapid degradation of this MOF itself in alkaline solution is intrinsically stemmed from the metastable nature of the Co–O coordination bonds in the Co-based paddle wheel. By simply applying an electric potential, these synthesized Co-MOFs can be decomposed into the 2-dimensional nanosheet structure mainly consisting Co(OH)2 and CoOOH. The resulting CoOxHy nanosheets exhibit excellent OER performance to reach an overpotential of only 344 mV at 10 mA cm−2, and its Tafel slope is calculated to be 66.4 mV dec−1 indicating the fast reaction kinetics. The structural and morphological evolution under electrolysis is further proposed and evidenced by relevant physicochemical characterizations and theoretical calculations. The demonstrated work proves a feasible strategy for electrochemical design and fabrication of 2-dimensional TM(O)OH nanosheets for efficient water oxidation, which can be further applied in the future energy applications.