Organic-inorganic hybrids of Fe-Co polyphenolic network wrapped Fe3O4 nanocatalysts for significantly enhanced oxygen evolution

The design of organic-inorganic hybrid nanostructures with carefully balanced properties is a promising approach for constructing advanced electrocatalysts using earth abundant elements. Here we describe hybrid electrocatalysts that have strongly coupled metal (Co-Fe) polyphenolic networks (MPNs) and Fe3O4 nanoparticles for catalyzing the oxygen evolution reaction (OER) with exceptional activity. These catalysts were produced by a tannic acid (TA) mediated conversion process that selectively converts the surface layers of pre-synthesized zeolitic imidazole framework-67 (ZIF-67)@Fe3O4 core-shell nanoparticles to uniformly wrapped organic MPN layers. The MPN layers are composed of metal-phenolic complexes that are rich in molecular metal hydro(oxy)oxide (M-OH, M-O-M) centers that not only increase the electrochemical surface area by approximately four times but also serve as highly active sites for the OER. As a result of the structural and compositional benefits, the hybrid catalysts only require an overpotential of 260 mV to produce oxygen at 10 mA cm(-2) and have a Tafel slope of only 33.6 mV dec(-1) in alkaline electrolytes, which are the lowest when compared with pristine ZIF-67@Fe3O4, Fe3O4 and the benchmark IrO2 catalysts.