Formation of hierarchical NiFe Prussian blue analogues/Prussian blue on nickel foam for superior water oxidation

A series of NiFe Prussian blue analogues (PBAs)/Prussian blue (PB) nanocubes (NizFe-PB-x-y) on nickel foam were synthesized using a one-pot redox reaction and deposition strategy. The growth and particle size of NizFe-PB-x-y can be adjusted by changing the ammonium persulfate concentration (x) and hydrothermal temperature (y). To explore the role of individual reactants, three other catalysts were synthesized by changing the reaction conditions, including sea urchin-like FeOOH, Fe4[Fe(CN)6]3 cube, and NiFe PBA/FeOOH grain. During the reaction, ammonium persulfate may acted as a promoter and oxidant, sodium citrate as a reducing agent and morphological regulator, potassium ferricyanide as a single iron source, and nickel foam as a nickel source and substrate. More importantly, compared with other catalysts, the electrochemically activated Ni0.59Fe-PB-3-110 catalyst manifests the most outstanding catalytic activity in 1.0 M KOH electrolyte solution, with current densities of 50 and 800 mA cm−2, requiring only 230 and 305 mV overpotential, respectively. It is anticipated that the novel strategy will not only contribute to the design and development of hierarchical three-dimensional PB or PBAs supported by conductive substrates, but also further promote their applications in the field of electrocatalysis and energy storage.