FeNi-Layered Double-Hydroxide Nanoflakes with Potential for Intrinsically High Water-Oxidation Catalytic Activity

Oxygen-evolution-reaction (OER) and oxygen-reduction-reaction (ORR) catalysts on a gas-diffusion carbon paper (CP) electrode have been explored as a current hot topic. Low-cost and earth-abundant FeNi (oxy)­hydroxides have the potential to be the best-performing OER catalyst families. Here, we report on Fe-rich FeNi-layered double-hydroxide (LDH) nanoflakes (Fe/Ni = 1:1.5 mol/mol) with a sheet dimension of 10–20 nm and bearing an increased number of OER-active sites. An aqueous dispersion solution of FeNi Prussian blue analog nanoparticles (PBA NPs) is drop-cast on CP, and their metal compositions and microgram-scale mass-loading amounts are systematically controlled. The PBA NPs are transformed into LDH nanoflakes in an alkaline aqueous solution. To the best of our knowledge, compared to the previously reported catalysts, the LDH nanoflakes intrinsically show potential comparable to that of catalysts with the highest activity, based on the lowest Tafel slope (15.1 mV dec–1) and the highest values of turnover frequency (1.58 s–1) and mass activity (10 600 A g–1) at a low overpotential of 300 mV. Drop-coated Mn2+ ions significantly enhance the intrinsic ORR activity of CP. The independently optimized OER and ORR catalysts are united on the same sheet of CP as a bifunctional pair.