Synergistic In-Layer Cobalt Doping and Interlayer Iron Intercalation into Layered MnO₂ Produces an Efficient Water Oxidation Electrocatalyst

Described is a synthetic method to enhance the electrocatalytic activity of the layered manganese oxide, birnessite, for the oxygen evolution reaction (OER) through the development of a Mn/Co/Fe ternary phase. The ternary phase was synthesized by the simultaneous doping of Co3+ into the manganese oxide lattice and intercalation of Fe2+ within the interlayer region of birnessite (KxFe[Co0.16Mn0.84O2]). The material was characterized by X-ray diffractometry, electron microscopy, X-ray photoelectron, energy dispersive, and Raman spectroscopies and electrochemical analysis. The KxFe[Co0.16Mn0.84O2] material demonstrated efficient OER electrocatalysis with an overpotential (η) of 375 mV (at 10 mA/cm2) and Tafel slope (b) of 56 mV/dec, surpassing the catalytic activity of both standard potassium birnessite (η ≈ 800 mV, b = 240 mV/dec) and cobalt-doped birnessite with a Co:Mn ratio of 1:5 (η ≈ 750 mV, b = 230 mV/dec) and with a catalytic lifetime 150-fold greater than that of standard birnessite and 100-fold greater than that of the iron-free cobalt-doped birnessite at 5 mA/cm2.