Cobalt-substituted iron-based wolframite synthesized via polyol route for efficient oxygen evolution reaction

Binary tungsten oxides with a wolframite crystal structure, such as FeWO4 and CoWO4, have poor electrocatalytic activity for the oxygen evolution reaction (OER). However, the incorporation of a third element into the crystalline framework increased the OER activity in an alkaline medium. Specifically, Co0.5Fe0.5WO4 prepared through a polyol route generated a current density of 10 mA cm(-2) at a considerably small overpotential (eta) and Tafel slope (331 mV and 36.8 mV dec(-1), respectively). This overpotential value was superior to those of Co0.5Fe0.5WO4 fabricated through a conventional hydrothermal route (eta at 10 mA cm(-2) = 360 mV) and commercial RuO2 (365 mV), a benchmark catalyst for the OER. The turnover frequency (TOF) of the polyol-synthesized Co0.5Fe0.5WO4 was estimated to be 0.235 s(-1) at an overpotential of 400 mV, while stable operation at 10 mA cm(-2) was maintained for at least 24 h.