Microwave-Assisted Synthesis of Cobalt-Based Selenides as Catalyst Precursors for the Alkaline Water Oxidation

When used to promote the oxygen evolution reaction (OER), transition-metal chalcogenides convert into oxyhydroxide/(hydr)oxide catalysts, the performance of which depends on the properties of the precursor. The present study aims to explore these effects for cobalt and cobalt–iron selenides (CoSe_n and Co₁Fe₁Se_n) prepared using a simple microwave-assisted method, in comparison to a reference material synthesized by high-temperature reaction of CoO_xH_y with Se vapors. Physical characterization of the microwave-synthesized CoSe_n demonstrates their sheet-like morphology and identifies Co₃Se₄ as the major phase, which is essentially completely transformed into CoOOH during the OER. The temperature during the microwave-assisted CoSe_n synthesis affects the crystallinity, the electrochemically active surface area, and thereby the performance of the resulting catalysts. Further improvements in the activity are achieved by combining cobalt with iron into a bimetallic Co₁Fe₁Se_n precursor, which transforms in situ into a CoOOH + FeOOH composite and sustains the OER rate of 100 mA cm⁻² (33 A g⁻¹) at an overpotential of ≈ 0.31 and 0.26 V at 24 ± 2 and 80 ± 1 °C, respectively. Satisfactory stability of the Co₁Fe₁Se_n-derived electrodes is demonstrated through a 4-day-long test at 80 ± 1 °C and 100 mA cm⁻².