Hydrothermal Synthesis of Monolithic Co₃Se₄ Nanowire Electrodes for Oxygen Evolution and Overall Water Splitting with High Efficiency and Extraordinary Catalytic Stability

Cobalt selenide has been proposed to be an effective low‐cost electrocatalyst toward the oxygen evolution reaction (OER) due to its well‐suited electronic configuration. However, pure cobalt selenide has by far still exhibited catalytic activity far below what is expected. Herein, this paper for the first time reports the synthesis of new monoclinic Co₃Se₄ thin nanowires on cobalt foam (CF) via a facile one‐pot hydrothermal process using selenourea. When used to catalyze the OER in basic solution, the conditioned monolithic self‐supported Co₃Se₄/CF electrode shows an exceptionally high catalytic current of 397 mA cm⁻² at a low overpotential (η) of 320 mV, a small Tafel slope of 44 mV dec⁻¹, a turnover frequency of 6.44 × 10⁻² s⁻¹ at η = 320 mV, and excellent electrocatalytic stability at various current densities. Furthermore, an electrolyzer is assembled using two symmetrical Co₃Se₄/CF electrodes as anode and cathode, which can deliver 10 and 20 mA cm⁻² at low cell voltages of 1.59 and 1.63 V, respectively. More significantly, the electrolyzer can operate at 10 mA cm⁻² over 3500 h and at 100 mA cm⁻² for at least 2000 h without noticeable degradation, showing extraordinary operational stability.