Charge State Manipulation of Cobalt Selenide Catalyst for Overall Seawater Electrolysis

Facile and controllable fabrication of highly active and stable bifunctional electrocatalysts for water electrolysis is important for hydrogen production. 3D cobalt selenide electrodes with CoSe and Co9Se8 phases are synthesized by one‐step calcination of Co foil with Se powder in a vacuum‐sealed ampoule. The charge state of Co species and the electrocatalytic performance of the prepared catalysts are manipulated by controlling Co to Se mass ratio. Mechanistic studies show that a high Co charge state favors oxygen evolution reaction performance and a low Co charge state promotes hydrogen evolution reaction activity for as‐prepared cobalt selenide electrocatalysts. The resultant materials can act as free‐standing bifunctional electrocatalytic electrodes for oxygen evolution reaction and hydrogen evolution reaction in alkaline media. Moreover, a 10.3 mA cm−2 current density at 1.8 V is achieved for overall seawater electrolysis through exploiting as‐synthesized cobalt selenide electrodes as both anode and cathode, which is three times higher than that for novel‐metal‐based seawater electrolyzer at the same voltage (2.9 mA cm−2). Experimental results reveal that the cobalt selenide electrodes show significantly higher electrocatalytic performance than that of integrated Ni/Ir–C and Ni/Pt–C electrodes. Consequently, these novel bifunctional electrodes are promising candidates for realistic large‐scale water electrolysis. The charge state of Co and the electrocatalytic activity of cobalt selenide are manipulated by calcination in a vacuum‐sealed ampoule. The catalytic mechanism is studied based on synchrotron‐based analysis. A high Co charge state favors oxygen evolution reaction performance and low Co charge state promote hydrogen evolution reaction activity. A 10.3 mA cm−2 current density at 1.8 V is achieved for overall seawater electrolysis.