Crystalline Copper Selenide as a Reliable Non‐Noble Electro(pre)catalyst for Overall Water‐Splitting

Electrochemical water-splitting remains a frontier research topic in the quest to develop artificial photosynthetic systems by using noble metal-free and sustainable catalysts. Herein, a highly crystalline block-shaped CuSe has been employed as active electrodes for overall water-splitting (OWS) in alkaline media. The pure-phase klockmannite CuSe deposited on the highly conducting nickel foam (NF) electrodes via electrophoretic deposition (EPD) displayed an overpotential of merely 297 mV for the reaction of oxygen evolution (OER) at a current density of 10 mAcm -2 while an overpotential of 162 mV was attained for the hydrogen evolution reaction (HER) at the same current density, superseding the Cu-based as well as the state-of-the-art RuO2 and IrO2 . The bifunctional behavior of the catalyst has successfully been utilized to fabricate an overall water-splitting device that exhibits a low cell voltage (1.68 V) with long-term stability. Post-catalytic analyses of the catalyst by ex-situ microscopic, spectroscopic and analytical methods confirm that under both OER and HER conditions, the crystalline and conductive CuSe behaves as an electro(pre)catalyst forming a highly reactive in-situ crystalline Cu(OH)2 overlayer to facilitate oxygen (O2) and an amorphous Cu(OH)2/CuOx active surface for hydrogen (H2) evolution. This study demonstrates a distinct approach to produce highly active copper-based catalysts to enhance the performance in durable bifunctional overall water splitting.