Hierarchical nanoflowers of Bi/Fe-based selenide as a bifunctional electrocatalyst for alkaline water electrolysis

The current study presents a freestanding bifunctional electrocatalyst comprising hierarchically assembled Bi/Febased selenide with a nanoflower-like morphology on Ni foam for water electrolysis application. The impact of systematically adding Fe ions to Bi2Se3 on the phase and morphology is elaborately discussed. It is shown that tuning the Bi/Fe molar ratio governs the phase, electronic bandgap, and morphology, driven by the evolution of hetero-interfacial chemistry. The existence of multivalent metal ions, lattice defects, and an extended surface area remarkably improves the electrocatalytic activity. The optimized nanoflower-like composite electrode (1Bi1Fe-Se@NF) exhibits robust electrocatalytic efficacy with extremely low overpotentials of -53 mV and -230 mV at 10 mA cm-2 for hydrogen and oxygen evolution reactions, respectively. The symmetrical alkaline electrolyser, utilizing 1Bi1Fe-Se@NF electrodes (+,-), operates at a cell voltage of -1.52 V at 10 mA cm-2, lower than the device equipped with commercial Pt/C@NF (-) and RuO2@NF (+) (-1.57 V). Even after 100 h of operation at 50 mA cm-2, the symmetrical cell maintains a stable voltage, highlighting the outstanding bifunctional catalytic activities of noble metal-free 1Bi1Fe-Se@NF for overall water electrolysis.