Rational design of bifunctional catalysts for chlorine-free, durable overall seawater electrolysis

•A bifunctional catalyst is synthesized by one-step thermal exfoliation.•The best catalyst shows overpotential of 254 mV at 10 mA/cm2 in alkaline seawater.•It exhibits excellent selectivity towards OER over hypochlorite formation.•The seawater electrolyzer shows a stability of 210 h at 20 mA/cm2.•A zero-gap electrolyzer is fabricated and performance is demonstrated. Developing bifunctional, non-precious catalysts for seawater electrolysis is pivotal yet remains challenging due to sluggish oxygen and hydrogen evolution reactions (OER and HER) and chlorine corrosion. Herein, Ni-NiFe2O4/rGO (NFO1/erGO) obtained by a one-step exfoliation is reported as a bifunctional catalyst for seawater electrolysis. The NFO1/erGO (85.3 % NiFe2O4, 14.7 % Ni) exhibits outstanding OER and HER activities in seawater. The NFO1/erGO/Carbon paper(CP)||NFO1/erGO/CP electrolyzer demonstrates low overall seawater splitting voltages of 1.74 V and 1.98 V to achieve 10 mA/cm2 and 100 mA/cm2, respectively. Electronic charge modulation across the metal centres, enhanced conductivity, optimum binding strength of reaction intermediates, and corrosion resistance ensure excellent stability and electrocatalytic activity. Interestingly, NFO1/erGO maintains its original phase even after seawater electrolysis, suggesting its exceptional structural durability. Finally, a membrane-less zero-gap seawater electrolyzer is fabricated, demonstrating an H2 production rate of 0.36 L/h. These observations boost the practical realization of seawater electrolyzers based on non-precious catalysts.