Interfacially coupled Ni with Fe-N doped carbon as a potential electrocatalyst for overall alkaline seawater splitting

Abstract

Water splitting is a promising way to generate H2 for a sustainable future. However, developing cost-effective bifunctional electrocatalysts for water electrolysis and seawater electrolysis (interference of corrosive Cl2 evolution) is still challenging. Based on that, we synthesized interfacially coupled metal oxides (NiFe2O4, NiO, and Fe2O3) embedded with nitrogen-doped carbon (N@C) by a cost-effective mechanochemical and calcination process, which exhibited highly efficient bifunctional activity and long-term stability towards overall water splitting. The three heterophase electrochemically active sites and nitrogen-doped carbon create a strong interfacial coupling effect that synergistically enhances the rapid electron transfer into the system. Furthermore, the porous carbon layers protect the heterophase structure from corrosion, and it helps to promote the active site exposure during electrolysis. The N@C-Ni1.2-Fe0.5 shows very low overpotential and Tafel slope of OER (310 mV & 80 mV dec-1) and HER (104 mV & 98 mV dec-1) in 1 M KOH at 10 mV cm-2 (without iR correction). N@C-Ni1.2-Fe0.5 exhibits 25 h long-term stability for OER and HER with low potential loss of about 2.4 % and 2.8 %. N@C-Ni1.2-Fe0.5 shows a low overpotential of 341 mV for OER and 146 mV for HER in 1M KOH + natural seawater. The N@C-Ni1.2-Fe0.5//N@C-Ni1.2-Fe0.5 exhibits the overall water splitting cell voltage of 1.63 V, 1.65 V, and 1.68 V in 1M KOH, 1M KOH + 1 M NaCl, and 1M KOH + seawater. Additionally, the homemade water electrolyzer (N@C-Ni1.2-Fe0.5//N@C-Ni1.2-Fe0.5) was powered by conventional and renewable solar energy for generating H2. Further, the generated green H2 was utilized to power the DC motor.