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 metal oxides with electrochemical 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 facilitate charge transport during electrocatalysis, thereby promoting active site exposure during electrolysis. N@C-Ni_1.2-Fe_0.5 shows a low overpotential and Tafel slope of 310 mV & 80 mV dec⁻¹ for the OER and 104 mV & 98 mV dec⁻¹ for the HER in 1 M KOH at 10 mV cm⁻² (without iR correction). N@C-Ni_1.2-Fe_0.5 exhibits 25 h long-term stability for the OER and HER with a low potential loss of about 2.4% and 2.8%. N@C-Ni_1.2-Fe_0.5 shows a low overpotential of 341 mV for the OER and 146 mV for the HER in 1 M KOH + natural seawater. N@C-Ni_1.2-Fe_0.5//N@C-Ni_1.2-Fe_0.5 exhibits an overall water splitting cell voltage of 1.63 V, 1.65 V, and 1.68 V in 1 M KOH, 1 M KOH + 1 M NaCl, and 1 M KOH + seawater. Additionally, a homemade water electrolyzer (N@C-Ni_1.2-Fe_0.5//N@C-Ni_1.2-Fe_0.5) was powered by conventional and renewable solar energy for generating H₂. Furthermore, the generated green H₂ was utilized to power a DC motor.