Synergistic Effects of Interlayer Anions in NiFe-LDH and Nickel Cobaltite Heterointerface for Energy-Efficient Alkaline Water Electrolysis

An energy-efficient, economically viable, and catalytically active bifunctional electrocatalyst with long-term stability could be a promising alternative to existing noble-metal-based electrocatalysts for producing carbon-neutral green hydrogen via alkaline water electrolysis (AWE). Here, we designed a nanostructured electrocatalyst, i.e., NiFe-LDH electrodeposited on hydrothermally grown Nickel Cobaltite (NCO) over a carbon cloth (CC) substrate, specified as NiFe-LDH/NCO@CC. A phase-pure synthesis is verified by an X-ray diffraction study, and field emission scanning electron microscopy suggests a core-shell (NiFe-LDH/NCO@CC) heterointerface composed of a core of NCO nanowires decorated with a shell of NiFe-LDH nanosheets for sulfate-anion intercalation and NiFe-LDH nanoparticles for nitrate-anion intercalation. The electrochemical analysis performed in 1 M KOH suggests that the optimized sulfate-intercalated NiFe-LDH/NCO@CC electrocatalyst shows superior electrochemical activity compared to pristine NiFe-LDH, NCO, and bare CC, with an overpotential η₁₀ of ∼141 and 226 mV for HER and OER, respectively. This superior performance is attributed to the heterointerface of anion-intercalated NiFe-LDH and NCO, which synergistically regulate the electronic structure, facilitating efficient charge transfer at the electrode-electrolyte interface. It can act as a bifunctional catalyst with an overall cell potential of ∼1.66 V, delivering a current density of 10 mA cm^-2. It shows a high turnover frequency (TOF) of 5.64 × 10^-2 H₂ s^-1 and 3.75 × 10^-2 O₂ s^-1 at an overpotential of 260 mV. An anion-exchange membrane-based alkaline water electrolyzer is also tested with the synthesized electrocatalyst, showing prolonged stability of ∼50 h in an alkaline medium. The estimation of H₂ production cost reveals that NFS/NCO24@CC requires $1.28/gasoline-gallon equivalent of H₂, which is less than the targeted cost set by the US Department of Energy for 2026. Thus, the present findings reveal that this heterostructure can be a feasible and cost-effective bifunctional electrocatalyst for energy-efficient overall water splitting.