Sustainable Synergistic Engineering of Co–Fe Borate/Exfoliated Graphite Composites for Efficient Alkaline Water Splitting: A Response Surface Approach

Abstract

Electrochemical water splitting is a promising route for energy conversion and chemical energy storage, yet its large-scale implementation is limited by sluggish reaction kinetics and the insufficient stability and activity of earth-abundant electrocatalysts. In this work, we report an amorphous bimetallic borate composite integrated with exfoliated graphite (Fe–CoBOx/EG) as a bifunctional, binder-free electrocatalyst deposited on commercial nickel foam. A central composite design approach was employed to systematically evaluate compositional effects and synergistic interactions between the metal borate constituents and to identify an optimal formulation. Under optimized conditions, the Fe–CoBOx/EG prepared by controlled mechanical pressing on a nickel foam electrode delivers high activity toward both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 0.1 M KOH. The overpotentials of 57 mV at 10 mA cm–2 for HER and 240 mV at 10 mA cm–2 for OER were obtained with corresponding Tafel slopes of 79 and 42 mV dec–1, respectively. Structural and morphological analyses by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) confirm the amorphous character, homogeneous dispersion of active species, and postelectrolysis structural integrity of the composite. The enhanced performance is attributed to the disordered borate framework, which provides abundantly accessible active sites, and the intimate electrical contact among the catalyst layers, exfoliated graphite, and nickel foam substrate, which facilitates rapid charge transport. These features provide a binder-free Fe–CoBOx/EG–Ni electrode with durable bifunctional activity for alkaline water splitting.