Reduced graphene oxide-supported bipyridyl iron(II) complex as an efficient electrocatalyst for hydrogen evolution

Abstract

A bipyridyl-containing iron(II) complex, [Fe(BPy)₂Cl₂]•BPy (Fe-BPy), was synthesized and immobilized on reduced graphene oxide (rGO) to construct a hybrid electrocatalyst (Fe-BPy/rGO) for the hydrogen evolution reaction (HER) in alkaline media. Comprehensive characterization, including single-crystal XRD, spectroscopic, and electrochemical analyses, confirmed the octahedral geometry of Fe(II) and its stable non-covalent integration with rGO. Glassy carbon electrodes modified with Fe-BPy/rGO at different loading densities (0.1–0.5 mg cm⁻²) were evaluated in 0.1 M KOH. The optimized catalyst (0.5 mg cm⁻²) demonstrated outstanding HER activity, achieving an onset potential of −21 mV vs. RHE, an exchange current density of 0.7 mA cm⁻², and a Tafel slope of −114 mV dec⁻¹ , delivering 10 mA cm⁻² at an overpotential of 119 mV. These performances rival those of commercial Pt/C under identical conditions and surpass most reported molecular electrocatalysts in alkaline electrolytes. The hybrid also exhibited excellent durability, retaining activity after 5000 CV cycles and 48 h chronoamperometry. This study underscores the critical role of rGO in enhancing charge transfer, catalytic site accessibility, and long-term stability. The findings provide design guidelines for future molecular HER electrocatalysts, emphasizing the benefits of integrating earth-abundant transition-metal complexes with conductive carbon supports. Such hybrid systems represent a viable pathway toward cost-effective, scalable, and sustainable hydrogen production technologies.