Reduced graphene oxide supported meso-pyridyl BODIPY-Cobaloxime complexes for electrocatalytic hydrogen evolution reaction

Creating innovative catalysts utilizing nonprecious metals for the electrocatalytic hydrogen evolution reaction (HER) poses a significant difficulty. We present a cobaloxime (Cox) complex having pyridine (2-Cox) and tetrafluorophenyl-thio-pyridine (4-Cox) functional groups, which contains a 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) moiety. This combination serves as a catalyst for proton reduction and is immobilized onto reduced graphene oxide (rGO) by π–π stacking between the cobaloxime complex and rGO. Moreover, the unique complex's structures were determined through the application of ultraviolet–visible spectroscopy (UV–Vis), Fourier Transform Infrared spectroscopy (FT-IR), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM). The electrocatalytic activity of the two rGO/2-Cox and rGO/4-Cox electrodes towards hydrogen (H₂) were examined under both alkaline and acidic conditions. The cobaloxime-modified rGO electrodes demonstrate superior electrocatalytic performance for the HER under acidic conditions compared to alkaline conditions. The overpotential at a current density of 10 mA cm⁻² for rGO/2-Cox in 0.5 M H₂SO₄ is −0.342 V, which is notably lower than the overpotential of rGO/4-Cox (−0.496 V). The Tafel slope for the rGO/2-Cox electrode in a 0.5 M H₂SO₄ solution is 111 mV.dec⁻¹, but for the rGO/4-Cox electrode it is 156 mVdec⁻¹. This discrepancy suggests that the rGO/2-Cox electrode demonstrates better performance in the HER compared to the rGO/4-Cox electrode.