Electrocatalytic Oxygen Evolution in Acidic and Alkaline Media by a Multistimuli-Responsive Cobalt(II) Organogel

Supramolecular gels and metallogels involving dynamic and reversible noncovalent interactions are touted as alternatives to gels based on polymeric materials for practical purposes and for an obvious edge in tailorability. A stimuli responsive Co(II) containing a low-molecular-weight metallo-organogel (CoGel) has been synthesized on a nitrogen-rich triazole platform. CoGel shows autonomous self-healing ability owing to the presence of extensive hydrogen bonding between exocyclic amines of the triazole moiety and the entrapped solvent molecules. CoGel-derived Co-xerogel (xerogel1), having a crumpled sheet-like morphology and a large effective surface area, has been calcined in air to obtain sea-urchin-like Co3O4. This Co3O4 has been compared with xerogell to understand the beneficial effect of the presence of exposed Co(II)-sites, and also, the presence of a ligand that stabilizes both Co2+ and Co3+ states, in designing efficient and stable electrocatalysts for oxygen evolution reaction (OER). Both xerogell and Co3O4 have shown excellent activity for electrocatalytic OER in acidic and in alkaline media. Combined electrochemical studies revealed that Co3O4 was more stable compared to xerogell and, consequently, delivered better activity in an acidic medium, whereas the trend was just reversed in an alkaline medium where xerogell was found to be a better catalyst. The xerogell in alkaline OER showed a high Faradaic efficiency (FE) of 91.72%, as observed from a rotating ring disc electrode (RRDE) experiment. Moreover, a time course study of O-2 evolution carried out by gas chromatography resulted in a FE in accordance with that observed from the RRDE experiment. Our results are comparable to reported cobalt-based electrocatalysts and introduce possibilities of developing efficient electrocatalytic systems in the future.