The mechanistic role of a support–catalyst interface in electrocatalytic water reduction by Co3O4 supported nanocarbon florets

Abstract

Comprehending the mechanistic involvement of a support–catalyst interface is critical for effective design of industrially relevant electrocatalytic processes such as the alkaline hydrogen evolution reaction (alHER). The understanding of the kinetically sluggish alHER exhibited by both Pt and Pt-group-metal-free catalysts is primarily derived from indirect electrochemical parameters such as the Tafel slope. To address these issues, we establish the critical role of a nanocarbon floret (NCF) based electrochemical support in generating a key cobalt-oxohydroxo (OH–CoO) intermediate during the alHER through operando Raman spectro-electrochemistry. Specifically, interfacial nano-engineering of a newly designed carbon support (NCF) with a spinel Co₃O₄ nanocube catalyst is demonstrated to achieve a facile alHER (−0.46 V@10 mA cm⁻²). Such an efficient alHER is mainly attributed to the unique lamellar morphology with a high mesoporous surface area (936 m² g⁻¹) of the NCF which catalyses the rate-determining water dissociation step and facilitates rapid ion diffusion. The dissociated water drives the formation of the OH–CoO intermediate, spectroscopically captured for the first time through the emergence of a νOH–CoO Raman peak (1074 cm⁻¹). The subsequent alHER proceeds through the Volmer–Heyrovsky route (119 mV dec⁻¹) via the T_d Co²⁺ ↔ Co³⁺ ↔ Co⁴⁺ oxidative pathway. Concomitant graphitization of the NCF through the disappearance of νsp³C–H (2946 cm⁻¹) supports the co-operative dynamics at the Co₃O₄–NCF interface. Thus, the NCF positively contributes towards the lowering of the overpotential with a low charge-transfer resistance (R_ct = 35.8 Ω) and high double layer capacitance (C_dl = 410 mF cm⁻²).