Unveiling the Electrocatalytic Activity of Crystal Facet-Tailored Cobalt Oxide-rGO Heterostructure Toward Selective Reduction of CO<sub>2</sub> to Ethanol
Suparna Saha, Soumyajit Maitra, Mausumi Chattopadhyaya, Arundhati Sarkar, Suhail Haque, Subhasis Roy, Kajari Kargupta
Abstract
Morphology-modulated and crystal facet-tailored electrocatalytic activity of Co3O4 nanocrystals (NCs) anchored on the reduced graphene oxide (rGO) sheet is explored for selective reduction of carbon dioxide (CO2) to C2 products. Specially engineered interconnected nanonetwork of the Co3O4 (111) facet dominated by tetrahedral Co(II) on rGO is synthesized by tuning the cobalt to GO ratio. The structural properties of of rGO–Co3O4 composite is analyzed by high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) techniques. Faradaic efficiencies (FE) of ethanol and ethylene attain the maximum value of 45.9 and 28.8%, respectively, at the optimum potential of −0.4 V vs RHE (FEethanol/ethylene = 1.7). The density functional theory (DFT) reveals strong dΠ–pΠ interactions between Co3O4 and graphene at interconnected morphology, which increases hybridization as well as electronic conductivity of the heterostructure compared to pristine Co3O4 (as supported by EIS and XPS analyses), causing deformation on the graphene sheet. The potential difference between the adjacent intermediates attached on tetrahedral Co(II) and octahedral Co(III) of (111) faceted Co3O4 NCs promote the C–C coupling and enhance the multi-electron transport through a circuit-like mechanism for the synthesis of ethanol. We explored that notable reactivity toward CO2 reduction is not solely associated with wt % of Co3O4 but also the morphological pattern of it on rGO that control the reaction intermediate (*CO) adsorption sites facilitating ethanol formation.