Insights into electrode/electrolyte interfacial processes and the effect of nanostructured cobalt oxides loading on graphene-based hybrids by scanning electrochemical microscopy

摘要

Nanostructured cobalt oxide polymorphs (CoO and Co_3O_4) deposited via electrodeposition allowed optimal loading on supercapacitive graphene nanosheets producing a set of graphene-based hybrids namely, CoO/GO, CoO/ErGO, Co_3O_4/GO, Co_3O_4/rGO, and Co_3O_4/ErGO, as pseudocapacitive electrochemical electrodes. We gained fundamental insights into the complex physicochemical interfacial processes at electrode surfaces and electrode/electrolyte (or solid/liquid) interfaces by scanning electrochemical microscopy operating in the feedback probe approach and imaging modes while monitoring and mapping the redox probe (re)activity behavior. We determined the various experimental descriptors including diffusion coefficient, electron transfer rate, and electro-active site distribution on electrodes. We emphasize the interplay of (1) heterogeneous basal and edge plane active sites, (2) graphene surface functional moieties (conducting/semiconducting), and (3) crystalline spinel cobalt oxides (semiconducting/insulating) coated graphene, reinforcing the available electron density of states in the vicinity of the Fermi level contributing to higher elec-troactivity, faster interfacial diffusion, and shorter distances for electron transfer, facilitated through molecular and chemical bridges obtained by electrodeposition as compared with the physical deposition.