Electrochemical and spectroscopic investigation of a binary Ni-Co oxide active material deposited on graphene/polyvinyl alcohol composite substrate

A composite material based on Polyvinyl alcohol (PVA) and graphene oxide (GO) was used as electrode substrate for the Ni-Co electrodeposition in neutral chloride bath containing 1.5 mM Ni(NO3)2 and 4.5 mM Co(NO3)2. Ni-Co particles were cathodically deposited by voltage cycling between − 0.5 V and 0.2 V vs. SCE (35 cycles). Voltammetric data show clearly an inhibition phenomenon of nickel oxide deposition upon increasing [Co2+] in the electroplating baths. Nevertheless, the presence of electrodeposited Co oxide species induces beneficial effects on the redox electrochemical behavior of the GC/PVA/GO/Ni-Co electrode in alkaline medium (0.1 M NaOH). The resulting electrode shows, a unique and reversible symmetrical cathanodic wave centered at about 0.3 V vs SCE. The SEM analysis shows the graphene oxide disposed as platelets in a agglomerate distribution randomly oriented within the PVA matrix. The electrodeposition process of Ni-Co species proceeds preferentially on the GO platelets surfaces. After the charge/discharge process in alkaline medium, the Ni-Co deposit shows a globular inhomogeneous distribution with an average diameter comprised between 50 nm and 300 nm. The XPS characterization of the electrodeposited Ni-Co catalyst reveals a surface chemical composition of about Ni16Co84, confirming an “anomalous” co-deposition process of the metals on the PVA/GO electrode substrate.