Graphene nanoclusters embedded nickel cobaltite nanofibers as multifunctional electrocatalyst for glucose sensing and water-splitting applications

Nickel cobaltite (NCO) attains the apex of Sabatier-type volcano plot for electrochemical reaction compared to simple oxides due to synergetic effect of mixed transition metal cations. The combination of high surface area, aspect ratio, and porosity of electrospun NCO nanofibers (NCO-NF) enhance their electrocatalytic performance by improved electron mobility and more active sites. In the present study, NCO-NF fabricated using poly (styrene-co-acrylonitrile) (SAN) as a sacrificial polymer, were embellished with graphene nanoclusters (GNC), which augment the electrocatalytic performance of the NCO-NF. The in situ formed GNC along the NCO-NF are result of the interaction between the polar functional groups of the polymer, and the cations of precursor salts during the calcination of precursor nanofibers. The GNC/NCO-NF with least crystallite size and high aspect ratio having porous NCO nanoparticles and in situ grown GNC were developed using sol-gel electrospinning process assisted by calcination of precursor nanofibers. This simple, eco-friendly, and economical synthesis route with unique structure chemistry of SAN to form GNC and the presence of dual cations (Ni and Co) provides enhanced performance and multifunctionality to GNC/NCO-NF electrodes for electrocatalytic applications, such as biosensors and water-splitting. In the present study, the modified electrodes (GNC/NCO-NF/graphite electrode) exhibited excellent non-enzymatic glucose detection over a wide range of concentration with a lower limit of 1.2 μM and sensitivity of 1827.5 μA mM⁻¹ mg⁻¹ in 0.1 M NaOH. Further, the modified electrodes were also tuned for H₂O₂ detection to aid enzymatic glucose sensing. When examined for bifunctional water-splitting in 1 M NaOH, the electrode reached an onset potential of −0.537 V and 0.735 V against reversible hydrogen reference electrode and a Tafel slope of 37.6 mV·dec⁻¹ and 67.0 mV·dec⁻¹ for hydrogen and oxygen evolution reactions, respectively. The results prove that GNC/NCO-NF are promising candidates as multifunctional electrocatalyst.