Efficient hydrogen production via overall water splitting using CuO/ZnO decorated reduced graphene oxide as bifunctional electrocatalyst

Abstract

Conjunction of ‘n’ and ‘p’-type materials have gained considerable attention for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) as potential substitutions to noble metal based nanomaterials. Current work has been designed to synthesize mixed-phase nanocomposite (NC) based on copper (CuO) and zinc oxide (ZnO) nanowires (NWs) and reduced graphene oxide (rGO). A facile chemical reduction method was used for the preparation of NWs, rGO were prepared using modified Hummer's method and lastly CuO/ZnO NWs were grafted on rGO to fabricate NC (CuO/ZnO@rGO) by wet-chemical approach. Characterization techniques were employed to confirm the formation as well as different morphological features of NC. Noticeable D and G bands in Raman spectrum confirmed the formation of NC and EDAX confirmed the presence of C, O, Zn and Cu. XRD analysis has confirmed hexagonal wurtzite structure of NC with a crystallite size of 10.1392 nm. Synthesized material was then investigated for OER and HER in an alkaline medium. As electrocatalyst, NC exhibited overpotential (OP) of 1.678 V to accomplish 10 mA/cm−2 current density (J) in OER and −358 mV (10 mA/cm−2) for HER respectively. Tafel curves of CuO/ZnO@rGO in OER (42 mV dec−1) and HER (270 mV dec−1) were found similar enough to others studies. Proliferated electrochemical activities are responsible for such a lower OP and Tafel slope values that may be due to electronic couplings of copper and zinc, or the homogenous distribution of both the metal oxides which gives polydispersity in their structure as confirmed by SEM images. Promising results of the current study indicated high-performance of synthesized electrocatalyst. Further studies can be designed to evaluate the efficiency of different combinations of noble/non-noble metals or metal oxides with rGO as potential candidate for electrochemical reactions.