Micro-wave synthesis of co-doped transition metal oxides anchored on reduced graphene oxide and their implementation as catalysts for water oxidation

Artificial photosynthesis is a very attractive and a desirable way to solve the rising energy demand. In order to harvest energy directly from sunlight catalyst for oxygen reduction and evolution reaction are at the core of key renewable-energy technologies including fuel cells and water splitting. Herein, tungsten oxide-reduced graphene oxide (WO3-rGO), cobalt oxidereduced graphene oxide (Co3O4-rGO) and tungsten oxide-cobalt oxide-reduced graphene oxide (WO3-Co3O4-rGO) nano-composites were synthesized via a facile, efficient, one-pot microwave assisted method as an efficient electro-catalyst for water oxidation. The structural and chemical compositions of the produced nano-structures were investigated by Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy as well as thremogravimetric analysis. Catalytic performances of the engineered nano hybrids for the oxygen evolution reaction (OER) were evaluated using a standard three electrode system in 0.1 M KOH aqueous solution, with a coiled Pt wire as the counter electrode and an Ag/AgCl as the reference electrode. In the produced nano-composites, WO3 and Co3O4 nano-particles are uniformly decorated on the reduced graphene oxide sheets without any agglomeration. The WO3-Co3O4-rGO hybrids afforded current density 1 mA/cm 2 at 1.693 V vs RHE and the Co3O4rGO reached the current density 1 mA/cm 2 at 1.769 V vs RHE regarding the catalytic performance for OER in alkaline solution. The over potential was significantly reduced by 76 mV after co-doping of WO3 with Co3O4-rGO nano hybrids. The WO3-Co3O4-rGO gives current density 1 mA/cm 2 at 1.658 V vs RHE. We also show that the over potential for oxygen evolution of the WO3-Co3O4-rGO was further reduced by illuminating the catalyst to visible light thus manifesting the photo-catalytic properties of the hybrid catalyst. Table of