The role of the WO₃ nanostructures in the oxygen reduction reaction and PEM fuel cell performance on WO₃-Pt/C electrocatalysts

Oxygen reduction reaction (ORR) was investigated on carbon supported platinum and tungsten oxide nanoparticles generated by chemical reduction. The results were correlated with the surface properties of these electrocatalysts. X-ray Photoelectron Spectroscopy (XPS), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Transmission Electron Microscopy (STEM), Energy Dispersive Spectroscopy (EDS) studies have been used to analyze the structure and surface properties of WO₃-Pt/C electrocatalysts. The analysis of the platinum Pt 4f peak by XPS showed that this metal is present in the surface as Pt⁰ with some oxidized platinum Pt²⁺, while tungsten oxide is present as W⁶⁺. The XPS results showed the strong interaction between Pt and WO₃. By electron microscopy techniques, it was observed that using this synthesis method, both, platinum and tungsten oxide are well dispersed on vulcan carbon, which may favor the formation of Pt-WO₃ interfaces. Thus, in comparison to conventional Pt/C, the 5%WO₃-Pt/C electrocatalyst exhibited higher electrocatalytic activity toward the oxygen reduction reaction in a single cell polymer electrolyte membrane (PEM) fuel cell. However, with the incorporation of tungsten oxide at higher contents the WO_x species are more dominating on the catalysts surface, reducing the accessibility of the reactants to the platinum active sites and therefore the electrochemical response in the ORR.