Structure – Catalytic Behavior Relationships in TiO ₂ -Carbon Composite Supported Pt Electrocatalysts: A Case Study

Abstract

Composite type of supports made of TiO2 and carbonaceous materials provide higher stability for the Pt electrocatalysts under the working conditions of polymer electrolyte membrane fuel cells than the traditional carbon supports. We have demonstrated in our previous works that composites describing with general formula of 75 wt.% Ti(1-x)Mox-25 wt.% C (x=0-0.2; C= traditional Black Pearls (BP) carbon) were promising supports which provided increased stability for the Pt electrocatalysts. In this work, the effect of nitrogen doping of the carbonaceous component of the composite was explored. 75 wt.% TiO2-25 wt.% carbon composite supports were prepared using graphite oxide (GO), N-doped GO and N-doped multilayer graphene. Electrocatalysts were made by loading the supports with 20 wt.% Pt. The systems were compared based on their physicochemical properties determined by low temperature nitrogen adsorption, X-ray powder diffraction (XRD), Transmission Electron Microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and conductivity measurements. The activity of the catalysts was investigated by conventional methods in 3-electrode electrochemical cell. The results of various characterization methods contributed to the understanding of the difference in the electrochemical behavior of N-free and N-containing catalyst samples. While GO provided favorable properties for this composite supported catalyst, its N-doping strongly influenced the growth of TiO2, forming an almost continuous coating of small TiO2 crystals. This quasi-insulating TiO2 layer between the Pt catalytic sites and the conductive part of the composite resulted in poor electrochemical activity. Mixing the sample with carbon, however, improved its conductivity, which resulted in significant increase in the oxygen reduction reaction activity.