Fundamental investigation of catalyst utilization at the electrode/solid polymer electrolyte interface: Part I. Development of a model system

The active layer of gas diffusion electrodes, widely used in low temperature polymer electrolyte fuel cells, contains either metal-blacks (mostly Pt-black) or metallic nanoparticles (mostly Pt particles or Pt based alloy particles) supported on high surface area carbon. Depending on the nature of the catalyst in the active layer and the applied pretreatment of the gas diffusion electrodes, cyclic voltammetry reveals varying H-adsorption/desorption characteristics and catalyst surface utilization properties. Our aim was the development of model electrodes with defined surface geometry and platinum distribution pattern, which exhibit electrocatalytic effects equal to the ones observed on gas diffusion electrodes with different active layers like e.g., Pt on carbon or Pt-black. We describe the successful application of microstructured glassy carbon model electrodes. These models allow a correlation between the electrochemically determined platinum surface area and the different parts of the model electrode. Differences in catalyst surface utilization depending on the different distribution patterns can then be determined quantitatively and related directly to differences of the structured electrodes. Possible H-adsorption and diffusion mechanisms are discussed, which could serve as an explanation for the observed effects.