Rotating Disk Electrode System for ORR Measurements at Elevated (>100 C) Temperature and Pressure Conditions

Rotating disk electrodes (RDE) are widely used for mimicking conditions in polymer electrolyte fuel cells (PEMFCs), for example for ex situ measurements of the catalytic activity of fuel cell catalysts. However, using RDE current densities are much lower compared to fuel cells, as in liquid electrolyte mass transport of dissolved reactant gases is limited by orders of magnitude lower concentrations and diffusion coefficients compared to gas phase. Furthermore, owing greatly reduced gas solubility by increasing vapor pressure of water at elevated temperatures, RDE studies in open systems have been limited to about 60 C. 1 Employing RDE at elevated pressure would allow increasing reactant gas solubility and raising the boiling point of water. In addition, conc. phosphoric acid (PA), which is typically not considered in RDE studies due its even lower gas solubility, could be used for RDE measurements at sufficient gas concentration. This presentation will discuss a developed RDE system that was integrated in an elevated pressure and temperature electrochemical cell setup reported earlier. 2 ,3 The RDE system is based on a magnet coupled drive, avoiding use of a rotary seal autoclave feed-through as proposed previously. 4 We tested the magnet coupled RDE up to 100 bar pressure by studying the ORR on polycrystalline Pt as a test reaction in 0.5 M H 2 SO 4 as well as conc. PA electrolyte. By increasing the pressure of oxygen in the closed cell, the diffusion limited current densities can be increased by almost two orders of magnitude in dilute electrolyte and RDE measurements in conc. PA are enabled. The RDE system also was successfully tested at elevated temperatures up to 140 C. Kinetic measurements of the ORR under elevated pressure conditions are currently in preparation. 1 U. Paulus, T.J. Schmidt, H. Gasteiger, and R.J. Behm, J. Electroanal. Chem. 495 , 134 (2001). 2 G.K.H. Wiberg, M.J. Fleige, and M. Arenz, Rev. Sci. Instrum. 85 , 085105 (2014). 3 M.J. Fleige, G.K.H. Wiberg, and M. Arenz, under Review. 4 J. McBreen, W.E. O’Grady, and R. Richter, J. Electrochem. Soc. 131 , 1215 (1984).