Mitigation strategy towards stabilizing the Electrochemical Interface under high CO and H2O containing reformate gas feed

Abstract

Despite the enhanced CO tolerance of the high temperature polymer electrolyte membrane (HT PEMFC) technology, the synergistic effect of CO and steam in the anodic reformate gas feed was proven to result in serious performance reduction and operation instabilities, due to the dynamic disturbance of the electrochemical interface (EI). In this work a mitigation strategy is presented by controlling the hydrophilicity of the catalytic layer in order to achieve the optimum structure of the EI. The thin and continuous film distribution of the phosphoric acid (PA) inside the catalytic layer (CL) without blocking the pores is the main characteristic property that determines the good quality of the EI. As shown, a hydrophilic catalytic layer is preferable, since the acid, being at any hydration level, will be able to spread over the catalytic surface aiming to the formation of a thin and continuous film so as to maximize the extend of the EI without blocking the pores of the catalytic layer. This facilitates the uninterrupted transport of protons and the fast diffusion of the reacting gases. Herein, this was accomplished by modifying the surface properties of the CL through the anchoring of pyridine moieties on the MWCNTs, which plays the role of the Pt catalyst support. The basic pyridine moieties enhance the hydrophilicity of the nanotubes through the acid (PA)-base (pyridine) interaction so that the contact angle between a PA drop and the catalytic layer is very close to zero. The good affinity of the PA with the pyridine based catalytic layer secures the PA thin film distribution and continuity. More importantly it is not affected even at high hydration levels of the PA, when the partial pressure of steam is increased at values>20kPa. Otherwise, on conventional C supports, hydrated PA has the tendency to shrink and create ganglia leading to the disruption of the EI. The pyridine modified catalytic layers approach Pt surface utilization values as high as 80% as compared to 50% utilization measured for the case of conventional Pt/C catalytic layers.