(Invited) Platinum Supported on Graphitized Carbon Cathode for PEMFC Fabricated with Reactive Spray Deposition Technology

Abstract

Proton exchange membrane fuel cell (PEMFC) attracts huge attention as a new source of power generation for automotive applications. One key requirement for automotive applications is that the fuel cell must be tolerant of frequent start-stop cycling. It was found that the air/fuel boundary developed at the anode side after a fuel cell shut down or during its restart caused extremely quick degradation of the cathode [1, 2]. High potentials occur at the air cathode when hydrogen is introduced into the air on the anode [3]. These high overpotentials lead to platinum oxidation and dissolution and carbon corrosion at the air cathode [2]. The damage to the cathode catalyst layer causes severe irrecoverable performance decay [2]. To mitigate carbon corrosion from frequent start-stop cycling, graphitized carbon black (GCB) are used to replace the traditional carbon black support [4, 5]. GCB is usually prepared through thermal treatment at elevated temperatures in an inert environment [4]. Thus, it is structurally distinct from the traditional carbon black with respect to surface area, porosity, and surface homogeneity [6], which could change its interaction with ionomer and Pt nanoparticles. In addition, we propose the use of a new technology called reactive spray deposition technology (RSDT) to lower the manufacturing cost and improve the fuel cell performance especially for very low catalyst loadings. Therefore, it is important to have a comprehensive understanding on how graphitized carbon support affect the fuel cell performance at both beginning-of-test (BOT) and end-of-test (EOT). In this study, low Pt loading cathode electrodes using graphitized carbon support are fabricated with RSDT. RSDT is an open-atmosphere, cost-effective process that combines the catalyst synthesis and deposition into one step. It also allows for independent control of the catalyst, support and ionomer compositions in the electrode. A six-step method [7] is used to analyze the polarization losses for the Pt/GCB cathodes. Figure 1 shows a step-by-step correction of BOT polarization overpotentials for a Pt/GCB cathode with Nafion/carbon ratio of 0.3 and platinum loading of 0.1 mg cm-2. Furthermore, comparison of the polarization overpotentials is made with high-surface-area carbon black to elucidate the effect of carbon microstructure on the polarization losses. Additionally, the effect of Nafion/carbon ratio and various types of perfluorosulfonic acid (PFSA) ionomers are studied to optimize the Pt/GCB cathode performance.