Strategies to mitigate Pt dissolution in low Pt loading proton exchange membrane fuel cell: I. A gradient Pt particle size design

The catalyst durability at low Pt loading remains a barrier for industrial commercialization of the proton exchange membrane fuel cell. Degradation of low loaded Pt catalyst not only reduced the electrochemical surface area but also revealed a Pt depletion zone adjacent to the cathode/membrane interface where about 80% of the Pt was lost due to dissolution and migration into the membrane. We hypothesized that the Pt degradation can be mitigated using a gradient cathode design without sacrificing the initial fuel cell performance. With a focus on the mitigation, the first of two companion papers focuses on the Type I cathode with larger Pt particles (5 nm average size) near the cathode/membrane interface. In the second of these two papers, the Type II cathode with higher Pt loading (60 wt.% Pt on carbon) near the cathode membrane interface will be investigated. The catalyst coated membranes with gradient cathode were fabricated by reactive spray deposition technology with low Pt loading of 0.05 mg cm-2 on the anode and 0.1 mg cm-2 on the cathode. The DOE defined accelerated stress test was performed by imposing a triangular wave potential cycling from 0.6 V to 1.0 V for 30,000 cycles at 50 mV s-1 scan rate. Results of accelerated stress test showed that the loss of electrochemical surface area and PEMFC performance were reduced for the Type I cathode compared to the control cathodes that consisted of 2 nm averaged Pt particle size only. Microscopy analysis suggested two possible mechanisms for this durability improvement: 1) the reduction of the amount of Pt lost due to Pt dissolution, and 2) the preservation of Pt particles at the cathode/membrane interface. Comparison with the control cathode showed that the loss of Pt near the cathode/membrane interfaced were reduced from 80% to 40% and the overall Pt loss of the cathode were reduced from 30% to 15%.