Improving Durability of PEMFC by Reducing the Impact of Operating Conditions on Electrode Degradation

Abstract

Meeting long-term durability targets with low Pt loading (<0.125 mg/cm2) still poses a significant challenge before wide-scale commercialization of PEM fuel cells is achieved. In our previous work with H2/N2 voltage cycling with single factor studies with the state-of-art (SOA) membrane electrode assembly (MEA), we have reported that electrode degradation rates significantly vary at different operating conditions [1,2]. To study the effect of operating conditions in depth and identify the interactions between the test factors, we have utilized a design of experiments approach. A 20-run design with three levels and temperature, relative humidity, upper potential limit, and upper potential hold time as the test factors was created. Tests were conducted in H2/N2 environment for 60,000 cycles. In-situ electrochemical diagnostics such as electrochemical surface area (ECSA), mass activity (MA), and specific activity (SA) along with polarization curves were measured at beginning-of-life (BOL) and after 30k and 60k voltage cycles. A platinum oxide coverage-based degradation model [3] was developed to predict ECSA loss. In the model, the damage factor is estimated as a function of the oxide current and oxide coverage which are dependent on temperature, relative humidity, and cell potential. Data from 20-run design is fit to the degradation model and fitting parameters are obtained. Simulations are run with drive cycles with varying operating conditions to calculate the damage factor and subsequently ECSA loss for each drive cycle is calculated. Based on the model results, benign operating conditions are identified which enable achieving 5000-hr durability. Figure 1 shows the results of 1000 hours of operation of the MEA with baseline drive cycle and drive cycle with benign operating conditions which were selected from results of the degradation model simulations. The results show that life-limiting electrode degradation rates can be significantly reduced by optimal selection of PEMFC operating conditions.References Kumaraguru, 2019 Annual Progress Report, https://www.hydrogen.energy.gov/pdfs/progress19/fc_fc156_kumaraguru_2019.pdf Ahluwalia, Rajesh K., et al. "Achieving 5,000-h and 8,000-h Low-PGM Electrode Durability on Automotive Drive Cycles." Journal of The Electrochemical Society (2021).Arisetty, Srikanth, et al. "Modeling platinum oxide growth of PEMFC cathode catalysts." ECS Transactions 69.17 (2015): 273. Figure 1