Material and system development needs for widespread deployment of hydroxide exchange membrane fuel cells in light-duty vehicles

Abstract

The hydroxide exchange membrane fuel cell (HEMFC) is a promising alternative to the proton exchange membrane fuel cell (PEMFC) and offers cost savings in stack component materials. In this study, we determine and analyze the cost of HEMFC systems for light-duty vehicle applications for the first time by developing a comprehensive HEMFC system model. More specifically, (i) we analyze the volumetric and cost-based activity of state-of-the-art carbon-supported precious metal (PM)-containing and PM-free oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) electrocatalysts. Based on the incorporation of the activity of the ORR–HOR electrocatalyst pairs into the HEMFC system cost analysis, we conclude that PM-containing PdMo/C and Ru₇Ni₃/C are the best ORR and HOR electrocatalysts for implementation in HEMFC systems; (ii) we perform a HEMFC system cost analysis based on the best state-of-the-art carbon-supported PM-free ORR–HOR electrocatalyst pair ((Fe–N–C)–Ni/N-doped C). We also compare the system cost of HEMFCs and PEMFCs based on the best state-of-the-art carbon-supported ORR and HOR electrocatalysts. Our comparison shows that the HEMFC system has a cheaper stack but a more expensive balance of plant (BOP) than the PEMFC system, resulting in a higher HEMFC system cost. The higher HEMFC system cost is due to the electrochemically driven CO₂ separator (EDCS) cost and higher humidification management system cost caused by the lower cathode outlet relative humidity of the HEMFC compared with that of the PEMFC; (iii) we determine the material and system developments needed to decrease the HEMFC system cost to $30 per kW_Net required for cost competitiveness with internal combustion engine vehicles (ICEVs) based on (PdMo/C-Ru₇Ni₃/C) and ((Fe–N–C)–Ni/N-doped C) ORR–HOR electrocatalyst pairs. We also perform a single variable sensitivity analysis and demonstrate the relative importance of EDCS operating parameters: H₂ consumed to CO₂ removed ratio, pressure drop, and area-based cost. Our analysis indicates that EDCS pressure drop significantly impacts the overall HEMFC system cost, comparable to the area-based cost, and that one must monitor its values in future studies; and (iv) we present a detailed stack and BOP cost and voltage-loss breakdown for all the systems studied in this paper and identify the cost and voltage-loss drivers. Overall, our system analysis provides invaluable and transformational guidelines and enables more targeted and informed future material and system component developments by identifying the highest cost and voltage-loss drivers in HEMFC systems and providing material and system developments needed to reach full cost parity with ICEVs.