Performance, durability, and modeling of hydroxide exchange membrane fuel cells
Date
2015
Authors
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Publisher
University of Delaware
Abstract
2015 marks the first year in which U.S. consumers can buy fuel cell cars like the Toyota Mirai. Instead of combustion engines, these cars are powered by proton exchange membrane fuel cells (PEMFCs), electrochemical devices that convert hydrogen and air directly into electricity and water. Unfortunately, PEMFCs’ reliance on scarce platinum catalyst may preclude the mass production of fuel cell vehicles. Hydroxide exchange membrane fuel cells (HEMFCs) are an emerging alternative to PEMFCs. Their high-pH operating conditions intrinsically support earth-abundant catalysts like nickel and silver. But at present, HEMFCs perform worse than PEMFCs and their durability is not well understood. In this work, membrane-electrode assemblies (MEAs), the core of a fuel cell, are manufactured with a robotic sprayer. This reproducible, high-volume fabrication process serves as a platform for investigating fuel cell performance and durability, with support from analytical and numerical models. To study performance, HEMFCs’ distinctive water transport behavior is modeled for the first time. Wetproofing, a common technique for keeping liquid water out of PEMFC electrodes, is shown to make flooding worse in HEMFCs. Electrode patterning is proposed as an unconventional approach to level out the cell water distribution. To study durability, a degradation mode already known to corrode the PEMFC cathode during device startup and shutdown is identified for the first time in HEMFCs. Anodes made with ruthenium (instead of platinum) significantly resist this corrosion; non-precious-metal catalysts like nickel could provide near-immunity. Future directions include designing highly porous gas diffusion architectures and screening anode catalysts with low oxygen reduction activity. More broadly, the priority in this field should be to develop novel materials: thermally resistant electrolytes and active, oxidation-resistant, reaction-specific catalysts.