Browsing by Author "Kaspar, Robert B."
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Item Manipulating Water in High-Performance Hydroxide Exchange Membrane Fuel Cells through Asymmetric Humidification and Wetproofing(The Electrochemical Society, 2015-02-20) Kaspar, Robert B.; Letterio, Michael P.; Wittkopf, Jarrid A.; Gong, Ke; Gu, Shuang; Yan, Yushan; Robert B. Kaspar, Michael P. Letterio, Jarrid A.Wittkopf, Ke Gong, Shuang Gu and Yushan Yan; Kaspar, Robert B.; Letterio, Michael P.; Wittkopf, Jarrid A.; Gong, Ke; Gu, Shuang; Yan, YushanHydroxide exchange membrane fuel cells (HEMFCs) are an emerging low-cost alternative to conventional proton exchange membrane fuel cells. In addition to producing water at the anode, HEMFCs consume water at the cathode, leading to distinctive water transport behavior. We report that gas diffusion layer (GDL) wetproofing strictly lowers cell performance, but that the penalty is much higher when the anode side is wetproofed compared to the cathode side. We attribute this penalty primarily to mass transport losses from anode flooding, suggesting that cathode humidification may be more beneficial than anode humidification for this device. GDLs with little or no wetproofing perform best, yielding a competitive peak power density of 737 mW cm−2.Item Performance, durability, and modeling of hydroxide exchange membrane fuel cells(University of Delaware, 2015) Kaspar, Robert B.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.Item Permethyl Cobaltocenium (Cp* 2Co+) as an Ultra-Stable Cation for Polymer Hydroxide-Exchange Membranes(Nature Publishing Group, 2015-06-29) Gu, Shuang; Wang, Junhua; Kaspar, Robert B.; Fang, Qianrong; Zhang, Bingzi; Coughlin, E. Bryan; Yan, Yushan; Shuang Gu, Junhua Wang, Robert B. Kaspar, Qianrong Fang, Bingzi Zhang, E. Bryan Coughlin & Yushan Yan; Gu, Shuang; Wang, Junhua; Kspar, Robert B.; Fang, Qianrong; Zhang, Bingzi; Yan, YushanHydroxide (OH−)-exchange membranes (HEMs) are important polymer electrolytes enabling the use of affordable and earth-abundant electrocatalysts for electrochemical energy-conversion devices such as HEM fuel cells, HEM electrolyzers, and HEM solar hydrogen generators. Many HEM cations exist, featuring desirable properties, but new cations are still needed to increase chemical stability at elevated temperatures. Here we introduce the permethyl cobaltocenium [(C5Me5)2Co(III)+ or Cp*2Co+] as an ultra-stable organic cation for polymer HEMs. Compared with the parent cobaltocenium [(C5H5)2Co(III)+ or Cp2Co+], Cp*2Co+ has substantially higher stability and basicity. With polysulfone as an example, we demonstrated the feasibility of covalently linking Cp*2Co+ cation to polymer backbone and prepared Cp*2Co+-functionalized membranes as well. The new cation may be useful in designing more durable HEM electrochemical devices.