Shi, Lin2022-10-142022-10-142022https://udspace.udel.edu/handle/19716/31481As an emerging alternative to proton exchange membrane fuel cells (PEMFCs), hydroxide exchange membrane fuel cells (HEMFCs) are more cost-effective due to platinum group metal-free (PGM-free) catalyst options, more affordable bipolar plate production, and other potential savings. However, unlike PEMFCs, the HEMFC technology is still in its early phases and there is a continuous effort to develop suitable membranes, ionomers, and catalysts. Additionally, the HEMFC membrane electrode assembly (MEA) preparation technique is immature, and the understanding of cell operating mechanisms is lacking. Recently, a family of hydroxide exchange membranes (HEMs) and ionomers (HEIs) based on poly(aryl piperidinium) (PAP) has been developed in our group. The specific chemical structure endows PAP HEMs with excellent chemical stability, high conductivity, and mechanical robustness, which makes PAP HEMs/HEIs one of the best choices for HEMFC electrolyte and provides a solid platform for HEMFC operation study. Here, we focused our work on improving HEMFC performance, durability, and CO2 removal from the air feed. ☐ Alkaline pretreatment is a controversial problem for HEMFC testing, whose exact function was never fully understood. Based on the investigation of MEA fabrication process and polarization curve behavior, we show that alkaline pretreatment is necessary in many cases because of generation of carboxylates, and it can be prevented in Pt/Pd-free HEMFCs. ☐ After addressing the anion contamination, optimizations of operating conditions and material selection are implemented for HEMFC performance and durability improvement. We demonstrate that high performance can be obtained by adjusting relative humidity, backpressure, and catalyst in HEMFCs. Moreover, we show thinner membrane is beneficial for prolonging HEMFC durability. ☐ During the process of water management, a unique plateau in the polarization curve under flooding conditions is observed and interpreted for HEMFCs. It is understood the stable voltage (Ebalance) is a result of the balance between water and heat generation, whose level is determined by temperature, pressure, and gas diffusion layer (GDL) properties. ☐ Building on the knowledge of HEMFC testing, we demonstrate high-performance and durable HEMFCs with either Pt-free anode or PGM-free cathode. The HEMFC with Ru7Ni3/C anode shows a peak power density of 2.03 W cm−2 in H2/O2 and 1.23 W cm−2 in H2/air (CO2-free). The HEMFC with Cu@Ag-Mn/C cathode achieves a peak power density of 1.5 Wcm−2 in H2/O2 and 0.9 Wcm−2 in H2/air (CO2-free). And both HEMFCs can operate stably with less than 5% voltage loss over 100 h. ☐ A well-known technical challenge for bringing HEMFC into the transportation market is CO2 in the ambient air, as carbonation of hydroxides is detrimental to HEMFC performance. As a result, we develop a shorted membrane electrochemical cell powered by hydrogen to remove CO2 from the air feed, which can be modularized like a typical separation membrane. The compact, low-cost, and efficient EDCS module is economically viable for HEMFC system and can be further modified for air revitalization in confined spaces.CO2 removalHydroxide exchangeMembrane fuel cellsThesis1347441980https://doi.org/10.58088/wrca-6k722022-08-10en