Maintaining high performance after extensive use remains a key challenge for low-Pt proton exchange membrane fuel cells for transportation applications. Strategically improving catalyst durability requires better understanding of the relationship between degradation mechanisms and catalyst structure. To investigate the effects of the carbon support morphology, we compare the electrochemical performance and durability of membrane electrode assemblies (MEAs) using Pt and PtCo_x catalysts with a range of porous, solid, and intermediate carbon supports (HSC, Vulcan, and acetylene black). We find that electrochemical surface area (ECSA) retention after a catalyst-targeted durability test tends to improve with increasing support porosity. Using electron microscopy, we investigate microstructural changes in the catalysts and reveal the underlying degradation mechanisms in MEA specimens. Pt migration to the membrane and catalyst coarsening, measured microscopically, together were quantitatively consistent with the ECSA loss, indicating that these were the only two significant degradation pathways. Changes in catalyst particle size, morphology, and PtCo core-shell structure indicate that Ostwald ripening is a significant coarsening mechanism for catalysts on all carbons, while particle coalescence is only significant on the more solid carbon supports. Porous carbon supports thus appear to protect against particle coalescence, providing an effective strategy for mitigating catalyst coarsening.

Relatively large O₂ transport resistance at the ionomer and Pt interface has been thought to be responsible for the large performance loss at high power for a low Pt loading proton-exchange-membrane fuel cell. A facile method to characterize the interface in the fuel cell electrode is needed. In this study, the CO displacement method was explored on polycrystalline Pt and carbon-supported Pt nanoparticles. The displacement charge coverages were used to quantify the adsorption of perchlorate, sulfate, and perfluorosulfonic acid ionomer. The application of this method in a fuel cell electrode was demonstrated.

The hydrogen/bromine flow battery is a promising candidate for large-scale energy storage due to fast kinetics, highly reversible reactions and low chemical costs. However, today's conventional hydrogen/bromine flow batteries use membrane materials (such as Nafion), platinum catalysts, and carbon-paper electrode materials that are expensive. In addition, platinum catalysts can be poisoned and corroded when exposed to HBr and Br_2, compromising system lifetime. To reduce the cost and increase the durability of H₂/Br₂ flow batteries, new materials are developed. The new Nafion/ polyvinylidene fluoride electrospun composite membranes have high perm-selectivity at a fraction of the cost of Nafion membranes; the new nitrogen-functionalized platinum-iridium catalyst possesses excellent activity and durability in HBr/Br₂ environment; and the new carbon-nanotube-based Br₂ electrodes can achieve equal or better performance with less materials when compared to baseline electrode materials. Preliminary cost analysis shows that the new materials reduce H₂/Br₂ flow-battery energy-storage system stack and system costs significantly. The resulting advanced H₂/Br₂ flow batteries offer high power, high efficiency, substantially increased durability, and expected reduced cost.

Intermittent renewable energy sources like wind and solar require energy storage to be fully exploited. The H₂-Br₂ flow battery has been identified as a great candidate for this application because of its high energy conversion efficiency and power density capability. To evaluate the performance of this system a fuel cell with a membrane electrode assembly made of a Nafion 212 membrane and electrodes with 0.55 mg Pt/cm² loading was tested at 22°C under the H₂-H₂, H₂-O₂, H₂-Br₂ modes to compare the performance between these systems. The exchange current density of the Br⁻/Br₂ reactions on platinum was found to be about a quarter of that of the hydrogen reactions on the same substrate (0.3 mA/cm² Pt versus 1.2 mA/cm² Pt). Peak power density during discharge was 0.30 W/cm² at a voltage efficiency of 70% for the H₂-Br₂ mode versus 0.17 W/cm² at 40% for the H₂-O₂ mode under similar conditions. The performance of the H₂-Br₂ fuel cell is determined mainly by the ohmic and mass transport resistances in the cell, which could be improved by using higher reactant concentrations, higher operating temperatures, more conductive membranes, and electrode and cell designs that enhance transport.

Achieving high power performance and durability with low Pt loadings are critical challenges for proton exchange membrane fuel cells. PtCo catalysts developed on new carbon black supports show promise by simultaneously providing good oxygen reduction kinetics and local oxygen transport. We investigate the role of nanoscale morphology in the performance of these catalysts supported on accessible (HSC-e and HSC-f) and conventional (Ketjen Black) porous carbons using 3D electron tomography, nitrogen sorption, and electrochemical performance measurements. We find that the accessible porous carbons have hollow interiors with mesopores that are larger and more numerous than conventional porous carbons. However, mesopore-sized openings (>2 nm width) are too rare to account for significant oxygen transport. Instead we propose the primary oxygen transport pathway into the interior is through 1–2 nm microporous channels permeating the carbon. The increased mesoporosity in the accessible porous carbons results in a shorter diffusion pathlength through constrictive, tortuous micropores in the support shell leading to lower local oxygen transport resistance. In durability testing, the accessible porous carbons show faster rates of electrochemical surface area loss, likely from fewer constrictive pores that would mitigate coarsening, but maintain superior high current density performance at end of test from the improved local oxygen transport.