Selective Removal of Micropores and Defect Healing in Carbon Supports Using Polyaromatic Hydrocarbon Molecules for Enhanced Durability of PEMFCs

Recently, with the aggravation of global warming, sustainable energy storage and conversion technologies have received attention as alternatives to fossil fuel combustion engines. Proton exchange membrane fuel cells (PEMFCs) are regarded as one of the most promising candidates because of their zero carbon dioxide emissions and rapid conversion response. However, the high cost of catalysts, primarily due to the use of platinum and its insufficient durability, hinders their commercialization. In particular, carbon corrosion that occurs during the start/stop cycles of PEMFCs significantly deteriorates the performance by not only corrosion of the carbon support but also CO poisoning and Pt detachment. To address this issue, many researchers have attempted to use highly graphitic carbon synthesized by heat treatment at high-temperature treatment as a catalyst support. However, the dispersion of Pt nanoparticles decreases with increasing temperature due to the reduction of surface roughness and loss of anchoring sites such as defects and micropores, leading to the detachment of the nanoparticles during the cell operation. Hence, a breakthrough technology is needed to realize defect-free carbon support with sufficient anchoring sites.<br/>In this study, we synthesized the carbon supports at temperatures below 200°C using polyaromatic hydrocarbon molecules (PAMs) extracted from the petroleum pitch. The structural and electrochemical properties of as-synthesized carbon supports were then investigated. Our composite carbon support with PAMs (C-PAMs) showed a lower I_D/I_G ratio in Raman spectroscopy and a larger basal plane (L_a) compared to the pristine carbon support, whereas it exhibited similar 2-theta and L_c values in XRD results. This indicated that the addition of PAMs into the carbon supports is more effective in healing vacancies and defects in the basal plane than in promoting graphitization. Interestingly, the electrochemical surface area (ECSA) of 20 wt% Pt/C-PAMs was reduced by only 35.0% after 60,000 cycles of the accelerated durability test (ADT), while Pt/C catalyst experienced about 50% loss in ECSA relative to its initial value. In addition, the former and the latter showed a decrease in half-wave potential of 10 mV and 33 mV, respectively. Remarkably, micropores with a diameter of 2 nm in C-PAMs significantly decrease compared to the pristine carbon support, suggesting the selective removal of these micropores due to the electrostatic interaction between the PAMs and the micropores. Consequently, a single-cell prepared using the Pt/C-PAMs catalyst demonstrated outstanding performance in the region of mass-transfer limitation. Therefore, this suggests that our selective and fine control of micropores and defects could facilitate the realization of highly active and durable electrocatalysts at lower temperatures.