Optimization of Ultra-low Loading Catalyst Layers for PEMFC and PEMW Using Reactive Spray Deposition Technology

The optimization of low catalyst loading electrode fabricated with reactive spray deposition technology (RSDT) is conducted for proton exchange membrane fuel cell (PEMFC) and proton exchange membrane water electrolyzer (PEMWE) applications. For PEMFC, the key catalyst layer parameters studied in this work include: ionomer-to-carbon (I/C) ratio, platinum particle size, and platinum loading on carbon. The RSDT-derived catalyst layers were shown to exhibit better ionomer coverage on the carbon support than traditional fabrication method, reducing the amount of ionomer needed for optimal fuel cell performance. Analysis on the fuel cell polarization sources for RSDT-derived catalyst layer was performed to further elucidate the influence of I/C ratio on the oxygen reduction reaction (ORR) activity and oxygen transport. The effect of platinum particle size and platinum loading on carbon were studied by employing two types of gradient cathode to mitigate platinum dissolution and migration to the electrolyte membrane. One type of the gradient cathode was made with platinum particle size of 5 nm near the membrane and platinum particle size of 2 nm toward the GDL. The platinum loading on carbon was kept constant at 40 wt% throughout the cathode. The other type of gradient cathode kept the platinum particle size of 2 nm throughout the cathode but used higher platinum loading on carbon (60 wt%) near the membrane and 40 wt% platinum toward the GDL. Accelerated stress test was performed using triangular wave potential cycling from 0.6V to 1.0V at 50 mV s-1for 30,000 cycles. The degradation mechanism was investigated using cross-sectional transmission electron microscopy (TEM). Durable anode catalyst layer for PEMWE was developed with an IrOx/Nafion composite thin film with the key catalyst layer parameters being the surface oxidation state of iridium and the homogeneity of the catalyst layer. The oxide rich iridium showed superior oxygen evolution reaction (OER) activity and higher catalyst stability in electrolyzer test. In addition, the catalyst layer homogeneity played an important role in the catalyst stability. The optimized electrolyzer durability achieved ~1400 hours with ~0.08 mg cm-2 iridium loading, more than 90% reduction compare to the commercial catalyst.