Electrochemical Studies of Ceramic Carbon Electrodes Prepared with Sulfonated Organosilane Precursors

State-of-the-art electrodes for proton exchange membrane fuel cells (PEMFCs) contain platinum catalyst and a Nafion proton-conducting binder. Optimal conditions for Nafion functionality are at 80°C and 100% relative humidity (RH). Ceramic carbon electrodes (CCEs), consisting of carbon particles supported by ceramic binder network, may be an alternative electrode structure which replaces Nafion with organosilane materials. CCEs are also attractive for their high surface area and durable nature. CCEs have been fabricated via an in-situ sol-gel polymerization process. Development of a novel electrode fabrication procedure included direct spray-deposition of CCEs onto a microporous/gas diffusion layer to facilitate adhesion and facile electrode preparation. CCEs were composed of commercial carbon-supported platinum catalyst and 3-trihydroxysilyl-1-propanesulfonic acid (TPS) or TPS and tetraethylorthosilicate (TEOS) to vary the level of sulfonation. CCEs were initially tested electrochemically in a half-cell set-up to evaluate electrode functionality.;An optimal loading of 42-48 wt% silane was determined for CCEs with only TPS to provide the highest electrochemically active surface area (ECSA) of platinum and proton conductivity. BET surface areas were low due to restriction of pore sizes by the sulfonated side chain. Composite CCEs of TPS/TEOS had enhanced electrochemical performance and high BET surface areas (>400 m 2 g-1), indicating high porosity. Excellent electrochemical results were obtained for the CCE with a TPS:TEOS ratio of 4:96 (40 wt% total silane).;The sulfonated TPS/TEOS CCE (SS-CCE) was further evaluated in a fuel cell. Electrochemical studies showcased higher accessibility of catalyst sites and good proton conductivity compared to Nafion-containing cathodes. At 80°C and 100% relative humidity (RH), CCEs performed similarly to Nafion electrodes at low current density but suffered from mass transport limitations due to flooding at high current density. Investigation at lower %RH conditions revealed superior performance for membrane electrode assemblies (MEAs) with SS-CCE cathodes compared to Nafion-based cathodes, resulting from back-diffusion of water from the cathode to the membrane.;SS-CCE durability was demonstrated over multiple start-up/shut-down conditions and 300 hours of continuous load testing. Carbon corrosion and silane backbone degradation were not observed, though ECSA was reduced. Transport phenomena related to performance losses were evaluated compared to Nafion cathodes. No performance drop was observed when air was the oxidant (vs. oxygen), suggesting excellent oxygen transport capabilities for SS-CCE cathodes. Oxygen diffusivity through the catalyst layer is enhanced by the silane-based ionomer, and the major contribution to performance loss is related to pore flooding, which could be alleviated under low humidity conditions.;Keywords: proton exchange membrane fuel cell, ceramic carbon electrode, electrochemistry, sulfonated organosilane, sol-gel, carbon-supported catalysts, microporous layer, relative humidity, durability, cyclic voltammetry, electrochemical impedance spectroscopy.