Precise Tailoring of Ir-FeOx Interfaces for Improved Catalytic Performance in Preferential Oxidation of Carbon Monoxide in Hydrogen

Preferential oxidation of CO in H-2 (PROX) has been regarded as the most promising on-board approach to remove the trace levels of CO (similar to 1%) present in hydrogen fuels and thus to protect the Pt electrodes of proton exchange membrane fuel cells (PEMFCs) against CO poisoning. However, development of an active and selective catalyst toward CO oxidation in a broad low-temperature range remains challenging due to the competitive hydrogen oxidation reaction. Here, we report that selective deposition of the FeOx overcoat onto SiO2-supported Ir nanoparticles using the atomic layer deposition (ALD) technique allows precisely tailoring Ir-FeOx interfaces for optimizing catalytic performance in the PROX reaction. Compared to the uncoated Ir/SiO2 sample, FeOx-coated Ir/SiO2 samples exhibited remarkable activity enhancements, where we observed a volcano trend of the improved activity as a function of the numbers of FeOx ALD cycles. The optimized catalytic performance was achieved on a 1.5 nm Ir/SiO2 sample with two cycles of FeOx overcoating, by achieving complete CO conversion in a broad temperature range of 60-180 degrees C in the PROX reaction, which is the broadest temperature range over Ir-based catalysts reported in the literature so far. We noticed that the activity improvement over these samples was much less pronounced in CO oxidation in the absence of H-2, which implies that the formation of hydroxyls on the FeOx overcoat might be attributed to the large activity enhancement in the PROX reaction.