CO-tolerant hydrogen oxidation on Pt enabled by ultrathin silica overlayers

Low-temperature electrochemical hydrogen compression can combine H₂ compression and purification, but CO impurities in practical H₂ feeds rapidly poison Pt anodes. Here, we use sputter- and electrodeposited Pt on Ti disk model electrodes to assess whether ultrathin polydimethylsiloxane (PDMS)-derived amorphous silica overlayers can improve CO tolerance during the hydrogen oxidation reaction (HOR). Fourier-transform infrared reflection-absorption and low-energy ion-scattering spectroscopy confirmed conformal and amorphous silica overlayer formation on Pt. Nominal thickness-dependent measurements revealed a narrow activity-protection window within the sub-10 nm regime. 2-3 nm silica overlayers provided limited CO tolerance, whereas increasing the nominal thickness from 7 to 8 nm strongly suppressed HOR activity. Benchmarking against active electrochemical regeneration showed that bare Pt operated at 0.15 V vs. RHE with 15 s CO-stripping pulses at 0.85 V vs. RHE delivered a 1.8 times higher time-averaged HOR power density than silica-coated Pt. However, the pulses introduced an 8% energy-efficiency loss and rely on repeated high-potential cycling that accelerates electrode degradation. Importantly, under fixed-current operation, silica-coated Pt reduced the cumulative HOR energy demand under CO contamination by a factor of up to 3.6. These results establish ultrathin silica overlayers as a promising interfacial design strategy for CO-tolerant hydrogen oxidation and motivate translation to gas-diffusion electrodes (GDEs), where homogeneous and selective coating of porous electrodes remains the key challenge.