Proton exchange membrane water electrolysis for green hydrogen production is typically designed for ultrapure water feeds. In offshore applications, for example, when coupled to desalination, residual chloride can still trigger the chlorine evolution reaction (CER), motivating the development of oxygen evolution reaction (OER)-selective anodes. Silicon oxide (SiO_x) nanocoatings exhibit chloride-blocking behavior and suppress Cl₂ formation. Previous studies used spin coating (SC) to fabricate SiO_x coatings, but enhanced OER selectivity was limited to smooth catalyst surfaces, and the coatings showed poor mechanical stability. Here, we introduce atomic layer deposition (ALD) as a vapor-phase alternative and benchmark it against SC to investigate how the SiO_x fabrication method influences chlorine suppression on rough amorphous IrO_x anodes. SiO_x-coated anodes were evaluated in a low-salinity acidic electrolyte using a rotating ring–disk electrode (RRDE) to quantify chlorine evolution and assess mechanical integrity. After 50 scans, plasma-enhanced ALD and spray coating at a SiO_x thickness of 0.5 nm both reduced CER selectivity by approximately 36% relative to uncoated IrO_x, whereas thermal ALD showed no selective CER suppression. These findings show that the chloride-blocking behavior of ultrathin SiO_x nanocoatings depends strongly on the deposition route and likely arises from multiple coupled chemical, structural, and interfacial properties.

In this study, we investigated the wettability and agglomeration characteristics of polymer microspheres coated with low-temperature deposited SiO₂ in a fluidized bed atomic layer deposition (ALD) setup. Surface characterization revealed the presence of a significant amount of deposited Si-OH groups within the first cycles. A drastic decrease in agglomerate size, water contact angle (WCA), and droplet absorption time of the powder was observed when coating was applied. Furthermore, we observed an increase in the amount of Si-OH present on the particle surface with increasing coating cycles, while no significant improvement in water affinity was found after the first coating cycles. Our findings suggest that surface coverage is the primary factor in improving the colloid stability of particles, coated at low temperatures. The low temperature operation of our system introduced a chemical vapor deposition (CVD) component to our coating process, which allowed full surface coverage to be achieved within the first two coating cycles.