Nanoscopic Silicon Oxide Overlayers Improve the Performance of Ruthenium Oxide Electrocatalysts Toward the Oxygen Evolution Reaction

RuO₂ is a highly active electrocatalyst for the oxygen evolution reaction (OER) but is unstable in acidic environments. Herein we investigate the encapsulation of RuO₂ nanoparticles with semipermeable, nanoscopic silicon oxide (SiO_x) overlayers as a strategy to improve their stability. SiO_x encapsulated RuO₂ (SiO_x|RuO₂) electrodes were prepared by drop-casting RuO₂ nanoparticles onto glassy carbon substrates followed by deposition of SiO_x overlayers of varying thickness by a room temperature photochemical deposition process. The best-performing SiO_x|RuO₂ electrodes consisted of 2-3 nm thick SiO_x overlayers on top of RuO₂ particles and 3-7 nm thick SiO_x on the glassy carbon substrate. Such electrodes exhibited lower overpotentials relative to bare RuO₂ due to an improved electrochemically active surface area while also demonstrating an ability to retain OER activity over time, especially at higher overpotentials. Surprisingly, it was found that the SiO_x coating was unable to prevent Ru dissolution, which was found to be proportional to the charge passed and independent of the presence or thickness of the SiO_x coating. Thus, other possible explanations for the improved current retention of SiO_x|RuO₂ electrodes are discussed, including the influences of the overlayer on bubble dynamics and the stability of the underlying glassy carbon substrate.