Competitive Oxygen Evolution in Acid Electrolyte Catalyzed at Technologically Relevant Electrodes Painted with Nanoscale RuO2.

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Using a solution-based, non-line-of sight synthesis, we electrolessly deposit ultrathin films of RuO2 ("nanoskins") on planar and 3D substrates and benchmark their activity and stability for oxygen-evolution reaction (OER) in acid electrolyte under device-relevant conditions. When an electrically contiguous ∼9 nm thick RuO2 nanoskin is expressed on commercially available, insulating SiO2 fiber paper, the RuO2@SiO2 electrode exhibits high current density at low overpotential (10 mA cm-2 @ η = 280 mV), courtesy of a catalyst amplified in 3D; however, the mass-normalized activity falls short of that achieved for films deposited on planar, metallic substrates (Ti foil). By wrapping the fibers with a <100 nm thick graphitic carbon layer prior to RuO2 deposition (RuO2@C@SiO2), we retain the high mass activity of the RuO2 (40-60 mA mg-1 @ η = 330 mV) and preserve the desirable macroscale properties of the 3D scaffold: porous, lightweight, flexible, and inexpensive. The RuO2@C@SiO2 anodes not only achieve the 10 mA cm-2 figure of merit at a low overpotential (η = ∼270 mV), but more importantly they do so while (1) minimizing the mass of catalyst needed to achieve this metric, (2) incorporating the catalyst into a practical electrode design, and (3) improving the long-term stability of the catalyst. Our best-performing anodes achieve state-of-the-art or better performance on the basis of area and mass, and do so with a catalyst density 300-580× less than that of bulk RuO2. By limiting the oxidizing potential required to evolve O2 at the electrode, even at 10 mA cm-2, we achieve stable activity for 100+ h.