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

Using a solution-based, non−line-of sight synthesis, we electrolessly deposit ultrathin films of RuO 2 (“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 RuO 2 nanoskin is expressed on commercially available, insulating SiO 2 fiber paper, the RuO 2 @SiO 2 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 RuO 2 deposition (RuO 2 @C@SiO 2 ), we retain the high mass activity of the RuO 2 (40–60 mA mg –1 @ η = 330 mV) and preserve the desirable macroscale properties of the 3D scaffold: porous, lightweight, flexible, and inexpensive. The RuO 2 @C@SiO 2 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 RuO 2 . By limiting the oxidizing potential required to evolve O 2 at the electrode, even at 10 mA cm –2, we achieve stable activity for 100+ h.