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

DeSario, Paul A., Chervin, Christopher N., Nelson, Eric S., Sassin, Megan B., Rolison, Debra R.
ACS Applied Materials & Interfaces 2017 v.9 no.3 pp. 2387-2395
anodes, carbon, catalysts, electrolytes, foil, oxygen, oxygen production, paper, silica, superoxide anion
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.