(Keynote) Effect of Architecturally Expressed Electrodes and Catalysts on Energy Storage/Conversion in Aqueous Electrolytes

Abstract

The design platform around which our team creates high-performance electrodes for electrochemical energy devices that use aqueous electrolytes entails the use of porous, aperiodic architectures. The electrode structures, which are based on such form factors as papers and foams, are mostly nothing. Fabrication is based on bench top and scalable protocols with the final 3D form comprising a solid, bonded network co-continuous in three dimensions (3D) with micro- and nanoscale void. Three recent examples include: (1) Demonstrating the activity and stability of conformal RuO2 “nanoskins” on technologically relevant, silica fiber paper for water oxidation in acid electrolyte. By wrapping the fibers with <100 nm–thick shells of conductive pyrolytic carbon before nanoskin deposition, the RuO2@C@SiO2 electrode evolves O2 with an overpotential of 330 mV at 40–60 mA mgRuO₂ –1 and retains the high specific activity of RuO2 nanoskins while using a catalyst density 300−580× less than that of bulk RuO2 [1]. (2) Fabricating dendrite-prone zinc into monolithic anodes with porous, aperiodic architectured form-factors (“sponges”) that innately suppress zinc migration and dendrite development in alkaline electrolyte. With unprecedented cyclability at high depths-of-discharge (theoretical DODZn), increased specific capacity relative to conventional powder-bed Zn electrodes, and tens of thousands of cycles at low-DODZn pulse-power profiles in prototype Ni–Zn cells [2], this breakthrough enables the entire family of alkaline Zn batteries (Ni–Zn, Ag–Zn, MnO2–Zn, and Zn–air) to be reconfigured in extensively rechargeable forms, with energy and power characteristics that are competitive with Li-ion batteries. Our second-generation emulsion protocol improves the volumetric density of the sponge thereby concomitantly improving the energy density and power density of the cell while adding mechanical ruggedness to the anode [3]. (3) Evaluating oxygen-evolution and -reduction electrocatalysts as a function of their pore–solid architecture in which the free volume can be adjusted from >85% (aerogel) to 40–70% (ambigel) to ~30% (xerogel). Cryptomelane MnO2 aerogel and xerogel yield identical electrocatalytic activity when cast as thin films onto rotating-disk electrodes, yet when formulated with conductive carbon and polymer binder into a microheterogeneous air cathode that balances the zinc sponge in a zinc–air button cell, the aerogel-catalyzed cell exhibits an overpotential for oxygen reduction lowered by ∼50 mV compared to the xerogel-based analog and improves discharge voltage by 100 mV at moderate-to-challenging current densities (5–125 mA cm–2) [4]. [1] P.A. DeSario, C.N. Chervin, E.S. Nelson, M.B. Sassin, and D.R. Rolison, Competitive oxygen evolution in acid electrolyte catalyzed at technologically relevant electrodes painted with nanoscale RuO2. ACS Appl. Mater. Interfaces, 9, 2387–2395 (2017). [2] J.F. Parker, C.N. Chervin, I.R. Pala, M. Machler, M.F. Burz, J.W. Long, and D.R. Rolison, Rechargeable nickel–3D zinc batteries: An energy-dense, safer alternative to lithium-ion. Science, 356, 415–418 (2017). [3] J.S. Ko, A.B. Geltmacher, B.J. Hopkins, D.R. Rolison, J.W. Long, and J.F. Parker, ACS Appl. Energy Mater. (doi: 10.1021/acsaem.8b01946). [4] J.S. Ko, J.F. Parker, M.N. Vila, M.A. Wolak, M.B. Sassin, D.R. Rolison, and J.W. Long, Electrocatalyzed oxygen reduction at manganese oxide nanoarchitectures: From electroanalytical characterization to device-relevant performance in composite electrodes. J. Electrochem. Soc., 165, H777–H783 (2018).