2.6 V Aqueous Battery with a Freely Diffusing Electron Acceptor

Abstract

Here we show a strategy to expand the working voltage of aqueous metal batteries beyond the thermodynamic limit of 1.23 V by modifying the interfacial chemistry existing at the cathode/electrolyte interface. Highly nonwettable carbon nanoparticle cathode/electrolyte interface with a freely diffusing electron acceptor kinetically muted water decomposition due to reduced contact between water and the electrode, expanding the working voltage far beyond 1.23 V. Zn battery equipped with hydrophobic carbon nanoparticle cathode delivered an open-circuit voltage (OCV) of 2.6 V with capacity (∼930 mAh/g), energy (∼2420 Wh/kg @ 50 mA/cm2), and power densities (∼83 W/kg) remarkably higher than conventional Pt-based aqueous Zn-air batteries (OCV = 1.5 V, ∼650 mAh/g, ∼1161 Wh/kg, and ∼43 W/kg). When probed with in situ and ex situ FTIR spectroelectrochemistry and galvanostatic intermittent titration technique, wettable carbon particles (contact angle = ∼20°) are found to catalyze parasitic oxygen evolution reaction, while their nonwettable counterpart (contact angle = ∼117°) dominantly catalyzed electron acceptor’s redox reaction by inhibiting any such parasitic chemistry. Zn batteries equipped with carbon cathode contribute to a Pt-free battery having a closed cathode, addressing the complexity of carbonate clogging and electrolyte evaporation often encountered in open-air batteries, and could be used to power electrical appliances.