Electrolytes for reversible zinc electrodeposition for dynamic windows

Abstract

Reversible metal electrodeposition is a promising approach for the construction of dynamic windows with electronically tunable transmission. In this manuscript, we study a series of aqueous electrolytes that support reversible Zn electrodeposition on transparent tin-doped indium oxide electrodes. By systematically altering the composition of the electrolytes, we develop relationships between the chemical identity of the halides, carboxylates, and haloacetates in the electrolytes and the electrochemical and optical properties of reversible Zn electrodeposition. This strategy enables us to design electrolytes with 99% coulombic efficiency that support reversible optical contrast on electrodes. X-ray diffraction and scanning electron microscopy analyses establish connections between the composition and morphology of the electrodeposits and the composition of the electrolytes. Although electrode degradation and H₂ evolution are thermodynamically favorable under the operating voltages of the electrolytes due to the negative standard reduction potential of Zn/Zn²⁺, we find that these reactions are kinetically passivated by the Zn and ZnO electrodeposits. An understanding of these electrochemical properties allows us to construct 25 cm² dynamic windows that switch with 64% optical contrast at 600 nm within 30 s. Because we utilize non-noble Zn as opposed to the noble metals commonly used in previous electrolytes, this work expands the chemical scope of electrolytes in dynamic windows based on reversible metal electrodeposition, which should lead to future advances in electrolyte design.