(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award) Tailoring Electrode-Electrolyte Interfaces through Non-Covalent Interactions for Electrochemical Energy Storage and Conversion

Abstract

Li-ion batteries and fuel cells play essential roles in electrifying transportation. Central to the electrochemical systems is the electrode-electrolyte interface, where (electro)chemical surface reactions or intercalation occur, and its thermodynamic and kinetic properties determine the energy density, power density, and lifetime of the electrochemical devices. However, the molecular structures at the electrical double layer and reaction mechanisms remain poorly understood, hindering the rational material design for more efficient electrochemical devices. This talk focuses on the mechanisms of (electro)chemical reactions and charges transfer kinetics at the electrode-electrolyte interface, providing design principles based on non-covalent interactions in electrolytes.First, an in situ Fourier-transform infrared spectroscopy (FTIR) method was developed for Li-ion batteries, which revealed unique evidence for dehydrogenation of carbonate electrolytes on Ni-rich lithium nickel, manganese and cobalt oxides (NMC), accounting for interface impedance build-up and battery capacity fading. Based on the proposed mechanism, strategies on suppressing electrode and electrolyte reactivity were demonstrated to improve battery cycling. Next, the kinetic mechanism for ion intercalation at the electrode-electrolyte interface will be discussed. Li-ion concentration-dependent intercalation kinetics was demonstrated from charge-adjusted electrochemical experiments and fit into a coupled ion-electron transfer mechanism, which governed the current-dependent maximum capacity and power density of intercalation batteries. Finally, for electrocatalytic reactions central to fuel cell technologies, we demonstrated tuning interfacial hydrogen bonding through protic ionic liquids with different acid dissociation constants and organic solvents with different donor numbers to tailor oxygen-reduction reaction (ORR) and hydrogen evolution reaction (HER). Strengthening hydrogen bonding between ORR products and ionic liquids, or between interfacial water molecules facilitated proton-coupled electron transfer kinetics, revealed by in situ surface-enhanced infrared absorption spectroscopy and density functional theory (DFT) calculations. The study can pave the way for the electrolyte and electrode design of electrochemical storage devices with improved energy and power density and cycle life.