(669f) Understanding the Atomic Interaction between Electrode and Electrolyte for Aqueous Electrochemical Energy Storage

New nanostructured materials are the key to energy conversion and storage processes, both of which are of great importance to meet the challenge of global warming and the finite nature of fossil fuels. In this talk, I will present our recent studies of metal oxide nanomaterials which offer unique properties as electrode materials for aqueous electrochemical energy storage. Aqueous electrochemical energy storage (EES) devices using earth-abundant electrode material (e.g., manganese oxide and vanadium oxide), a low-cost and safe aqueous electrolyte and the charge carriers beyond lithium (e.g., sodium or potassium) ions, offer a transformative technology for portable electronics and transportation compared with non-aqueous lithium-ion batteries (LIBs). However, key technical challenges for aqueous EES to rival the performance of LIBs include its limited storage capacity and narrow potential window of ~ 1.2 V. Here I will present our new approach to overcome these limitations of aqueous storage. Particularly, the talk will focus on our recent discovery of a new type of manganese oxide (Mn₅O₈) nanoparticles with a hydroxylated interphase, validated by synchrotron- and/or neutron-based adsorption and total scattering (pair distribution function analysis) measurements. Such electrode materials not only have high overpotential towards HER and OER in aqueous environments, but also retain high reversibility and effectiveness for Na-ion storage. This new “game-changing” electrode material demonstrates stable potential windows of 2.5 V in a half-cell, as well as excellent energy density, power density and cycle life. Our results offer a new paradigm for developing electrode materials with a wide potential window and facile charge transfer for aqueous energy storage devices, which exhibits the performance comparable to that of non-aqueous LIBs, but much safer, less costly and more environmentally benign.