Abstract
Interfacial charge transfer reactions involving cations and electrons are fundamental to (photo/electro) catalysis, energy storage, and beyond. Lithium-coupled electron transfer (LCET) at the electrode-electrolyte interfaces of lithium-ion batteries (LIBs) is a preeminent example to highlight the importance of charge transfer in modern-day society. The thermodynamics of LCET reactions define the minimal energy for charge/discharge of LIBs, and yet, these parameters are rarely available in the literature. Here, we demonstrate the successful incorporation of tungsten oxides (WO(x)) within a chemically stable Zr-based metal-organic framework (MOF), MOF-808. Cyclic voltammograms (CVs) of the composite, WO(x)@MOF-808, in Li(+)-containing acetonitrile (MeCN)-based electrolytes showed an irreversible, cathodic Faradaic feature that shifted in a Nernstian fashion with respect to the Li(+) concentration, i.e., ∼59 mV/log [(Li(+))]. The Nernstian dependence established 1:1 stoichiometry of Li(+) and e(-). Using the standard redox potential of Li(+/0), the apparent free energy of lithiation of WO(x)@MOF-808 (ΔG(app,Li)) was calculated to be -36 ± 1 kcal mol(-1). ΔG(app,Li) is an intrinsic parameter of WO(x)@MOF-808, and thus by deriving the similar reaction free energies of other metal oxides, their direct comparisons can be achieved. Implications of the reported measurements will be further contrasted to proton-coupled electron transfer (PCET) reactions on metal oxides.