There is an urgent global need for electrochemical energy storage that includes materials that can provide simultaneous high power and high energy density. One strategy to achieve this goal is with pseudocapacitive materials that take advantage of reversible surface or near-surface Faradaic reactions to store charge. This allows them to surpass the capacity limitations of electrical double-layer capacitors and the mass transfer limitations of batteries. The past decade has seen tremendous growth in the understanding of pseudocapacitance as well as materials that exhibit this phenomenon. The purpose of this Review is to examine the fundamental development of the concept of pseudocapacitance and how it came to prominence in electrochemical energy storage as well as to describe new classes of materials whose electrochemical energy storage behavior can be described as pseudocapacitive.
In this proof-of-concept study, we introduce and demonstrate MXene as a novel type of intercalation electrode for desalination via capacitive deionization (CDI).
There
is widespread interest in determining the structural features
of redox-active electrochemical energy storage materials that enable
simultaneous high power and high energy density. Here, we present
the discovery that confined interlayer water in crystalline tungsten
oxide hydrates, WO3·nH2O, enables highly reversible proton intercalation at subsecond time
scales. By comparing the structural transformation kinetics and confined
water dynamics of the hydrates with anhydrous WO3, we determine
that the rapid electrochemical proton intercalation is due to the
ability of the confined water layers to isolate structural transformations
to two dimensions while stabilizing the structure along the third
dimension. As a result, these water layers provide both structural
flexibility and stability to accommodate intercalation-driven bonding
changes. This provides an alternative explanation for the fast energy
storage kinetics of materials that incorporate structural water and
provides a new strategy for enabling high power and high energy density
with redox-active layered materials containing confined fluids.
We introduce a hybrid energy storage system combining zinc iodide (ZnI2) as redox electrolyte with a nanoporous activated carbon fiber (ACF) cathode and a zinc disk anode.
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