<i>Operando</i> Atomic Force Microscopy
Reveals Mechanics of Structural Water Driven Battery-to-Pseudocapacitor
Transition
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Abstract
The
presence of structural water in tungsten oxides leads to a
transition in the energy storage mechanism from battery-type intercalation
(limited by solid state diffusion) to pseudocapacitance (limited by
surface kinetics). Here, we demonstrate that these electrochemical
mechanisms are linked to the mechanical response of the materials
during intercalation of protons and present a pathway to utilize the
mechanical coupling for local studies of electrochemistry. <i>Operando</i> atomic force microscopy dilatometry is used to
measure the deformation of redox-active energy storage materials and
to link the local nanoscale deformation to the electrochemical redox
process. This technique reveals that the local mechanical deformation
of the hydrated tungsten oxide is smaller and more gradual than the
anhydrous oxide and occurs without hysteresis during the intercalation
and deintercalation processes. The ability of layered materials with
confined structural water to minimize mechanical deformation likely
contributes to their fast energy storage kinetics