2 research outputs found
Physical Interpretation of Cyclic Voltammetry for Hybrid Pseudocapacitors
This
study aims to elucidate the respective contributions of faradaic
reactions and electric double layer formation to charge storage in
hybrid pseudocapacitors. It also aims to provide physical interpretation
of experimental cyclic voltammetry (CV) measurements. First, a physicochemical
transport model was derived from first-principles for simulating coupled
interfacial, transport, and electrochemical phenomena in hybrid pseudocapacitors.
The model simultaneously accounted for (i) charge transport in both
electrodes and electrolyte, (ii) the dynamics of the electric double
layer, (iii) steric repulsion due to finite ion sizes, (iv) redox
reactions, and (v) intercalation. Then, CV curves were simulated for
different electrode thicknesses and Li diffusion coefficients in the
planar pseudocapacitive electrode. Particular attention was paid to
the so-called <i>b</i>-value characterizing the power law
evolution of the total current with respect to scan rate for a given
potential. Overall, trends observed in numerically generated CV curves
showed good agreement with experimental measurements. In addition,
the results indicated that a <i>b</i>-value of unity across
the potential window can be associated with purely faradaic charge
storage with fast ion intercalation in the thin-film pseudocapacitive
electrode. The study also demonstrates that under diffusion-limited
conditions of Li intercalation in the pseudocapacitive electrode,
the CV curves exhibited two distinct regimes: a faradaic regime dominated
by faradaic reactions and a capacitive regime dominated by electric
double layer formation. The <i>b</i>-value was near 1.0
in both regimes. However, a dip in the <i>b</i>-value, often
observed experimentally, was also obtained and attributed to the transition
between the capacitive and the faradaic regimes