Background:Since the pandemic outbreak of coronavirus disease 2019 (COVID-19), the health system capacity in highly endemic areas has been overwhelmed. Approaches to efficient management are urgently needed. We aimed to develop and validate a score for early prediction of clinical deterioration of COVID-19 patients.
Variations of the double layer capacitances (DLCs) at a platinum electrode with concentrations and kinds of salts in aqueous solutions were examined in the context of facilitating orientation of solvent dipoles. With an increase in ionic concentrations, the DLCs increased by ca. a half and then kept constant at concentrations over 1 mol dm−3. This increase was classically explained in terms of the Gouy–Chapman (GC) equation combined with the Stern model. Unfortunately, measured DLCs were neither satisfied with the Stern model nor the GC theory. Our model suggests that salts destroy hydrogen bonds at the electrode–solution interface to orient water dipoles toward the external electric field. A degree of the orientation depends on the interaction energy between the salt ion and a water dipole. The statistical mechanic calculation allowed us to derive an equation for the DLC as a function of salt concentration and the interaction energy. The equation took the Langmuir-type in the relation with the concentration. The interaction energy was obtained for eight kinds of salts. The energy showed a linear relation with the interaction energy of ion–solvent for viscosity, called the B-coefficient.
Potential-step chronoamperometry
was made at a platinum wire electrode
in KCl aqueous solution at the aim of finding the behavior of the
power law of the time or the constant phase element for the double-layer
(DL) capacitances. The logarithmic current decays linearly with the
time shorter than 0.1 ms, and then it obeys the power law in which
it has a linear relation with the logarithmic time in the millisecond
time domain. The transition from the exponential decay to the power
law was expressed theoretically for the model of a series combination
of the resistance and the DL capacitance. The expression predicts
that the double logarithmic plots of the current–time provide
a capacitance value at 1 s from the intercept, independent of the
resistance. This prediction was demonstrated experimentally in KCl
solutions of which concentrations ranged from 1 mM to 0.5 M. The capacitance
can be evaluated simply by chronoamperometry on a 1 s time scale without
considering any resistance effect. The capacitance values did not
vary with the applied potential.
Voltage vs. time curves of double layer capacitances (DLCs) by current-controlled charge and discharge steps have been recognized to be composed of triangular waves. They are deviated slightly from triangles from the viewpoint of the time dependence or the constant phase element of the DLC. In order to evaluate the deviation, we measured DLCs of a platinum (Pt) electrode in KCl solution by current-control. Each time-voltage curve was convex rather a line, and was followed by the power law. Even if the time dependence was subtracted from each curve, the enhancement of the DLC was noticeable with an increase in the time well as the voltage. It can be attributed to the electric field effect, in which dipoles of solvents are oriented on an electrode so strongly that the DLC may be increased. The field dependence can be justified with the kinetic theory of interacting dipoles of solvents on an electrode through the observed linearity of the logarithmic DLC with the net voltage. This concept was applied to a commercially available super-capacitor to demonstrate a significant contribution of the field effect.
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