Determining the Gibbs Energy Contributions of Ion and Electron Transfer for Proton Insertion in ϵ‐MnO₂

Abstract

Electrochemically active ϵ‐MnO2 and ɣ‐MnO2 as tunnel‐type host‐guest structures have been extensively studied by crystallography and electrochemical techniques for application in battery cathode materials. However, the Gibbs energies of the underlying ion and electron transfer processes across the electrode interfaces have not yet been determined. Here we report for the first time these data for ϵ‐MnO2. This was possible by measuring the mid‐peak potentials in cyclic voltammetry and the open‐circuit potentials under electrochemically reversible conditions.

Cation Co‐intercalation in Potassium Copper(II) Hexacyanoferrates

“…(4) can be represented as the sum of the process of ion insertion described by Eq. (6) and a process of electron transfer non‐mediated by electrolyte cations, [34–37] $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr \{{\rm M}{_{x}}{\rm K}{_{a}}{\rm Cu}{_{b}}{\rm Fe}{_{c}}[{\rm Fe}{^{{\rm II}}}({\rm CN}){_{6}}]{^{x+}}\}{_{{\rm s}}}+x{\rm e}{^{- }}{\stackrel{{\leftarrow}} {{\rightarrow} } }\hfill\cr \{{\rm M}{_{x}}{\rm K}{_{a}}{\rm Cu}{_{b}}{\rm Fe}{_{c}}[{\rm Fe}{^{{\rm II}}}({\rm CN}){_{6}}]\}{_{{\rm s}}}\hfill\cr}}$$$ …”

“…At the mid‐peak potential, the activities of solid phases cancel so that the difference between the mid‐peak potential recorded in CV measurements and the OCP should be constant and independent on the concentration of M + in the electrolyte. In turn, assuming that the solid‐state transformations are topotactic, one can take, as in the case of ϵ‐MnO 2 , [37] E ° Mox = E ° Mrd . Then, the electronic contribution, given by E II , can be separated from the ionic one, given by E OCP , taking, $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr E_{{\rm{II}}} = {\rm{E}}_{{\rm{mp}}} - E_{{\rm{OCP}}} = E^{\rm{o}} _{\rm{I}} - E^{\rm{o}} _{{\rm{OCP}}} \hfill\cr}}$$$ …”

“…A case of particular interest is that where ion co‐insertion can occur [25,40,41] . In the current report, it is presented a theoretical description of reductive/oxidative ion insertion processes for these cases based on the model of Malaie et al [37] . and considering that of Erinmwingbovo et al [25] .…”

“…[29][30][31][32][33] Recent analysis of electrochemical ion insertion processes permits the separation of the electronic and ionic contributions to thermochemical parameters combining voltammetric and open circuit potential (OCP) measurements. [34] This is of application to different ion-permeable solids [35][36][37] offering new possibilities in the analysis of thermochemical data in the context of ths three-phase electrochemistry. [38,39] A case of particular interest is that where ion co-insertion can occur.…”

“…[38,39] A case of particular interest is that where ion co-insertion can occur. [25,40,41] In the current report, it is presented a theoretical description of reductive/oxidative ion insertion processes for these cases based on the model of Malaie et al [37] and considering that of Erinmwingbovo et al [25] The model is applied to experimental data on the insertion of alkali ions into K-containing copper(II) hexacyanoferrate (KCuHCF) in contact with Li + , Na + , and K + -containing DMSO electrolytes. These systems, of application in lithium-ion batteries, [10] have been studied combining cyclic voltammetric (CV), OCP and chronoamperometric (CA) measurements.…”