The ever increasing power of electronic devices creates a taxing demand on energy storage technology to increase the energy and power density available. Typical energy storage devices that have met this demand in the past are batteries and capacitors. A growing need for high energy and power dense materials leads to a new set of devices called pseudocapacitors, typically made from battery electrode materials but on a nanometer scale, which push the limit of both energy and power density available in a single device. The charge storage system of pseudocapacitors can be broken into several parts: double-layer capacitance, underpotential deposition, redox and intercalation pseudocapacitance which occurs through quick intercalation and surface redox reactions on the electrode.¹ Therefore, to maximize the capabilities of pseudocapacitors the surface area must be increased for double-layer capacitance as well as allowing fast and reversible faradaic reduction-oxidation reactions. The exact nature of these redox reactions are not fully understood with respect to the oxidation state of the atoms. A typical pseudocapacitor material is Ruthenium Oxide (RuO₂) which exhibits great pseudocapacitor properties but becomes expensive when looking to make on a large scale. The goal of this work is to better understand the material properties of pseudocapacitive materials, such as RuO₂, that permit them to have the qualities of a pseudocapacitor as opposed to that of a battery. To do this work, the use of highly efficient and high throughput computation models, such as density functional theory (DFT), are used to proficiently calculate material properties in order to exclude material systems that do not meet designated outcomes. A particular method of interest for this process is the Self-Consistent Continuum Solvation model (SCCS)² which allows DFT to correctly model the dielectric properties of a solvent. From the values calculated in DFT we are able to predict the change in the Gibbs free energy as well as the change in the chemical potential of the system as the surface of the material is covered with ions. Furthermore, charged surface calculations allow for the prediction of the change in the material properties at different levels of coverage³ and charge. For future and current work we would apply these models to pseudocapacitor systems to examine if they have intrinsic properties or if the material could be manipulated on the structural level to have the abilities of an extrinsic pseudocapacitor.

References

1.        Augustyn, V., Simon, P. & Dunn, B. Pseudocapacitive oxide materials for high-rate electrochemical energy storage. Energy Environ. Sci. 7, 1597 (2014).

2.        Andreussi, O., Dabo, I. & Marzari, N. Revised self-consistent continuum solvation in electronic-structure calculations. J. Chem. Phys. 136, 064102 (2012).

3.        Bonnet, N. & Marzari, N. First-principles prediction of the equilibrium shape of nanoparticles under realistic electrochemical conditions. Phys. Rev. Lett. 110, 1–5 (2013).