Probing the pseudocapacitance and energy-storage performance of RuO2 facets from first principles

The energy density of ruthenia (RuO2) pseudocapacitor electrodes is critically dependent on their surface structure. To understand this dependence, we simulate the electrochemical response of RuO2(110), RuO2(100), and RuO2(101) in aqueous environments using a self-consistent continuum solvation (SCCS) model of the solid-liquid interface. The insertion of protons into the RuO2(110) sublayer is found to profoundly affect the voltage-dependent characteristics of the system, leading to a sharp transition from a battery-type to capacitor-type response. The calculated charge-voltage properties for RuO2(101) are in qualitative agreement with experiment, albeit with a pseudocapacitance that is significantly underestimated. In contrast, the RuO2(100) facet is correctly predicted to be pseudocapacitive over a wide voltage window, with a calculated pseudocapacitance in close agreement with experimental voltammetry. These results establish the SCCS model as a reliable approach to predict and optimize the facet-dependent pseudocapacitance of polycrystalline systems.