Rethinking Pseudocapacitance: A Way to Harness Charge Storage of Crystalline RuO2

With its huge pseudocapacitance and excellent stability, ruthenium dioxide (RuO2) is considered to be one of the best electrode materials for supercapacitors. However, such properties are only obtained with hydrous RuO2 in an amorphous phase, limiting the range of possible deposition techniques. Herein we report a detailed understanding of reactions of protons (H+) occurring in crystalline RuO2 with regard to its orientation using density functional theory. In particular, we show that migration pathways are energetically favorable along the [001] direction, leading to a deeper H+ penetration within the bulk of the active material and a much higher charge storage ability.