Design rules of pseudocapacitive electrode materials: ion adsorption, diffusion, and electron transmission over prototype TiO2

The development of a high-performing pseudo-capacitor requires a comprehensive understanding of electrode materials from the aspects of electron transfer and electrolyte ion adsorption and diffusion. Herein, these factors are considered over the prototype TiO2, and a high pseudo-capacitance is achieved via the introduction of various defects, i.e., oxygen defect (VO) and co-doped defect (VO+NO). The study is based on joint explorations of first-principle calculations and the transfer matrix method. Relative to pristine TiO2 (300 F g−1), defective TiO2 produces pseudocapacitance as high as 1700 F g−1. Moreover, defects induce small barriers for electron transmission caused by surface band bending. The climbing image nudged elastic band diffusion of H ions displays a much higher barrier in TiO2−VO than in TiO2−VO+NO. Such a result indicates easy H diffusion in the co-doped system. This work provides insights into the adsorption and diffusion of electrolyte ions and the influence of defects on electron transfer. The results are also significant for the design and optimization of electrode materials for the next generation of supercapacitors.