Electrochemical performance of Bi2O3 supercapacitors improved by surface vacancy defects

Vacancy defects have important impacts on the physical-chemical properties of metal oxides. In the present work, two types of Bi2O3 powders with different morphologies were synthesized for supercapacitor electrodes by calcination (denoted as c-Bi2O3) and two-step hydrothermal methods (donated as h-Bi2O3). Vacancy clusters of V'BiVO++V'''(Bi) with different concentrations were observed in these two samples by positron annihilation lifetime spectroscopy. The results of electrochemistry revealed that the charge storage behavior of h-Bi2O3 with more V'''BiVO++V'''(Bi) defects obeyed both semi-infinite diffusion-controlled battery-type mechanism and surface-controlled pseudo-capacitance mechanism, while that of the calcined c-Bi2O3 electrode with a lower concentration of V'''BiVO++V'''(Bi) defects followed only the semi-infinite diffusion-controlled battery-type mechanism. The pseudocapacitance of h-Bi2O3 could be attributed to the insertion/extraction process of more K+ ions in the V'''BiVO++V'''(Bi) Bi surface defects. Due to the partial pseudo-capacitance and improved conductivity caused by more V'''BiVO++V'''(Bi) defects, the h-Bi2O3 electrode had a larger capacitance (1043 F g(-1) at 1 A g(-1)), a higher rate performance (560 F g(-1) at 60 A g(-1)), and better cycle stability (93% retention at 50 A g(-1) after 2000 cycles). Furthermore, because of the high-concentration of V'''BiVO++V'''(Bi) defects, the Ni/Co-MOF//h-Bi2O3 asymmetric supercapacitor delivered a relatively higher specific energy density of 47 Wh kg(-1) at 1125 W kg(-1). Taken together, these results indicate that surface vacancy clusters play an important role in boosting the electrochemical performance of metal oxide electrodes.

Automated summary

This study investigated the impact of vacancy defects on the physical-chemical properties of Bi2O3 powders used as supercapacitor electrodes. It was found that the h-Bi2O3 sample with more V'''BiVO++V'''(Bi) defects exhibited better cycle stability and rate performance, attributed to the insertion/extraction process of K+ ions in the surface defects. Furthermore, the high concentration of V'''BiVO++V'''(Bi) defects in the h-Bi2O3 electrode led to improved conductivity and higher specific energy density in an asymmetric supercapacitor configuration.