Solution dependence of quantum capacitors of doped carbon nanotubes

Abstract

By first-principles calculations, the stability, quantum capacitance, and surface charge storage of doped carbon nanotubes in electrolytes were studied. The results show that the doping of B or N has obvious effect on the enhancement of quantum capacitance (CQ). The quantum capacitance of B- and N- doped carbon nanotubes can reach 143.52 μF•cm−2 and 195.59 μF•cm−2, respectively, which are 131.69 and 215.75% higher than that of the pristine carbon nanotubes. Meanwhile, we found that the acidity and alkalinity of the electrolyte have a significantly effect on the quantum capacitance of the electrode material. At the negative bias, the quantum capacitance of B- or N-doped carbon nanotubes in acidic electrolyte is respectively 137.63 or 97.72 μF•cm−2, which increased by 122.19% or 57.74% compared with the pristine carbon nanotubes. At positive bias, the quantum capacitance of B-doped carbon nanotubes in alkaline electrolyte is 126.34 μF•cm−2, which is 104.02% higher than that of pristine carbon nanotubes. The quantum capacitance of N-doped carbon nanotubes decreases in either acidic or alkaline electrolytes. Therefore, B- or N-doped carbon nanotubes are good cathode materials in acidic electrolytes or anode materials in neutral electrolytes, respectively.