江苏留学网

Prof. Xia Hui's team from the Herbert Gleiter Institute of Nanoscience, Nanjing University of Science and Technology, has found the cation pre-insertion in α-MnO₂ can greatly improve pseudocapacitive performance as electrode materials for supercapacitors.

Accordingly, the team published their research results in ACS Applied Materials Interfaces (2016, 8 (49), pp 33732-33740), a SCI indexed journal.

The lead author of the paper, Jabeen Nawishta, is a Pakistani student who has been enrolled in a doctorate program at Nanjing University of Science and Technology since 2013. Nawishta is one of many talented foreign students granted scholarships by the Chinese government for demonstrating academic excellence.

The team demonstrated that supercapacitors with metal oxides as the electrode materials can achieve higher specific capacitance and energy density by utilizing redox reactions between the multiple valence states of the metal ions.

These supercapacitors have wider application potential than electric double-layer capacitors (EDLC). However, pseudocapacitive electrode materials have poor electronic conductivity, meaning their overall performance has difficulty meeting the requirements of many modern day electronic devices.

The MnO₂ used in this work has a high theoretical capacity of nearly 1400 F g^-1. Due to its abundant availability and relatively low cost, MnO₂ has become a heavily researched compound as a potential material for supercapacitors.

However, its poor electronic conductivity means it has a limited level of electrochemical performance. Consequently, developing a high-performance MnO₂ electrode is of great importance to many researchers hoping to create high-quality supercapacitors.

Figure 1, Cation preinserted MnO₂ obtains high specific capacitance and wide working potential window.

Under the guidance of Prof. Xia Hui, Nawishta tried to adjust the chemical structure of MnO₂ by metal cation intercalation, as a means of further improving its electrochemical performance. Finally, the α-MnO₂ electrode material containing K⁺ ions was successfully synthesized by simple hydrothermal methods.

Inserting K⁺ ions facilitates the fast transportation of electrons in α-MnO₂ and serves to improve the oxygen evolution potential. The stable working window of KxMnO₂ electrode material can be extended up to 1.2 V (vs. Ag/AgCl) and the energy density is increased to 52 Wh kg⁻¹, which greatly enhances the comprehensive performance of MnO₂-based electrode materials.

This is not the first time Nawishta had modified nano-sized electrode materials. Previously, she improved the electrochemical cycling performance of polyaniline by electrodepositing polyaniline in a porous NiCo2O4 scaffold. (ACS Appl. Mater. Interfaces,C2016,08 016Appl. Mater)