Two-dimensional (2D) carbon materials with pseudocapacitive charge storage capacity are promising for high-performance micro-supercapacitors (MSCs).

Borocarbonitride, containing the C, B, N element in different proportions, has the similar structure with graphene. It is considered as a hybrid of graphene and hexagonal boron/nitrogen (BN).

Recently, a research group led by Prof. WU Zhongshuai from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. LEI Weiwei from Deakin University, revealed the charge storage mechanism of 2D borocarbonitride nanomesh (BCNN) for high-performance MSCs.

This study was published in Energy Storage Materials on July 31.

The researchers synthesized 2D BCNN by carbonizing gel precursor of milk powder and boron oxide in 700, 800, and 900 °C, respectively, denoted as BCNN700, BCNN800, and BCNN900, as electrode for MSCs.

They found that the areal capacitance increased from 30.5 mF cm^-2 for BCNN700-MSCs to 80.1 mF cm^-2 for BCNN900-MSCs with a hydrogel electrolyte. Notably, BCNN900-MSCs could provide a high energy density of 67.6 mWh cm^-3 with an ion-gel electrolyte, powering a liquid crystal display for 328 s.

Moreover, they investigated the electrochemical properties of BCNN900 by theoretical calculations. The models were designed with four parts, including a pure hexagonal carbon matrix (Pure-BCNN), porous carbon matrix (Pore-BCNN), nitrogen-doped carbon matrix (N-BCNN), and boron/nitrogen co-doped area (BN-BCNN).

They found that the charges mainly accumulated on the defects of N-BCNN and BN-BCNN network, while few charges gathered on Pore-BCNN and pure carbon network. This indicated that the B and N elements doping would facilitate the charge transfer and increase the electrolyte adsorption, contributing to the improvement of capacitance. The micro-pores could improve the capacitance in the lower-voltage section and the boron/nitrogen doping improve the capacitance in the higher-voltage section.

This work paves a new avenue for designing two-dimensional carbon materials for high-performances MSCs. It was supported by National Key R&D Program of China and Dalian National Laboratory for Clean Energy.