In collaboration with Professor Chen Shaowei of the University of California, Santa Cruz, Professor Li Jun of the School of Energy and Power Engineering, Chongqing University has published a research paper titled “Graphene oxide-supported zinc cobalt oxides as effective cathode catalysts for microbial fuel cell: High catalytic activity and inhibition of biofilm formation” in Nano Energy. Chongqing University is the primary corresponding organization, and Doctoral Candidate Yang Wei of the School of Energy and Power Engineering is the first author. Professor Li Jun and Professor Chen Shaowei are both corresponding co-authors.

Microbial fuel cell is a kind of energy device that is able to degrade the organic pollutants and convert them into electric energy by utilizing microorganisms attached onto the anodic surface. This device has a broad application prospect in sewage treatment and renewable energy sources. In particular, the air cathode microbial fuel cell, due to the air-breathing design of the cathode, is able to directly utilize oxygen contained in the air as the cathode electron acceptor, and supply of oxygen requires no input of extra energy. It is an extremely practical microbial fuel cell structure. Air cathode is a major component of the cell. Its performance poses a direct impact on the power output of the microbial fuel cell as a whole. Researches have indicated that the low cathode oxygen reduction catalytic activity, insufficient internal ion transmission of cathode and formation of cathode biological film would seriously influence the performance of air cathode. By now, it has been proposed in many research papers that the application of efficient oxygen reduction catalyst to microbial fuel cell would, to a certain extent, strengthen the power output of cells. However, due to formation of the cathode biological film, the cathode catalyst is contaminated, resulting in a lower catalytic activity. Furthermore, the internal ion transmission of cathode is seriously restricted, which would result in high concentration overpotential. It is unable to meet the requirements for practical use of microbial fuel cells by just strengthening the electro-catalytic activity of the cathode. Therefore, the air cathode performance can be significantly improved and the overall power output of microbial fuel cells can be enhanced by inhibiting biological film on the cathode surface, strengthening internal ion transmission of cathode and designing a high-activity oxygen reduction catalyst.

The research is based on substitution of non-active Co2+ at the tetrahedron site with Zn2+ by ZnCo⁠2O⁠4. The purpose is to improve the utilization rate of active Co3+ at the octahedron site. Considering the evaporability of ZnO at a high temperature, it is used as the pore forming substance to increase the internal pore structures of catalyst, so as to expose the active sites and strengthen ion transmission. This way, the half-wave potential that is only 20mV lower than Pt/C and similar limiting current density are obtained. Furthermore, the anti-bacterial properties of graphene/ZnO are utilized to inhibit formation of cathode biological film. Test of cell performance has revealed that the cathode for catalyst preparation is able to inhibit biological film on the cathode surface, strengthen internal ion transmission of cathode and improve the oxygen reduction performance of cathode, thus effectively increasing the stability of operation of cathode of microbial fuel cells. The research has revealed the importance of the inhibition of formation of biological film, ion transmission properties and air cathode catalytic performance of microbial fuel cells, and has provided new ways of thinking for design of cathode and catalyst for microbial fuel cells in the future.

Fig. 1 Performance test of microbial fuel cells: a. Discharging curve; b. Power density curve; c. Biomass of cathode surface operation of cathode of 1 month

This research project has been supported by Outstanding Youth Fund of National Natural Science Foundation, the Entrepreneurship and Innovation Support Program for International Students of Chongqing, the Fundamental Sciences and Cutting-edge Technology Program of Chongqing, the Outstanding Scientific Research Talent Reserves Training Program of Chongqing University and the basic scientific research operational funds for colleges and universities allocated by the central government.

Link of the paper:

https://www.sciencedirect.com/science/article/pii/S2211285518310024