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Recently, the Chinese State Key Laboratory of Catalysis and the Clean Energy National Laboratory of Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Li Can's team made new advances in the field of solar light-electricity conversion and fuel cell chemical energy-electric energy conversion. The catalytic activity of the oxygen reduction reaction (ORR) can be significantly promoted, and based on this, the concept of a laminated solar cell coupled with a polymer solar cell and an H2-O2 fuel cell is proposed. The related research results are published in the form of communication in German Applied Chemistry (Angew). In the journal of Chem. Int. Ed.) (DOI: 10.1002/anie.201607118) (The first author of the article is Zhang Bingqing, a doctoral student in the joint training program of South China University of Technology).
H2-O2 fuel cells can directly and efficiently convert hydrogen into widely applicable electric energy, and at the same time produce water molecules that are friendly to human living environment. It is one of the important directions for the development of advanced sustainable clean energy systems. Among them, the ORR of the cathode is the speed-controlling reaction of the H2-O2 fuel cell (especially for the proton membrane fuel cell PMFC), which is directly related to the open circuit potential and the output power of the entire cell. Precious metal platinum is the best catalyst for ORR, but the higher cost has severely constrained the development and commercialization of fuel cell technology. In order to solve this problem, a large number of researchers around the world have devoted themselves to the development of alternative Pt or Pt catalysts, such as Pt alloys, Pt core-shell catalysts, C-based catalysts, etc. However, as of now, the overpotential of catalyzed ORR remains Need at least 0.2V or so. Therefore, it is very important to develop new catalytic strategies and new ideas to reduce O2 activation overpotential and increase the activity of ORR reaction.
In this work, the researchers introduced photocatalysis to ORR. It was found that the use of polymer semiconductor photocatalyst and light irradiation can significantly promote the electrocatalytic activity of ORR. The initial potential shifts from 0.66V to 1.34V (far more than commercial platinum catalysts. 1.0V), and the current increased by 44 times at 0.6V. In the optically driven conceptual H2-O2 fuel cell thus constructed, the illumination increases the open circuit voltage of the fuel cell from 0.64 V to 1.18 V and the short circuit current increases by a factor of two. Photocatalysis increases the potential of the semi-reactive ORR and the full cell reaction by 0.68 V and 0.54 V, respectively, and this voltage value is close to the voltage of most currently studied polymer solar cells (0.6-0.8 V). The light-driven conceptual H2-O2 fuel cell can be considered as the result of the coupling of polymer solar cells and H2-O2 fuel cell stacks. The mechanism of photo-promoted molecular oxygen reduction may be that the photo-excited polymer electrons move from the valence band to the conduction band, and the excited state electrons on the conduction band have enough potential to transfer to the anti-bonding orbital of the oxygen molecule (2p*, 2s*). This makes oxygen reduction easier. The results of this study open up new ideas for solving the problem of ORR reaction kinetics in fuel cells and show potential application value.
This work was supported by the "973" project of the Ministry of Science and Technology, the National Natural Science Foundation, and the iChEM Solar Energy Research Project of the Ministry of Education.
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