New energy storage system: pack solar energy into batteries

Zhang He is in the experiment.

Zhang He, a doctoral student from the Changchun Institute of Applied Chemistry at the Chinese Academy of Sciences, sat alone in front of the experimental bench and continuously adjusted the connection mode of the device manually by observing the operation of the electrochemical workstation data. This is the epitome of his daily work in recent times.

"Sometimes the cyclic test may take more than ten hours, and the operator must stay in step in front of the experimental device," he told the China Science Daily.

Recently, Zhang He was finally able to relax briefly. Under the guidance of Academician Dong Shaojun of the Chinese Academy of Sciences, his team successfully realized the continuous conversion and storage of solar energy under the integrated system by building a biophotoelectrochemical model based on the water / oxygen cycle. Related results have been published in the Journal of the American Chemical Society.

Uninterrupted solar energy

The rotation of the earth has caused the alternation of day and night in nature, which has led to the intermittent and discontinuous regional sunlight exposure.

For traditional photovoltaic devices, in order to obtain continuous power output, continuous light is the most basic condition for the normal operation of the device. However, the energy conversion (light energy to electricity) in photovoltaic devices is a discontinuous process due to the influence of regional light intermittent. To a large extent, this limits the direct use of solar energy, making it unable to meet the power needs of day and night in actual production and life.

To solve this problem, scientists have proposed a corresponding energy reserve strategy. By combining the photoelectrochemical system with the secondary battery or flow battery system, the conversion and storage of solar energy are realized.

"However, the multi-system connection has the disadvantages of complex system, high cost, and serious energy transmission loss." Zhang He, the first author of the paper, analyzed that on the one hand, multi-system connection needs to consider the matching problem between systems, on the other hand, the energy Inevitable loss in the form of heat energy is likely to occur during transmission and transfer. In this way, it not only increases the cost of equipment, but also is not conducive to the effective use of stored energy.

In 2018, the team successfully constructed a biophotoelectrochemical cell based on the water / oxygen cycle by matching the n-type semiconductor photoanode with the multi-copper oxidase biocathode to achieve light energy in the system water / oxygen cycle. Continuous and stable conversion from chemical energy to electrical energy.

However, like the traditional photoelectrochemical system, the operation of this system is completely controlled by the external light, and it needs to be further revised.

"Based on previous research work, our team established an integrated biophotoelectrochemical model system by introducing an energy storage module (polypyrrole capacitor electrode). Under the state of water / oxygen self-circulation in the system, illumination was achieved And the continuous output of power under dark field conditions. "Zhang He said.

Store solar energy

For the study of the battery system, the team started from examining the electrochemical behavior of a single electrode, from a single electrode to a single battery to the entire system, from simple and complicated to investigate the various components and overall performance of the model system built.

The first difficulty encountered is the choice of energy storage modules.

Huang Liang, one of the authors of the thesis and a PhD student at the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, told the China Science Journal that in order to ensure the normal energy storage of solid capacitor electrodes, on the one hand, the charge / discharge potential window must be between the two electrodes of the photobiofuel cell Between potentials; on the other hand, it is necessary to ensure that the electrode has a high and stable capacitance in a neutral electrochemical system. "After various aspects of optimization selection and testing, we chose polypyrrole capacitor electrode as the energy storage module."

As expected, the dual role played by the polypyrrole capacitor electrode has realized the integrated use of the photoelectrochemical system and the battery system.

Under light conditions, in the photoelectrochemical system, the polypyrrole capacitor electrode serves as the cathode to receive the photoelectrons generated from the anode, and stores it by virtue of its own capacitance performance to realize the conversion of light energy into electrical energy and chemical energy; under dark field conditions, In the battery system, the polypyrrole capacitor electrode acts as an anode to transfer the stored photoelectrons to the biocathode, thereby realizing the conversion of chemical energy into electrical energy.

The second major difficulty lies in the matching of potentials between the electrodes during storage and storage of the system.

"It is necessary to determine the charge / discharge potential of the capacitor electrode." Zhai Junfeng, one of the authors and an associate researcher at the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, told the China Science Journal that in the photoelectrochemical system, anode photocatalytic water oxidation (OER) potential is Below -0.1 V, the storage of photo-generated charge on the capacitor electrode can be effectively achieved, so the titanium dioxide electrode can be used as a suitable photocatalytic material in this system.

In the biofuel cell system, the cathode catalytic oxygen reduction potential needs to be higher than 0.3 V to effectively release the photogenerated charge from the capacitor electrode. Therefore, the team chose bilirubin oxidase as a suitable biocatalytic material for application in this system.

Experimental data analysis shows that the conceptual model obtains maximum power density output of 0.34 ± 0.01 and 0.19 ± 0.02 mW cm-2 under light and dark field conditions, respectively, and exhibits stable solar energy storage and cycling performance. In addition, by changing the capacitance of the energy storage module (polypyrrole capacitor electrode), the system charge / discharge time can be effectively regulated.

Helping the development of green and new energy

Zhang He believes that the establishment of this model system is expected to realize the development of solar storage systems to simplify, miniaturize and low cost, and provide a new research idea for the development of environmentally friendly green new energy.

"Through the simple water / oxygen cycle in the system, solar energy can be continuously converted, stored and released in this integrated device, achieving continuous power output under light and dark field conditions, avoiding the intermittent regional light The problem of discontinuous conversion of solar energy. "Zhang He introduced, this is also the innovation of the study.

He believes that with the support of relevant industrial technologies, the model is expected to be developed in the commercial application of emerging green energy devices. "For example, through the series connection of batteries, commercial applications of small energy devices can be realized to meet the use of mobile phone charging equipment, household backup power supplies, and small street lights in daily life."

In the next step, the team will use the research as a basic model to improve and optimize the system for some specific problems in actual production and life in order to expand the relevant application prospects of the model. (■ Cheng Weijia, a trainee reporter of this newspaper)