The new design enables efficient hydrogen production

Professor Lv Gang’s research group of Nanjing University of Technology, in cooperation with the University of Electronic Science and Technology of China and the Technical University of Darmstadt in Germany, designed a new plasmon composite material as an efficient and stable hydrogen evolution photocatalyst, with a turnover rate of up to 4650 per hour. This method is also expected to be applied to carbon dioxide reduction, nitrogen fixation and other fields. The results of the study were recently published in Nature Communications.

The plasmon structure was used to improve the efficiency of the cobalt porphyrin molecular catalyst for hydrogen production. Photo courtesy of the research group

It is reported that metal porphyrin catalysts are used in hydrogen evolution reactions due to their unique conjugated structure (conjugation, which means that electrons are arranged into a pair according to certain rules, and the four pyrrole rings in porphyrins are connected by conjugated double bonds), excellent photoelectric properties and other advantages, but their light absorption capacity and photostability are poor.

Metal nanoparticles such as gold, silver and copper can show the local surface plasmon resonance effect in the visible light and/or near-infrared spectral region, that is, the phenomenon of collective oscillation of free electrons on the metal surface, with excellent optical properties. Under the action of light, local electromagnetic fields, local heating and excitation of thermoelectrons will be generated near the plasma nanostructure, which can effectively promote the chemical reaction activity of nearby molecules. However, thermal electrons (i.e., electrons in excited states) generated by plasmons are difficult to efficiently separate in one-component nanostructures, limiting their application in chemical reactions. In order to solve this problem, the development of plasmon composites is becoming the mainstream of plasmon-mediated photocatalysis.

“Based on the local surface plasmon effect, the catalytic activity of these molecular catalysts around the plasmon nanostructure can be significantly improved.” Lv Gang introduced that the research group successfully developed an efficient and stable hydrogen evolution photocatalyst by compounding the cobalt porphyrin molecule with four pyridine groups at the outer end with gold nanoparticles, and using the plasmon effect of gold particles to stimulate the activity of cobalt porphyrin molecular catalyst, thereby improving the efficiency of the catalytic reaction, and successfully developed an efficient and stable hydrogen evolution photocatalyst, with a turnover frequency of up to 4650 per hour.

The results show that the excellent photocatalytic hydrogen evolution activity of the system can be attributed to the strong synergy between gold particles and cobalt porphyrin molecules. Lv Gang said that the experimental results and theoretical calculations show that the lifetime of plasmon gold nanoparticles to produce thermal electrons at the gold particles-cobalt porphyrin interface is extended, and the thermal electrons can be transferred to the lowest unoccupied orbit of cobalt porphyrin molecules, which is conducive to promoting the hydrogen evolution reaction. ” 。

This method has the advantages of simple preparation process and high cost-effectiveness, and this study also provides a new method for the design and preparation of high-efficiency hybrid nanocatalysts (catalysts formed after mixing of nanomaterials). The method can also be extended to other photocatalytic systems, such as carbon dioxide reduction, nitrogen fixation, etc. “The reduction of carbon dioxide to prepare carbon-containing compounds, such as carbon monoxide, methanol, methane, ethanol, ethylene, etc., is mainly to use the plasmon effect to stimulate the activity of the corresponding molecular catalyst, thereby improving the efficiency of the catalytic reaction. Here, for example, plasmon nanostructures can be combined with molecular catalysts that catalyze carbon dioxide reduction, and plasmons can be used to enhance the activity of molecular catalysts, thereby improving the efficiency of carbon dioxide reduction. Sheng Huixiang, the first author of the paper and a master’s student at Nanjing University of Technology, said. (Source: China Science News, Wen Caifei, Zhou Wei)

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