A professor from Sun Yat sen University proposes a new clean energy technology for laser manufacturing

Energy conversion technology is an important research direction in modern science and engineering. Scientists are exploring new catalytic chemical methods to achieve the conversion of energy chemicals, such as photocatalysis and electrocatalysis. However, these highly anticipated catalytic chemistry technologies still have some problems in practical applications, and there is still a certain distance from industrialization. So, can we go beyond catalytic chemistry and open up a new way of energy conversion?

Recently, Professor Yang Guowei's research group at Sun Yat sen University proposed a novel laser manufacturing clean energy technology called laser foaming in liquids (LBL), bringing new hope to the field of clean energy conversion. LBL uses pulsed laser to induce the formation of microbubbles in the liquid phase as a microreactor for chemical reactions. The peak temperature inside the bubble can reach tens of thousands of K, and micro bubbles can achieve rapid heating and cooling, with a rate of up to 108K/s. This is clearly a state far from thermodynamic equilibrium, providing an extreme environment for chemical reactions. Many chemical reactions that require the use of catalysts under normal conditions can easily occur within small bubbles. This method not only does not involve any catalytic chemical processes (without catalysts and complex catalytic reaction devices), but also operates under normal conditions, simple, clean, and efficient (Figure 1). It is obvious that for exploring simple, green, and efficient clean energy manufacturing technologies under normal conditions outside of catalytic chemistry, the LBL method has opened up a door and also opened up a path beyond catalytic chemical reactions. At present, Professor Yang Guowei's research team has collaborated with Professor Ke Zhuofeng's team to apply LBL technology to clean energy manufacturing, achieving a series of important research progress.

Figure 1. (a) Schematic diagram of LBL device; (b) Schematic diagram of the action period of pulsed laser; (c) Schematic diagram of the evolution process of microbubbles within a single laser pulse cycle.

1. Laser direct decomposition of methanol for hydrogen production
Methanol, as a liquid hydrogen source, can undergo catalytic reforming with water vapor to generate hydrogen and carbon dioxide, typically at 200-300 ° C. Although methanol reforming technology for hydrogen production is relatively mature, the efficiency and stability of catalysts urgently need to be improved, and the treatment of by-product carbon dioxide is still an important issue for environmental protection.

Figure 2. Schematic diagram of liquid phase laser decomposition of methanol for hydrogen production.

Dr. Cao Weiwei, Associate Researcher Li Yinwu, and Postdoctoral Yan Bo collaborated to use LBL technology to achieve ultra fast and efficient preparation of hydrogen gas under normal temperature, pressure, and catalyst free conditions (Figure 2). More importantly, the entire LBL process did not generate carbon dioxide, but instead synthesized carbon monoxide, which has more chemical application value. At the same time, they simulated the thermodynamics and molecular dynamics of the LBL reaction process, and obtained the reaction path and thermodynamic conditions for methanol decomposition. The LBL method does not require complex reactors or harsh reaction conditions, is simple to operate and environmentally friendly, demonstrating its enormous potential in future clean energy production (Research 6 (2023) 0132, co first authors Cao Weiwei, Li Yinwu, and Yan Bo, and co corresponding authors Yang Guowei and Ke Zhuofeng).

2. Laser decomposition of ammonia water for hydrogen production
Ammonia (NH3) is a hydrogen storage material that is easy to compress and liquefy, making storage and transportation more convenient. At present, most of the catalysts used for ammonia catalytic decomposition to produce hydrogen rely on precious metals such as ruthenium (Ru), which is expensive, resource scarce, and the catalytic process is usually above 400 ° C.

Figure 3. Schematic diagram of hydrogen production from LBL decomposition of ammonia water.

Postdoctoral researcher Yan Bo, Associate Researcher Li Yinwu, and Dr. Cao Weiwei collaborated to develop a new method for ultra fast and efficient extraction of hydrogen from ammonia using LBL technology (Figure 3). They chose water as the liquid phase medium for ammonia in LBL hydrogen production, avoiding the compression and cooling liquefaction procedures of ammonia during the water medium selection process. They achieved a hydrogen production rate of up to 33.7 mmol/h using the LBL method. They conducted first principles simulation calculations and identified possible reaction pathways and thermodynamic conditions for laser induced ammonia decomposition. Future research can further explore the application of LBL method in other chemical reactions (JACS 146 (2024) 4864, with Yan Bo, Li Yinwu, and Cao Weiwei as co first authors and Yang Guowei as corresponding authors).

3. Laser direct complete hydrolysis of water to produce hydrogen and hydrogen peroxide
Hydrogen production through water splitting is a widely studied and applied method for hydrogen production, and the combustion product of hydrogen is also water, which is clean and pollution-free throughout the entire cycle. Therefore, hydrogen production through water splitting has attracted the interest of a large number of researchers. However, the water splitting reaction requires overcoming high activation energy, which is a major challenge for any catalytic system.

Figure 4. Schematic diagram of hydrogen production process through laser decomposition of water.

Postdoctoral Yan Bo and Dr. Cao Weiwei collaborated with Professor Ouyang Gang's team from Hunan Normal University and Researcher Meng Sheng's team from the Institute of Physics, Chinese Academy of Sciences to achieve direct laser decomposition of pure water to produce hydrogen and hydrogen peroxide (Figure 4). The experimental results show that the conversion efficiency of laser light energy to hydrogen energy in this method exceeds the conversion efficiency of most non sacrificial agent photocatalytic water splitting for hydrogen production. They studied the process of laser induced nucleation of high-energy active particles through theoretical calculations and simulations, as well as the theoretical process of water decomposition to generate hydrogen and hydrogen peroxide using TDDFT. The research results indicate that laser induced high temperature and rapid cooling are crucial for efficient generation of hydrogen and hydrogen peroxide (PNAS 121 (2024) e2319286121, with Yan Bo, Gu Qunfang, Cao Weiwei, and Cai Biao as co first authors, and Yang Guowei, Ouyang Steel, and Meng Sheng as co corresponding authors).

4. Liquid phase laser direct reduction of carbon dioxide to carbon monoxide
Carbon dioxide reduction to produce carbon monoxide is one of the important technical means to achieve carbon cycling and reduce greenhouse gas emissions. Electrochemical reduction, photocatalytic reduction, and thermal catalytic reduction have been widely studied and applied in carbon dioxide reduction reactions, and can be coupled with solar and wind energy to ensure the sustainability of the process. However, its drawbacks lie in the selection of catalysts, stability, and cost of precious metals. Typically, reducing agents such as hydrogen and carbon are required, which can generate additional carbon dioxide emissions and violate the principles of green chemistry.

Figure 5. Schematic diagram of efficient reduction of carbon dioxide to carbon monoxide using LBL technology in pure water.

Postdoctoral researcher Yan Bo collaborated with Associate Researcher Li Yinwu and Dr. Cao Weiwei to study the application of LBL technology in the field of carbon dioxide reduction (Figure 5). They utilized the LBL method to achieve efficient reduction of carbon dioxide to carbon monoxide in pure water. Meanwhile, they delved into the mechanism and reaction pathway of carbon dioxide reduction through density functional theory (DFT) calculations. In the future, the goal of green chemistry and sustainable development will be achieved through further optimization of laser systems, in-depth research on reaction mechanisms, and exploration of multiple chemical applications (Joule 6 (2022) 2735, with Yan Bo, Li Yinwu, and Cao Weiwei as co first authors, and Yang Guowei and Ke Zhuofeng as co corresponding authors).

5. Laser nitrogen fixation synthesis of ammonia and nitric acid
The process of reacting nitrogen and hydrogen in the atmosphere to produce ammonia (NH3) under high temperature and pressure, as well as the action of a catalyst, usually requires a high temperature of 400-500 ° C and high pressure of 200-300 atmospheres under harsh reaction conditions. Other methods such as electrochemical nitrogen fixation and photocatalytic nitrogen fixation face issues such as catalyst selection and optimization, low reaction efficiency, and limited operating conditions, which have not yet been industrialized.

Figure 6. Development history of nitrogen fixation and ammonia synthesis technology.

Dr. Cao Weiwei, Associate Researcher Li Yinwu, and Postdoctoral Yan Bo collaborated to use LBL technology to achieve efficient nitrogen solidification and activation at room temperature and pressure under pure water and nitrogen without any catalyst. During the LBL process, nitrogen reduction reaction (NRR) and oxygenation reaction (NOR) were achieved. This study demonstrates that the LBL method can achieve efficient synthesis of ammonia and nitric acid at room temperature and pressure without catalysts, and has important scientific significance and application prospects (Figure 6). At the same time, it indicates the advantages of LBL technology in nitrogen solidification and activation, including safety, simplicity, environmental protection, easy control, and low energy consumption, and demonstrates its potential in industrial applications (JACS 146 (2024) 14765, co first authors Cao Weiwei, Li Yinwu, and Yan Bo, and co corresponding authors Yang Guowei and Ke Zhuofeng).

LBL technology, as a new laser manufacturing clean energy technology, has achieved localized chemical reactions under extreme non-equilibrium conditions, and can achieve efficient clean conversion and preparation of energy chemicals under normal conditions, demonstrating enormous industrial application potential. Future research can achieve higher electro-optical conversion efficiency by developing efficient and low-cost lasers, thereby expanding and enhancing the scale of LBL reactions. In summary, through continuous optimization of laser systems, in-depth research on micro reaction mechanisms, and exploration of multiple chemical applications, LBL technology can be expected to be a simple, green, and efficient clean energy manufacturing technology and green synthesis method beyond catalytic chemistry.

This series of work was supported by the National Natural Science Foundation of China (5183201121973113) and the State Key Laboratory of Optoelectronic Materials and Technology of Sun Yat sen University.

Source: School of Materials Science and Engineering, Sun Yat sen University