Research section - In situ solid peroxide production (UCR)

Recently, our research group has successfully developed a novel electrochemical technology that can efficiently separate urea from urine in solid form. The research results of this technology have been accepted by Nature Catalysis.

In urban wastewater treatment, urea is the main nitrogen-containing substance in urine, and extracting and converting urea is crucial for wastewater treatment and resource recovery. We have achieved effective separation of urea under mild conditions and precipitated it in high-purity solid form through our independently developed electrochemical technology. This technology not only reduces the energy consumption of traditional treatment methods, but also greatly simplifies the subsequent treatment process, making it particularly suitable for centralized and decentralized urine treatment systems. The solid form of urea product has significant potential for application in agriculture and environmental fields. As a slow-release fertilizer, it can gradually release nutrients in farmland, promote crop growth, increase yield, and improve soil quality. In addition, in terms of sewage treatment, this technology effectively separates nitrogen from urine, reducing water pollution and providing an efficient way of resource recovery.

Thanks to our in-depth research and optimization of catalytic materials and reaction conditions, this electrochemical technology has demonstrated extremely high separation efficiency and operability without requiring a large amount of energy investment, and has broad application value. We will continue to explore further optimization of this technology and its large-scale applications in different fields.

Article information: Xinjian Shi1*, et al. Nature catalysis accepted 2024. https://doiorg/10.1038/s41929-024-01277.3

Illustrations:

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Research section - Anode hydrogen peroxide production (2e WOR)

Hydrogen peroxide is widely used in industrial and environmental fields, especially playing an important role in papermaking, textiles, and wastewater treatment. However, traditional hydrogen peroxide production processes consume a lot of energy and pose safety hazards during transportation and storage. Our team is committed to generating hydrogen peroxide directly on the anode through electrochemical methods, providing a more efficient, convenient, and safe alternative solution. Unlike the traditional four electron water oxidation reaction that produces oxygen, the two electron water oxidation reaction can directly generate hydrogen peroxide, avoiding the problem of by-product oxygen. By optimizing the electrochemical reaction conditions, we significantly improved the efficiency of hydrogen peroxide generation. This method is particularly suitable for on-site preparation, reducing the instability and safety risks associated with long-distance transportation. Catalysts play a crucial role in the generation process of hydrogen peroxide. We have systematically studied the catalytic performance of various metal oxides and found that bismuth vanadate has the highest catalytic activity and selectivity, greatly improving the efficiency of hydrogen peroxide generation. By regulating the surface structure of the catalyst and doping with metal elements such as strontium and ruthenium, we effectively improved the stability of the catalyst, enabling efficient hydrogen peroxide generation at lower voltages. In addition, we found through theoretical calculations and experimental verification that the energy regulation of intermediates on the catalyst surface is crucial for reaction efficiency. By adjusting the adsorption energy of intermediates such as OH *, the generation rate of hydrogen peroxide was further improved. In order to ensure the stability of the catalyst in long-term applications, we optimized the surface of bismuth vanadate and other metal oxides to maintain good reaction activity under high load conditions. Meanwhile, through metal doping, we have increased the reaction rate of the catalyst under light conditions, reduced the overpotential requirement, and enhanced the durability of the material. In the future, our team will continue to research new metal oxide catalysts and other material combinations to further improve the efficiency of hydrogen peroxide electrochemical synthesis and the stability of catalysts.

Selected paper:

Shi, Xinjian, et al. "Understanding activity trends in electrochemical water oxidation to form hydrogen peroxide." Nature communications 8.1 (2017): 701.

Kelly, Sara R., Shi, Xinjian, et al. "ZnO as an active and selective catalyst for electrochemical water oxidation to hydrogen peroxide." ACS Catalysis 9.5 (2019): 4593-4599.

Shi, Xinjian, et al. "Electrochemical synthesis of H2O2 by two-electron water oxidation reaction." Chem 7.1 (2021): 38-63.

Illustrations:

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Research Section - Efficient Photocatalysts

Photocatalysts play an important role in clean energy and environmental protection, especially in water splitting and catalytic reactions. Our team focuses on developing efficient and stable photocatalysts to improve the performance of photocatalytic technology and promote its widespread application. In our research, bismuth vanadate is one of the key materials. Although bismuth vanadate has good photoresponsiveness, there is still room for improvement in its photoelectric conversion efficiency. To this end, we significantly enhanced the light absorption efficiency of the material by doping molybdenum into bismuth vanadate and introducing gold nanospheres for modification. This structure utilizes the energy transfer mechanism induced by plasma, which not only enhances the absorption of photons, but also effectively improves the separation and transmission efficiency of charges, significantly enhancing photocatalytic activity and demonstrating great potential in photocatalytic reactions. In addition, we explored the application of calcium tin oxide in the production of hydrogen peroxide. Through the two electron water oxidation reaction, the catalyst exhibits high selectivity and stability in generating hydrogen peroxide, and can reduce the overpotential of the reaction, making it suitable for long-term stable operation. This material is suitable for small-scale and on-site production, providing new possibilities for distributed hydrogen peroxide production. We have designed an iridium doped tungsten oxide catalyst for the water oxidation reaction under acidic conditions. This catalyst maintains excellent catalytic activity and durability while significantly reducing the amount of precious metals used. Iridium doping optimizes the binding energy of oxide intermediates, significantly improves catalytic efficiency, and exhibits long-term stability under acidic conditions, providing a low-cost and efficient solution for electrolytic water technology in hydrogen production. In the future, we will continue to explore and optimize new catalysts to further enhance the photoelectric conversion efficiency and material stability, in order to promote the widespread application of photocatalytic technology in the fields of clean energy and environmental protection.

Selected paper:

Kim, Jung Kyu, Shi, Xinjian, et al. "Enhancing Mo: BiVO4 solar water splitting with patterned Au nanospheres by plasmon﹊nduced energy transfer." Advanced Energy Materials 8.5 (2018): 1701765.

Park, So Yeon, Hadi Abroshan, Xinjian Shi, et al. "CaSnO3: an electrocatalyst for two-electron water oxidation reaction to form H2O2." ACS Energy Letters 4.1 (2018): 352-357.

Shi, Xinjian, et al. "Efficient and stable acidic water oxidation enabled by low-concentration, high-valence iridium sites." ACS Energy Letters 7.7 (2022): 2228-2235.

Illustrations:

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Research Section - Photovoltaic Devices

With the increasing demand for renewable energy, the importance of photovoltaic devices in solar energy utilization is becoming increasingly prominent. Our team focuses on improving the efficiency of photovoltaic devices and driving technological progress through structural optimization and material modification. We have developed a wireless series device that combines photocatalysis and dye-sensitized solar cells, significantly improving energy conversion efficiency. The device uses a tungstate thin film sensitized with bismuth tungstate as the front layer, which can efficiently utilize short wavelength light for hydrogen production reaction and transmit long wavelength light to the dye-sensitized solar cell in the back layer, achieving more efficient photon utilization and electrical energy output. In order to further improve the photoelectric conversion efficiency, we introduced photon recovery technology by designing a composite reflector on the back of the front layer photoelectrode to reflect short wavelength light to enhance the light absorption of the front layer, while ensuring that long wavelength light passes through to the back layer battery. This design effectively improves the overall performance of photovoltaic devices. In terms of materials, we have improved the light absorption and charge separation efficiency of the device through the heterojunction design of tungstate and bismuth vanadate. In addition, doping with elements such as molybdenum and tungsten further enhances the conductivity and optoelectronic properties of the material, resulting in significant improvements in device stability and efficiency. We will continue to explore the design of photovoltaic devices with new materials and structures, committed to improving energy conversion efficiency and providing more efficient and stable solutions for future solar energy applications.

Selected paper:

Shi, Xinjian, et al. "Unassisted photoelectrochemical water splitting beyond 5.7% solar-to-hydrogen conversion efficiency by a wireless monolithic photoanode/dye-sensitised solar cell tandem device." Nano Energy 13 (2015): 182-191.

Shi, Xinjian, et al. "Unassisted photoelectrochemical water splitting exceeding 7% solar-to-hydrogen conversion efficiency using photon recycling." Nature communications 7.1 (2016): 1-6.

Illustrations:

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Research section - First principles calculations

Our research team utilized first principles calculations to delve into the key mechanisms involved in electrochemical catalysis, particularly in the generation of hydrogen peroxide and water oxidation reactions. Our research not only helps optimize the design of existing catalysts, but also provides a theoretical basis for the development of new catalytic materials. Through density functional theory (DFT) calculations, we can effectively analyze the activity of catalytic sites, determine catalytic pathways, and regulate key steps in catalytic reactions.

We first combined first principles calculations and experimental verification to systematically analyze and validate the key mechanism of electrochemical water oxidation to generate hydrogen peroxide. By calculating the adsorption energy of intermediates such as OH * and OOH *, we have confirmed for the first time that the surface reaction mechanism of oxides plays a decisive role in their catalytic activity and selectivity. This is the first pioneering work in the entire 2e-WOR field to successfully study and verify the regulation of the pathway and performance of oxidized water and hydrogen peroxide through theoretical guidance experiments. It can provide guidance and reference for subsequent work and the development of this field.

Based on this paradigm, we validated the crystal plane dependence in the production of binary oxide hydrogen peroxide using ZnO as an example, and successfully designed the first highly selective and stable catalyst CaSnO3 with ternary perovskite phase by quantifying the adsorption behavior of surface intermediates. The experiment verified the excellent performance of the material in the generation of hydrogen peroxide, especially in the two electron water oxidation reaction. Furthermore, we have revealed the crucial role of doping sites in the adsorption and dissociation of oxygen species, providing theoretical support for the design and optimization of oxide catalysts.

List of published papers:

Shi, X., Siahrostami, S., Li, GL. et al. Understanding activity trends in electrochemical water oxidation to form hydrogen peroxide. Nat Commun 8, 701 (2017)

Shi, Xinjian, et al. ZnO As an Active and Selective Catalyst for Electrochemical Water Oxidation to Hydrogen Peroxide. ACS Catalysis 2019 9 (5), 4593-4599

Shi, Xinjian, et al. CaSnO3: An Electrocatalyst for Two-Electron Water Oxidation Reaction to Form H2O2 ACS Energy Letters. 2019. 4 (1), 352-357

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Research section - Hydrogen Production (HER)

With the increasing demand for clean energy, the application of photocatalytic technology in hydrogen production has attracted widespread attention. Our team focuses on improving photocatalytic efficiency through material design and promoting the development of hydrogen production technology through water splitting. One of the research focuses of our team is the application of tungstate in photocatalytic water. Tungstate has good photostability, but its photogenerated charge separation efficiency is low. To improve this issue, we combined tungstate with bismuth vanadate and designed a spiral nanostructure. This structure not only increases light absorption, but also effectively enhances charge separation ability, greatly improving the efficiency of photocatalytic hydrogen production. In order to further enhance the catalytic performance, we introduced cobalt element into tungsten based materials to enhance the activity of the catalyst in hydrogen evolution reaction. Our research shows that after cobalt doping, the overpotential of the catalyst is significantly reduced, the reaction rate is significantly accelerated, and thus the hydrogen production is significantly increased. Based on experiments and theoretical calculations, we found that cobalt doping can regulate the surface hydrogen adsorption capacity of materials, further optimizing catalytic performance. This result provides theoretical support for future material design. Through material modification and structural optimization, our team has significantly improved the efficiency of photocatalytic hydrogen production. In the future, we will continue to explore combinations of different materials to promote the advancement of photocatalytic technology and contribute to the widespread application of clean energy.

Selected paper:

Shi, Xinjian, et al. "Efficient photoelectrochemical hydrogen production from bismuth vanadate-decorated tungsten trioxide helix nanostructures." Nature communications 5.1 (2014): 4775.

Shi, Xinjian, et al. "Rapid flame doping of Co to WS2 for efficient hydrogen evolution." Energy & Environmental Science 11.8 (2018): 2270-2277.

Illustrations:

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