Catalysts for Solar Energy

Catalysts for Converting Solar Energy into Chemical Energy

• The three important reactions of solar to chemical energy conversion include: light-driven water splitting, light-driven CO₂ reduction, organic photosynthesis, and other photocatalytic reactions.
• Solar-driven water splitting is a promising method for sustainable hydrogen production. The ideal photocatalyst should have the characteristics of low price, abundant reserves and low toxicity. Traditionally used photocatalyst materials are mainly limited to inorganic semiconductor materials such as oxides (such as TiO₂, Cu₂O) and sulfides.
• In addition, some semiconductors and their nanostructured composite materials have become star materials and show high efficiency in these reactions, such as transition metal oxygen-containing salts (phosphate, tungstate, vanadate, titanate), composite oxidation Materials (multi-metal oxides, oxynitrides, oxysulfides, oxyhalides), non-metallic materials (carbon, nitride, black phosphorus), etc. Among them, the nanocomposite photocatalyst based on gC₃N₄ is used as a low-cost, strong, visible light active photocatalyst for water splitting, CO₂ conversion and organic synthesis.

Figure 1. Metal-free graphite C₃N₄-based nanocomposite photocatalyst [1]

Catalyst for Photothermal Catalysis

• Photothermal catalysis (PTC) can use full-spectrum sunlight to stimulate the synergy between photocatalysis (PC) and thermal catalysis (TC), which not only realizes the high utilization efficiency of solar energy, but also minimizes the energy consumption compared with a separate PC and TC.
• Photothermochemical materials play a key role in achieving high photothermal catalytic activity. The ideal material must meet several functional requirements: (1) Collect the complete sunlight spectrum from UV to VIS with minimum transmittance and reflectivity, even NIR wavelength; (2) Strongly couple the harvested photons into heat and effective catalytically active sites; (3) Suitable thermal catalytic activity. Examples of materials currently under development include metals, semiconductors, and carbon-based nanostructures. Some typical photothermal chemical materials are shown below.

Figure 2. Summary of photothermochemical materials [2]

Photocatalysts for Air Purification

• Purify various pollutants through photocatalytic oxidation (PCO), such as volatile organic compounds (VOC) or inorganic gases (NOx, SOx, CO, H₂S, ozone, etc.) at relatively low concentrations. Photocatalysis has used a variety of materials as catalysts. For example, metal oxides include binary compounds (TiO₂, ZnO, WO₃, Fe₂O₃, ZrO₂, etc.), ternary compounds (vanadate, tantalate, tungstate and bismuthate, etc.) and other complex oxyhalides. [3]

Figure 3. Photocatalysts for air purification

References

1. Feifan Wang. (2017). "Recent Progress in Semiconductor-Based Nanocomposite Photocatalysts for Solar-to-Chemical Energy Conversion." Advanced Energy Materials 7(23): 1700529.
2. Rong Ma. (2020). "Review of synergistic photo-thermo-catalysis: Mechanisms, materials and applications." International Journal of Hydrogen Energy 45(55): 30288-30324.
3. Yash Boyjoo. (2017). "A review on photocatalysis for air treatment: From catalyst development to reactor design." Chemical Engineering Journal 310(2): 537-559.