Prof. Jinhua Ye and Associate Researcher Yaguang Li's team from Hebei University published a forward-looking review article on photothermal catalytic CO₂ reduction in the February issue of "ACS Nano." The article describes several important design strategies for nanomaterials, including enhancing light absorption, reducing thermal energy loss, to improve the absorption and utilization of solar energy. It also elaborates on the latest progress in photothermal catalytic CO₂ hydrogenation and provides significant insights into the opportunities and challenges faced by the application of photothermal catalytic CO₂.
Compared to photocatalysis or thermocatalysis, photothermal catalytic CO₂ hydrogenation has its unique advantages:
(1) High solar absorption advantage. Photothermal catalysts are narrow or zero-bandgap materials that can absorb ultraviolet, visible, and infrared light, achieving nearly 100% solar absorption, thus improving light utilization;
(2) Ultra-high CO₂ conversion rate advantage. The current state-of-the-art photocatalytic CO₂ conversion rate is limited to 1 mmol·g-1·h-1, while the photothermal catalytic CO₂ conversion rate exceeds 100 mmol·g-1·h-1.
The article mentions two modes of photothermal catalysis: Thermo-assisted Photo catalysis and Photo-assisted Thermo catalysis.
● In the Thermo-assisted Photo catalysis mode, thermal energy comes from partial conversion of light or external auxiliary heating, giving the photocatalytic process lower activation energy barriers and enhanced carrier/mass migration rates.
● In Photo-assisted Thermo catalysis, the reaction is mainly driven by thermal energy, which comes from the solar light's photothermal conversion.
To achieve efficient photothermal catalytic CO₂ hydrogenation, there needs to be a synergistic effect between strong broadband solar energy absorption, effective photothermal conversion, thermal energy storage capacity, and high catalytic activity. The design strategy of nanostructured materials during the photothermal catalytic CO₂ hydrogenation process is crucial for building photothermal devices, designing and preparing catalysts, and obtaining optimal photothermal CO₂ hydrogenation performance.
The article focuses on summarizing the design strategies of nanocatalytic materials in three thermo-assisted photocatalytic processes:
1. Surface engineering of nanomaterials to enhance solar light collection;
2. Nanostructure heat-insulating materials to reduce thermal conduction;
3. Heat-insulating nanolayers.
This article is noteworthy for proposing views and prospects on the construction of future photothermal catalytic systems:
1. Explore strategies to improve photothermal conversion efficiency: the use of ultra-thin film materials can increase the material's solar irradiation temperature. Simultaneously, large-area films are needed to increase solar energy utilization. Therefore, designing large-area ultra-thin catalytic materials and matching light reactors are essential means to enhance photothermal catalytic performance;
2. Explore the physical principles and relaxation mechanisms of thermoelectrons to improve CO₂ activation efficiency;
3. Develop energy storage devices to achieve stable and enduring self-driven photothermal catalytic CO₂ reduction under changing light conditions;
4. Develop a system for photothermal catalytic CO₂ hydrogenation to produce high-carbon products under micro-positive pressure or atmospheric pressure;
5. Explore low-cost hydrogen production strategies;
6. Explore efficient and stable catalysts for reverse water-gas-shift (RWGS) to expand the large-scale application of RWGS reaction.
Finally, the authors propose their own ideas for the design of photothermal catalytic devices. The authors believe that pressure, illumination, and temperature are the core elements that need to be considered in the design of photothermal catalytic devices.
Since the products of CO₂ hydrogenation are currently mainly focused on low-carbon products, to obtain high-carbon products, it is necessary to pressurize the reaction system. A catalytic reactor that can continuously provide stable high-pressure reaction gas is crucial for improving the efficiency and value of CO₂ conversion.
The PLR-RP series photothermal catalytic reaction evaluation device can provide high-temperature and high-pressure reaction conditions, and currently, there are five versions available for selection:
Due to the significant impact of light intensity, illuminated area, and catalyst loading on the reaction results, using a standard reactor to label these variable conditions can improve the comparability of data between different literature, thereby better selecting potential photothermal catalytic materials.
The PLR-RP series photothermal catalytic reaction evaluation device adopts a structure with quartz light-guiding columns and a quartz reactor. While ensuring the efficiency of light input, it effectively increases the illuminated area of the catalyst. Through simulation and calculation of the fixed position of the quartz light-guiding column relative to the catalyst, the maximum light efficiency is obtained.
The innovative ambient light-type reactor strictly limits the thickness of the catalyst bed to 3 mm. This ensures effective illumination of the catalyst, increases the illuminated area of the catalyst, enhances the utilization of light by the catalyst, and calculates the illuminated area and packing volume of the catalyst according to the filling height, ensuring the repeatability of the experiment.
Reducing heat loss is a key way to improve light utilization efficiency in photothermal catalysis under the premise that light can be fully absorbed.
The PLR-RP series photothermal catalytic reaction evaluation device's preheating-assisted heating module can effectively reduce the temperature gradient between the catalyst and the reaction system, thereby reducing heat loss in photothermal catalytic reactions. It also has a dual thermocouple temperature measurement device that can real-time monitor the external temperature of the reactor and the surface temperature of the reaction catalyst, grasping the dynamic temperature changes during the reaction process.
Regarding the interpretation of the literature, it is only a translation and summary based on the referenced literature by the author. If there are any errors, please correct them!
Cuncai Lv, Yaguang Li*, Jinhua Ye*, et al. Nanostructured Materials for Photothermal Carbon Dioxide Hydrogenation: Regulating Solar Utilization and Catalytic Performance [J]. ACS Nano, 2023, 17(3): 1725-1738.
 Meng X, Zuo G, Zong P, et al. A rapidly room-temperature-synthesized Cd/ZnS:Cu nanocrystal photocatalyst for highly efficient solar-light-powered CO₂ reduction [J]. Applied Catalysis B: Environmental, 2018, 237: 68-73.
 Chen Y, Zhang Y, Fan G, et al. Cooperative catalysis coupling photo-/photothermal effect to drive Sabatier reaction with unprecedented conversion and selectivity [J]. Joule, 2021, 5(12): 3235-3251.