Photocatalytic technology has made significant progress over more than 50 years of development and has been widely applied in various fields, including photocatalytic hydrogen production, photocatalytic CO₂ reduction, and photocatalytic pollutant degradation. However, the rapid recombination of photo-generated electrons (e⁻) and holes (h⁺) during photocatalytic reactions leads to low overall reaction efficiency, posing numerous challenges to the industrialization of photocatalytic technology. To address this issue, researchers have begun to explore multi-field synergistic photocatalytic technology to enhance the efficiency and selectivity of photocatalytic reactions.
Multi-field synergistic photocatalysis refers to the combination of light fields with other physical fields (such as electric fields, thermal fields, magnetic fields, piezoelectric fields, and plasma fields, etc.) to enhance the separation and transport of photo-generated charge carriers through multi-field synergistic effects, thereby improving the activity and stability of the catalyst. Among these physical fields, piezoelectric field synergistic photocatalysis has garnered increasing attention from researchers due to its significant improvement in charge carrier separation efficiency and catalytic activity.
Since Academician Wang Zhonglin pioneered piezoelectric photocatalysis technology in 2010[1], the field has rapidly developed over the past decade. Semiconductor photocatalysts with piezoelectric properties can simultaneously absorb and convert mechanical energy and solar energy, using piezoelectric potential and polarized charges to provide driving force for the migration of photo-generated electrons/holes. The polarized charges and induced piezoelectric potential enable the photo-generated charges in piezoelectric semiconductor photocatalysts to migrate in specific directions, promoting their separation and reducing recombination. As of now, piezoelectric photocatalysis has attracted great interest in various scientific fields, including physics, chemistry, energy, and environmental science, and has been applied in hydrogen production, CO₂ reduction, organic synthesis, biological applications, environmental remediation, and small molecule catalysis.
Figure 1 Illustration of Piezoelectric Photocatalysis
When piezoelectric materials are subjected to mechanical stress, the internal lattice structure of the material deforms, causing a displacement of the positive and negative charge centers. This displacement generates strain-induced polarization and produces charges on the surface of the material, forming an internal electric field. Common methods of applying mechanical stress include mechanical stirring, external pressure, and ultrasonic vibrations. Ultrasonic cleaners are widely used in piezoelectric photocatalysis to apply mechanical stress due to their high intensity and strong operability.
Under mechanical stretching or strain along an asymmetric direction, the centers of positive and negative charges in the unit cell of piezoelectric photocatalysts displace, leading to spontaneous polarization. As a result, positive and negative charges are generated on two opposing surfaces, creating an internal electric field. Furthermore, the generated internal electric field can induce band bending at the solid-liquid interface, further enhancing catalytic activity.[2] For example, Professor Jiang Hailong's research team synthesized MOF material UIO-66-NH₂(Hf) using a hydrothermal method, which exhibited a hydrogen production efficiency 2.2 times higher than that of UIO-66-NH₂(Zr) under ultrasonic synergistic photocatalytic conditions[3]. However, these two MOFs showed similar activity in photocatalytic hydrogen production without ultrasonic irradiation. Comparative experiments clearly indicated that the piezoelectric effect of UiO-66-NH₂(Hf) was the key factor for its higher activity in piezoelectric photocatalysis. The piezoelectric properties of the two MOFs were studied using Atomic Force Microscopy (AFM) with Kelvin Probe Force Microscopy (KPFM) and Piezoelectric Response Force Microscopy (PFM) modules. Results showed that the piezoelectric response of UiO-66-NH₂(Hf) was significantly stronger than that of UiO-66-NH₂(Zr). Under light irradiation, the surface potential of UiO-66-NH₂(Hf) decreased from 54.4 mV to 41.0 mV, indicating that the internal electric field facilitated the separation of photo-generated charge carriers. Additionally, the study optimized ultrasonic parameters, finding that ultrasonic conditions of 200 W and 53 kHz could maximize the photocatalytic efficiency of UiO-66-NH₂(Hf).
Figure 2 (a) Hydrogen production rate of two catalysts under different conditions, (b) Hydrogen production rate of UiO-66-NH₂(Hf) under different ultrasonic frequencies, (c) Hydrogen production rate of UiO-66-NH₂(Hf) under different ultrasonic frequencies, (d) Kinetic curve of photocatalytic hydrogen production of UiO-66-NH₂(Hf) in cyclic experiments under ultrasonic power of 200 W and frequency of 50 kHz.
Figure 3 (a) Surface potential images, (b) Surface potential curves, (c) Piezoelectric response phase hysteresis loop, (d) Amplitude butterfly loop of UiO-66-NH₂(Hf).
In addition to piezoelectric photocatalysis, piezoelectric field synergistic electro/photoelectrocatalysis has also received extensive attention from researchers in recent years. Based on this, Beifilai Technology has innovatively developed the Ultrasonic Coupled Electro/Photoelectrolyzer, which is the industry's first reaction device that deeply integrates piezoelectric fields with electro/photoelectrocatalysis, providing new solutions for clean energy, environmental management, and green chemistry.
Beifilai Ultrasonic Coupled Electro/Photoelectrolyzer is equipped with a 120 W transducer (60 W on each side), with precisely adjustable ultrasonic power and an ultrasonic frequency of 40 kHz (frequency can be customized), which can significantly enhance the efficiency and selectivity of catalytic reactions. This electrolyzer can display the reaction temperature in real-time, facilitating researchers to monitor reaction conditions accurately. For more information about this product, please call 400-1161-365.
The efficiency and effectiveness of piezoelectric catalytic reaction experiments are influenced by various factors, including the selection of piezoelectric materials, the surface area and morphology of the catalyst, the method of applying mechanical stress, reaction conditions, and the external environment (such as ultrasonic frequency and power) as well as reactor design. The higher the piezoelectric coefficient of the piezoelectric material, the stronger the generated piezoelectric potential, which is more favorable for the separation and transport of photo-generated charge carriers. A high specific surface area and appropriate morphology of the catalyst can increase reactive active sites and improve reaction efficiency. Optimization of reaction conditions, such as appropriate light intensity, reaction temperature, and solution pH, can further enhance catalytic activity. Additionally, the design of piezoelectric catalytic reactors is particularly important, and a reasonable reactor design should meet the following conditions:
◆ The internal physical conditions of the reactor, such as temperature, pressure, and mass transfer, should be optimized to improve the activity and selectivity of the catalyst;
◆ Ensure sufficient contact between the catalyst and reactants based on the distribution, shape, and size of the catalyst to increase the reaction rate;
◆ Use stable and durable materials to ensure long-term reliability, as the reactor may encounter mechanical stress and chemical corrosion during operation;
◆ Consider the scalability of the reactor from laboratory to industrial scale, including reactor size, material costs, and manufacturing processes;
◆ Include effective monitoring and control systems to precisely control operational conditions such as temperature, pH, and reactant concentration, ensuring the reaction occurs under optimal conditions.
Beifilai offers customized services for photocatalytic reactors, which can meet the characteristics of "structurally robust, easy sampling, suitable for sampling and testing of different forms of products." Please feel free to inquire!
Consultation Phone: 400-1161-365
[1] Yang Q , Guo X , Wang W ,et al.Enhancing Sensitivity of a Single ZnO Micro-/Nanowire Photodetector by Piezo-phototronic Effect[J].Acs Nano, 2010, 4(10):6285.
[2] Guo S L , Lai S N , Wu J M .Strain-Induced Ferroelectric Heterostructure Catalysts of Hydrogen Production through Piezophototronic and Piezoelectrocatalytic System[J].ACS nano, 2021, 15(10):16106-16117.
[3] Zhang C , Lei D , Xie C ,et al.Piezo-Photocatalysis over Metal–Organic Frameworks: Promoting Photocatalytic Activity by Piezoelectric Effect[J].Advanced Materials,2021,33(51):1
