Fully hydrolyzed photocatalyst with quantum efficiency beyond 100%.

On April 10, 2023, Professor Li Xuanhua’s team from Northwestern Polytechnical University published a report entitled “Internal quantum efficiency higher than 100% achieved by combining doping and quantum effects for photocatalytic overall water splitting” in Nature Energy Research results.

In this study, a photocatalytic water splitting strategy enhanced by the multi-exciton effect is reported. This strategy realizes the wide-range regulation of the band structure and built-in electric field strength of CdTe/V-In2S3 heterojunction photocatalyst through the co-regulation of quantum effect and doping engineering, which provides a strong migration driving force for the extraction of excitons. Under the combined action of the built-in electric field and gradient band structure of the strong interface, the effective utilization of the multi-exciton effect in the field of photocatalytic water decomposition is realized, and the internal quantum efficiency of more than 100% is obtained.

The corresponding author of the paper is Professor Li Xuanhua, and the first author is PhD student Zhang Youzi.

Using solar energy to achieve water splitting on semiconductor materials and directly converting them into sustainable hydrogen energy is an effective way to solve the energy crisis and environmental pollution. In the past few decades, researchers have carried out a lot of exploration to obtain a highly efficient photocatalyst for total water lysis. For example, element doping, crystal plane regulation, defect regulation, and construction of heterojunction photocatalysts. However, the low carrier separation efficiency in the photocatalytic water splitting process is still the key difficulty in limiting the photocatalytic activity. The multi-exciton effect, that is, when a 0D quantum dot absorbs a high-energy photon (the photon energy is much greater than the 0D quantum dot band gap), two or more electron-hole pairs will be generated, which can effectively improve the photoelectric conversion efficiency. In the field of optoelectronic devices, the multi-exciton effect can achieve internal quantum efficiency of up to 700%. However, the effective use of the multi-exciton effect in photocatalytic water splitting systems has not been specifically reported.

In this work, the team of Professor Li Xuanhua of the Nanoenergy Center of Northwestern Polytechnical University realized the effective use of the multi-exciton effect in the field of photocatalytic water splitting for the first time through the co-regulation strategy of quantum effect and doping effect. As a proof of concept, taking the CdTe/V-In2S3 heterojunction photocatalyst as the research object, by optimizing the size of CdTe quantum dots and the amount of V doping in V-In2S3 at the same time, the Fermi level difference between the two was effectively widened, and the electron transfer at the CdTe/V-In2S3 interface was promoted, and the built-in electric field strength enhancement of up to 14.14 times was finally achieved. At the same time, the In 5s and S 3p orbitals at the CdTe/V-In2S3 interface are hybridized to form an interface electronic state that can capture electrons. Under the action of strong interfacial built-in electric field and interfacial electronic state, the relaxation rate of thermal electrons generated by optical excitation of CdTe quantum dots is effectively reduced, and the thermoelectrons with sufficient energy are induced to produce the multi-exciton effect. When the incident light energy is greater than 2.75 times the CdTe quantum dot bandgap, CdTe/V-In2S3 produces a multi-exciton effect, and an average absorption of 1 high-energy photon (excitation wavelength of 350 nm, that is, 3.14 times the CdTe quantum dot bandgap) can produce 1.69 excitons. Finally, by loading Pt and CoOx as cocatalysts, Pt-CdTe/V-In2S3-CoOx photocatalysts with gradient band structure were obtained, which effectively improved the photolysis activity, the quantum efficiency reached 114% at 350nm, and the conversion efficiency from solar to hydrogen energy was 1.31%.

Figure 1: Schematic diagram of the regulation of the band structure

Figure 2: Photocatalyst structure and micromorphology

Figure 3: Interface electronic structure and built-in electric field characterization

Figure 4: Schematic diagram of quantum efficiency and multi-exciton effect extraction

Figure 5: Photocatalytic water splitting activity and mechanism

This study provides a new research direction for the design of high-efficiency photolysis water catalysts, and reveals a new design idea for the effective use of the multi-exciton effect in the field of photocatalysis. (Source: Science Network)

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