Using Atomic Layer Deposition, a Group of Scientists Prompted the Generation of Fe-In-S Clusters in ZnInS, Enhancing Pec Outcomes.
In Nature Communications, a group of scientists from China and Thailand published their research that targets the performance enhancement of hydrogen energy production (electrolysis). By implementing atomic layer deposition (ALD), they could prompt the generation of Fe-In-S clusters in the semi-conducting nanosheet, ZInS, thus leading to higher catalytic outcomes.
With climate change and resource depletion becoming more and more urgent matters, hydrogen energy, as a substitute for fossil fuel, offers a potential solution to the world’s rising problems. Hydrogen energy can be produced from water using solar light and a semiconducting material (Photoanode) through photoelectrochemical (PEC) water splitting.
However, the bulk recombination of the resulting charged carriers and the slow surface oxygen evolution reaction (OER) have made PEC inefficient and at times, impractical. Liang Li conceptualized using atomic layer deposition to load Fe-In-S (iron-indium-sulfur) clusters in a vertically arranged ZInS nanosheet. This was shown to improve the performance of the photoanode and increase its photocurrent, as well as its onset potential.
Liang Li's research team saw that the Fe-In-S clusters lower the energy barrier for the photoelectrochemical reaction at the surface of the photoanode, specifically through modifying the second and third steps of oxygen evolution reaction (OER). While using a pure ZInS nanosheet in PEC is efficient and stable enough for visible light absorption compared to binary semiconductors, its applications are limited by the unfavorable recombination of the generated charge carriers and the sluggish rates of OER.
The method implemented by the research team targets the improvement of the photoanode’s bulk separation efficiency (ηsep) to limit the charge carrier recombination, as well as enhance oxygen evolution reaction kinetics. This is through yielding Fe-In-S clusters on the ZInS nanosheet surface using ALD technique. Usually, without applying ALD, there exists a disordered layer on the ordered ZInS nanosheet that significantly affects the separation efficiency and increases the energy barrier.
Linxing Meng and Weiwei Xu synthesized a ZISZ/Fe nanosheet by introducing Fe and O atoms using atomic layer deposition to ZInS photoelectrode, generating Fe-In-S clusters and Zn-O bonds. With this new structure, the ZISZ/Fe nanosheet possesses reduced interfacial recombination and, as a result, enhanced OER kinetics. In addition, the ZISZ/Fe Photoanode now shows aligned gradient energy and no longer exhibits a disordered layer between the substrate and the ZInS nanosheet due to the presence of Zn-O bonds.
As the DFT results calculated by Run Long and Jinlu He show, Fe atoms replace In atoms due to the lower formation energy (i.e. energy barrier) than that in Fe-Zn replacement. The Fe atoms are distant and repelled from Zn atoms, thus building bonds with the surrounding ‘In’ and ‘S’ atoms, forming Fe-In-S clusters. DFT calculations further confirm the enhancement of the catalytic performance of ZISZ/Fe photoelectrode.
Moreover, Xiaolong Zhou and Yongbing Tang joined Pinit Kidkhunthod at Synchrotron Light Research Institute in Thailand to perform and analyze the measurements of XAS (X-ray absorption spectroscopy) experiment. They were able to reach the conclusion that Fe–In–S clusters were formed on the surface of the semiconducting photoanode.
The catalytic performance proves to be far more efficient than that of other sulfide-based photoanodes, as ZISZ/Fe photoanode, i.e. Zn10 In16 S34 loaded with Fe-In-S clusters, exhibits a clearly enhanced photocurrent (J) and an improved onset potential (Von). And the results, as the authors wrote, confirm “the feasibility of ALD to manipulate chemical bonds and energy band structure of photoelectrodes towards improved energy conversion technology”.
Meng, L., He, J., Zhou, X. et al. Atomic layer deposition triggered Fe-In-S cluster and gradient energy band in ZnInS photoanode for improved oxygen evolution reaction. Nat Commun 12, 5247 (2021). https://doi.org/10.1038/s41467-021-25609-0