Advanced Photoelectrochemical Cells with MoS2 Nanoflakes

Researchers are leading an initiative aimed at developing environmentally friendly energy sources, such as photoelectrochemical (PEC) cells, for hydrogen generation using solar energy. In their recent study, they demonstrated the use of 3D porous MoS2/CSF photoelectrodes, incorporating carbon spun fabric (CSF) as electrode materials, which exhibited excellent mechanical and structural stability.

In the process of manufacturing a 3D porous MoS2/CSF photoelectrode, the Oxi-PAN staple fibers were used and applied as intersected warps and wefts in the plain weave process, leading to excellent mechanical and structural stability. Image Credit: Beijing Zhongke Journal Publising Co. Ltd.

Dong Ick Son (Department of Nanomaterials and Nano Science, University of Science and Technology, Republic of Korea); Institute of Advanced Composite Materials, Korea Institute of Science and Technology; and Donghee Park (Center for Opto-Electronic Materials and Devices, Post-Silicon Semiconductor Institute, Korea Institute of Science and Technology, Republic of Korea) are the research leaders for this initiative.

Many scientists are working on creating environmentally benign energy sources to take the place of fossil fuels to reduce global warming, which is endangering the ecology. One of the noteworthy research projects is the usage of photoelectrochemical (PEC) cells, which produce environmentally acceptable hydrogen through PEC reactions using an endless supply of solar energy.

Through photocatalytic reactions on semiconductor electrodes, the PEC process produces hydrogen gasses through the breakdown of water, resulting in environmentally benign hydrogen generation.

Furthermore, the solar-to-hydrogen (STH) conversion efficiency is very high. Because the PEC process employs solar energy instead of continuous power for electrocatalysis, it is more efficient than the water-splitting approach. High recombination losses of photogenerated electron-hole pairs have long been compensated for by increasing the surface area of the photoanode in PEC cells.

With electrolytes, nano-structured photoactive materials might boost light absorption by increasing the specific surface area. Even with these engineering efforts to create photoactive material layers, improving hydrogen production for use in real-world scenarios is still difficult.

Carbon fiber textiles, such as carbon spun fabric (CSF) or carbon fiber bundles, have been regarded as one of the most promising electrode materials for PEC applications due to their porosity, flexibility, conductivity, and chemical and mechanical stability.

Previous research that used hydrothermal techniques saw the growth of decorative materials on carbon fiber textiles in the form of nanoflakes or nanorods, which increased the surface area on top and improved the photochemical performance.

Their porous nature facilitates the construction of large-area 3D composite structures with increased interface regions that interact with electrolytes, more easily than rigid and flat substrates. These findings demonstrate the importance of optimizing nanostructures on porous carbon textiles as the substrate; nevertheless, there is currently no research on the relationship between coating morphologies and PEC performances.

MoS2 has been incorporated into various industries, including batteries, electronics, and catalysts. The optical and structural features of MoS2 make it a desirable photoanode for PEC cell devices. At the vacuum level, the valence band of MoS2 is lower than the oxidation potential of O2/H2O (-5.67 eV), while the conduction band (CB) is higher than the reduction potential of H+/H2 (-4.44 eV).

The bandgap of MoS2 varies from 0.86 eV to 1.9 eV based on thickness and structure. MoS2-based heterostructures that included other semiconductors worked well to encourage hydrogen production. These findings also imply that to synthesize the top layer, the coating morphologies of the bottom layer should be adjusted.

The study demonstrated the PEC performances of MoS2-coated photoanodes on a three-dimensional carbon star fund (CSF) as well as the influence of coating morphologies. An approach known as low-temperature hydrothermal coating was used to create 3D porous MoS2/CSF photoanodes. MoS2 coating morphologies that were optimized for hydrothermal growing time and MoS2 precursor quantity resulted in film-like MoS2 on CSF with the highest photocurrent density and biggest surface area.

Furthermore, sputtering techniques were used to create the bottom layer (TiO2) and hydrothermal synthesis was used to create the top layer (MoS2) of conformal MoS2/TiO2 heterojunction structures on 3D porous CSFs. When compared to the PEC cell with the MoS2/CSF structure, the PEC performances of the PEC cell with the MoS2/TiO2/CSF photoanode were even better.

Journal Reference:

Cho, H., et. al. (2024) High-performance photoelectrochemical cells with MoS2 nanoflakes/TiO2 photoanode on 3D porous carbon spun fabric. Advanced Sensor and Energy Materials. doi:10.1016/j.asems.2023.100088.

Source: https://www.kist.re.kr/ko/index.do

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