In recent years, engineers have been trying to design new technologies to produce and store energy sustainably to overcome global dependence on fossil fuels and tackle climate change. One solution that has attracted much attention is the conversion of solar energy into hydrogen through a process known as water separation.

Water separation is a chemical process in which water can be broken down into two main components: hydrogen and oxygen. Photoelectrochemical (PEC) water separation processes will enable the production of green hydrogen from sunlight and water.

To be implemented on a large scale, PEC devices must be inexpensive and long-lasting. However, developing devices that are stable over time using widely available and affordable materials have so far been challenging.

Past studies have shown that photoelectrodes made from materials abundant on Earth, such as light-absorbing semiconductors, tend to rust easily when sunlight is exposed. This significantly hinders the development of PEC devices based on these excellent and more affordable materials.

Researchers at Yonsei University have recently developed a new strategy to improve photoelectrodes’ stability in PEC water separation devices. This method, introduced in a paper published in Nature Energy, requires using a hydrogel-based and transparent layer that can protect the photocathodes (i.e., negatively charged electrodes that emit electrons when exposed to radiant energy light).

“The lifetime of photoelectrochemical devices is compromised by severe photocorrosion of semiconductors and instability of photocatalysts,” Jeiwan Tan and colleagues write in their paper. “We report a strategy for stabilizing photoelectrochemical devices that uses a polyacrylamide hydrogel as a highly permeable and transparent on-device protector.”

Photosynthetic marine plants inspire the absorbent and transparent protective layer designed by Tan and colleagues. These plants, including seaweed, have nanoporous cells with a protective hydrogel. This hydrogen can prevent cell deformation and rupture caused by forces in the aquatic environment and physical contact with the organism.

When seaweed cells are coated with this hydrogen, they can transmit light and maintain water levels. The researchers sought to create a similar protective layer that could prevent photoelectrodes’ corrosion, thereby increasing PEC devices’ stability. They tested this layer on a photocathode made of antimony triselenide (Sb2Se3).

“A hydrogel-protected Sb2Se3 photocathode exhibits stability over 100 hours, retains ~70% of the initial photocurrent, and the decay rate gradually decreases to saturation,” the researchers write in their paper. “The structural stability of a Pt/TiO2/Sb2Se3 photocathode remains unchanged beyond this time and effective bubble escape is achieved through the micro gas tunnel created in the hydrogel to achieve a mechanically stable shield.”

The first tests carried out by the researchers showed promising results; This suggested that their protective hydrogen could prevent degradation and corrosion of Sb2Se3-based photodetectors for water separation applications. Tan and colleagues also demonstrated that hydrogel preservatives are compatible with electrolytes over a wide pH range, always using an SnS photocathode and a BiVO4 photoanode with a ~500 h lifetime.

In the future, the hydrogel-based shielding introduced in their paper could protect photocathodes inside various PEC devices for water separation. This could facilitate the large-scale implementation of these devices and ultimately help combat climate change.

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Alice is the Chief Editor with relevant experience of three years, Alice has founded Galaxy Reporters. She has a keen interest in the field of science. She is the pillar behind the in-depth coverages of Science news. She has written several papers and high-level documentation.


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