Sustainable Superhydrophilic Hydrogel-Based Photocatalyst for Green Hydrogen Production

Superhydrophilic hydrogels with 3D frameworks are the next-generation photocatalyst for sustainable high-performance hydrogen generation. Con­ven­tion­ally, highly active powder catalysts are used for hydrogen generation. The major bottlenecks that impede the commercial applications of powder catalysts are the instability of photocatalysts, poor catalyst recovery, reverse reactions and metal aggregation. A hydrogel-based photocatalyst with strong adsorption capabilities, excellent total surface areas and good compatibility with the environment can be used to overcome these obstacles. These hydrogel-based photocatalysts focus on fast gas separation, easy water transport through hydrogel porous structure and effective light delivery. Furthermore, these types of hydrogel-based photocatalysts perform long-term stable hydrogen generation in non–saline as well as saline-alkaline turbid water. Hydrogel photocatalysts based on organic polymers were investigated for solar hydrogen generation, where each hydrogel millisphere serves as a microreactor for the production of hydrogen. The hydrogel-based photocatalyst's high hydrophilicity has a significant impact on the hydrogen generation rate and the continuous operation of the photoreactor. The toxic effect of the powder catalyst can be minimized through encapsulation in the hydrogel 3D network. In this review, inorganic or organic semiconductors and hydrogel-based photocatalysts are classified according to their fabrication methods and their role in green hydrogen generation through solar water splitting is discussed.