Polymeric Hydrogels for Hydrogen (H2) Storage: A Comprehensive Review

Hydrogen is widely recognized as a green and renewable energy carrier that is essential for the transition to sustainable energy systems. Traditional hydrogen storage methods, such as compressed gas, metal hydrides, and metal-organic frameworks (MOFs), offer high storage densities but are often associated with safety concerns, high energy requirements, and limited practical applicability. In contrast, polymeric hydrogels present a versatile platform for hydrogen storage due to their tunable porosity, high water uptake, and reversible functional groups. This review highlights recent advances in the design, synthesis, and functionalization of hydrogels for hydrogen storage, focusing on key mechanisms such as physisorption, chemisorption, and hydrogen entrapment. Importantly, hydrogels facilitate reversible hydrogen uptake and release under mild conditions, making them promising candidates for integration into flexible and smart energy devices. Recent progress in nanocomposite hydrogels, stimulus-responsive systems, and metal–hydrogel hybrids has further improved storage capacity and control. Although their current gravimetric hydrogen capacity is lower than that of MOFs or metal hydrides, polymeric hydrogels offer superior processability, safety, scalability, and multifunctionality. These advantages position them as highly promising materials for future hydrogen storage applications in both stationary and portable systems.