This paper aims to present an overview of the current state of hydrogen storage methods, and materials, assess the potential benefits and challenges of various storage techniques, and outline future research directions towards achieving effective, economical, safe, and scalable storage solutions. Hydrogen is recognized as a clean, secure, and cost-effective green energy carrier with zero emissions at the point of use, offering significant contributions to reaching carbon neutrality goals by 2050. Hydrogen, as an energy vector, bridges the gap between fossil fuels, which produce greenhouse gas emissions, global climate change and negatively impact health, and renewable energy sources, which are often intermittent and lack sustainability. However, widespread acceptance of hydrogen as a fuel source is hindered by storage challenges. Crucially, the development of compact, lightweight, safe, and cost-effective storage solutions is vital for realizing a hydrogen economy. Various storage methods, including compressed gas, liquefied hydrogen, cryo-compressed storage, underground storage, and solid-state storage (material-based), each present unique advantages and challenges. Literature suggests that compressed hydrogen storage holds promise for mobile applications. However, further optimization is desired to resolve concerns such as low volumetric density, safety worries, and cost. Cryo-compressed hydrogen storage also is seen as optimal for storing hydrogen onboard and offers notable benefits for storage due to its combination of benefits from compressed gas and liquefied hydrogen storage, by tackling issues related to slow refueling, boil-off, and high energy consumption. Material-based storage methods offer advantages in terms of energy densities, safety, and weight reduction, but challenges remain in achieving optimal stability and capacities. Both physical and material-based storage approaches are being researched in parallel to meet diverse hydrogen application needs. Currently, no single storage method is universally efficient, robust, and economical for every sector especially for transportation to use hydrogen as a fuel, with each method having its own advantages and limitations. Moreover, future research should focus on developing novel materials and engineering approaches in order to overcome existing limitations, provide higher energy density than compressed hydrogen and cryo-compressed hydrogen storage at 70 MPa, enhance cost-effectiveness, and accelerate the deployment of hydrogen as a clean energy vector.

Supercapacitors (SCs) have received much interest due to their enhanced electrochemical performance, superior cycling life, excellent specific power, and fast charging–discharging rate. The energy density of SCs is comparable to batteries; however, their power density and cyclability are higher by several orders of magnitude relative to batteries, making them a flexible and compromising energy storage alternative, provided a proper design and efficient materials are used. This review emphasizes various types of SCs, such as electrochemical double-layer capacitors, hybrid supercapacitors, and pseudo-supercapacitors. Furthermore, various synthesis strategies, including sol-gel, electro-polymerization, hydrothermal, co-precipitation, chemical vapor deposition, direct coating, vacuum filtration, de-alloying, microwave auxiliary, in situ polymerization, electro-spinning, silar, carbonization, dipping, and drying methods, are discussed. Furthermore, various functionalizations of SC electrode materials are summarized. In addition to their potential applications, brief insights into the recent advances and associated problems are provided, along with conclusions. This review is a noteworthy addition because of its simplicity and conciseness with regard to SCs, which can be helpful for researchers who are not directly involved in electrochemical energy storage.