Where to go for the Development of High-Performance H2 Storage Materials at Ambient Conditions?

Hydrogen is expected to overcome energy resource depletion because it is the most abundant element in the universe and because an ideal hydrogen energy cycle has the potential to exploit energy infinitely. Conventionally, hydrogen storage utilizes compression under high pressure (350-700 bar) into a tank and liquefaction in the cryotemperature regime (20 K). To mitigate the impractical operating conditions researchers have conducted adsorption-dependent research to increase the specific surface area (SSA) in physisorption and to decrease the H-2 binding energy in chemisorption. Nevertheless, these strategies are still unlikely to reach the required the U.S. Department of Energy (DOE) targets. To this end, researchers have tried to find hydrogen storage material to fit the H-2 binding energy between the physisorption region and chemisorption region. Previous governing parameters, the SSA, and the H-2 binding energy show no correlation to gravimetric H-2 storage capacity (GHSC). In addition, no correlation between the H-2 densification index (HDI) and the H-2 binding energy is found as well, which means the latter cannot describe the H-2-adsorbent interaction thoroughly. The several notable findings presented here suggest that the development of high-performance H-2 storage materials can be realized through the optimal modulation of an underlying parameter that dominates the H-2-adsorbent interaction. This paper highlights the necessity of research on what the underlying parameter that dominates the H-2-adsorbent interaction is and on how it affects GHSC to develop H-2 storage materials that meet the DOE targets.