Hydrogen absorption/desorption properties of light metal hydroxide systems

Abstract

Summary In light metal hydroxide systems, hydrogen desorption generally occurs in exothermic reactions; therefore, these reactions are irreversible in principle. However, according to theoretical calculation of thermodynamics, some of these systems can desorb hydrogen in endothermic reactions. In this research, several hydroxide systems were studied to clarify the reversibility of these systems. Six types of hydroxide systems (XH + Y(OH)n, X: Li, Na, Y: Li, Na, Mg) were prepared by ball‐milling, then the desorption properties of these systems were evaluated. As a result, NaH + LiOH and NaH + NaOH systems desorbed hydrogen in endothermic reactions. Also, NaH + NaOH system absorbed hydrogen almost 100% reversibly under 300°C and 1.0 MPa H2 pressure. The reversibility in NaH + LiOH system was not accomplished in our experimental condition, because high pressure of GPa order is required for the rehydrogenation. In order to modify the desorption kinetics, we added KH catalyst to NaH + LiOH and NaH + NaOH systems. The hydrogen desorption temperature of the two systems was decreased by addition of 1 mol% of KH. The catalytic effect on hydrogen desorption properties was sustained even after the rehydrogenation of KH‐added NaH + NaOH system.

Preparation and application of sulfonated polysulfone in an electrochemical hydrogen storage system

“…Several researches in this area are focused on metal hydrides, metal organic frameworks and carbon materials while these materials are suffered from slow kinetics, inappropriate thermodynamics and low efficiencies 43 . Organic polymers, due to the structural flexibility, thermomechanical, and physicochemical properties, are recently developed as the host for hydrogen sorption in the electrochemical systems 44 . The physisorption of hydrogen is a reversible process with continuous adsorption and desorption profiles.…”

“…43 Organic polymers, due to the structural flexibility, thermomechanical, and physicochemical properties, are recently developed as the host for hydrogen sorption in the electrochemical systems. 44 The physisorption of hydrogen is a reversible process with continuous adsorption and desorption profiles. Since the hydrogen density is low, almost weak interactions occur between hydrogen and solid materials.…”

Dehydrogenation properties of hydride‐hydroxide systems containing potassium

“…MgH 2 ‐LiBH 4 system desorbs hydrogen as follows: LiH‐LiNH 2 system absorbs and desorbs hydrogen as follows 8 : Also, Li‐Mg‐N‐H system has low value of enthalpy change and lower temperature of around 180°C for hydrogen absorption/desorption. The overall reaction of Li‐Mg‐N‐H system is described as follows 5 : So far, a lot of research on complex hydrides has been reported; however, the research on hydroxides has not been reported very much 6,9,10 . In this study, we focused on the hydride hydroxide systems, because we expected that promising hydrogen storage material would be developed from hydride hydroxide systems.…”

“…LiOH desorbs H 2 O by thermal decomposition. On the other hand, LiH‐LiOH system desorbs H 2 as follows 10 : …”

“…Among them, KH have attracted attention in M‐N‐H, M‐B‐H, and M‐O‐H systems 15,16 . It is reported that LiH‐LiNH 2 system desorbs hydrogen in lower temperature with addition of KH 10 . In this system, KH reacts with NH 3 to form KNH 2 .…”