High pressure thermal hydrogen compression employing Ti1.1CrMn metal hydride material

Abstract

Abstract The use of Ti1.1CrMn metal hydride material in a thermal hydrogen compression system is investigated. The thermodynamic properties of the material, initially synthesized and annealed at 900 °C for 48 h (for quantities on the order of 10 kg), are assessed performing pressure–concentration–temperature equilibrium tests for hydrogen absorption and desorption at pressure up to about 900 bar. Results show flat plateaus and reduced hysteresis. The calculated absorption enthalpy and entropy are 20.55 ± 0.13 kJ mol H 2 − 1 and 102.16 ± 3.00 J mol H 2 − 1 K−1 respectively. The desorption enthalpy and entropy are 22.89 ± 0.45 kJ mol H 2 − 1 and 107.80 ± 10.45 J mol H 2 − 1 K−1, respectively. The metal hydride achieves a weight capacity of approximately 1.8% at room temperature and maintain an approximately constant weight capacity during the cycling testing. This makes the material a suitable candidate for high pressure hydrogen compressors, achieving pressures on the order of 450 bar at temperatures of approximately 140 °C. The same material composition is synthesized at laboratory scale quantities (on the order of 50 g), applying a modified annealing procedure (1200 °C for 240 h). This allows higher operating pressures to be achieved, but the modified annealing process also produces (at least) an additional phase, namely the C15 Laves phase, present in the material along with the C14 Laves phase. Consequently, two pressure plateaus are present at each operating temperature, reducing the effective material weight capacity available for the compression application. A two-stage hybrid compressor concept is also presented, with the thermal hydride compressor paired with a lower pressure electrochemical unit. In principle, the system can compress hydrogen with a compression ratio of 45 from 10 to 450 bar without any external thermal input and recovering the electrochemical unit waste heat to drive the thermal stage.