| Summary: | Disproportionation and phase separation are big issues that occur under extreme pressure and temperature conditions during hydrogen compressor cycles, which makes metal hydrides inactive and reduces compression efficiency. It is important to identify boundary conditions to avoid such unwanted phase separation. However, no investigation related to this problem has been carried out so far. Thus we propose a method to investigate the critical temperature and pressure condition for the alloy degradation during the hydrogen compressor cycle. The V<sub>20</sub>Ti<sub>32</sub>Cr<sub>48</sub> alloy was chosen as a model system for the purpose. The influence of two important parameters (i.e., hydrogen content and temperature) was investigated individually. The disproportionation of V<sub>20</sub>Ti<sub>32</sub>Cr<sub>48</sub> alloy during the hydrogen compressor cycle test occurred at temperatures higher than 200 °C and 75% H<sub>2</sub> content of the total capacity at the initial condition. A clear and obvious boundary condition between disproportionation and keeping the initial phase intact is defined herein. It can be treated as a general method for any hydrogen storage alloy to be utilized for hydrogen compressor efficiently and safely.
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