Optimization of TiFe-based alloys for low pressure hydrogen storage in hydrogen energy storage system

초록

This study optimized TiFe-based alloys for low pressure hydrogen storage in hydrogen energy storage systems (HESS) and examined their hydrogen storage properties. The TiFe0.8Mn0.2 alloy exhibits adequate hydrogen storage properties at low pressures; however, it suffers from sluggish room-temperature activation. To address this limitation, a small amount of Fe was substituted with Cr to produce the TiFe0.78Mn0.2Cr0.02 alloy, and the hydrogen absorption behaviors and hydrogen storage properties of both alloys were comparatively evaluated. Both alloys exhibited a dual-phase microstructure consisting of the B2 phase matrix and the precipitated C14 Laves phase, with the Cr-containing alloy showing a higher fraction of the Laves phase, which enhanced room-temperature activation. Notably, after 7 days of air exposure, hydrogen absorption was significantly suppressed in the TiFe0.8Mn0.2 alloy, whereas the TiFe0.78Mn0.2Cr0.02 alloy absorbed hydrogen without thermal activation. Pressure-composition-temperature (PCT) measurements at 20, 30, 50, and 60 degrees C revealed that both alloys exhibited smoothing behavior at the first and second plateau pressures, with similar PCT curve profiles and plateau pressure slopes. The TiFe0.78Mn0.2Cr0.02 alloy exhibited reduced hysteresis between hydrogen absorption and desorption at 20 degrees C. To evaluate practical hydrogen storage performance, the effective hydrogen storage capacity was assessed under simulated HESS operating conditions. Assuming hydrogen supply from an alkaline water electrolyzer, hydrogen absorption was estimated at 6 bar and 20 degrees C, while hydrogen desorption was determined at 1 bar and 60 degrees C, corresponding to proton exchange membrane fuel cell operation. The TiFe0.78Mn0.2Cr0.02 alloy exhibited a higher effective hydrogen storage capacity than the TiFe0.8Mn0.2 alloy owing to reduced hysteresis, making it a promising candidate for HESS applications.

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