Review of TiFe-based Hydrogen Storage Alloys and Methodologies for Overcoming Their Initial Hydrogenation Problem

TiFe-based hydrogen storage alloys have received significant attention as a next-generation hydrogen storage material due to their advantages, including abundant raw materials, a high theoretical hydrogen storage capacity (approximately 1.9 wt%), and mild operating conditions near room temperature and atmospheric pressure. However, there is a major drawback, which is the difficulty of initial hydrogenation (activation) caused by coherent surface oxide layers. To address this issue, various research efforts have been undertaken. This paper provides an overview of TiFe-based alloys and comprehensively reviews three primary approaches to improve initial hydrogenation performance such as alloy element substitution, mechanical processing, and surface modification/catalyst addition. Based on these research trends, we present future research directions for the commercialization of TiFe-based alloys. We also emphasize the approach to find the optimal balance between material cost and hydrogen storage performance.