Hydrogen storage in modified iron oxides: The effect of additives on the cyclic stability

In the steam-iron process the indirect storage and release of hydrogen are achieved through the cyclic reduction of with hydrogen to iron and the oxidation of iron with water vapor to produce hydrogen. Its primary challenge is the decreasing activity with an increasing number of cycles due to sintering. In this work, the effect of adding Ce, Mo, and Al on the cyclic stability was investigated in a fixed bed reactor using metal oxide powder with a particle size of 100–200 µm. Mo exhibits the most stable performance across multiple cycles. This can be attributed to the mitigation of sintering and the ability of molybdenum to store and release hydrogen. In addition to the additive, the synthesis method also plays a decisive role. The synthesis of the modified iron oxide particles via impregnation leads to a higher additive concentration on the particle surface, thereby reducing sintering compared to iron oxide produced by co-precipitation. Iron oxide impregnated with Mo maintains 72 % of its initial hydrogen storage capacity after 50 cycles of hydrogen storage and release, demonstrating superior cyclability compared to unmodified iron oxide.