Beyond Fertilizers: NH₄ZnPO₄ for the Reversible Chemical Storage of Ammonia

Abstract Enhancing NH 3 as a carbon‐free energy carrier of H 2 and next‐generation fuel is a promising approach for a sustainable society. Chemically storing NH 3 molecules in crystal structures offers better selectivity and reusability than storage in traditional porous materials based on physicochemical adsorption; however, designing materials that can be reversibly stored in structural gaps is still a significant challenge. Herein, the use of NH 4 ZnPO 4 , which is previously used as a fertilizer, is proposed as an NH 3 uptake material through a chemical storage mechanism. The NH 4 ZnPO 4 particles synthesized by a wet mechanochemical method with monoclinic and hexagonal crystal structures can incorporate NH 3 molecules and directly transform them into NH 4 Zn(NH 3 )PO 4 without producing byproducts. The chemical storage mechanism depends on the particle morphology; therefore, the uptake amount per surface area surpasses that of porous materials. NH 4 ZnPO 4 exhibited excellent cycling performance due to its reusability, which is regenerated by releasing NH 3 from NH 4 Zn(NH 3 )PO 4 when heated in air at ≈100 °C. Taking inspiration from previously used and familiar fertilizers further extends this new area of innovative materials that can be used for the reversible storage of low‐molecular‐weight gases.