Free-standing 3D-printed monoliths of SrCl2 for ammonia storage as a hydrogen carrier

The alkaline earth metal halides (AEMHs), such as strontium chloride (SrCl2), are promising sorbents for hydrogen storage in the form of ammonia. However, these sorbents suffer from structural disintegration problems due to the extraordinary volume expansion during ammonia sorption. This study reports the fabrication of 3D-printed SrCl2 monoliths scaffolded with bentonite using the direct ink writing technique. The optimized monolith with a 60 % SrCl2 loading exhibited an ammonia storage capacity of 488 mg/g, maintaining remarkable structural integrity and effectively accommodating volumetric changes during sorption and desorption over 20 cycles. The kinetics data revealed that ammonia sorption followed a pseudo-second-order model, and intercrystalline diffusion was the rate-controlling step in the 3D-printed SrCl2 structures. High-pressure sorption isotherms were explained by the dual-site Langmuir-Freundlich model due to surface heterogeneity in terms of energies and binding sites for metal-amine complex formation. Thus, cognitively designed AEMHs monoliths present the potential for ammonia storage in various applications by effectively overcoming structural challenges.