Densified HKUST-1 Monoliths as a Route to High Volumetric and Gravimetric Hydrogen Storage Capacity.

We are currently witnessing the dawn of hydrogen (H2) economy, where H2 will soon become a primary fuel for heating, transportation, and long-distance and long-term energy storage. Among diverse possibilities, H2 can be stored as a pressurized gas, a cryogenic liquid, or a solid fuel via adsorption onto porous materials. Metal-organic frameworks (MOFs) have emerged as adsorbent materials with the highest theoretical H2 storage densities on both a volumetric and gravimetric basis. However, a critical bottleneck for the use of H2 as a transportation fuel has been the lack of densification methods capable of shaping MOFs into practical formulations while maintaining their adsorptive performance. Here, we report a high-throughput screening and deep analysis of a database of MOFs to find optimal materials, followed by the synthesis, characterization, and performance evaluation of an optimal monolithic MOF (monoMOF) for H2 storage. After densification, this monoMOF stores 46 g L-1 H2 at 50 bar and 77 K and delivers 41 and 42 g L-1 H2 at operating pressures of 25 and 50 bar, respectively, when deployed in a combined temperature-pressure (25-50 bar/77 K → 5 bar/160 K) swing gas delivery system. This performance represents up to an 80% reduction in the operating pressure requirements for delivering H2 gas when compared with benchmark materials and an 83% reduction compared to compressed H2 gas. Our findings represent a substantial step forward in the application of high-density materials for volumetric H2 storage applications.

Elucidating the Mechanism of Li Insertion into Fe1-xS/Carbon via In Operando Synchrotron Studies.

The detailed understanding of kinetic and phase dynamics taking place in lithium-ion batteries (LIBs) is crucial for optimizing their properties. It was previously reported that Fe1-xS/C nanocomposites display a superior performance as anode materials in LIBs. However, the underlying lithium storage mechanism was not entirely understood during the 1st cycle. In this work, in operando synchrotron techniques are used to track lithium storage mechanisms during the 1st (de)-lithiation process in the Fe1-xS/C nanocomposite. The combination of in operando techniques enables the uncovering of the phase fraction alternations and crystal structural variations on different length-scales. Additionally, the investigation of kinetic processes, morphological changes, and internal resistance dynamics is discussed. These results reveal that the phase transition of Fe1-xS → Li2Fe1-xS2 → Fe0 + Li2S occurs during the 1st lithiation process. The redox reaction of Fe2+ + 2e- ⇌ Fe0 and the Fe K-edge X-ray absorption spectroscopy (XAS) transformation process are confirmed by in operando XAS. During the 1st de-lithiation process, Fe0 and Li2S convert to Li2-yFe1-xS2 and Li+ is extracted from Li2S to form Li2-yS. The phase transition from Li2S to Li2-yS is not detected in previous reports. After the 1st de-lithiation process, amorphous lithiated iron sulfide nanoparticles are embedded within the remaining Li2S matrix.