Sodium Manganese Ferrite Water Splitting Cycle: Unravelling the Effect of Solid-Liquid Interfaces in Molten Alkali Carbonates.

In this work, the Na2CO3 of the sodium manganese ferrite thermochemical cycle was substituted by different eutectic or eutectoid alkali carbonate mixtures. Substituting Na2CO3 with the eutectoid (Li0.07Na0.93)2CO3 mixture resulted in faster hydrogen production after the first cycle, shifting the hydrogen production maximum toward shorter reaction times. Thermodynamic calculations and in situ optical microscopy attributed this fact to the partial melting of the eutectoid carbonate, which helps the diffusion of the ions. Unfortunately, all the mixtures exhibit a significant loss of reversibility in terms of hydrogen production upon cycling. Among them, the nonsubstituted Na mixture exhibits the highest reversibility in terms of hydrogen production followed by the 7%Li-Na mixture, while the 50%Li-Na and Li-K-Na mixtures do not produce any hydrogen after the first cycle. The loss of reversibility is attributed to both the formation of undesired phases and sintering, the latter being more pronounced in the eutectic and eutectoid alkali carbonate mixtures, where the melting of the carbonate is predicted by thermodynamics.

Quality-dependent performance of hydrophobic ZIF-67 upon high-pressure water intrusion-extrusion process.

Zeolitic imidazolate framework (ZIF) microporous materials have already been employed in many fields of energetic and environmental interest since the last decade. The commercial scale production of some of these materials makes them more accessible for their implementation in industrial processes; however, their massive synthesis may entail modifications to the preparation protocols, which may result in a loss in the optimization of this process and a drop in the material's quality. This fact may have implications for the performance of these materials during their lifetime, especially when they are used in applications such as energy dissipation, in which they are subjected to several operating cycles under high pressures. This study focuses on ZIF-67, a material that has demonstrated in the past its ability to dissipate energy through the water intrusion-extrusion process under high pressure. Two ZIF-67 samples were synthesized using different protocols, and 2 batches of different qualities (labelled as high quality (HQ) and low quality (LQ)) were obtained and analysed by water porosimetry to study their performance in the intrusion-extrusion process. Unexpectedly, minor structural differences, which are typically neglected especially under production conditions, had a dramatic effect on their performance. The results presented in this study reiterate the importance of quality control with respect to reproducibility of experimental results. In a broader perspective, they are critical to the technology transfer from academia to industry.

Jet-Injection In Situ Production of PVDF/PCM Composite Fibers for Thermal Management.

Thermal management protects against external agents and increases the lifetime and performance of the devices in which it is implemented. Because of their ability to store and release a high amount of energy at a nearly constant temperature, phase change materials (PCMs) are promising thermoregulatory materials. Thus, the manufacture of PVDF fibers containing PCMs has advantages since PVDF is already used in elements that are susceptible to thermal management as a binder in batteries or as a base material for fabrics. This work presents a simple, versatile, in situ, cost-effective, and easy-to-scale-up method to produce PVDF-based fibers containing paraffin RT-28HC for thermal management. To achieve that goal, the microfluidic approach of coaxial flows was simplified to gravity-aided laminar jet injection into a bulk fluid, where fibers were produced by the solvent extraction mechanism. With this methodology, hollow PVDF fibers and core-shell PVDF fibers containing paraffin RT-28HC have been produced. The proposed approach resulted in fibers with up to 98 J/g of latent heat, with a hierarchical porous structure. SEM study of the fiber morphology has shown that PCM is in the form of slugs along the fibers. Such PCM distribution is maintained until the first melting cycle, when molten PCM spreads within the fiber under capillary forces, which was observed by an infrared camera. Manufactured composite fibers have shown low thermal conductivity and high elasticity, which suggest their potential application as a thermal insulation material with thermal buffer properties. Leakage tests revealed outstanding retention capacity with only 3.5% mass loss after 1000 melting/crystallization cycles. Finally, tensile tests were carried out to evaluate the mechanical properties of the fibers before and after thermal cycling.