Materials for hydrogen storage: current research trends and perspectives.

Storage and transport of hydrogen constitutes a key enabling technology for the advent of a hydrogen-based energy transition. Main research trends on hydrogen storage materials, including metal hydrides, porous adsorbents and hydrogen clathrates, are reviewed with a focus on recent developments and an appraisal of the challenges ahead. .

High-density storage of H2 in microporous crystalline silica at ambient conditions.

Molecular hydrogen was encapsulated in the cages of clathrasil decadodecasil 3R (DD3R) during the hydrothermal synthesis of this microporous silicate. The crystalline structure of DD3R facilitates high-density hydrogen storage at ambient conditions. Prompt gamma activation analysis (PGAA) revealed that on average about one molecule of H2 is trapped in each (5(12)) cage of DD3R. The presence of molecular hydrogen inside the DD3R framework was confirmed by solid-state 1H NMR spectroscopy. Temperature-programmed decomposition (TPD) in combination with mass spectrometry showed that the encapsulated hydrogen is released upon decomposition of the clathrasil structure. This release can be promoted by the presence of water.

Molecular dynamics-based approach to study the anisotropic self-diffusion of molecules in porous materials with multiple cage types: application to H2 in losod.

The anisotropic self-diffusion of molecular hydrogen in the multiple cage clathrasil losod (LOS) is modeled by means of molecular dynamics (MD) simulations of up to 1 micros for the temperature range 900-1200 K while treating the framework as fully flexible. The LOS diffusion tensor is calculated employing an analytical method based on hopping rates. The diffusion in the c-direction of the unit cell is found to be approximately two times more rapid than in the a- and the b-directions, a characteristic of importance for the application of LOS as a membrane. The overall diffusion is based on five different hop types for which the individual hopping rates and diffusion barriers are calculated separately. We show explicitly that the shape and volume of the cages have a significant effect on the hopping rates and further that even small deformations of the circular Si6O6 apertures have a large influence on the energetic barrier for hydrogen diffusion. Compared to the single cage clathrasils dodecasil 3C (MTN) and sodalite (SOD), LOS has a lower diffusion rate. However, from a technical point of view this rate (at 573 K) is still fast enough for LOS to be interesting as a size-selective membrane or as a hydrogen-adsorption medium.

Synthesis, structural characterization, and thermal stability of a new layered germanate structure, Na4Ge16O28(OH)12.

The new layered germanate structure Na4Ge16O28(OH)12 has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, FTIR, and SEM. The crystal lattice parameters are a = 7.3216(6) A, b = 14.3986(9) A, c = 7.7437(6) A, alpha = 90.0 degrees, beta = 100.179(7) degrees, gamma = 90.0 degrees, and V = 803.5(1) A3. The space group is C2/m with Z = 1. The germanium oxide sheets are connected non-covalently via electrostatic interactions with the sodium cations and H-bridging. At temperatures above 400 degrees C, the structure starts decomposing into sodium enneagermanate (Na4Ge9O20), germanium dioxide, and water as determined by powder X-ray diffraction, TGA, DTA, DSC, and GCMS.