High-temperature Hydrogen Environments Research Articles

(Invited) Multiscale Simulations of Materials Degradation in Hydrogen Production and Storage Applications

Most hydrogen production and storage technologies rely on controlled chemical or electrochemical reactions occurring at complex interfaces. However, under actual operating conditions, competing mechanisms of chemistry, transport, and phase evolution can activate other processes that compete with or deactivate the desired processes. In certain cases, such mechanisms can lead to critical degradation of materials and their performance. In this talk, I will discuss how multiscale, multiphysics materials modeling from atomistic to continuum scales is being applied to understand fundamentals of degradation in materials relevant to hydrogen technology. Topics will include modeling of competing reaction pathways for hydrogen-rich chemicals, secondary phase formation in high-temperature hydrogen environments, impeded transport pathways in metals for hydrogen storage, and corrosion and oxidation of secondary components and contacts. In each case, I will show how HPC-accelerated models are being integrated across scales and interfaced with microscopy and spectroscopy, as well as modern data science approaches, to gain new physicochemical understanding and guide efforts towards improvement. Examples will be drawn from current efforts within the DOE HydroGEN, HyMARC, and H2NEW hydrogen production and storage multi-laboratory consortia, as well as closely related activities within the Corrosion Science Strategic Initiative at Lawrence Livermore National Laboratory. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Microstructural evolution of Mo-UO2 cermets under high temperature hydrogen environments

Ceramic-metallic (cermet) materials show promise for use in nuclear thermal propulsion applications due to attractive thermophysical properties including high temperature stability and high thermal conductivity. In this work, molybdenum-uranium dioxide (Mo-UO2) cermet fuel elements were fabricated by means of spark plasma sintering (SPS) and were subsequently exposed to hydrogen at high temperatures (2500 K). Mo-UO2 samples pre- and post-exposure were characterized by means of optical microscopy, scanning electron microscopy, and X-ray diffraction (XRD). Microscopy analyses of the as-produced material displayed microscopic cracking on the interior of the spherical UO2 fuel particles but confirmed that the fuel particles were fully encapsulated in the Mo matrix. The results further showed mass loss, macroscopic swelling, and cracking in the cermet samples which occurred during high temperature hydrogen testing. Nanoscale swelling was evidenced by XRD in the Mo matrix and UO2 fuel structure due to the incorporation of defects and accompanied microstrain.

Impact of Hot Bending on the High-Temperature Performance and Hydrogen Damage of 2.25Cr-1Mo-0.25V Steel

The impact of hot bending forming process on the high-temperature mechanical properties and hydrogen damage of 2.25Cr-1Mo-0.25V steel was investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive spectrum (EDS) and the slow strain rate tensile (SSRT) test in high-temperature hydrogen environment. The samples containing hot bending residual influence were extracted from a real hydrogenation reactor shell fabricated through hot bending–welding process. SEM images of the material demonstrated that the density and size of carbides in 2.25Cr-1Mo-0.25V increased after forming. TEM and EDS results revealed that ferrite matrix of the formed material was purified. The mechanical properties measured by SSRT test manifested that 2.25Cr-1Mo-0.25V was softened after forming. Moreover, it was observed that high-temperature hydrogen environment embrittled the material and the susceptibility to hydrogen damage increased after forming. The role of hot bending process on the evolution of mechanical properties and hydrogen damage susceptibility was discussed. Possible mechanism for the impact of hot bending process on the high-temperature hydrogen damage was proposed.

Structural changes in ScCeSZ–NiO ceramics in a high-temperature hydrogen environment

It is shown that, in a solid oxide cell with ceramic Ni-containing anodes, in the first working cycle, the anode material is reduced in hydrogen, which causes changes in its microstructure and properties. We analyze structural changes in the anode material with different contents of NiO from the nonreduced (ScCeSZ–NiO) to the reduced (ScCeSZ–Ni) state, which are connected with its electric conductance.