Transmission, Distribution & Storage

The ever-increasing demand for energy coupled with dwindling fossil fuel resources make the establishment of a clean and sustainable energy system a compelling need. Hydrogen-based energy systems offer potential solutions. Although in the long-term the ultimate technological challenge is large-scale hydrogen production from renewable sources the pressing issue is how to store hydrogen efficiently on board hydrogen fuel-cell vehicles.

Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is also investigated to understand the relevance of short-range ordering effects. So-called E21-Fe3AlC κ-carbides are frequently observed in Fe-Mn-Al-C alloys. Since H tends to occupy the same positions as C in these precipitates the interaction and competition between both interstitials is also investigated via DFT-based simulations. While the individual H–H/C–H chemical interactions are generally repulsive the tendency of interstitials to increase the lattice parameter can yield a net increase of the trapping capability. An increased Mn content is shown to enhance H trapping due to attractive short-range interactions. Favorable short-range ordering is expected to occur at the interface between an Fe matrix and the E21-Fe3AlC κ-carbides which is identified as a particularly attractive trapping site for H. At the same time accumulation of H at sites of this type is observed to yield decohesion of this interface thereby promoting fracture formation. The interplay of these effects evident in the trapping energies at various locations and dependent on the H concentration can be expressed mathematically resulting in a term that describes the hydrogen embrittlement

This paper presents a simplified procedure to analyse the Hydrogen Induced Cracking (HIC) of structural steels by means of the Small Punch Test (SPT). Two types of notched specimens were used: one with through-thickness lateral notch and another with surface longitudinal notch. The results for conventional specimens were compared with those for hydrogen pre-charged specimens. For this purpose two different methods to introduce hydrogen in the specimens were used: cathodic/electrochemical pre-charging and pressurized gaseous hydrogen pre-charging. The results obtained with both methods are also discussed.

As a promising hydrogen storage material the practical application of magnesium is obstructed by the stable thermodynamics and sluggish kinetics. In this paper three kinds of NiTiO₃ catalysts with different mole ratio of Ni to Ti were successfully synthesized and doped into nanocrystalline Mg to improve its hydrogen storage properties. Experimental results indicated that all the Mg-NiTiO₃ composites showed prominent hydrogen storage performance. Especially the Mg-NiTiO3/TiO₂ composite could take up hydrogen at room temperature and the apparent activation energy for hydrogen absorption was dramatically decreased from 69.8 ± 1.2 (nanocrystalline Mg) kJ/mol to 34.2 ± 0.2 kJ/mol. In addition the hydrogenated sample began to release hydrogen at about 193.2 °C and eventually desorbed 6.6 wt% H₂. The desorption enthalpy of the hydrogenated Mg-NiTiO₃ -C was estimated to be 78.6 ± 0.8 kJ/mol 5.3 kJ/mol lower compared to 83.9 ± 0.7 kJ/mol of nanocrystalline Mg. Besides the sample revealed splendid cyclic stability during 20 cycles. No obvious recession occurred in the absorption and desorption kinetics and only 0.3 wt% hydrogen capacity degradation was observed. Further structural analysis demonstrates that nanosizing and catalyst doping led to a synergistic effect on the enhanced hydrogen storage performance of Mg-NiTiO₃ -C composite which might serve as a reference for future design of highly effective hydrogen storage materials.

A key issue in understanding and effectively managing hydrogen embrittlement in complex alloys is identifying and exploiting the critical role of the various defects involved. A chemo-mechanical model for hydrogen diffusion is developed taking into account stress gradients in the material as well as microstructural trapping sites such as grain boundaries and dislocations. In particular the energetic parameters used in this coupled approach are determined from ab initio calculations. Complementary experimental investigations that are presented show that a numerical approach capable of massive scale-bridging up to the macroscale is required. Due to the wide range of length scales accounted for we apply homogenisation schemes for the hydrogen concentration to reach simulation dimensions comparable to metallurgical process scales. Via a representative volume element approach an ab initio based scale bridging description of dislocation-induced hydrogen aggregation is easily accessible. When we extend the representative volume approach to also include an analytical approximation for the ab initio based description of grain boundaries we find conceptual limitations that hinder a quantitative comparison to experimental data in the current stage. Based on this understanding the development of improved strategies for further efficient scale bridging approaches is foreseen.

In this study electrochemical measurements immersion tests and slow strain rate tensile (SSRT) tests were applied to investigate the electrochemical and stress corrosion cracking (SCC) behavior of X70 steel in simulated seawater with the interference of different alternating current (AC) densities. The results indicate that AC significantly strengthens the cathodic reaction especially the oxygen reduction reaction. Simultaneously hydrogen evolution reaction occurs when the limiting diffusion current density of oxygen reaches and thus icorr sharply increases with the increase in AC density. Additionally when AC is imposed the X70 steel exhibits higher SCC susceptibility in the simulated seawater and the susceptibility increases with the increasing AC density. The SCC mechanism is controlled by both anodic dissolution (AD) and hydrogen embrittlement (HE) with the interference of AC.

This work focuses in investigating the effect of cold deformation on the cathodic hydrogen charging of 5083 aluminum alloy. The aluminium alloy was submitted to a cold rolling process until the average thickness of the specimens was reduced by 7% and 15% respectively. A study of the structure microhardness and tensile properties of the hydrogen charged aluminium specimens with and without cold rolling indicated that the cold deformation process led to an increase of hydrogen susceptibility of this aluminum alloy.

The global energy crisis and environmental pollution have caused great concern. Hydrogen is a renewable and environmentally friendly source of energy and has potential to be a major alternative energy carrier in the future. Due to its high capacity and relatively low cost of raw materials alanate has been considered as one of the most promising candidates for hydrogen storage. Among them LiAlH₄ and NaAlH₄ as two representative metal alanates have attracted extensive attention. Unfortunately the high desorption temperature and sluggish kinetics restrict its practical application. In this paper the basic physical and chemical properties as well as the hydrogenation/dehydrogenation reaction mechanism of LiAlH₄ and NaAlH₄ are briefly reviewed. The recent progress on strategic optimizations toward tuning the thermodynamics and kinetics of the alanate including nanoscaling doping catalysts and compositing modification are emphatically discussed. Finally the coming challenges and the development prospects are also proposed in this review.

Hydrogen accumulation and distribution in pipeline steel under conditions of enhanced corrosion has been studied. The XRD analysis optical spectrometry and uniaxial tension tests reveal that the corrosion environment affects the parameters of the inner and outer surface of the steel pipeline as well as the steel pipeline bulk. The steel surface becomes saturated with hydrogen released as a reaction product during insignificant methane dissociation. Measurements of the adsorbed hydrogen concentration throughout the steel pipe bulk were carried out. The pendulum impact testing of Charpy specimens was performed at room temperature in compliance with national standards. The mechanical properties of the steel specimens were found to be considerably lower and analogous to the properties values caused by hydrogen embrittlement.

A viable hydrogen economy has thus far been hampered by the lack of an inexpensive and convenient hydrogen storage solution meeting all requirements especially in the areas of long hauls and delivery infrastructure. Current approaches require high pressure and/or complex heat management systems to achieve acceptable storage densities. Herein we present a manganese hydride molecular sieve that can be readily synthesized from inexpensive precursors and demonstrates a reversible excess adsorption performance of 10.5 wt% and 197 kgH₂ m^-3 at 120 bar at ambient temperature with no loss of activity after 54 cycles. Inelastic neutron scattering and computational studies confirm Kubas binding as the principal mechanism. The thermodynamically neutral adsorption process allows for a simple system without the need for heat management using moderate pressure as a toggle. A storage material with these properties will allow the DOE system targets for storage and delivery to be achieved providing a practical alternative to incumbents such as 700 bar systems which generally provide volumetric storage values of 40 kgH₂ m^-3 or less while retaining advantages over batteries such as fill time and energy density. Reasonable estimates for production costs and loss of performance due to system implementation project total energy storage costs roughly 5 times cheaper than those for 700 bar tanks potentially opening doors for increased adoption of hydrogen as an energy vector.