A correct perspective for hydrogen from engineered diagenesis

Wind and solar photovoltaic electricity production have already reached very low levels of levelized cost of energy (LCOE). Electrolyzers have already reached high efficiencies which are further improving, while costs are dramatically reducing. They are commercial products. Green hydrogen (H₂) is the product of excess wind and solar electricity, specifically electricity that will be otherwise wasted, without the huge energy storage needed presently almost completely missing. By growing the installed capacity of wind and solar power plants, there will be a non-dispatchable production by wind and solar more often in excess, but sometimes also in defect, of the grid demand, in presence of limited energy storage. H₂ is one of the key energy storage technologies needed to ensure grid stability. Production of H₂ above what is needed to stabilize the grid significantly helps in applications such as land, and sea but especially air transport where the storage of energy onboard in a fuel is preferable to the storage of energy as electricity into a battery. The engineered diagenesis for H₂ is unlikely better than green hH₂. Apart from being a nice idea to be proven workable, with a technology readiness level (TRL) presently of zero, and thus impossible to be objectively compared with commercial products, the engineered diagenesis for H₂, even if possible, also does not help with non-dispatchable renewable energy production. The concept may also have negative environmental aspects similar to fracking which have not been considered yet, and also bear huge economic costs in addition to environmental. Here we review the pros and cons of this novel technology, which once proven workable, which is not the case yet, should be considered as a possible way to complement rather than replace green H₂ production.     

Enhanced hydrogen storage properties of Ti–Cr–Nb alloys by melt-spin and Mo-doping

Ti–Cr–Nb hydrogen storage alloys with a body centered cubic (BCC) structure have been successfully prepared by melt-spin and Mo-doping. The crystalline structure, solidification microstructural evolution, and hydrogen storage properties of the corresponding alloys were characterized in details. The results showed that the hydrogen storage capacity of Ti–Cr–Nb ingot alloys increased from 2.2 wt% up to around 3.5 wt% under the treatment of melt-spin and Mo-doping. It is ascribed that the single BCC phase of Ti–Cr–Nb alloys was stabilized after melt-spin and Mo-doping, which has a higher theoretical hydrogen storage site than the Laves phase. Furthermore, the melt-spin alloy after Mo doping can further effectively increase the de-/absorption plateau pressure. The hydrogen desorption enthalpy change ΔH of the melt-spin alloy decreased from 48.94 kJ/mol to 43.93 kJ/mol after Mo-doping. The short terms cycling test also manifests that Mo-doping was effective in improving the cycle durability of the Ti–Cr–Nb alloys. And the BCC phase of the Ti–Cr–Nb alloys could form body centered tetragonal (BCT) or face center cubic (FCC) hydride phase after hydrogen absorption and transform to the original BCC phase after desorption process. This study might provide reference for developing reversible metal hydrides with favorable cost and acceptable hydrogen storage characteristics.     

Effect of low concentration of impurity gases on the hydrogen absorption performance of uranium

The performance of uranium as a hydrogen storage material has attracted much attention. Herein, the hydrogen absorption properties of depleted uranium in impure hydrogen containing He, Ar, CH₄, N₂, CO, CO₂ and O₂ were studied by PVT method and XPS analysis. When these impurity gases were mixed in H₂ at low concentrations (0.1%∼1.5%), their behavior can be classified into three categories. The He, CH₄ and Ar were chemically inert to the activated uranium powder under room condition. These three gases inhibited the absorption kinetics during the whole stage by hindering the diffusion of H₂ molecules, showing a blanketing effect. The N₂ and O₂ did not affect the absorption kinetics but reduced the capacity by forming nitrides and oxides. The poisoning effect of N₂ was weaker than that of O₂. The CO and CO₂ not only affected the hydrogen absorption capacity, but also strongly inhibited the absorption kinetics. These two gases are chemically adsorbed on the uranium surface to form passivation layers, thus inhibiting the adsorption and dissociation of H₂ molecules and the diffusion of H atoms. The poisoning and retardation effect of CO₂ were much stronger than that of CO. The above conclusions are important to further study the reactivity of mixed gas with uranium, and can also be used as a reference for other hydrogen storage systems.     

In situ construction of heterostructure NiSe–NiO nanoarrays with rich oxygen vacancy on MXene for efficient oxygen evolution

Developing high-efficiency, non-noble, earth-available electrocatalysts for the oxygen evolution reaction (OER) is vital for electrochemical energy conversion, but it is still challenging. Herein, we ingeniously designed a partial selenization method to construct NiSe–NiO heterostructure grown in situ on Ta₄C₃T_x MXene (denoted as NiSe–NiO/Ta₄C₃T_x MXene). NiSe–NiO/Ta₄C₃T_x MXene's plethora of heterointerfaces provides a wealth of active sites, fast charge and mass transfer, and favorable adsorption energies for OER intermediates, all of which contribute synergistically to the oxidation of alkaline water. As expected, taking advantage of the strong chemical and electron synergistic effects of NiSe and NiO, the synthesized NiSe–NiO/Ta₄C₃T_x MXene exhibits excellent activity for OER with a low overpotential of 255 mV at 10 mA cm⁻², a small Tafel slope of 47.4 mV dec⁻¹, as well as excellent long-term stability, exceeding that of its competitors. This study offers a novel synthetic route toward developing high-performance OER electrocatalysts for renewable energy conversion/storage systems and beyond by optimizing the catalysts' composition and architecture.