Hydrogen, the smallest and the lightest atomic element, is reversibly incorporated into interstitial sites in vanadium dioxide (VO2), a correlated oxide with a 3d(1) electronic configuration, and induces electronic phase modulation. It is widely reported that low hydrogen concentrations stabilize the metallic phase, but the understanding of hydrogen in the high doping regime is limited. Here, we demonstrate that as many as two hydrogen atoms can be incorporated into each VO2 unit cell, and that hydrogen is reversibly absorbed into, and released from, VO2 without destroying its lattice framework. This hydrogenation process allows us to elucidate electronic phase modulation of vanadium oxyhydride, demonstrating two-step insulator (VO2)-metal (HxVO2)-insulator (HVO2) phase modulation during inter-integer d-band filling. Our finding suggests the possibility of reversible and dynamic control of topotactic phase modulation in VO2 and opens up the potential application in proton-based Mottronics and novel hydrogen storage.

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Cationic ordering in Sr2FeReO6 (SFRO) and Sr2CrReO6 (SCRO) is investigated using magnetic property measurement, atomic-scale imaging, and first-principles calculations. We find that the nature of cationic ordering strongly depends on the host oxides, although they have the same crystal symmetry and chemical formula. Firstly, adding Re is effective to enhance the cationic ordering in SFRO, but makes it worse in SCRO. Secondly, the microscopic structure of antisite (AS) defects, associated with the level of cationic ordering, is also distinguishable; the AS defects in SFRO are clustered in the form of an antiphase-boundary-like feature, while they are randomly scattered in SCRO. Interestingly, we observe that the clustered AS defects deteriorate the ferromagnetism more than the scattered defects. Our findings elevate the importance of the AS defect configuration as well as the amount of defects in terms of magnetic property.

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Nanofluids with enhanced thermal properties are candidates for thermal management in automotive systems, with scope for improving energy efficiency. In particular, many studies have reported on dispersions of nanoparticles with long-term stability in the base fluid, with qualitative evaluations of the dispersion stability via either the naked eye or optical instruments. Additives such as surfactants can be used to enhance the dispersion of nanoparticles; however, this may diminish their intrinsic thermal properties. Here, we describe molecular dynamics simulations of nanofluids containing graphene sheets dispersed in ethylene glycol and water. We go on to suggest a quantitative evaluation method for the degree of dispersion, based on the ratio of the total number of nanoparticles to the number of clustered nanoparticles. Moreover, we investigate the effects of functional groups on the surface of graphene, which are expected to improve the dispersion without requiring additives such as surfactants due to steric hindrance and chemical affinity for the surrounding fluid. We find that, for pure graphene, the degree of dispersion decreased as the quantity of graphene sheets increased, which is attributed to an increased probability of aggregation at higher loadings; however, the presence of functional groups inhibited the graphene sheets from forming aggregates.

During the operation of a PEMFC, the polymer membrane is degraded by electrochemical reactions and mechanical stresses. We investigated the effects of repeated electrochemical and mechanical degradations in a membrane. For mechanical degradation, the membrane and MEA were repeatedly subjected to wet/dry cycles; for electrochemical degradation, the cell was operated under open-circuit voltage (OCV)/low-humidity conditions. The repeated wet/dry cycles led to a decrease in the mechanical strength of the membrane. When the MEA was degraded electrochemically, repeated wet/dry cycling resulted in the formation of pinholes in the membrane. In the case of different MEAs that were first degraded electrochemically, the extents of their hydrogen crossover currents increased due to repeated wet/dry cycling being different. Therefore, these results indicated that the membrane durability could be evaluated by these methods of repeated electrochemical degradation and wet/dry cycles.

Wear behaviour of aluminium matrix composites is characterized by the dry spindle wear test under various conditions (volume fractions of reinforcements, sliding distances and speeds). Wear resistance of composites is improved due to the presence of reinforcements, but no noticeable improvements are observed in the wear resistance with more than 20% addition of reinforcements. To anatyse wear mechanisms, wear surfaces are examined by scanning electron microscopy (SEM). The major wear mechanisms of discontinuous metal matrix composites (MMC)s are strongly dependent on sliding speeds. Dominant mechanism is the adhesive-abrasive wear at low and intermediate sliding speeds, and melt wear at high sliding speeds. Weight loss is linearly increased with the sliding distance. The effect of reinforcements' Orientations on wear behaviours is also discussed.