Low Nickel, Ceria Zirconia-Based Micro-Tubular Solid Oxide Fuel Cell: A Study of Composition and Oxidation Using Hydrogen and Methane Fuel

The study examines the effect of using low nickel (Ni) with high ceria (CeO2) anode content towards the oxidation of H2 and CH4 fuel by evaluating the activation energy of the ohmic process and charge transfer process. Using a micro-tubular solid oxide fuel cell (MT-SOFC), the anodes are made up of 50% YSZ with varying NiO:CeO2 percentages from 0% NiO, 50% CeO2 to 50% NiO, 0% CeO2. The performance is measured based on maximum power density (MPD), electrochemical impedance spectroscopy (EIS) and activation energy, Ea of the ohmic (Rohm) and charge transfer (Rct) processes. We found that by lowering the Ni content to lower than 50% NiO, anode conductivity will drop by 7-fold. An anode containing 37.5% NiO, 12.5% CeO2 yield MPD of 41.1 and 2.9 mW cm−2 when tested on H2 and CH4 fuels thus have the lowest Ni content without an abrupt negative effect on the MPD and EIS. The significant effect of conductivity drops on MPD and EIS are observed to occur at 25% NiO, 25% CeO2 and lower NiO content. However, anode content of 25% NiO, 25% CeO2 has the lowest Ea for Rct (29.74 kJ mol−1) for operation in CH4, making it the best anode composition to oxidize CH4. As a conclusion, an anode containing 25% NiO:25% CeO2:50% YSZ and 37.5% NiO:12.5% CeO2:50% YSZ shows promising results in becoming the low Ni anode for coking-tolerant SOFC.

The Mitigation of CO Present in the Water–Gas Shift Reformate Gas Over IR-TiO2 and IR-ZrO2 Catalysts

CO hydrogenation and oxidation were conducted over Ir supported on TiO2 and ZrO2 catalysts using a feed mimicking the water–gas shift reformate stream. The influence of the support interaction with Ir and the catalysts’ redox and CO chemisorption properties on activity and selectivity were evaluated. Both catalysts oxidised CO to CO2 in the absence of H2, and a conversion of 70% was obtained at 200 °C. For the CO oxidation in the presence of H2 over these catalysts, the oxidation of H2 was favoured over CO due to H2 spillover occurring at the active metal and support interface, resulting in the formation of interstitials catalysed by Ir. However, both catalysts showed promising activity for CO hydrogenation. Ir-ZrO2 was more active, giving 99.9% CO conversions from 350 to 370 °C, with high selectivity towards CH4 using minimal H2 from the feed. Furthermore, results for the Ir-ZrO2 catalyst showed that the superior activity compared to the Ir-TiO2 catalyst was mainly due to the reducibility of the support and its interaction with the active metal. Controlling the isoelectric point during the synthesis allowed for a stronger interaction between Ir and the ZrO2 support, which resulted in higher catalytic activity due to better metal dispersions, and higher CO chemisorption capacities than obtained for the Ir-TiO2 catalyst.

Steam Atmospheres and Magma Oceans on Planets

A magma ocean is a global layer of partially or fully molten rocks. Significant melting of terrestrial planets likely occurs due to heat release during planetary accretion, such as decay heat of short-lived radionuclides, impact energy released by continuous planetesimal accretion, and energetic impacts among planetary-sized bodies (giant impacts). Over a magma ocean, all water, which is released upon impact or degassed from the interior, exists as superheated vapor, forming a water-dominated, steam atmosphere. A magma ocean extending to the surface is expected to interact with the overlying steam atmosphere through material and heat exchange. Impact degassing of water starts when the size of a planetary body becomes larger than Earth’s moon or Mars. The degassed water could build up and form a steam atmosphere on protoplanets growing by planetesimal accretion. The atmosphere has a role in preventing accretion energy supplied by planetesimals from escaping, leading to the formation of a magma ocean. Once a magma ocean forms, part of the steam atmosphere would start to dissolve into the surface magma due to the high solubility of water into silicate melt. Theoretical studies indicated that as long as the magma ocean is present, a negative feedback loop can operate to regulate the amount of the steam atmosphere and to stabilize the surface temperature so that a radiative energy balance is achieved. Protoplanets can also accrete the surrounding H2-rich disk gas. Water could be produced by oxidation of H2 by ferrous iron in the magma. The atmosphere and water on protoplanets could be a mixture of outgassed and disk-gas components. Planets formed by giant impact would experience a global melting on a short timescale. A steam atmosphere could grow by later outgassing from the interior. Its thermal blanketing and greenhouse effects are of great importance in controlling the cooling rate of the magma ocean. Due to the presence of a runaway greenhouse threshold, the crystallization timescale and water budget of terrestrial planets can depend on the orbital distance from the host star. The terrestrial planets in our solar system essentially have no direct record of their earliest history, whereas observations of young terrestrial exoplanets may provide us some insight into what early terrestrial planets and their atmosphere are like. Evolution of protoplanets in the framework of pebble accretion remains unexplored.

Biological Responses to Hydrogen Molecule and its Preventive Effects on Inflammatory Diseases

: Because multicellular organisms do not have hydrogenase, H2 has been considered to be biologically inactive in these species, and enterobacteria to be largely responsible for the oxidation of H2 taken into the body. However, we showed previously that inhalation of H2 markedly suppresses brain injury induced by focal ischemia–reperfusion by buffering oxidative stress. Although the reaction constant of H2 with hydroxyl radical in aqueous solution is two to three orders of magnitude lower than that of conventional antioxidants, we showed that hydroxyl radical generated by the Fenton reaction reacts with H2 at room temperature without a catalyst. Suppression of hydroxyl radical by H2 has been applied in ophthalmic surgery. However, many of the anti-inflammatory and other therapeutic effects of H2 cannot be completely explained by its ability to scavenge reactive oxygen species. H2 administration is protective in several disease models, and preculture in the presence of H2 suppresses oxidative stress-induced cell death. Specifically, H2 administration induces mitochondrial oxidative stress and activates Nrf2; this phenomenon, in which mild mitochondrial stress leaves the cell less susceptible to subsequent perturbations, is called mitohormesis. Based on these findings, we conclude that crosstalk between antioxidative stress pathways and the anti-inflammatory response is the most important molecular mechanism involved in the protective function of H2 , and that regulation of the immune system underlies H2 efficacy. For further medical applications of H2 , it will be necessary to identify the biomolecule on which H2 first acts.

Hydrogenases and the Role of Molecular Hydrogen in Plants

Molecular hydrogen (H2) has been suggested to be a beneficial treatment for a range of species, from humans to plants. Hydrogenases catalyze the reversible oxidation of H2, and are found in many organisms, including plants. One of the cellular effects of H2 is the selective removal of reactive oxygen species (ROS) and reactive nitrogen species (RNS), specifically hydroxyl radicals and peroxynitrite. Therefore, the function of hydrogenases and the action of H2 needs to be reviewed in the context of the signalling roles of a range of redox active compounds. Enzymes can be controlled by the covalent modification of thiol groups, and although motifs targeted by nitric oxide (NO) can be predicted in hydrogenases sequences it is likely that the metal prosthetic groups are the target of inhibition. Here, a selection of hydrogenases, and the possibility of their control by molecules involved in redox signalling are investigated using a bioinformatics approach. Methods of treating plants with H2 along with the role of H2 in plants is also briefly reviewed. It is clear that studies report significant effects of H2 on plants, improving growth and stress responses, and therefore future work needs to focus on the molecular mechanisms involved.