Design and evaluation of a novel plan for thermochemical cycles and PEM fuel cells to produce hydrogen and power: Application of environmental perspective.

In the present article, a green and efficient multi-generation system equipped with proton exchange membrane (PEM) fuel cells as the main mover is presented and thoroughly examined. The proposed novel approach dramatically reduces the amount of carbon dioxide produced by using biomass as the primary energy source for PEM fuel cells. The waste heat recovery method is offered as a passive energy enhancement strategy for efficient and cost-effective output production. It uses the extra heat generated by the PEM fuel cells to produce cooling through the chillers. In addition, the thermochemical cycle is included to recover the waste heat from syngas exhaust gases and produce hydrogen, which will significantly help the process of going green transition. The suggested system's effectiveness, affordability, and environmental friendliness are assessed via a developed engineering equation solver program code. Additionally, the parametric analysis assesses the impact of major operational factors on the model's performance from thermodynamic, exergo-economic, and exergo-environmental indicators. According to the results, the suggested efficient integration achieves an acceptable total cost rate and environmental impact while obtaining high energy and exergy efficiencies. The results further reveal that the biomass moisture content is significant since it highly impacts the system's indicators from various aspects. From the conflictive changes between the exergy efficiency and exergo-environmental metrics, it can be concluded that choosing a proper design condition satisfying more than one aspect is highly important. According to the Sankey diagram, the worst equipment from the energy conversion quality is gasifier and fuel cells, with the highest irreversibility rate of 8 kW and 6.3 kW, respectively.

Putative Iron-Sulfur Proteins Are Required for Hydrogen Consumption and Enhance Survival of Mycobacteria.

Aerobic soil bacteria persist by scavenging molecular hydrogen (H2) from the atmosphere. This key process is the primary sink in the biogeochemical hydrogen cycle and supports the productivity of oligotrophic ecosystems. In Mycobacterium smegmatis, atmospheric H2 oxidation is catalyzed by two phylogenetically distinct [NiFe]-hydrogenases, Huc (group 2a) and Hhy (group 1h). However, it is currently unresolved how these enzymes transfer electrons derived from H2 oxidation into the aerobic respiratory chain. In this work, we used genetic approaches to confirm that two putative iron-sulfur cluster proteins encoded on the hydrogenase structural operons, HucE and HhyE, are required for H2 consumption in M. smegmatis. Sequence analysis show that these proteins, while homologous, fall into distinct phylogenetic clades and have distinct metal-binding motifs. H2 oxidation was reduced when the genes encoding these proteins were deleted individually and was eliminated when they were deleted in combination. In turn, the growth yield and long-term survival of these deletion strains was modestly but significantly reduced compared to the parent strain. In both biochemical and phenotypic assays, the mutant strains lacking the putative iron-sulfur proteins phenocopied those of hydrogenase structural subunit mutants. We hypothesize that these proteins mediate electron transfer between the catalytic subunits of the hydrogenases and the menaquinone pool of the M. smegmatis respiratory chain; however, other roles (e.g., in maturation) are also plausible and further work is required to resolve their role. The conserved nature of these proteins within most Hhy- or Huc-encoding organisms suggests that these proteins are important determinants of atmospheric H2 oxidation.

Metallic iron limits silicate hydration in Earth's transition zone.

The Earth's mantle transition zone (MTZ) is often considered an internal reservoir for water because its major minerals wadsleyite and ringwoodite can store several oceans of structural water. Whether it is a hydrous layer or an empty reservoir is still under debate. Previous studies suggested the MTZ may be saturated with iron metal. Here we show that metallic iron reacts with hydrous wadsleyite under the pressure and temperature conditions of the MTZ to form iron hydride or molecular hydrogen and silicate with less than tens of parts per million (ppm) water, implying that water enrichment is incompatible with iron saturation in the MTZ. With the current estimate of water flux to the MTZ, the iron metal preserved from early Earth could transform a significant fraction of subducted water into reduced hydrogen species, thus limiting the hydration of silicates in the bulk MTZ. Meanwhile, the MTZ would become gradually oxidized and metal depleted. As a result, water-rich region can still exist near modern active slabs where iron metal was consumed by reaction with subducted water. Heterogeneous water distribution resolves the apparent contradiction between the extreme water enrichment indicated by the occurrence of hydrous ringwoodite and ice VII in superdeep diamonds and the relatively low water content in bulk MTZ silicates inferred from electrical conductivity studies.

Novel insights into the bioenergetics of mixed-acid fermentation: can hydrogen and proton cycles combine to help maintain a proton motive force?

Escherichia coli possesses four [NiFe]-hydrogenases that catalyze the reversible redox reaction of 2H(+) + 2e(-) ↔ H2. These enzymes together have the potential to form a hydrogen cycle across the membrane. Their activity, operational direction, and interaction with each other depend on the fermentation substrate and particularly pH. The enzymes producing H2 are likely able to translocate protons through the membrane. Moreover, the activity of some of these enzymes is dependent on the F0 F1 -ATPase, thus linking a proton cycle with the cycling of hydrogen. These two cycles are suggested to have a primary basic role in modulating the cell's energetics during mixed-acid fermentation, particularly in response to pH. Nevertheless, the mechanisms underlying the physical interactions between these enzyme complexes, as well as how this is controlled, are still not clearly understood. Here, we present a synopsis of the potential impact of proton-hydrogen cycling in fermentative bioenergetics.