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The hunt for a cleaner energy carrier leads us to consider a source that produces no toxic byproducts. One of the targeted alternatives in this approach is hydrogen energy, which, unfortunately, suffers from a lack of efficient storage media. Solid-state hydrogen absorption systems, such as lithium amide (LiNH2) systems, may store up to 6.5 weight percent hydrogen. However, the temperature of hydrogenation and dehydrogenation is too high for practical use. Various molar ratios of LiNH2 with sodium hydride (NaH) and potassium hydride (KH) have been explored in this paper. The temperature of hydrogenation for LiNH2 combined with KH and NaH was found to be substantially lower than the temperature of individual LiNH2. This lower temperature operation of both LiNH2-NaH and LiNH2-KH systems was investigated in depth, and the eutectic melting phenomenon was observed. Systematic thermal studies of this amide-hydride system in different compositions were carried out, which enabled the plotting of a pseudo-binary phase diagram. The occurrence of eutectic interaction increased atomic mobility, which resulted in the kinetic modification followed by an increase in the reactivity of two materials. For these eutectic compositions, i.e., 0.15LiNH2-0.85NaH and 0.25LiNH2-0.75KH, the lowest melting temperature was found to be 307 °C and 235 °C, respectively. Morphological studies were used to investigate and present the detailed mechanism linked with this phenomenon.

Several monosubstituted oxiranes were polymerized with suspension of potassium hydride (KH) in tetrahydrofuran (THF) at room temperature. This heterogeneous process resulted in polyethers with various starting groups depending on the kind of monomer. The macromolecules formed in ring-opening polymerization of monosubstituted oxiranes were analyzed by Matrix Assisted Laser Desorption/Ionization - Time of Flight Mass Spectrometry (MALDI-TOF MS). It was stated, that initiation of propylene oxide (PO) polymerization with KH proceeded via three ways, i.e. cleavage of oxirane ring in the β-position, monomer deprotonation and deoxygenation. Potassium isopropoxide, potassium allyloxide and potassium hydroxide were the real initiators. The main reactions, which occur in the initiation step, depend on the type of monomer used. In the case of allyl glycidyl ether (AGE) and phenyl glycidyl ether (PGE) deprotonation of the monomer did not occur. During initiation of glycidyl ethers oxirane ring was opened and also linear ether bond between glycidyl group and oxygen atom was cleaved under influence of KH. Interestingly, formation of new kinds of macromolecules was observed in the systems containing glycidyl ethers, which do not possess mers of the monomers used. Mechanisms of the studied processes were presented and discussed. Carbon-13 Nuclear Magnetic Resonance ( 13 C NMR) was used as supporting technique for analysis of the obtained polymers. Number average molar masses of the polymers (M n ) determined by Size Exclusion Chromatography (SEC) were about two times higher than calculated ones. It indicated that half of used KH did not take part in the initiation step. Graphical abstract Scheme of ROP of monosubstituted oxiranes in the presence of potassium hydride

Due to the high energy needed to break the N ≡ N bond (945 kJ mol −1 ), a key step in ammonia production is the activation of dinitrogen, which in industry requires the use of transition metal catalysts such as iron (Fe) or ruthenium (Ru), in combination with high temperatures and pressures. Here we demonstrate a transition-metal-free catalyst—potassium hydride-intercalated graphite (KH 0.19 C 24 )—that can activate dinitrogen at very moderate temperatures and pressures. The catalyst catalyses NH 3 synthesis at atmospheric pressure and achieves NH 3 productivity (µmol NH3 g cat −1  h −1 ) comparable to the classical noble metal catalyst Ru/MgO at temperatures of 250–400 °C and 1 MPa. Both experimental and computational calculation results demonstrate that nanoconfinement of potassium hydride between the graphene layers is crucial for the activation and conversion of dinitrogen. Hydride in the catalyst participates in the hydrogenation step to form NH 3 . This work shows the promise of light metal hydride materials in the catalysis of ammonia synthesis. Ammonia is industrially synthesized through an established process based on iron or ruthenium transition metal catalysts, although the quest for alternative and more sustainable processes is still ongoing. Here, the authors show that potassium hydride confined between graphene layers can reduce dinitrogen and catalyse ammonia synthesis under mild conditions.

Neutron powder diffraction and thermoelectric characterization of SnSe:Kx intermetallic alloys are presented. Nanostructured ingots were prepared by arc-melting elemental tin and selenium along with potassium hydride. Up to x = 0.1 of K can be incorporated into SnSe. Rietveld refinement of the diffractograms locates potassium on the Sn site in the high-temperature Cmcm structure. However, in the low-temperature Pnma structure, K cannot be localized by difference Fourier maps, indicating the incorporation of K in a disordered form in the interlayer space. STEM-EELS indicates the incorporation of K into the SnSe grains. The resistivity upon K-doping at intermediate temperatures decreases by 1–2 orders of magnitude, but at high temperature is higher than the undoped SnSe. The Seebeck coefficient of K-doped SnSe remains p-type and almost temperature independent (400 μV/K for x = 0.1). The ultralow thermal conductivity of undoped SnSe decreases further upon K-doping to below 0.3 W/m K.

Background and aimsNeutralization of adverse environmental effects of agriculture intensification to sustain population growth, requires ecologically sound alternatives for plant growth. We used as biostimulants towards germination of basil seeds and early growth of maize, two different humic materials: a potassium humate from leonardite (KH), and compost tea (CT) from a green compost made of coffee husks, and a 1:1 combination of the two (MIX). After their thorough chemical, molecular and conformational characterization, a relation between structure and bioactivity was investigated.ResultsCT showed the largest bioactivity on either seed germination or maize plantlets growth due to its great content of polar bioactive molecules including oxidized lignin fragment, saccharides and peptides. The more hydrophobic KH, rich of alkyl and aromatic moieties, also exerted a significant bioactivity on maize, though to a lesser extent. The application of MIX to hydroponically grown maize plantlets showed a smaller bioactivity of polar CT molecules due to their entrapment into new suprastructures stabilized by hydrogen bonds formed with complementary functions of KH hydrophobic components. However, while the KH hydrophobicity in MIX ensured adhesion to roots, its conformational flexibility was still sufficient to provide a greater bioactivity than control, by releasing bioactive CT components capable to enhance both biomass yield and root elongation.ConclusionsOur study suggests that a combination of humic materials with diverse and well-characterized molecular properties may become a new tool to produce innovative and ecologically viable plant growth promoters, whose bioactivity may be modulated.

In recent years, many solid-state hydride-based materials have been considered as hydrogen storage systems for mobile and stationary applications. Due to a gravimetric hydrogen capacity of 5.6 wt% and a dehydrogenation enthalpy of 38.9 kJ/mol H2, Mg(NH2)2 + 2LiH is considered a potential hydrogen storage material for solid-state storage systems to be coupled with PEM fuel cell devices. One of the main challenges is the reduction of dehydrogenation temperature since this system requires high dehydrogenation temperatures (~ 200 °C). The addition of KH to this system significantly decreases the dehydrogenation onset temperature to 130 °C. On the one hand, the addition of KH stabilizes the hydrogen storage capacity. On the other hand, the capacity is reduced by 50% (from 4.1 to 2%) after the first 25 cycles. In this work, the particle sizes of the overall hydride matrix and the potassium-containing species are investigated during hydrogen cycling. Relation between particle size evolution of the additive and hydrogen storage kinetics is described by using an advanced synchrotron-based technique: Anomalous small-angle X-ray scattering, which was applied for the first time at the potassium K-edge for amide-hydride hydrogen storage systems. The outcomes from this investigation show that, the nanometric potassium-containing phases might be located at the reaction interfaces, limiting the particle coarsening. Average diameters of potassium-containing nanoparticles double after 25 cycles (from 10 to 20 nm). Therefore, reaction kinetics at subsequent cycles degrade. The deterioration of the reaction kinetics can be minimized by selecting lower absorption temperatures, which mitigates the particle size growth, resulting in two times faster reaction kinetics.

Potassium (K) is an indispensable nutrient element in the development of fruit trees in terms of yield and quality. It is unclear how a stable or unstable supply of K affects plant growth. We studied the root morphology and physiological and molecular changes in the carbon and nitrogen metabolism of M9T337 apple rootstock under different K levels and supply methods using hydroponics. Five K supply treatments were implemented: continuous low K (K L ), initial low and then high K (K LH ), appropriate and constant K (K AC ), initial high and then low K (K HL ), and continuous high K (K H ). The results showed that the biomass, root activity, photosynthesis, and carbon and nitrogen metabolism of the M9T337 rootstocks were inhibited under K L , K H , K LH and K HL conditions. The K AC treatment promoted root growth by optimizing endogenous hormone content, enhancing carbon and nitrogen metabolism enzyme activities, improving photosynthesis, optimizing the distribution of carbon and nitrogen, and upregulating the transcription levels of nitrogen assimilation-related genes (nitrate reductase, glutamine synthetase, glutamate synthase, MdNRT1.1, MdNRT1.2, MdNRT1.5, MdNRT2.4 ). These results suggest that an appropriate and constant K supply ensures the efficient assimilation and utilization of nitrogen and carbon.

In the current study, we investigated the effect of potassium humate (Kh) and salicylic acid (SA) in mitigating the salinity stress of common bean plants. Common bean seedlings were treated with 0.2 g/L SA as a foliar application and 0.3 g/L Kh as a soil application individually or in combination. After 7 days of germination, plants were treated with 50 mM NaCl and normal water as a control. Our results indicate that salt treatment reduced the plant growth (fresh and dry shoots and roots), leaf pigments (total chlorophyll and carotenoids), ascorbic acid (AA), glutathione (GSH), and potassium (K) contents. On the contrary, proline content; sodium (Na); hydrogen peroxide (H2O2); superoxide anion (O2•−); and antioxidant enzymes, including catalase (CAT), peroxidase (POX), and superoxide dismutase (SOD), were increased by saline stress. However, applying either individual Kh and SA or their combination stimulated seedling growth under salinity stress by increasing growth parameters, leaf pigment contents, AA, GSH, proline content, K content, and antioxidant enzymes compared with the control. Additionally, Na content, H2O2, and O2•− were reduced by all applications. The application of the Kh (0.3 g/L) + SA (0.2 g/L) combination was more effective than using the individual compounds. In conclusion, applications of Kh + SA can mitigate salt stress and improve the seedling growth of common bean.

Previous studies have demonstrated the impact of potassium humate (KH) and chitosan (CH) on ameliorating drought effects, but their combined applications in promoting these benefits are still unfound. Therefore, the current study aims to evaluate the efficacy of KH and CH on corn growth, yield, nutrient contents, and water productivity under full and limited irrigation conditions. Under the drip irrigation system, a split-plot experiment was performed with three replications in the second week of February in the seasons of 2021 and 2022. The main plot was equipped with a valve and a flow emitter to control the amount of the targeted irrigation levels (full irrigation and limited irrigation from the development stage onwards), as well as four foliar applications in the subplot (0, CH 500 mg l −1 , KH 3000 mg l −1 , and CH 500 mg l −1 + KH 3000 mg l −1 ). It was found that separate foliar applications of KH or combined foliar applications of KH + CH had a significant impact on the most examined traits. However, compared to the control, adopting limited irrigation and applying combined applications thereof have significantly increased iron, zinc, manganese, oil, protein, yield, and water productivity. In addition, this combination decreased proline, and the maximum reduction was observed for the combined application with adopting full irrigation. In arid regions, the researcher recommends treating stressed plants with combined foliar applications of KH + CH, which could help plants overcome the negative effects of drought and attain the highest yield and water productivity.

Alkali metal intercalation into polyaromatic hydrocarbons (PAHs) has been studied intensely after reports of superconductivity in a number of potassium- and rubidium-intercalated materials. There are, however, no reported crystal structures to inform our understanding of the chemistry and physics because of the complex reactivity of PAHs with strong reducing agents at high temperature. Here we present the synthesis of crystalline K 2 Pentacene and K 2 Picene by a solid–solid insertion protocol that uses potassium hydride as a redox-controlled reducing agent to access the PAH dianions, and so enables the determination of their crystal structures. In both cases, the inserted cations expand the parent herringbone packings by reorienting the molecular anions to create multiple potassium sites within initially dense molecular layers, and thus interact with the PAH anion π systems. The synthetic and crystal chemistry of alkali metal intercalation into PAHs differs from that into fullerenes and graphite, in which the cation sites are pre-defined by the host structure. Reports of superconductivity in K x Picene spurred interest in alkali-intercalated polyaromatic hydrocarbon (PAH) compounds, but their compositions and structures have remained unclear. Now crystalline K 2 Pentacene and K 2 Picene — neither of which are superconducting — have been prepared by mild synthesis. Structural analysis shows that the cation sites arise within the molecular layers from reorientation of the PAHs within a herringbone packing.