REVIEW | doi:10.20944/preprints202002.0112.v1
Online: 9 February 2020 (17:11:44 CET)
The ever-rising demands for energy dense electrochemical storage systems have been driving interests in beyond Li-ion batteries such as those based on lithium and magnesium metals. These high energy density batteries suffer from several challenges, several of which stem from the flammability/volatility of the electrolytes and/or instability of the electrolyte with either the negative, positive electrode or both. Recently, hydride-based electrolytes have been paving a path towards overcoming these issues. Namely, highly performing solid state electrolytes have been reported and several key challenges in multivalent batteries were overcome. In this review, the classes of hydride-based electrolytes reported for energy dense batteries are discussed. Future perspectives are presented to guide research directions in this field.
REVIEW | doi:10.20944/preprints202106.0617.v1
Subject: Materials Science, Biomaterials Keywords: energy transition; hydrogen; hydrogen storage; metal hydride; complex hydride; hydrogen tank; social impact; gender
Online: 25 June 2021 (11:44:46 CEST)
This paper aims at addressing the exploitation of solid-state carriers for hydrogen storage, with attention paid both to the technical aspects, through a wide review of the available integrated systems, and to the social aspects, through a preliminary overview of the connected impacts from a gender perspective. As for the technical perspective, carriers to be used for solid-state hydrogen storage for various applications can be classified into two classes: metal and complex hydrides. Related crystal structures and corresponding hydrogen sorption properties are reviewed and discussed. Fundamentals of thermodynamics of hydrogen sorption evidences the key role of the enthalpy of reaction, which determines the operating conditions (i.e. temperatures and pressures). In addition, it rules the heat to be removed from the tank during hydrogen absorption and to be delivered to the tank during hydrogen desorption. Suitable values for the enthalpy of hydrogen sorption reaction for operating conditions close to ambient (i.e. room temperature and 1-10 bar of hydrogen) are close to 30 kJ·molH2 1. The kinetics of hydrogen sorption reaction is strongly related to the microstructure and to the morphology (i.e. loose powder or pellets) of the carriers. Usually, kinetics of hydrogen sorption reaction is rather fast, and the thermal management of the tank is the rate determining step of the processes. As for the social perspective, various scenarios for the applications in different socio-economic contexts of solid-state hydrogen storage technologies are described. As it occurs with the exploitation of other renewables innovative technologies, a wide consideration of the social factors connected to these processes is needed to assess the extent to which a specific innovation might produce positive or negative impacts in the recipient socio-economic system and to explore the potential role of the social components and dynamics in fostering the diffusion of the innovation itself. Attention has been addressed to the gender perspective, in view of the enhancement of hydrogen-related energy storage systems, intended both in terms of the role of women in triggering the exploitation of hydrogen-based storage as well as to the impact of this innovation in their current conditions, at work and in daily life.
REVIEW | doi:10.20944/preprints202007.0034.v1
Subject: Life Sciences, Biophysics Keywords: hydrogen; biocatalysis; hydride chemistry; photochemistry; infrared spectroscopy
Online: 3 July 2020 (12:12:12 CEST)
Hydrogenases are iron-sulfur enzymes that catalyze proton reduction and H2 oxidation with outstanding efficiency. They are considered blueprints for the design of transition metal complexes, e.g. as heterogenous catalysts in the context of H2 production from water. Moreover, hydrogenases are biological model systems for metal hydride chemistry and proton-coupled electron transfer. Depending on the composition of the active site cofactor, [NiFe]-hydrogenases are distinguished from [FeFe]-hydrogenases. The former binds a hetero bimetallic nickel/iron site, embedded in the protein by four cysteine ligands. The later, by contrast, carries a homo bimetallic iron/iron site attached to the protein by only a single cysteine. Carbon monoxide and cyanide ligands (CO/CN) at the active site facilitated detailed investigations of hydrogenase catalysis by infrared spectroscopy, owing to strong signals and redox-dependent frequency shifts. However, the details of proton transfer have not been addressed experimentally.We found that specific redox state transitions in [NiFe]- and [FeFe]-hydrogenase can be triggered by visible light to record extremely sensitive ‘light-minus-dark’ infrared difference spectra monitoring key amino acid residues as shown in the ToC figure. As these transitions are coupled to protonation changes, our data allowed investigating dynamic hydrogen-bonding changes that go well beyond the resolution of protein crystallography. In [NiFe]-hydrogenase, photolysis of the bridging hydride ligand in the ‘Ni-C’ state was followed by rapid accumulation of the ‘Ni-SIa’ state and/or ‘Ni-L’ state. Infrared difference spectra in various isotopic media clearly indicated the formation of a protonated cysteine residue as well as hydrogen-bonding changes involving the COOH group of a glutamic acid residue and a ‘dangling water’ molecule. These findings are in excellent agreement with crystallographic analyses of [NiFe]-hydrogenase in the Ni-R state and allowed devising a molecular precise model of catalytic proton transfer. In [FeFe]-hydrogenase, an external redox dye was used to accumulate the ‘Hred’ state over the oxidized resting state ‘Hox’. Infrared difference spectra of wild-type enzyme and numerous amino acid variants indicated hydrogen-bonding changes involving the COOH groups of two glutamic acid residues. Moreover, we noted the deprotonation of an arginine residue. Crystallographic analyses of [FeFe]-hydrogenase in the Hox state failed to explain the rapid proton transfer due to a ‘breach’ in the succession of residues. To this end, our findings facilitated a molecular precise model of ‘discontinued’ proton transfer.The comparison of catalytic proton transfer in bimetallic hydrogenases emphasizes the role of the outer coordination sphere. We suggest that the stable protonation of a nickel-ligating cysteine in [NiFe]-hydrogenase has a crucial influence on the preferred direction of proton flow and catalysis (i.e., H2 oxidation). On the contrary, proton transfer in [FeFe]-hydrogenase involves an adjacent cysteine as a relay group that promotes both proton release and proton uptake. We presume that this causes the notable bidirectionality of [FeFe]-hydrogenase. These observations must guide the design of biomimetic compounds for the production or consumption of H2.
SHORT NOTE | doi:10.20944/preprints202112.0188.v2
Subject: Physical Sciences, Condensed Matter Physics Keywords: hydride superconductor; room temperature superconductor; pressure; diamond anvil cell; ac magnetic susceptibility; raw data; background signal; random noise
Online: 21 December 2021 (09:00:23 CET)
Room temperature superconductivity has recently been reported for a carbonaceous sulfur hydride (CSH) under high pressure by Snider et al . The paper reports sharp drops in magnetic susceptibility as a function of temperature for five different pressures, that are interpreted as signaling a superconducting transition. Here I question the validity and faithfulness of the magnetic susceptibility data presented in the paper by comparison with the measured raw data reported by two of the authors of ref. . This invalidates the assertion of the paper  that the susceptibility measurements support the case for superconductivity in this compound.
ARTICLE | doi:10.20944/preprints201912.0313.v1
Subject: Physical Sciences, Condensed Matter Physics Keywords: near-room-temperature superconductivity; hydride superconductors; yttrium superhydrides
Online: 24 December 2019 (08:47:09 CET)
Recently, Troyan et al (2019 arXiv:1908.01534) and Kong et al (2019 arXiv:1909.10482) extended near-room-temperature superconductors family by new yttrium superhydride polymorphs, YHn (n = 4,6,7,9), which exhibit superconducting transition temperatures in the range of Tc = 210-243 K at pressure of P = 160-255 GPa. In this paper, temperature dependent upper critical field data, Bc2(T), for highly-compressed mixture of YH4+YH6 phases (reported by Kong et al 2019 arXiv:1909.10482) is analysed to deduce the ratio of Tc to the Fermi temperature, TF. Our analysis shows that in all considered scenarios the YH4+YH6 mixture has the ratio 0.01 ≤ Tc/TF ≤ 0.04. As the result, YH4+YH6 falls in the unconventional superconductors band in the Uemura plot. It is also found that the characteristic temperature of the order parameter amplitude fluctuations, Tfluc, in the YH4+YH6 mixture is only several percent above observed Tc, and thus the superconducting transition in yttrium superhydride polymorphs is fundamentally limited by thermodynamics fluctuations.
REVIEW | doi:10.20944/preprints201902.0238.v1
Subject: Chemistry, Analytical Chemistry Keywords: hydride surface; silicon-carbon bond; aqueous normal phase; retention mechanism
Online: 26 February 2019 (11:33:15 CET)
The development of a stationary phase material for high performance liquid chromatography based on a surface of silica hydride as opposed to silanols on ordinary silica is discussed including synthetic approaches, characterization and applications. There are several synthetic approaches available to create a silica hydride surface. Modification of the Si-H moiety on the silica surface can be accomplished through use of a hydrosilation reaction. Both the intermediate silica hydride and the material modified with an organic moiety can be characterized by a number of spectroscopic as well as a variety of other methods. Further insights into the retention mechanism are provide through chromatographic measurements. The ultimate utility of any chromatographic stationary phase material is determined by its success for solving challenging analytical problems. A broad range of applications are reviewed to illustrate the versatility and usefulness of silica hydride-based stationary phases.
REVIEW | doi:10.20944/preprints201909.0244.v1
Subject: Chemistry, Applied Chemistry Keywords: cofactor F420; deazaflavin; oxidoreductase; hydride transfer; hydrogenation; asymmetric synthesis; cofactor biosynthesis
Online: 21 September 2019 (01:28:13 CEST)
Asymmetric reduction of enoates, imines and ketones are among the most important reactions in biocatalysis. These reactions are routinely conducted using enzymes that use nicotinamide cofactors as reductants. The deazaflavin cofactor F420 also has electrochemical properties that make it suitable as an alternative to nicotinamide cofactors for use in asymmetric reduction reactions. However, cofactor F420-dependent enzymes remain under-explored as a resource for biocatalysis. In this review, we consider the cofactor F420-dependent enzyme families with greatest potential for the discovery of new biocatalysts: the flavin/deazaflavin-dependent oxidoreductases (FDORs) and the luciferase-like hydride transferases (LLHTs). We discuss characterized F420-dependent reductions that have potential for adaptation for biocatalysis, and we consider the enzymes best suited for use in the reduction of oxidized cofactor F420 to allow cofactor recycling in situ. We also discuss recent advances in the production of cofactor F420 and its functional analog FO-5’- phosphate, which remains an impediment to the adoption of this family of enzymes for industrial biocatalytic processes. Finally, we discuss the prospects for the use of this cofactor and dependent enzymes as a resource for industrial biocatalysis.
ARTICLE | doi:10.20944/preprints202202.0005.v2
Subject: Physical Sciences, Condensed Matter Physics Keywords: hydride superconductor; room temperature superconductor; pressure; ac magnetic susceptibility; raw data; background signal
Online: 4 February 2022 (10:31:10 CET)
In Ref.  Snider et al reported room temperature superconductivity in carbonaceous sulfur hydride (CSH) under high pressure. Recently the data for the temperature dependent ac magnetic susceptibility shown in figures of Ref  have appeared in the form of tables corresponding to different pressures . Here we provide an analysis of the data for a pressure of 160 GPa. This work was performed in collaboration with D. van der Marel.
ARTICLE | doi:10.20944/preprints201704.0125.v1
Subject: Chemistry, Inorganic & Nuclear Chemistry Keywords: alane; aluminium; hydrogen formation; magnesium; magnesium hydride; metal hydrides; methanediides; N,N'-chelation
Online: 19 April 2017 (13:11:04 CEST)
Substituted bis(iminophosphoranyl)methanes are CH acidic compounds that can form complexes with formally dianionic central carbon centres. The reaction of H2C(Ph2P=NDip)2 (≡ H2L), Dip = 2,6-diisopropylphenyl, with one equivalent of di-n-butylmagnesium afforded the methanide complex [HLMgnBu] 1. Treatment of complex 1 with phenylsilane in aromatic solvents at elevated temperatures afforded the methanediide complex [(LMg)2] 2 presumably via the MgH intermediate [(HLMgH)n] (n = 1 or 2). The reaction of 1 with LiAlH4 in diethyl ether yielded the AlH complex [HLAlH2] 3. Alternatively, this complex was also obtained from the reaction of H2L with AlH3∙NMe3. The molecular structures of [HLMgnBu] 1, [(LMg)2] 2, and [HLAlH2] 3 are reported. Complex 3 shows no sign of H2 elimination to a methanediide species at elevated temperatures in contrast to the facile elimination of the putative reaction intermediate [(HLMgH)n] (n = 1 or 2) to form [(LMg)2] 2. The chemical properties of complex 2 were investigated and this complex appears to be stable against coordination with strong donor molecules.
ARTICLE | doi:10.20944/preprints201806.0025.v1
Subject: Engineering, Energy & Fuel Technology Keywords: high pressure hydrogen; metal hydride-based high pressure compression; techno-economic analysis; Ti-based AB2 metal hydrides; mini-channel heat exchanger
Online: 4 June 2018 (09:36:54 CEST)
Traditional high pressure mechanical compressors account for over half of the car station’s cost, have insufficient reliability and are not feasible for a large-scale fuel cell market. An alternative technology, employing a two-stage, hybrid system based on electrochemical and metal hydride compression technologies, represents an excellent alternative to conventional compressors. The high-pressure stage, operating at 100-875 bar, is based on a metal hydride thermal system. A techno-economic analysis of the metal hydride system is presented and discussed. A model of the metal hydride system was developed, integrating a lumped parameter mass and energy balance model with an economic model. A novel metal hydride heat exchanger configuration is also presented, based on mini-channel heat transfer systems, allowing for effective high-pressure compression. Several metal hydrides were analyzed and screened, demonstrating that one selected material, namely (Ti0.97Zr0.03)1.1Cr1.6Mn0.4, is likely the best candidate material to be employed for high-pressure compressors under the specific conditions. System efficiency and costs were assessed based on the properties of currently available materials at industrial levels. Results show that the system can reach pressures on the order of 875 bar with thermal power provided at approximately 150 °C. The system cost is comparable with the current mechanical compressors and can be reduced in several ways as discussed in the paper.