Production Of Molecular Hydrogen Research Articles

Enhanced production of hydrogen via catalytic methane decomposition on a Pt7-Ni (110) substrate: a reactive molecular dynamics investigation

Abstract Numerous researchers in the energy field are engaged in a competitive race to advance hydrogen as a clean and environmentally friendly fuel. Studies have been conducted on the different aspects of hydrogen, including its production, storage, transportation and utilization. The catalytic methane decomposition technique for hydrogen production is an environmentally friendly process that avoids generating carbon dioxide gas, which contributes to the greenhouse effect. Catalysts play a crucial role in facilitating rapid, cost-effective and efficient production of hydrogen using this technique. In this study, reactive molecular dynamics simulations were employed to examine the impact of Pt7 cluster decoration on the surface of a Ni (110) catalyst, referred to as Pt7-Ni (110), on the rates of methane dissociation and molecular hydrogen production. The reactive force field was employed to model the atomic interactions that enabled the formation and dissociation of chemical bonds. Our reactive molecular dynamics simulations using the Pt7-Ni (110) catalyst revealed a notable decrease in the number of methane molecules, specifically ~11.89 molecules per picosecond. The rate was approximately four times higher than that of the simulation system utilizing a Ni (110) catalyst and approximately six times higher than that of the pure methane, no-catalyst system. The number of hydrogen molecules generated during a simulation period of 150 000 fs was greater on the Pt7-Ni (110) surface than in both the Ni (110) and pure methane systems. This was due to the presence of numerous dissociated hydrogen atoms on the Pt7-Ni (110) surface.

Production of hydrogen via water oxidation using mesoporous‐assembled SiO2@TiN nanocomposite electrocatalyst

AbstractElectrochemical water splitting is one of the promising approaches for the production of molecular hydrogen as well as to meet the clean and sustainable energy demand of the modern world. However, the key task for the research communities is to design a cost‐effective and efficient electrocatalyst to contribute positively to recent world crises. This study presents a novel SiO2@TiN nanocomposite and utilize it for oxygen evolution reaction (OER) as an electrocatalysts. The different techniques use for the characterization of SiO2@TiN nanocomposite. The electrochemical investigations encompass linear sweep voltammetry (LSV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) which collectively yield critical parameters for assessing electrocatalytic performance. At a current density of 10 mAcm−2 the SiO2@TiN nanocomposite has a substantially lower overpotential of 256 mV compared to pure SiO2 and TiN. The composite also shows smaller tafel slope of 40 mV dec−1 as well as lower overpotential. The SiO2@TiN nanocomposite also demonstrates the enhanced redox activity as a result of its synergistic effect. Consequently, the increased electrical conductivity of TiN facilitates the attachment of metal oxides and more active sites are exposed to improve the OER activity of the fabricated materials.

Investigating the role of undercoordinated Pt sites at the surface of layered PtTe2 for methanol decomposition

Transition metal dichalcogenides, by virtue of their two-dimensional structures, could provide the largest active surface for reactions with minimal materials consumed, which has long been pursued in the design of ideal catalysts. Nevertheless, their structurally perfect basal planes are typically inert; their surface defects, such as under-coordinated atoms at the surfaces or edges, can instead serve as catalytically active centers. Here we show a reaction probability > 90 % for adsorbed methanol (CH3OH) on under-coordinated Pt sites at surface Te vacancies, produced with Ar+ bombardment, on layered PtTe2 — approximately 60 % of the methanol decompose to surface intermediates CHxO (x = 2, 3) and 35 % to CHx (x = 1, 2), and an ultimate production of gaseous molecular hydrogen, methane, water and formaldehyde. The characteristic reactivity is attributed to both the triangular positioning and varied degrees of oxidation of the under-coordinated Pt at Te vacancies.

Incorporation of (Co-Ni)P Based Electrocatalysts in Tin Sulfide Photoelectrodes

Ever since the industrial revolution, available energy sources have been closely related to technological development. Therefore, energy has become the main component towards the productivity of industrialized nations. The indiscriminate use of fossil fuel has produced a gradual decrease of oil reserves that affects the worldwide price of this product. The above-mentioned causes uncertainty because price fluctuations in the international value of oil directly affects nation economies.The development of industrialized societies has, unfortunately, proved to be non-sustainable, due to its strong dependency of fossil fuels and the environmental damage produced by the combustion that this kind of fuel generates. Consequently, this has led to a search of alternative energy sources, highlighting technologies based on molecular hydrogen (carrier energy), and photovoltaic devices. However, nowadays the high cost of production of molecular hydrogen makes it necessary to search new alternatives in order to produce it. Thus, photoelectrochemical water splitting becomes an attractive option that should be considered, due to the use of solar energy as a renewable energy source [1]. However, in photoelectrochemical systems, photocurrent loss is one of the biggest problems present. This is a consequence of the recombination process, either of electron-hole pairs or majority carriers with intermediaries bounded to the electrode surface. The latter is caused by slow transfer kinetics between the carriers photogenerated and the reaction intermediaries. On the other hand, the use of electrocatalyst (materials that catalyzes an electrochemical reaction) allows reduce the electric energy consumption of the electrochemical reactions involved in this process. In this way, for electrocatalytic water splitting, studies are centered on electrocatalysts for OER (anodic reaction) and electrocatalysts for HER (cathodic reaction). Thus, electrocatalysts can be a key issue in the study of light-driven overall water splitting systems [2].In this study, the synthesis of different electrocatalysts based on CoP and NiP was carried out through a hydrothermal procedure following by a thermal phosphorization reaction. The electrocatalysts obtained were characterized through X-ray diffraction, scanning electron microscopy, and polarization curves. These characterization techniques confirm the formation of different CoxNi(1-x)P compounds (where 1 ≥ x ≥ 0) showing in some cases an improvement in the kinetic parameters of the hydrogen evolution reaction (HER). In this way, the best performance (Co-Ni)P electrocatalysts were deposited on a SnS surface (p-type semiconductor), which was electrodeposited from an acidic solution employing SnSO4 and Na2S2O3 as tin and sulfur precursors, respectively. The deposition of the electrocatalysts was carried out through spin-coating technique, employing an ethanolic suspension of the (Co-Ni)P compounds. The SnS surface modification with the (Co-Ni)P based electrocatalysts was confirmed through SEM images. Thus, the modified SnS was employed as a photocathode in a photoelectrochemical cell in order to study its performance as an efficient photoelectrode in the hydrogen evolution reaction. In comparison with the unmodified SnS photoelectrode, an improvement in the photoelectrode stability was observed, which is attributed to the presence of electrocatalysts in the SnS surface.Acknowledgement This study was supported by Fondecyt (Chile) project 1210548References A. Grimes, O.K. Varghese, S. Ranjan, Light, water, hydrogen. The solar generation of hydrogen by water photoelectrolysis, Springer, New York, 2008.M. Peter, K.G. Upul Wijayantha, Photoelectrochemical water splitting at semiconductor electrodes: Fundamental problems and new perspectives, ChemPhysChem. 15 (2014) 1983–1995. Figure 1

Plasmonic-Assisted Water–Gas Shift Reaction of Gold Particles on TiO2

The Localized Surface Plasmon (LSP) effect of 5 nm mean size Au particles deposited on TiO2 P25 was investigated during the photo-thermal water gas shift reaction (WGSR). The effects of CO concentration, excitation light flux and energy, and molecular oxygen addition during the reaction were investigated. The photocatalytic WGSR rate under light excitation with wavelengths extending from 320 to 1100 nm was found to be higher than the thermal reaction alone at the same temperature (85 °C). A H2/CO2 ratio of near unity was found at high concentrations of CO. The addition of molecular oxygen during the reaction resulted in a slight decrease in molecular hydrogen production, while the rates of CO2 formation and CO consumption changed by one order of magnitude. More importantly, it was found that the WGSR rates were still high under only visible light excitation (600–700 nm). The results prove that Au LSP alone triggers this chemical reaction without requiring the excitation of the semiconductor on which they are deposited.

Reverse pH-dependent fluorescence protein visualizes pattern of interfacial proton dynamics during hydrogen evolution reaction

Reverse pH-dependent fluorescent protein, including dKeima, is a type of fluorescent protein in which the chromophore protonation state depends inversely on external pH. The dependence is maintained even when immobilized at the metal-solution interface. But, interestingly, its responses to the hydrogen evolution reaction (HER) at the interface are not reversed: HER rises the pH of the solution around the cathode, but, highly active HER induces chromophore deprotonation regardless of the reverse pH dependence, reflecting an interface-specific deprotonation effect by HER. Here, we exploit this phenomenon to perform scanning-less, real-time visualization of interfacial proton dynamics during HER at a wide field of view. By using dKeima, the HER-driven deprotonation effect was well discriminated from the solution pH effect. In the electrodes of composite structures with a catalyst, dKeima visualized keen dependence of the proton depletion pattern on the electrode configuration. In addition, propagations of optical signals were observed, which seemingly reflect long-range proton hopping confined to the metal-solution interface. Thus, reverse pH-dependent fluorescent proteins provide a unique tool for spatiotemporal analysis of interfacial proton dynamics, which is expected to contribute to a better understanding of the HER process and ultimately to the safe and efficient production of molecular hydrogen.

Predictive Modeling of Molecular Mechanisms in Hydrogen Production and Storage Materials.

Hydrogen has been widely considered to hold promise for solving challenges associated with the increasing demand for green energy. While many chemical and biochemical processes produce molecular hydrogen as byproducts, electrochemical approaches using water electrolysis are considered to be a predominant method for clean and green hydrogen production. We discuss the current state-of-the-art in molecular hydrogen production and storage and, more significantly, the increasing role of computational modeling in predictively designing and deriving insights for enhancing hydrogen storage efficiency in current and future materials of interest. One of the key takeaways of this review lies in the continued development and implementation of large-scale atomistic simulations to enable the use of designer electrolyzer-electrocatalysts operating under targeted thermophysical conditions for increasing green hydrogen production and improving hydrogen storage in advanced materials, with limited tradeoffs for storage efficiency.

The genome-scale metabolic model for the purple non-sulfur bacterium Rhodopseudomonas palustris Bis A53 accurately predicts phenotypes under chemoheterotrophic, chemoautotrophic, photoheterotrophic, and photoautotrophic growth conditions.

The purple non-sulfur bacterium Rhodopseudomonas palustris is recognized as a critical microorganism in the nitrogen and carbon cycle and one of the most common members in wastewater treatment communities. This bacterium is metabolically extremely versatile. It is capable of heterotrophic growth under aerobic and anaerobic conditions, but also able to grow photoautotrophically as well as mixotrophically. Therefore R. palustris can adapt to multiple environments and establish commensal relationships with other organisms, expressing various enzymes supporting degradation of amino acids, carbohydrates, nucleotides, and complex polymers. Moreover, R. palustris can degrade a wide range of pollutants under anaerobic conditions, e.g., aromatic compounds such as benzoate and caffeate, enabling it to thrive in chemically contaminated environments. However, many metabolic mechanisms employed by R. palustris to breakdown and assimilate different carbon and nitrogen sources under chemoheterotrophic or photoheterotrophic conditions remain unknown. Systems biology approaches, such as metabolic modeling, have been employed extensively to unravel complex mechanisms of metabolism. Previously, metabolic models have been reconstructed to study selected capabilities of R. palustris under limited experimental conditions. Here, we developed a comprehensive metabolic model (M-model) for R. palustris Bis A53 (iDT1294) consisting of 2,721 reactions, 2,123 metabolites, and comprising 1,294 genes. We validated the model using high-throughput phenotypic, physiological, and kinetic data, testing over 350 growth conditions. iDT1294 achieved a prediction accuracy of 90% for growth with various carbon and nitrogen sources and close to 80% for assimilation of aromatic compounds. Moreover, the M-model accurately predicts dynamic changes of growth and substrate consumption rates over time under nine chemoheterotrophic conditions and demonstrated high precision in predicting metabolic changes between photoheterotrophic and photoautotrophic conditions. This comprehensive M-model will help to elucidate metabolic processes associated with the assimilation of multiple carbon and nitrogen sources, anoxygenic photosynthesis, aromatic compound degradation, as well as production of molecular hydrogen and polyhydroxybutyrate.

Valorization of whey-based side streams for microbial biomass, molecular hydrogen, and hydrogenase production.

Side streams of the dairy industry are a suitable nutrient source for cultivating microorganisms, producing enzymes, and high-value chemical compounds. The heterotrophic Escherichia coli and chemolithoautotroph Ralstonia eutropha are of major biotechnological interest. R. eutropha is a model organism for producing O2-tolerant [NiFe]-hydrogenases (Hyds) (biocatalysts), and E. coli has found widespread use as an expression platform for producing recombinant proteins, molecular hydrogen (H2), and other valuable products. Aiming at developing suitable cultivation media from side streams of the dairy industry, the pre-treatment (filtration, dilution, and pH adjustment) of cheese (sweet) whey (SW) and curd (acid) whey (AW), with and without the use of ß-glucosidase, has been performed. Growth parameters (oxidation-reduction potential (ORP), pH changes, specific growth rate, biomass formation) of E. coli BW25113 and R. eutropha H16 type strains were monitored during cultivation on filtered and non-filtered SW and AW at 37°C, pH 7.5 and 30°C, pH 7.0, respectively. Along with microbial growth, measurements of pH and ORP indicated good fermentative growth. Compared to growth on fructose-nitrogen minimal salt medium (control), a maximum cell yield (OD600 4.0) and H2-oxidizing Hyd activity were achieved in the stationary growth phase for R. eutropha. Hyd-3-dependent H2 production by E. coli utilizing whey as a growth substrate was demonstrated. Moreover, good biomass production and prolonged H2 yields of ~ 5mmol/L and cumulative H2 ~ 94mLg/L dry whey (DW) (ß-glucosidase-treated) were observed during the cultivation of the engineered E. coli strain. These results open new avenues for effective whey treatment using thermostable β-glucosidase and confirm whey as an economically viable commodity for biomass and biocatalyst production. KEY POINTS: • Archaeal thermostable β-glucosidase isolated from the metagenome of a hydrothermal spring was used for lactose hydrolysis in whey. • Hydrogenase enzyme activity was induced during the growth of Ralstonia eutropha H16 on whey. • Enhanced biomass and H2 production was shown in a genetically modified strain of Escherichia coli.

Z-scheme driven photocatalytic activity of CNTs-integrated Bi2S3/WO3 nanohybrid catalysts for highly efficient hydrogen evolution under solar light irradiation

Harvesting solar energy for the production of molecular hydrogen through photocatalytic approach is a clean and sustainable pathway to deal with the energy crisis and pollution. In this connection, direct Z-scheme interfaced noble metal free CNTs integrated Bi2S3-WO3 ternary composite was designed and developed through simple hydrothermal and wet impregnation strategies. This combination was manifested for the first time to tackle the photo-corrosion of Bi2S3 through Z-scheme heterojunction formation, and its effective contribution in the mitigation of charge carrier recombination was investigated. 9 wt% WO3 loaded Bi2S3 (WB-9) delivered a notable H2 production rate of 4.85 mmol.h−1.g-1cat over 5 vol% glycerol as a sacrificial reagent under simulated solar light irradiation. This enhancement was six folds higher than the pristine Bi2S3 photocatalytic activity. To enhance the reduction half-reaction further, electron mobility was regulated with CNT integration, which not only triggers the successive transport of electrons through its tubular channel, but also facilitate an excellent reduction co-catalyst to support rapid reduction of protons to form H2 molecules. Upon optimization of CNTs loading, 1 wt% CNTs loaded WB-9 (CWB-4) produced two-folds higher H2 production rates than WB-9, which is about 9.91 mmol.h−1. g−1cat. The observed efficiency, stability, and recyclability of CWB-4 attributed to the effective utilization of generated charge carriers across the system and suppressed photo-corrosion of Bi2S3 through the Z-scheme interface.

Toward a synthetic hydrogen sensor in cyanobacteria: Functional production of an oxygen-tolerant regulatory hydrogenase in Synechocystis sp. PCC 6803.

Cyanobacteria have raised great interest in biotechnology, e.g., for the sustainable production of molecular hydrogen (H2) using electrons from water oxidation. However, this is hampered by various constraints. For example, H2-producing enzymes compete with primary metabolism for electrons and are usually inhibited by molecular oxygen (O2). In addition, there are a number of other constraints, some of which are unknown, requiring unbiased screening and systematic engineering approaches to improve the H2 yield. Here, we introduced the regulatory [NiFe]-hydrogenase (RH) of Cupriavidus necator (formerly Ralstonia eutropha) H16 into the cyanobacterial model strain Synechocystis sp. PCC 6803. In its natural host, the RH serves as a molecular H2 sensor initiating a signal cascade to express hydrogenase-related genes when no additional energy source other than H2 is available. Unlike most hydrogenases, the C. necator enzymes are O2-tolerant, allowing their efficient utilization in an oxygenic phototroph. Similar to C. necator, the RH produced in Synechocystis showed distinct H2 oxidation activity, confirming that it can be properly matured and assembled under photoautotrophic, i.e., oxygen-evolving conditions. Although the functional H2-sensing cascade has not yet been established in Synechocystis yet, we utilized the associated two-component system consisting of a histidine kinase and a response regulator to drive and modulate the expression of a superfolder gfp gene in Escherichia coli. This demonstrates that all components of the H2-dependent signal cascade can be functionally implemented in heterologous hosts. Thus, this work provides the basis for the development of an intrinsic H2 biosensor within a cyanobacterial cell that could be used to probe the effects of random mutagenesis and systematically identify promising genetic configurations to enable continuous and high-yield production of H2 via oxygenic photosynthesis.

Importance of the radiations in water splitting for hydrogen generation

The review article examines the production of molecular hydrogen from the decomposition of water by various irradiation methods. The article shows different types of radiation: UV radiation, visible radiation, gamma radiation, X-ray radiation and neutron radiation. Electrons generated by radiation inside a nanoparticle of radius R suspense in fluid water are diffused with equal probability in all directions inside the particle and gradually lose their kinetic energy as a result of elastic and inelastic collisions. Some of these electrons are transported to the nanoparticle surface during the physical and physicochemical stages of the process and emitted into the water. It is extremely important for the formation of nanostructured materials after exposure to ordered nanostructure from the new phase with a period of a few nanometers, promoting the preservation of the properties of materials under high irradiation.

Photoelectrochemical Degradation of Organic Pollutants Coupled with Molecular Hydrogen Generation Using Bi2O3/TiO2 Nanoparticle Arrays

The growing world population is closely associated with the increased demand of safe drinking water and sustainable energy production. This drives the focus of the scientific community to work toward water remediation and clean energy generation. The combination of photoelectrooxidation of pollutants at the anode with simultaneous hydrogen gas production at the cathode is a smart strategy to address these problems. Herein, we have designed a bifunctional photoelectrocatalytic system consisting of a self-standing photoanode to degrade the water pollutant molecules with simultaneous production of molecular hydrogen at the cathode. The photoanode was prepared by coating Bi2O3 over the surface of self-standing TiO2 nanorods. Thus, prepared photoelectrodes show high degradation efficiency for rhodamine molecules, where direct oxidation of rhodamine by the holes generated under solar light illumination was detrimental for its activity. During simultaneous pollutant removal and energy production experiments, the anode shows 100% degradation of pollutant molecules while the cathode shows high hydrogen gas production (128 mM cm–2 h–1). The prepared composite showed higher efficiency of visible-light absorbance, high charge generation capability, and low charge transfer resistance at the interface as determined via several characterizations, compared to the bare titania. The catalyst is easy to prepare and robust in activity for several kinds of pollutant molecules tested. Its robust activity, high stability, and durability open up an avenue for the wastewater treatment with simultaneous renewable energy production technologies.

Photochemical production of molecular hydrogen in the presence of substituted acridine salts

The photocatalytic properties of new representatives of the family of metal-free catalysts, 10-hydro-9-phenylacridine, 10-methyl-9-phenylacridinium chloride, and 10-phenyl-9-phenylacridinium chloride, were studied with respect to the reaction of molecular hydrogen generation in the presence of acids of different strength (HClO4, CH3SO3H, and CF3COOH) and reducing agents ([Bu4N]Cl, [Bu4N]Br, and [Bu4N]I). It was found that the strength of acids (p K a) and the nature of the reducing agent ( E 0) significantly affect the efficiency, i.e. turnover frequency (TOF), of the process under study. The amount of formed molecular hydrogen reaches its maximum in the case of the combination HClO4 and [Bu4N]I, characterized by minimal p K a and E0 values, respectively. The influence of the nature of substituents at the nitrogen atom in 9-phenylacridine on the efficiency of the molecular hydrogen production was analyzed. It was shown that the limiting stage of the process is the protonation of the formed radical.

Electrocatalytic study of the hydrogen evolution reaction on MoS2/BP and MoSSe/BP in acidic media.

Molecular hydrogen (H2) production by the electrochemical hydrogen evolution reaction (HER) is being actively explored for non-precious metal-based electrocatalysts that are earth-abundant and low cost like MoS2. Although it is acid-stable, its applicability is limited by catalytically inactive basal planes, poor electrical transport and inefficient charge transfer at the interface. Therefore, the present work examines its bilayer van der Waals heterostructure (vdW HTS). The second constituent monolayer boron phosphide (BP) is advantageous as an electrode material owing to its chemical stability in both oxygen and water environments. Here, we have performed first-principles based calculations under the framework of density functional theory (DFT) for the HER in an electrochemical double layer model with the BP monolayer, MoS2/BP and MoSSe/BP vdW HTSs. The climbing image nudged elastic band method (CI-NEB) has been employed to determine the minimum energy pathways for Tafel and Heyrovsky reactions. The calculations reveal that the Tafel reaction shows no reaction barrier. Thereafter, for the Heyrovsky reaction, we obtained a low reaction barrier in the vdW HTSs as compared to that in the BP monolayer. Subsequently, we have observed no significant difference in the reaction profile of MoS2/BP and MoSSe/BP vdW HTSs in the case of 2 × 2 supercell configuration. However, in the case of 3 × 3 and 4 × 4 configurations, MoSSe/BP shows a feasible Heyrovsky reaction with no reaction barrier. The coverages with 1/4H+ concentration (conc.) deduced high coverage with low conc. and low coverage with high conc. to be apt for the HER via the Heyrovsky reaction path. Finally, on observing the activation barrier of the Heyrovsky pathway along with that of second H adsorption at the surface, the Heyrovsky path is expected to be favoured.

Valorizing the carbon byproduct of methane pyrolysis in batteries

While low-cost natural gas remains abundant, the energy content of this fuel can be utilized without greenhouse gas emissions through the production of molecular hydrogen and solid carbon via methane pyrolysis. In the absence of a carbon tax, methane pyrolysis is not economically competitive with current hydrogen production methods unless the carbon byproducts can be valorized. In this work, we assess the viability of the carbon byproduct produced from methane pyrolysis in molten salts as high-value-added anode or conductive additive for secondary Li-ion and Na-ion batteries. Raman characterization and electrochemical differential capacity analysis demonstrate that the use of molten salt mixtures with catalytically-active FeCl3-or MnCl2 result in more graphitic carbon co-products. These graphitic carbons exhibit the best electrochemical performance (up to 272 mAh/g of reversible capacity) when used as Li-ion anodes. For all carbon samples studied here, disordered carbon domains and retained salt species trapped and/or intercalated into the carbon structure were identified by X-ray photoelectron and multinuclear solid-state nuclear magnetic resonance spectroscopy. The latter lead to reduced electrochemical activity and reversibility, and poorer rate performance compared to commercial carbon anodes. The electronic conductivity of the pyrolyzed carbons is found to be highly dependent on their purity, with the purest carbon exhibiting an electronic conductivity nearly on par with that of commercial carbon additives. These findings suggest that more effective removal of the salt catalyst could enable applications of these carbons in secondary batteries, providing a financial incentive for the large-scale implementation of methane pyrolysis for “low-carbon” hydrogen production.

Photochemical Production of Molecular Hydrogen in the Presence of Substituted Acridine Salts

Photochemical Production of Molecular Hydrogen in the Presence of Substituted Acridine Salts

(Digital Presentation) Engineering of Ni-Based Electrocatalysts for Direct Urea Oxidation

In the water-energy nexus framework, the alternate renewable energy sources can be stored into molecular hydrogen or electricity with simultaneous water purification through wastewater electrolysis cell or wastewater fuel cell. Urea oxidation reaction (UOR) has been interrogated to enhance the energy efficiency and to recover energy from urea-rich wastewater. Nickel-based catalysts are up-to-date the most widely investigated materials as the UOR electrocatalyst. This presentation introduces our recent approaches for preparation of the UOR electrocatalysts by i) galvanostatic electro-deposition of mixed metal (oxy)hydroxide (NiFeOx or NiCoOx) with variable mixing ratios, ii) potentiostatic dealloying of commercial alloys (e.g. Ni-Fe, Fe-Ni, and Ni-Cr-Co) under variable pH, and iii) one-pot thermochemical treatment of NiFe alloy foam (NFF), both as substrate and catalyst source to create a self-supporting UOR electrocatalyst. The secondary elements (Fe and Co) were found to accelerate the formation of NiOOH (the active site for UOR), by partial charge transfer among the mixed metals. On the other hand, oxalic acid treatment of NFF generated prismatic NiFe-oxalate (O-NFF) which marked surprisingly small overpotential and Tafel slope for UOR. The coexistence of Fe and oxalate ligand simultaneously shift the surface electronic structure which in-turn affected the adsorption of reactants and desorption of products. The UOR on the engineed electrocatalysts could be further utilized for urea electrolysis (for molecular hydrogen production) or urea fuel cell.

High-pressure synthesis and storage of solid organic compounds in active subduction zones.

Recent thermodynamic and experimental studies have suggested that volatile organic compounds (e.g., methane, formate, and acetate) can be produced and stabilized in subduction zones, potentially playing an important role in the deep carbon cycle. However, field evidence for the high-pressure production and storage of solid organic compounds is missing. Here, we examine forearc serpentinite clasts recovered by drilling mud volcanoes above the Mariana subduction zone. Notable correlations between carbon and iron stable-isotope signatures and fluid-mobile element (B, As and Sb) concentrations provide evidence for the percolation of slab-derived CO2-rich aqueous fluids through the forearc mantle. The presence of carbonaceous matter rich in aliphatic moieties within high-temperature clasts (>350°C) demonstrates that molecular hydrogen production associated with forearc serpentinization is an efficient mechanism for the reduction and conversion of slab-derived CO2-rich fluids into solid organic compounds. These findings emphasize the need to consider the forearc mantle as an important reservoir of organic carbon on Earth.

Influence of plutonium oxidation state on the formation of molecular hydrogen, nitrous acid and nitrous oxide from alpha radiolysis of nitric acid solution

Abstract The study of the formation of radiolytic products, such as molecular hydrogen and nitrous acid, is of primary importance in the reprocessing of spent nuclear fuel and the storage of aqueous solutions containing radioactive materials. The radiolytic yields of molecular hydrogen, nitrous acid and nitrous oxide from alpha radiolysis of nitric acid solutions containing plutonium have been experimentally investigated. The results have shown that the yields of radiolytic products depends on the nitric acid concentration as well as the oxidation state of plutonium. However, the influence of plutonium oxidation state on radiolytic yields is less notable as the nitric acid concentration increases. Molecular hydrogen production decreases with increasing nitric acid concentration while nitrous acid and nitrous oxide productions increase. While radiolytic yields from plutonium(IV) nitric acid solutions have been previously investigated, this study provides radiolytic yields from alpha radiolysis of plutonium(III) and plutonium(VI) nitric acid solutions for molecular hydrogen, nitrous acid and nitrous oxide. These information provide insight into the role played by plutonium redox behaviour on the formation of radiolytic products.