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YMgNi4-based alloys exhibit reversible hydrogen absorption and desorption reactions at near room temperature. Here, we report that Co-substituted YMgNi4-based alloys exhibited higher hydrogen contents and lower hydrogen absorption and desorption reaction pressures than unsubstituted alloys. The effects of Co-substitution viewed from atomic arrangements were particularly clarified by synchrotron radiation powder X-ray diffraction, neutron diffraction, and inelastic neutron scattering. Powder neutron diffraction of the Co-substituted alloy at 5 MPa of D-2 pressure suggested the formation of gamma-phase deuteride (higher deuterium content) from beta-phase deuteride (lower deuterium content). However, no gamma-phase deuteride was observed in the unsubstituted alloys at 5 MPa. Therefore, the gamma-phase deuteride formation of the Co-substituted alloy at lower pressure led to higher hydrogen contents than the unsubstituted alloys. The combined results of powder neutron diffraction and inelastic neutron scattering suggested that the gamma-phase hydride of the Co-substituted alloy was continuously generated due to additional H atoms at the H atom sites in the beta-phase hydride because of the disordered H atomic arrangement involving H-H interactions. As a result, hydrogen absorption and desorption reaction pressures for the gamma-phase deuteride formation with higher hydrogen storage capacity were lowered.

The atomically dispersed transition metal with nitrogen-doped carbon (M-N-C) has been studied as a possible replacement for platinum group metal (PGM) catalysts in fuel cell electrodes. In this work, the Fe-N-C and Co-N-C are used as a hydrogen peroxide reduction reaction (PRR) catalysts in direct borohydride fuel cells (DBFCs). Using half-cell and membrane electrode assembly (MEA) configurations, the PRR activity and durability of M-N-C are assessed. The Fe-N-C has higher activity on PRR than Co-N-C. Co-N-C is more stable than Fe-N-C under DBFC cathode, where hydrogen peroxide and sulfuric acid electrolyte are used as fuel. In the DBFC durability test, Fe-N-C demonstrates a performance loss of 18.6% following an accelerated durability test, whereas Co-N-C shows a more stable performance with a performance loss of only 6.7%. To examine the degradation mechanism of M-N-C, post-mortem XPS and Raman spectroscopy measurements are conducted. In addition, the density functional theory (DFT) simulation supports the Co-N-C stability on the catholyte. The usage of PGM catalysts is all replaced to transition metal catalysts in liquid fuel-operated DBFC systems.

Catalytic reduction of CO2 to valuable products is an attractive route for CO2 recycling. CeO2-supported Cu catalysts have shown high activity and selectivity for the hydrogenation of CO2 to CO. To...

Nanoparticles (NPs) have wide applications in physical and chemical processes, and their individual properties (e.g., shape, size, and composition) and ensemble properties (e.g., distribution and homogeneity) can significantly affect the performance. However, the extrapolation of information from a single particle to the ensemble remains a challenge due to the lack of suitable techniques. Herein, we report a high-throughput single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS)-based protocol to simultaneously determine the size, count, and elemental makeup of several thousands of (an)isotropic NPs independent of composition, size, shape, and dispersing medium with atomistic precision in a matter of minutes. By introducing highly diluted nebulized aqueous dispersions of NPs directly into the plasma torch of an ICP-MS instrument, individual NPs are atomized and ionized, resulting in ion plumes that can be registered by the mass analyzer. Our proposed protocol includes a phase transfer step for NPs synthesized in organic media, which are otherwise incompatible with ICP-MS instruments, and a modeling tool that extends the measurement of particle morphologies beyond spherical to include cubes, truncated octahedra, and tetrahedra, exemplified by anisotropic Cu NPs. Finally, we demonstrate the versatility of our method by studying the doping of bulk-dilute (

We demonstrate the ability of tetraalkylammonium borohydrides to capture large amounts of CO2 , even at low CO2 concentrations, and reduce it to formate under ambient conditions. These materials show CO2 absorption capacities up to 30 mmol CO 2 g-1 at room temperature and 1 bar CO2 . Every BH4 - anion can react with three CO2 molecules to form triformatoborohydride ([HB(OCHO)3 ]- ). The thermodynamics and kinetics of the reaction were monitored by a magnetic suspension balance (MSB). Direct CO2 capture and reduction from air was achieved with tetraethyl, -propyl, and -butylammonium borohydride. The alkyl chain length played an important role in the kinetics and thermodynamics of the reaction, especially in CO2 diffusivity (crystallinity and free-volume), activation energy (charge-transfer dependent on the alkyl chain), and hydrophobicity. Adding HCl gave formic acid and the corresponding chloride ammonium salt, which can be recycled. In addition, transfer of formate was achieved for the N-formylation of an amine.

Indium-based catalysts exhibit excellent performance for CO2 hydrogenation to methanol, yet their nature and chemical evolution under reaction conditions are still elusive, thus hindering an understanding of their reaction mechanism. In this work, near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is employed to investigate the chemical properties and the catalytic role of indium/copper model catalysts under CO2 hydrogenation conditions. We found that the deposition of In on the surface of a Cu foil led to the formation of Cu-In alloy, whereas upon CO2 exposure, In was partially oxidized to In2O3-x and Cu remains metallic. Due to the presence of In2O3-x, CO2 was activated on the surface of In/Cu samples mainly in the form of carbonate. In addition, compared with the pure In foil reference, both the fraction of oxygen vacancies and the coverage density of carbonate were higher on the In/Cu samples, indicating the promotion effect of Cu-In alloy in the activation of CO2. These results reveal the evolution of the active sites of indium/copper catalysts and inspire the design of advanced In-based bimetallic catalysts for CO2 hydrogenation.

The relation between catalytic reactivities and metal/metal oxide ratios, as well as the functions of the metal and the metal oxides were investigated in the CO2 hydrogenation reaction over highly active Cox(CoO)1–x catalysts in operando. The catalytic reactivity of the samples in the CO2 methanation improves with the increased CoO concentration. Strikingly, the sample with the highest concentration of CoO, i.e., Co0.2(CoO)0.8, shows activity at temperatures lower than 200 °C where the other samples with less CoO are inactive. The origins of this improvement are the increased amount and moderate binding of adsorbed CO2 on CoO sites. The derivative adsorption species are found to be intermediates of the CH4 formation. The metallic Co functions as the electronically catalytic site which provides electrons for the hydrogenation steps. As a result, an abundant amount of CoO combined with Co is the optimal composition of the catalyst for achieving the highest reactivity for CO2 hydrogenation.

The hydrogen storage properties and crystal structures of YMgNi4-based alloys, which were synthesized from (2 - x)YNi2 and xMgNi(2) (0.6

Metallic electrodes based on iron, nickel, and/or cobalt have re-emerged as promising cost-effective anodes for the alkaline oxygen evolution reaction (OER) due to their simplicity and their in sit...

Supported aluminum-based complex hydrides (alanates) were investigated in view of their interaction at the interface. Nickel-containing porous carbon sheets (Ni-PCSs) were combined with various ala...

The metal- and solvent-free capture and reduction of large amounts of CO2 to formate under ambient conditions is achieved by combining a pyrrolidinium-based ionic liquid with a borohydride anion. This material demonstrates one of the highest CO2 capacities at room temperature and 1 bar with up to 1 g CO 2 g-1 IL . CO2 gas reacts with the BH4 - anion to give triformatoborohydride, [HB(OCHO)3 ]- . The reaction occurs without loss in capacity at low CO2 concentration (6 vol % diluted with N2 ). The thermodynamics and kinetics of the reaction were monitored by using a magnetic suspended balance. In addition, more than 1 mol CO 2 mol-1 [ EMPY ] [ BH 4 ] is captured and reduced if air is used as a CO2 source. The product can be then treated with HCl to give formic acid and the corresponding ionic liquid chloride, which can be recycled. This ionic liquid borohydride demonstrates great potential as a CO2 absorber and reducer to produce alternative fuels.

The differences between Ru- and Ni-based catalysts for the Sabatier reactor are assessed on the basis of appropriate kinetic models and reactor designs. The origin of the higher performance of the Ru-based catalyst is analysed in detail. Ru activates the reactor and initiates the thermal runaway at about 100 °C lower than commercial Ni/Mg/Al2O3 catalysts and 10–20 °C lower than Ni/Al2O3 catalysts. In addition, the higher catalytic activity at low temperature of Ru-based catalysts allows the thermodynamic curve to be followed-up to the region of high CO2 conversion. Over steam reforming Ni catalysts, the highest attainable conversion is instead limited to 90%, while tailored Ni catalysts for CO2 methanation can reach 96% conversion in a single pass reactor. In the intermediate conversion areas, the two catalysts show comparable activity, due to the reaction limitations related to the required cooling and to the diffusional limitations that are more pronounced in the highly active Ru. We developed a reactor design routine to define the amount of catalyst required to reach grid-compatible CO2 conversion, and found that 99.5% conversion is attainable in a single step with a 0.5% Ru/Al2O3 catalyst or with a high load of Ni/Al2O3 by introducing an intermediate water condensation step. As a consequence, we calculated that the cost of the catalyst is approximately two to three times higher for the Ru-based reactor than the Ni-based. However, this difference in catalyst cost cannot compensate for the cost of a more complex system, including several different units, when developing energy storage solutions at a small-scale. For this reason, the Ru-based system is, at the current price and technological state, the most economical solution for small-scale applications, while efficient Ni-based catalysts can be the ideal choice for large scale applications.

The synthesis of fuels from CO2 has made tremendous progress in recent years, although practical applications remain limited. Herein, we describe a cyclic process that produces MeOH from CO2via formamide intermediates, which are initially reduced using NaBH4 to form methanol and concomitantly release the corresponding amine, from which the formamide is subsequently regenerated in the presence of CO2/NaBH4. By tuning the substituents on the formamide/amine, the selectivity of both steps can be controlled, allowing the process to proceed in high yields, either in two separate steps or in a single step process. The observed trends in reactivity were rationalized with a resonance model of the formamide, which supports the observed trends in reactivity, and further consolidated by spectroscopy and calculations. Fil: Uranga, Jorge Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. École Polytechnique Fédérale de Lausanne; Suiza Fil: Gopakumar, Aswin. École Polytechnique Fédérale de Lausanne; Suiza Fil: Pfister, Tim. École Polytechnique Fédérale de Lausanne; Suiza Fil: Imanzade, Gunay. École Polytechnique Fédérale de Lausanne; Suiza Fil: Lombardo, Loris. École Polytechnique Fédérale de Lausanne; Suiza Fil: Gastelu, Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Züttel, Andreas. École Polytechnique Fédérale de Lausanne; Suiza Fil: Dyson, Paul. École Polytechnique Fédérale de Lausanne; Suiza

Ni0.5 Ti2 (PO4 )3 /C NASICON-type phosphate is introduced as a new anode material for lithium-ion batteries (LIBs). Ni0.5 Ti2 (PO4 )3 /C was synthesized through the sol-gel route and delivered some remarkable electrochemical performances. Specifically, the Ni0.5 Ti2 (PO4 )3 /C electrode demonstrates a high rate capability performance and delivers high reversible capacities ranging from 130 mAh g-1 to about 111 mAh g-1 at current rates ranging from 0.1 C to 5 C in the voltage window of 1.85-3 V (vs. Li+ /Li). In the same voltage range, the material reaches an initial capacity of 105 mAh g-1 with a capacity retention of about 82 % after 1000 cycles at the high current rate of 10 C. The electrodes are also tested in the wider voltage range of 0.5-3 V (vs. Li+ /Li) and show good reversibility and rate capability performance. Moreover, the Ni0.5 Ti2 (PO4 )3 /C electrodes enable fast Li+ diffusion (in the order of 10-13 cm2 s-1 ) compared with other NASICON-type materials. As a result, a first discharge capacity of 480 mAh g-1 is reached.

Platinum (Pt) alloy catalysts on nitrogen doped carbon black was prepared and applied to a proton exchange membrane fuel cell, and the effects of nitrogen doping on the electrochemical properties were investigated. Pt was alloyed with 3d transition metals (Fe, Ni and Pd) in 3:1 atomic ratio and deposited onto nitrogen-doped carbon black (NCB). Alloying 3d transition metal causes an electron transfer from the Pt atom to the alloying element, depending on the work function and electronegativity of the element. The cell performances of Pt 3Fe1 before and after N doping are almost the same due to the facilitation of electron transfer from Fe to Pt. It is attributed to the smallest work function of Fe, increasing the number of electron in the Pt 5d orbital. However, N doping for Pt–Pd and Pt–Ni alloys increases the total number of electrons per Pt atom, enhancing the oxygen reduction reaction (ORR) and the dispersion of Pt nanoparticles. The rotating disk electrode clearly shows an increase of onset potential upon nitrogen doping, suggesting the enhancement of the ORR. The accelerated durability test demonstrates the enhancement in durability and less agglomeration after 1200 cycles of operation upon nitrogen doping.

The CO2 hydrogenation reaction was experimentally investigated over pristine Co, Ni and an Al2O3-supported Ru catalyst with 0.5 wt% Ru loading. We developed a reaction model which takes the kinetical, diffusional -and thermodynamic reaction regimes into account and enables the description of the reaction over a broad temperature range. The model is based on a fractional rate law with experimentally determined reaction orders. We found that the overall reaction orders on the different catalysts are in proximity to zero order (0.13 for Co, 0.14 for Ni and 0.38 for Ru/Al2O3), which leads to the interpretation that the reaction is limited by the available surface sites in the underlying reaction conditions. We demonstrate on the example of Ru/Al2O3 that the reaction rate strongly depends on the partial pressure of CO2 in the gas phase. Upon reducing the partial pressure of CO2 in the reaction gas stream via He dilution, the reaction approaches a higher reaction order. Furthermore, the supported Ru catalyst is less limited by pore-diffusion compared to pristine Co. With the derived model we can accurately calculate the CO2 conversion over a broad temperature range; the temperature of maximum conversion is predicted within 15 K and the deviation between simulation and experiment is mostly less than 20%. This enables the simple and rapid prediction of the influence of different reaction parameters such as the activation energy or the diffusional limitations on the CO2 conversion.

This study analyses the power to methane - and to methanol processes in the view of their efficiency in energy storage. A systematic investigation of the differences on the two production systems is performed. The energy storage potential of CO2 to methanol and methane is assessed in a progressive way, from the ideal case to the actual simulated process. In ideal conditions, where no additional energy is required for the reaction and CO2 is fully converted into products, energy storage is 8% more efficient in methanol than methane. However, the Sabatier reaction can be performed with a lower degree of complexity compared to the CO2 to methanol reaction. For this reason, the methanol production process is analysed in detail. The influence of the process configuration and the energy requirements for the various necessary unit operations is investigated, and an efficiency ranking among the various alternatives is obtained. Single stage, recycle and cascade reactors are compared and assessed in terms of energy requirements for the operation and energy storage in the product. For small scale applications, the cascade reactor is the most suitable process technology, because it does not require additional energy and allows high yield to methanol. With the current technology, we demonstrate that a hybrid process, including both the CO2 hydrogenation to methanol and methane, is the most effective method to achieve a high conversion of renewable energy to carbon-based fuels with a significant fraction of liquid product.

Stability of borohydrides is determined by the localization of the negative charge on the boron atom. Ionic liquids (ILs) allow to modify the stability of the borohydrides and promote new dehydrogenation pathways with a lower activation energy. The combination of borohydride and IL is very easy to realize and no expensive rare earth metals are required. The composite of the ILs with complex hydrides decreases the enthalpy and activation energy for the hydrogen desorption. The Coulomb interaction between borohydride and IL leads to a destabilization of the materials with a significantly lower enthalpy for hydrogen desorption. Here, we report a simple ion exchange reaction using various ILs, such as vinylbenzyltrimethylammonium chloride ([VBTMA][Cl]), 1-butyl-3-methylimidazolium chloride ([bmim][Cl]), and 1-ethyl-1-methylpyrrolidinium bromide ([EMPY][Br]) with NaBH4 to decrease the hydrogen desorption temperature. Dehydrogenation of 1-butyl-3-methylimidazolium borohydride ([bmim][BH4]) starts below 100 °C. The quantity of desorbed hydrogen ranges between 2.4 wt% and 2.9 wt%, which is close to the theoretical content of hydrogen. The improvement in dehydrogenation is due to the strong amine cation that destabilizes borohydride by charge transfer.

This work presents an in-depth investigation of different techniques used to accurately determine pressure-composition isotherms (pcI) as well as thermodynamic and kinetic parameters of metal hydrides. A case study is presented for an alloy of the type LaNi5. The results combine experimental measurements with theoretical modeling. Firstly, the numerical work presented discusses a numerical method for the evaluation of pcI raw data in order to minimize the experimental error. A simple, efficient iterative algorithm is presented to solve for the van der Waals equation of state in order to take into account the compressibility of hydrogen. Secondly, the measurements of dynamic (mass-flow) and quasi-static (Sievert's type) isotherms at different temperatures and different flow rates are presented. The dead volume of the apparatus as well as its experimental error, which is key parameter for the accurate calculation of hydrogen capacity, are also measured. Finally, important thermodynamic and kinetic parameters are deduced from the pcI curves. The kinetics of the absorption and desorption reactions are modelled and the reaction rate constants are found using both dynamic and quasi-static methods. The presented work goes beyond the calculation of the entropy and enthalpy of reaction, as the lattice gas model is also used to determine the critical temperature as well as the interaction energy between hydrogen-metal atoms and hydrogen-hydrogen atoms.

Earth-abundant electrocatalysts are desirable for the efficient and selective reduction of CO2 to value-added chemicals. Here, a low-cost porous Zn electrocatalyst is synthesized using a facile electrodeposition method to boost the performance of CO2 electrocatalytic reaction (CO2RR). In an H-cell reactor, the porous Zn catalyst can convert CO2 to CO at a remarkably high faradaic efficiency (FE, ∼95%) and current density (27 mA cm–2) at −0.95 V versus the reversible hydrogen electrode. Detailed electrokinetic studies demonstrate that instead of the enhanced intrinsic activity, the dramatically increased active sites play a decisive role in improving the catalytic activity. In addition, the high local pH induced by the highly porous structure of Zn results in enhanced CO selectivity because of the suppressed H2 evolution. Furthermore, we present a straightforward strategy to transform the porous Zn electrode into a gas diffusion electrode. This way, the CO2RR current density can be boosted to 200 mA cm–2 w...

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) investigations of molecules at the surface of catalysts exhibit a strong overlap of the adsorption peaks. Therefore, the investi...

LaNi5-type alloys are commercial materials for the negative electrode in Ni-MH rechargeable batteries. Partial substitution of La by mischmetal (Mm) and of Ni by elements like Co, Al, and Mn significantly improve the cycle stability and high-rate discharge capacity of the electrodes. The partial substitution of Ni by Cu was studied previously for several selected ternary alloys with a special focus on crystal structure change upon substitution and gas phase hydrogen absorption. We present in this paper the results of the study of the electrochemical activation, discharge kinetics, equilibrium charge/discharge, and cycle life of electrodes made from four different LaNi5-xCux (x = 0.1, 0.5, 0.9, 1) alloys in order to provide full insights into utilization of these alloys.

The electrochemical reduction of CO2 to higher hydrocarbons is a very challenging process that has high potential for the storage of large amounts of renewable energy with a high gravimetric and volumetric energy density. The distribution of hydrocarbons from the electrocatalytic reduction of CO2 is primarily determined by the interaction of the cathode material with the CO2 in the electrolyte. While the research on the electrochemical CO2 reduction focuses on the cathode metal and surface structure of the metals, recently evidence was found that the metal itself may not be the active species but rather the product formed from the metal and CO2. In this paper, we report about the synthesis, catalytic activity and selectivity of nanostructured metal carbonate, i.e. malachite, as a highly active catalyst for the electrochemical synthesis of C2 hydrocarbons. These first results obtained on Cu2(OH)2CO3 nanorod-structured “trees” show that carbonate, not the pure metal, is the active catalytic species. This new catalyst favors the production of ethylene (C2H4) and ethane (C2H6) with significantly higher Faradaic efficiency than that of the pure Cu surface.

Nanostructured copper materials are catalytically active for the electrochemical reduction of CO2 (CO2RR) to produce hydrocarbons. However, most of these catalysts were investigated in conventional batch reactors at low current densities ( 40%) for converting CO2 to multi-carbon products, e.g. C2H4 and ethanol, at commercially relevant current densities (>100 mA cm−2) and low overpotentials (η < 0.65 V). The GDEs are stable for more than 6 hours at current densities higher than 100 mA cm−2. Moreover, the nondestructive method allows us to directly compare the product distributions of the nanostructured Cu catalysts in a batch reactor and flow reactor and to demonstrate the influence of the reaction environment and mass transport on the CO2RR. While the CO2RR in the H-cell shows high selectivity towards CO and formate, the reaction in the flow cell produces a greater amount of multi-carbon products due to the fast CO2 diffusion and high pH. Combined, the electrode design strategies and the experimental findings presented in this work are valuable for the development of other self-supported electrodes for practical applications.

The methanation of carbon dioxide is an option for chemical storage of renewable energy together with greenhouse gas reutilization because it offers a product with a high energy density. The reaction CO2 + 4H2 ↔ CH4 + 2H2O is performed on a Ru/Al2O3 catalyst and is strongly exothermal. For this reason, the reactor design must take into account an efficient thermal management system to limit the maximal temperature and guarantee high CO2 conversion. Additionally, the methanation reactor is subject to parameter sensitivity. This phenomenon can generate instability in the operation of a power to gas plant, due to the variability in the hydrogen production rate. Here we present a parametric study of the thermal properties of the reaction and determine the minimal feed temperature for the normal operation of a reactor. The minimal temperature required is determined by several parameters, such as pressure, space velocity and properties of the cooling system. For adiabatic reactors, the required feed temperature is 210 °C for a space velocity of 3000 h−1 and a pressure of 10 bar. The space velocity strongly affects the positioning of the ignition point, causing a large variability of the feed temperature required. At the same time, the optimal working point of the reactor is at the minimal activation temperature. The properties of cooled reactors are elucidated, showing how the interrelationship between cooling and feed temperature makes the management of this class of reactors more challenging. On the base of the modelling results, we propose a reactor configuration that adjusts the thermodynamic limitations and respects the minimal requirements for reaction ignition, allowing a more stable operation and avoiding the functioning at excessive temperature.

The electrochemical reduction of CO2 requires highly active, selective as well as stable electrocatalysts. Herein, we report a three-dimensional hierarchical porous indium catalyst for the electroreduction of CO2 to formate. In aqueous bicarbonate solution, the catalyst exhibits a high faradaic efficiency for formate (∼90%) in the potential range of −1.0 to −1.2 V (vs. reversible hydrogen electrode) and reaches an unprecedented formate production rate of 1.14 mmol cm−2 h−1 at −1.2 V. Additionally, the catalyst also displays a long-term stability (24 h). Density functional theory calculations reveal the catalytically selective nature of In for formate production. Independent of the crystal facet, In surfaces stabilise *OCHO, a key intermediate for the formate pathway, much more effectively than the *H (for the H2 pathway) and *COOH (for the CO pathway) intermediates. Experimental results demonstrate that the improved CO2 reduction selectivity on the porous In catalyst originates from the reduced evolution of H2, which is induced by the high local pH in the vicinity of the electrode. Furthermore, the porous In can also serve as a template to synthesise a porous Pd–In catalyst for tuning the selectivity of formate and CO, demonstrating its promising potential for CO2 electroreduction.