Search

Corrosion of carbon-based electrodes and bipolar plates is a major hurdle and can be a cause of failure in commercial vanadium redox flow batteries (VRFBs). Carbon corrosion was found to occur in a commercial VRFB (10 kW/40 kWh), whereby cracks through bipolar plates enabled the electrolyte to leach the copper current collectors at the end of the stacks, contaminating the entire electrolyte solution. In this work, the effects of copper contaminants on the operation of a VRFB were studied. A simple and effective procedure to identify copper contamination on-site and to purify the electrolyte was developed. The process was used to purify large quantities (6000 L) of copper-contaminated electrolytes to levels below 1 ppm.

In this work, the viability of polyaniline as a solid charge storage material in an aqueous redox-mediated flow battery is investigated. Fe(III/II) and V(IV/III) were identified as potential redox mediators to target the emeraldine-pernigraniline and leucoemeraldine-emeraldine redox transitions of the polymer. An indirect chemical cycling method was developed and used to investigate the charging/discharging of the polymer by the selected redox mediators. With Fe(III/II) as a redox mediator, respectable specific capacity and cycling stability were demonstrated over 25 cycles. V(IV/III) was deemed unsuitable as a redox mediator, due to rather poor kinetics. When added to the electrolyte tanks of a complete flow battery, a conductive composite of polyaniline and carbon black provided a significant improvement in capacity, exhibiting a specific capacity of 64.8 mA h g−1 at a current density of 38.5 mA cm−2. This represents a three-fold improvement in volumetric capacity, compared with the electrolyte alone. Moreover, the addition of the polyaniline composite was observed to lower the average potential at the positive electrode, providing a considerable improvement in voltage efficiency. This work demonstrates the potential of utilizing redox mediators to enable bulk solid-phase charge storage in the tanks of aqueous redox flow batteries

peer-reviewed The concept of efficient electrolysis by linking photoelectrochemical biphasic H2 evolution and water oxidation processes in the cathodic and anodic compartments of an H-cell, respectively, is introduced. Overpotentials at the cathode and anode are minimised by incorporating light-driven elements into both biphasic reactions. The concepts viability is demonstrated by electrochemical H2 production from water splitting utilising a polarised water-organic interface in the cathodic compartment of a prototype H-cell. At the cathode the reduction of decamethylferrocenium cations ([Cp2*Fe(III)]+) to neutral decamethylferrocene (Cp2*Fe(II)) in 1,2-dichloroethane (DCE) solvent takes place at the solid electrode/oil interface. This electron transfer process induces the ion transfer of a proton across the immiscible water/oil interface to maintain electroneutrality in the oil phase. The oil-solubilised proton immediately reacts with Cp2*Fe(II) to form the corresponding hydride species, [Cp2*Fe(IV)(H)]+. Subsequently, [Cp2*Fe(IV)(H)]+ spontaneously undergoes a chemical reaction in the oil phase to evolve hydrogen gas (H2) and regenerate [Cp2*Fe(III)]+, whereupon this catalytic Electrochemical, Chemical, Chemical (ECC’) cycle is repeated. During biphasic electrolysis, the stability and recyclability of the [Cp2*Fe(III)]+/Cp2*Fe(II) redox couple were confirmed by chronoamperometric measurements and, furthermore, the steady-state concentration of [Cp2*Fe(III)]+ monitored in situ by UV/vis spectroscopy. Post-biphasic electrolysis, the presence of H2 in the headspace of the cathodic compartment was established by sampling with gas chromatography. The rate of the biphasic hydrogen evolution reaction (HER) was enhanced by redox catalysis in the presence of floating catalytic molybdenum carbide (Mo2C) microparticles at the immiscible water/oil interface. The use of a superhydrophobic organic electrolyte salt was critical to ensure proton transfer from water to oil, and not anion transfer from oil to water, in order to maintain electroneutrality after electron transfer. The design, testing and successful optimisation of the operation of the biphasic electrolysis cell under dark conditions with Cp2*Fe(II) lays the foundation for the achievement of photo-induced biphasic water electrolysis at low overpotentials using another metallocene, decamethylrutheneocene (Cp2*Ru(II)). Critically, Cp2*Ru(II) may be recycled at a potential more positive than that of proton reduction in DCE.

peer-reviewed Detailed studies on hydrogen evolution by decamethylruthenocene ([Cp*2RuII]) highlighted that metallocenes are capable of photoreducing hydrogen without the need for an additional sensitizer. Electrochemical, gas chromatographic, and spectroscopic (UV/Vis, 1H and 13C NMR) measurements corroborated by DFT calculations indicated that the production of hydrogen occurs by a two‐step process. First, decamethylruthenocene hydride [Cp*2RuIV(H)]+ is formed in the presence of an organic acid. Subsequently, [Cp*2RuIV(H)]+ is reversibly reduced in a heterolytic reaction with one‐photon excitation leading to a first release of hydrogen. Thereafter, the resultant decamethylruthenocenium ion [Cp*2RuIII]+ is further reduced with a second release of hydrogen by deprotonation of a methyl group of [Cp*2RuIII]+. Experimental and computational data show spontaneous conversion of [Cp*2RuII] to [Cp*2RuIV(H)]+ in the presence of protons. Calculations highlight that the first reduction is endergonic (ΔG0=108 kJ mol−1) and needs an input of energy by light for the reaction to occur. The hydricity of the methyl protons of [Cp*2RuII] was also considered. ACCEPTED peer-reviewed

Multi-stall fast charging stations are often thought to require megawatt-range grid connections. The power consumption profile of such stations results in high cost penalties due to monthly power peaks and expensive linkage fees. A local energy storage system (ESS) can be used to address peak power demands. However, no appropriate sizing method is available to match specific constraints, such as the contracted power available from the grid and the projected recharging demand. A stochastic distribution of charging events was used in this paper to model power demand profiles at the station, with a one minute resolution. Based on 100 simulated months, we propose an optimum number of charging points, and we developed an algorithm to return the required local ESS capacity as a function of the available grid connection. The role of ESSs in the range of 100 kWh to 1 MWh was studied for all stations with up to 2000 charging events per week. The relevance of ESS implementation was assessed along three parameters: the number of charging points, the available grid connection, and the ESS capacity. This work opens new possibilities for multi-stall charging station deployment in locations with limited access to the medium voltage grid, and provides sizing guidelines for effective ESSs implementation. In addition, it helps build business cases for charging station operators in regions with high demand charges.

An all-vanadium dual circuit redox flow battery is an electrochemical energy storage system capable to function as a conventional battery, but also to produce hydrogen and perform desulfurization when surplus of electricity is available by chemical discharge of the battery electrolytes. The hydrogen reactor chemically discharging the negative electrolyte has been designed and scaled up to kW scale, while different options to discharge the positive electrolyte have been evaluated, including oxidation of hydrazine, SO2 and H2S. The system is well suited to convert sulfur dioxide and hydrogen sulfide to harmless compounds while producing hydrogen, with overall system efficiencies from 50 to 70 % for hydrogen production.

Corrosion of carbon-based electrodes and bipolar plates is a major challenge and a common cause of failure in commercial vanadium redox flow batteries (VRFB). Herein, we describe a typical carbon corrosion that occurred on several stacks of a 10kW/40kWh and a 200kW/400kWh commercial vanadium redox flow batteries (VRFB) installed in the framework of a demonstrator. Cracks through graphite bipolar plates enabled the electrolyte to leach the copper current collectors and contaminated the entire electrolyte solution with copper. In this work, we first highlighted the deleterious effects of copper contaminants on the operation of a VRFB. It was observed that metallic copper enhanced the parasitic hydrogen evolution reaction (HER) on the negative side and accelerated the oxidation state imbalance between the two redox electrolytes. To tackle the problems related to copper pollution, a simple, eco-friendly and cost-effective procedure to identify copper contamination on-site and to purify the electrolyte was developed. A classical VRFB stack was used to plate out the copper ions contaminants. The optimal cathode potential for copper deposition onto carbon felt electrode was determined to be −100 mV vs. SHE. The process described was successfully used to purify on-site 6000 L of vanadium electrolyte (V+3/V+4 mixture) to levels below 1 ppm. At the end of the purification, the stack was regenerated by flashing 20-30 L of electrolyte that represents only a fraction of what would have been necessary to dispose the contaminated electrolyte. This work has been accepted as a full paper in ChemSusChem. [1] [1] D. Reynard, H. Vrubel, C. R. Dennison, A. Battistel, H. Girault, ChemSusChem 2019, 12, 1222. Figure 2 A. Schematic illustration of the purification process developed to remove copper contaminants from the vanadium electrolytes B. SEM images of fresh carbon felt (a), carbon felt sample close to the inlet (b) and the outlet of the single-cell (c), and carbon felt sample after re-generation (d) C. Evolution of copper concentration (ICP-MS) at the negative-side outlet and the container electrolyte with time of purification Figure 1

Earth-abundant hydrogen evolution catalysts are essential for high-efficiency solar-driven water splitting. Although a significant amount of studies have been dedicated to the development of new catalytic materials, the microscopic assembly of these materials has not been widely investigated. Here, we describe an approach to control the three-dimensional (3D) assembly of amorphous molybdenum sulfide using polymer brushes as a template. To this end, poly(dimethylaminoethyl methacrylate) brushes were grown from highly oriented pyrolytic graphite. These cationic polymer films bind anionic MoS42– through an anion-exchange reaction. In a final oxidation step, the polymer-bound MoS42– is converted into the amorphous MoSx catalyst. The flexibility of the assembly design allowed systematic optimization of the 3D catalyst. The best system exhibited turnover frequencies up to 1.3 and 4.9 s–1 at overpotentials of 200 and 250 mV, respectively. This turnover frequency stands out among various molybdenum sulfide catalysts. The work demonstrates a novel strategy to control the assembly of hydrogen evolution reaction catalysts.

Photoionic cells are a simple and scalable concept for direct solar energy storage, where the redox fuels produced by the photoreaction are separated in different phases to prevent recombination. The presence of chaotropic agents such as urea, that break the structure of water, was found to drastically enhance the quantum yield; a 10-fold increase of quantum yield to over 13% was achieved by addition of chaotropes into a system based on the reductive quenching of Azure B by Co(II)EDTA in water and the extraction of the leuco dye in 1,2-dichloroethane.

Water oxidation catalysed by iridium oxide nanoparticles (IrO2 NPs) in water–acetonitrile mixtures using [RuIII(bpy)3]3+ as oxidant was studied as a function of the water content, the acidity of the reaction media and the catalyst concentration. It was observed that under acidic conditions (HClO4) and at high water contents (80% (v/v)) the reaction is slow, but its rate increases as the water content decreases, reaching a maximum at approximately equimolar proportions (≈25% H2O (v/v)). The results can be rationalized based on the structure of water in water–acetonitrile mixtures. At high water fractions, water is present in highly hydrogen-bonded arrangements and is less reactive. As the water content decreases, water clustering gives rise to the formation of water-rich micro-domains, and the number of bonded water molecules decreases monotonically. The results presented herein indicate that non-bonded water present in the water micro-domains is considerably more reactive towards oxygen production. Finally, long term electrolysis of water–acetonitrile mixtures containing [RuII(bpy)3]2+ and IrO2 NPs in solution show that the amount of oxygen produced is constant with time demonstrating that the redox mediator is stable under these experimental conditions.

The reduction of protons into dihydrogen is important because of its potential use in a wide range of energy applications. The preparation of efficient and cheap catalysts for this reaction is one of the issues that need to be tackled to allow the widespread use of hydrogen as an energy carrier. In this paper, we report the study of an amorphous molybdenum sulfide (MoSx) proton reducing electrocatalyst under functional conditions, using in situ X-ray absorption spectroscopy. We probed the local and electronic structures of both the molybdenum and sulfur elements for the as prepared material as well as the precatalytic and catalytic states. The as prepared material is very similar to MoS3 and remains unmodified under functional conditions (pH = 2 aqueous HNO3) in the precatalytic state (+0.3 V vs RHE). In its catalytic state (−0.3 V vs RHE), the film is reduced to an amorphous form of MoS2 and shows spectroscopic features that indicate the presence of terminal disulfide units. These units are formed concomitantly with the release of hydrogen, and we suggest that the rate-limiting step of the HER is the reduction and protonation of these disulfide units. These results show the implication of terminal disulfide chemical motifs into HER driven by transition-metal sulfides and provide insight into their reaction mechanism.

A solar energy conversion concept based on the photoinduced separation of a pair of redox species in a biphasic liquid cell is presented. The redox pair is subsequently discharged in an electrochemical flow cell to generate electricity. To illustrate this generic concept, we have revisited the thionine/cobalt EDTA system where, upon light excitation, the excited thionine dye is quenched in the aqueous solution by the (Co(II)EDTA) 2� complex to form both (Co(III)EDTA) � and reduced thionine, namely leucothionine, that partitions to the organic phase. As a result, solar energy is converted to a redox pair, leucothionine/(Co(III)EDTA) � . The two immiscible liquid phases are separated, and the redox energy is stored in the respective electrolyte solutions. These two solutions can then be electrochemically discharged in a flow cell to generate electricity on demand. The electrode reactions involved are the reoxidation of leucothionine to thionine in the organic solvent and the reduction of the Co(III) complex in water.

peer-reviewed Electrocatalysis of water oxidation was achieved using fluorinated tin oxide (FTO) electrodes modified with layer-by-layer deposited films consisting of bilayers of negatively charged citrate-stabilized IrO2 NPs and positively charged poly(diallyldimethylammonium chloride) (PDDA) polymer. The IrO2 NP surface coverage can be fine-tuned by controlling the number of bilayers. The IrO2 NP films were amorphous, with the NPs therein being well-dispersed and retaining their as-synthesized shape and sizes. UV/vis spectroscopic and spectro-electrochemical studies confirmed that the total surface coverage and electrochemically addressable surface coverage of IrO2 NPs increased linearly with the number of bilayers up to 10 bilayers. The voltammetry of the modified electrode was that of hydrous iridium oxide films (HIROFs) with an observed super-Nernstian pH response of the Ir(III)/Ir(IV) and Ir(IV)–Ir(IV)/Ir(IV)–Ir(V) redox transitions and Nernstian shift of the oxygen evolution onset potential. The overpotential of the oxygen evolution reaction (OER) was essentially pH independent, varying only from 0.22 V to 0.28 V (at a current density of 0.1 mA cm 2), moving from acidic to alkaline conditions. Bulk electrolysis experiments revealed that the IrO2/PDDA films were stable and adherent under acidic and neutral conditions but degraded in alkaline solutions. Oxygen was evolved with Faradaic efficiencies approaching 100% under acidic (pH 1) and neutral (pH 7) conditions, and 88% in alkaline solutions (pH 13). This layer-by-layer approach forms the basis of future large-scale OER electrode development using ink-jet printing technology. ACCEPTED peer-reviewed

The photochemical reactivity of osmocene in a biphasic water-organic solvent system has been investigated to probe its water splitting properties. The photoreduction of aqueous protons to hydrogen under anaerobic conditions induced by osmocene dissolved in 1,2-dichloroethane and the subsequent water splitting by the osmocenium metal-metal dimer formed during H 2 production were studied by electrochemical methods, UV-visible spectrometry, gas chromatography, and nuclear magnetic resonance spectroscopy. Density functional theory computations were used to validate the reaction pathways.

Molybdenum disulfide microparticles in suspension in an aqueous acidic solution adsorb at the interface with an organic electrolyte solution containing the reducing agent decamethylferrocene to catalyse hydrogen evolution. This catalytic process has been investigated by voltammetry at the water/12 dichloroethane interface and by biphasic reactions monitored by gas chromatography and UV visible spectroscopy. © 2011 The Royal Society of Chemistry.

A service station for electric vehicles (EVs) and fuel cell EVs (FCEVs) has been constructed based on a vanadium redox flow battery (200kW-400kWh). This battery is used to fast charge EVs using a DC-DC converter operating at 80kW. We also operate two electrolyzers (one alkaline 50kW, one PEM 25 kW) to produce hydrogen. This hydrogen is dried, purified and stored at 200 bars. A service station for hydrogen has been built with reservoirs at 500 bars to fill a car (Renault Kangoo/Swiss hydrogen) operating at 350 bars and at 900 bars to fill a car operating at 700 bars (Hyundai). We shall discuss the figures of merit of electric and hydrogen mobility and our experience to run a service station in the Alps. We shall also present a new technology to produce hydrogen on demand and under pressure directly from a Vanadium (III)/(II) solution from the redox flow battery using a Mo2C catalyst. We shall also discuss the use of solid boosters to enhance the storage in the tanks of a redox flow battery.

Solid catalysts were obtained by the formation of silica matrixes in the presence of oxomolybdenum(VI) complexes via the acid catalyzed hydrolytic sol–gel method using tetraethyl orthosilicate (TEOS). The obtained solids were tested as catalysts for the oxidation of cyclooctene and cyclohexene with t-butyl hydroperoxide. All performed reactions were selective for production of the corresponding epoxide, with formation of small traces of 2-cyclohexen-1-ol and 2-cyclohexen-1-one (

Blowing bubbles: Hydrogen evolution by proton reduction with [(C5Me5)2Fe] occurs at a soft interface between water and 1,2-dichloroethane (DCE). The reaction proceeds by proton transfer assisted by [(C5Me5)2Fe] across the water–DCE interface with subsequent proton reduction in DCE. The interface essentially acts as a proton pump, allowing hydrogen evolution by directly using the aqueous proton.

Blowing bubbles: Hydrogen evolution by proton reduction with [(C(5)Me(5))(2)Fe] occurs at a soft interface between water and 1,2-dichloroethane (DCE). The reaction proceeds by proton transfer assisted by [(C(5)Me(5))(2)Fe] across the water-DCE interface with subsequent proton reduction in DCE. The interface essentially acts as a proton pump, allowing hydrogen evolution by directly using the aqueous proton.

Sodium molybdate (Na2MoO4) has been synthesized and investigated as a heterogeneous catalyst for the methanolysis of different types of renewable lipid sources derived from the soybean oil. Transesterification reactions occurred under relatively mild conditions, requiring low temperatures, short times and normal pressure. The methyl esters synthesized were characterized by reverse-phase and size-exclusion chromatography and hydrogen-nuclear magnetic resonance spectroscopy. The catalyst was characterized by X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared spectroscopy (FTIR). It is very efficient for the transesterification reaction of triglycerides with methanol, with yields higher than 95% of methyl esters. The molybdenum(VI)-complex has a high Lewis acidity and most certainly act on alcohol O–H bond leading to a transient species which has high nucleophilic character. The catalyst was easily recovered and after being washed showed capacity of recyclability for another catalytic reaction with similar activity.

[MoO2(acac)2] (acac = acetylacetonate) promotes the disproportionation of hydrazine in THF solutions. The active catalytic species, [MoVIO2]2+, are produced according to the reaction: [MoO2(C5H7O2)2] + 2N2H4 → [MoO2]2+ + 2C5H8N2 + 2OH− + 2H2O. The main product of the reduction of hydrazine is ammonia while 3,5-dimethylpyrazole (C5H8N2) was isolated as a side-product. A catalytic cycle was proposed and the probable reaction intermediate is a hydrazido-complex, [MoIV NNH2(OH2)2]2+. The intermediate species, [MoVIO2NH3]2+ reacts with hydroxide ion leading to the complex cis-[MoVIO2(OH)2(NH3)], which was isolated and characterized.

The cluster compounds [FeIII3O(CH3CO2)6(H2O)3]CH3COO, [FeIII2FeIIO(CH3COO)6(H2O)3], [FeIII2CoIIO(CH3COO)6(H2O)3], [FeIII2NiIIO(CH3COO)6(H2O)3], [VIII2FeIIO(CH3COO)6(H2O)3] and [VIII2CoIIO(CH3COO)6(H2O)3 were prepared by new synthetic routes. Homometallic clusters can be isolated from a clean reaction between the metal hydroxide and acetic acid. The heterobimetallic compounds were obtained by the reaction of the iron(III) or vanadium(III)-homometallic cluster, in water, with an excess of iron(II), cobalt(II) and nickel(II) acetates. The new route give pure products with much higher yields when compared with the classical methods. The compounds were characterized by atomic absorption and elemental analysis, electrochemistry and IR spectroscopy.

Concerns over climate change resulting from accumulation of anthropogenic carbon dioxide in the atmosphere and the uncertainty in the amount of recoverable fossil fuel reserves are driving forces for the development of renewable, carbon-neutral energy technologies. A promising clean solution is photoelectrochemical water splitting to produce hydrogen using abundant solar energy. Here we present a simple and scalable technique for the deposition of amorphous molybdenum sulphide films as hydrogen evolution catalyst onto protected copper(I) oxide films. The efficient extraction of excited electrons by the conformal catalyst film leads to photocurrents of up to -5.7 mA cm(-2) at 0 V versus the reversible hydrogen electrode (pH 1.0) under simulated AM 1.5 solar illumination. Furthermore, the photocathode exhibits enhanced stability under acidic environments, whereas photocathodes with platinum nanoparticles as catalyst deactivate more rapidly under identical conditions. The work demonstrates the potential of earth-abundant light-harvesting material and catalysts for solar hydrogen production.

Simple methods to self-assemble coatings and films encompassing nanoparticles are highly desirable in many practical scenarios, yet scarcely any examples of simple, robust approaches to coat macroscopic droplets with continuous, thick (multilayer), reflective and stable liquid nanoparticle films exist. Here, we introduce a facile and rapid one-step route to form films of reflective liquid-like gold that encase macroscopic droplets, and we denote these as gold metal liquid-like droplets (MeLLDs). The present approach takes advantage of the inherent self-assembly of gold nanoparticles at liquid-liquid interfaces and the increase in rates of nanoparticle aggregate trapping at the interface during emulsification. The ease of displacement of the stabilizing citrate ligands by appropriate redox active molecules that act as a lubricating molecular glue is key. Specifically, the heterogeneous interaction of citrate stabilized aqueous gold nanoparticles with the lipophilic electron donor tetrathiafulvalene under emulsified conditions produces gold MeLLDs. This methodology relies exclusively on electrochemical reactions, i.e., the oxidation of tetrathiafulvalene to its radical cation by the gold nanoparticle, and electrostatic interactions between the radical cation and nanoparticles. The gold MeLLDs are reversibly deformable upon compression and decompression and kinetically stable for extended periods of time in excess of a year.

Hydrogen peroxide reacts with [MoO2Cl2(dmso)2] to produce orange crystals of the title complex, [MoO(O2)Cl2(dmso)2]. The structure is orthorhombic with distorted pentagonal bipyramidal geometry around the molybdenum ion. A short O-O bond length suggested the presence of a superoxide, but electron paramagnetic resonance measurements definitely supported the peroxo structure.

Electrochemical impedance spectroscopy is used to identify a slow electron transport process in hydrogen evolution catalysed by amorphous molybdenum sulphides on glassy carbon. A new chemical synthesis leads to an amorphous molybdenum sulfide catalyst with a higher electronic conductivity.

Amorphous molybdenum sulfide films, prepared by electrodeposition, are a class of highly active catalysts for hydrogen evolution. The growth mechanism of the films and the true active species were unclear. Herein, we report a study of the growth and activation of these films using Electrochemical Quartz Crystal Microbalance (EQCM) and X-ray photoelectron spectroscopy (XPS). Three processes, including oxidative deposition, reductive corrosion, and reductive deposition, are occurring during the growth of a molybdenum sulfide film. Deposition method, precursor concentration, and potential window are among the factors influencing the film growth. Regardless of deposition methods, all films exhibit similar catalytic activity on a per mass base. Potentiostatic oxidation (anodic electrolysis) is the method for fastest film growth; it produces a MoS3 film precatalyst which can be electrochemically activated. The activity of the MoS3 precatalyst scales with catalyst loading; at a loading of 0.2 mg/cm2, the current density is 20 mA/cm2 at an overpotential of 170 mV. Films differently deposited have different initial compositions, but the active catalysts in all films are the same MoS2+x species, whose XPS characteristics are distinct from those of crystalline MoS2. The activation process of a MoS3 film precatalyst involves a reductive removal of slightly less than one equivalent of sulfide to form MoS2+x.

The excitation of the weak electron donor decamethylosmocene on illumination with white light produces an excited state species capable of reducing organic solubilised protons under biphasic conditions. Insights into the mechanism and kinetics of light driven biphasic hydrogen evolution were obtained by analysis with gas chromatography cyclic voltammetry UV/vis and 1H NMR spectroscopy. The formation of the decamethylosmocenium hydride occuring prior to hydrogen evolution is a rapid step relative to hydrogen release and takes place independently of light activation. Remarkably hydride formation occurs with a greater efficiency (ca. 90 conversion) under biphasic conditions than when the reaction is carried out in an acidified single organic phase (ca. 20 conversion). Cyclic voltammetry studies reveal that decamethylosmocene has a higher proton affinity than either decamethylferrocene or osmocene i.e. the decamethylosmocenium hydride is a stronger Brønsted base.

Molybdenum boride (MoB) and carbide (Mo2C) are excellent catalysts for electrochemical hydrogen evolution at both pH 0 and pH 14.

Social, economic, and political pressures are causing a shift in the global energy mix, with a preference toward renewable energy sources. In order to realize widespread implementation of these resources, large-scale storage of renewable energy is needed. Among the proposed energy storage technologies, redox flow batteries offer many unique advantages. The primary limitation of these systems, however, is their limited energy density which necessitates very large installations. In order to enhance the energy storage capacity of these systems, we have developed a unique dual-circuit architecture which enables two levels of energy storage; first in the conventional electrolyte, and then through the formation of hydrogen. Moreover, we have begun a pilot-scale demonstration project to investigate the scalability and technical readiness of this approach. This combination of conventional energy storage and hydrogen production is well aligned with the current trajectory of modern energy and mobility infrastructure. The combination of these two means of energy storage enables the possibility of an energy economy dominated by renewable resources.

Amorphous molybdenum sulfide films are efficient hydrogen evolution catalysts in water. The films are prepared via simple electro-polymerization procedures and are characterized by XPS, electron microscopy and electronic absorption spectroscopy. Whereas the precatalysts could be MoS3 or MoS2, the active form of the catalysts is identified as amorphous MoS2. Significant geometric current densities are achieved at low overpotentials (e.g., 15 mA cm−2 at η = 200 mV) using these catalysts. The catalysis is compatible with a wide range of pHs (e.g., 0 to 13). The current efficiency for hydrogen production is quantitative. A 40 mV Tafel slope is observed, suggesting a rate-determining ion+atom step. The turnover frequency per active site is calculated. The amorphous molybdenum sulfide films are among the most active non-precious hydrogen evolution catalysts.

Rarely reported low cost molybdenum boride and carbide microparticles both of which are available in abundant quantities due to their widespread use in industry adsorb at aqueous acid 12 dichloroethane interfaces and efficiently catalyse the hydrogen evolution reaction in the presence of the organic electron donor decamethylferrocene. Kinetic studies monitoring biphasic reactions by UV/vis spectroscopy and further evidence provided by gas chromatography highlight (a) their superior rates of catalysis relative to other industrially significant transition metal carbides and silicides as well as a main group refractory compound and (b) their highly comparable rates of catalysis to Pt microparticles of similar dimensions. Insight into the catalytic processes occurring for each adsorbed microparticle was obtained by voltammetry at the liquid liquid interface.© 2013 the Owner Societies.

Redox flow batteries (RFBs) are particularly well suited for storing the intermittent excess supply of renewable electricity; so-called “junk” electricity. Conventional RFBs are charged and discharged electrochemically, with electricity stored as chemical energy in the electrolytes. In the RFB system reported here, the electrolytes are conventionally charged but are then chemically discharged over catalytic beds in separate external circuits. The catalytic reaction of particular interest generates hydrogen gas as secondary energy storage. For demonstration, indirect water electrolysis was performed generating hydrogen and oxygen in separated catalytic reactions. The electrolyte containing V(II) was chemically discharged through proton reduction to hydrogen on a molybdenum carbide catalyst, whereas the electrolyte comprising Ce(IV) was similarly discharged in the oxidation of water to oxygen on a ruthenium dioxide catalyst. This approach is designed to complement electrochemical energy storage and may circumvent the low energy density of RFBs especially as hydrogen can be produced continuously whilst the RFB is charging.

Molybdenum sulfide materials have been shown as promising non-precious catalysts for hydrogen evolution. This paper describes the study of the promotional effects of certain transition metal ions on the activity of amorphous MoS3 films. Ternary metal sulfide films, M–MoS3 (M = Mn, Fe, Co, Ni, Cu, Zn), have been prepared by cyclic voltammetry of aqueous solutions containing MCl2 and (NH4)2[MoS4]. Whereas the Mn–, Cu–, and Zn–MoS3 films show similar or only slightly higher catalytic activity as the MoS3 film, the Fe–, Co–, and Ni–MoS3 films are significantly more active. The promotional effects of Fe, Co, and Ni ions exist under both acidic and neutral conditions, but the effects are more pronounced under neutral conditions. Up to a 12-fold increase in exchange current density and a 10-fold increase in the current density at an overpotential of 150 mV are observed at pH = 7. It is shown that Fe, Co, and Ni ions promote the growth of the MoS3 films, resulting a high surface area and a higher catalyst loading. These changes are the main contributors to the enhanced activity at pH = 0. However, at pH = 7, Fe, Co, and Ni ions appear to also increase the intrinsic activity of the MoS3 film.

This work presents a detailed breakdown of the energy conversion chains from intermittent electricity to a vehicle, considering battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs). The traditional well-to-wheel analysis is adapted to a grid to mobility approach by introducing the intermediate steps of useful electricity, energy carrier and on-board storage. Specific attention is given to an effective coupling with renewable electricity sources and associated storage needs. Actual market data show that, compared to FCEVs, BEVs and their infrastructure are twice as efficient in the conversion of renewable electricity to a mobility service. A much larger difference between BEVs and FCEVs is usually reported in the literature. Focusing on recharging events, this work additionally shows that the infrastructure efficiencies of both electric vehicle (EV) types are very close, with 57% from grid to on-board storage for hydrogen refilling stations and 66% for fast chargers coupled with battery storage. The transfer from the energy carrier at the station to on-board storage in the vehicle accounts for 9% and 12% of the total energy losses of these two modes, respectively. Slow charging modes can achieve a charging infrastructure efficiency of 78% with residential energy storage systems coupled with AC chargers.

Amorphous MoS3 particles are prepared using a simple chemical method. Several deposition techniques are developed to fabricate electrodes loaded with MoS3 particles. These electrodes are highly active for hydrogen evolution. The catalytically active species appear to be reduced molybdenum sulfide that contains disulfide ligands. The MoS3 particles are annealed to form polycrystalline and single crystalline MoS3 and MoS2 particles. These particles, as well as commercial MoS2 micro-crystals, show inferior catalytic activity compared to the amorphous MoS3 particles.

Polydispersed dinickel phosphide (Ni2P) nanoparticles were synthesized by a simple and scalable solid-state reaction. These nanoparticles are an excellent and robust catalyst for the electrochemical hydrogen evolution reaction, operating in both acidic and basic solutions.

High-purity standards are required for hydrogen used in fuel cell vehicles. The relative abundance of contaminants is highly influenced by the production pathway. Hydrogen obtained from water electrolysis presents three main pollutants: Nitrogen, Oxygen and Water. Herein, the engineering and implementation of removal techniques in a commercial 50 kW alkaline electrolyzer are reported. The full system was characterized with various analytical techniques including gas chromatography and mass spectrometry. A reduction of contaminant levels compatible with ISO 14687:2019 standard was achieved. From cold start, 100 min of operation are required to reach the desired nitrogen levels. Oxygen was removed in one step with a catalytic converter. Drying of hydrogen was achieved by using an innovative vacuum assisted pressure swing adsorption system. Sub-ppm levels of water are obtained with a power consumption of only 0.5 kWh/kg H2 and 98.4% of product recovery.

Phosphane complexes of the putative formula [CoX2(dppe)] [X = Cl, Br, I; dppe = bis(diphenylphosphanyl)ethane] are frequently used catalyst precursors in cobalt-catalyzed reactions. Despite their widespread use, these complexes have not been structurally characterized. We demonstrate that synthetic procedures for [CoX2(dppe)] afford complexes of the formula [Co4X8(dppe)5] instead. Crystallographic analyses of these complexes reveal an ionic structure with pentacoordinate [CoX(dppe)2]+ cations and a dinuclear [Co2X6(dppe)]2– anion. The bromido and iodido complexes crystallize in two forms, which differ in the geometry of the cation (square-pyramidal vs trigonal-bipyramidal).

Air driven gas boosters are often deployed in small scale compression systems. Manufacturers specifications, reporting outlet flow for a fixed inlet pressure, do not reflect the batch operation from a limited source storage. Thus, the dynamic variation of critical process parameters such as efficiency, temperature and flow are not documented. Using a hydrogen refueling station demonstrator, the data from more than 20′000 compression cycles is compiled and analyzed. Experimentally derived correlations are determined for an air driven gas booster feeding a cascade storage. A specific analysis of the clearance volume and the working air pressure is introduced. An engineering tool was developed in MATLAB for performance forecasting. It allows the user to simulate the process trends with an accuracy of ±5%. In the context of a hydrogen refueling station, duration, temperature, compression cycles and air consumption data can be used for process management and maintenance planning.

MoO2 microparticles act as an active catalyst for the electrochemical reduction of CO2 in organic solvents such as acetonitrile and dimethylformamide. The catalytic activity and product selectivity depend on temperature and water content of the solvent.