Evolved Hydrogen Gas Research Articles

Nanosized Pd@Ag heterojunction with tunable shapes: Morphological modulation for improving plasma-mediated catalytic hydrogen evolution

Catalytic ability of bi-metal hybrid nanoagents largely depends on their phase constitution and morphology, also bearing a close correlation to the fabrication process. We herein design and develop a modified polyol protocol with inorganic ion induction for rationally constructing Ag nanoagents with tunable shapes (nanowire, nanocube, and nanoparticle), followed by evenly anchoring of stepwise reduced Pd nanograins on the surface of Ag nanoagents to foster Ag core - Pd shell (i.e. Pd@Ag) nanosized heterostructure. A home-made photochemical reaction device is used to scientifically evaluate the catalytic ability of the Pd@Ag nanoagents on hydrolyzing ammonia borane to evolve hydrogen gas. The ample characterization reveals that the fabricated Ag nanoagents hold the expected regular and uniform shapes, with 10–15 nm thick Pd layer cladded on their surfaces. The particular shapes of the Ag nanoagents can be duly manipulated via the induction of inorganic ions, and the thickness and compactness of the Pd shell can also be suitably regulated by controlling reduction duration. The verified formation of electron synergistic effect among the both metals is favorable to elevate the catalytic ability. The bimetal Pd@Ag nanoagents perform the superior catalytic activity under visible light irradiation, far exceeding that of the respective monometal counterparts, with the order of catalytic activity: Pd@Ag-NWs > Pd@Ag-NCs > Pd@Ag-NPs. The hydrolysis reaction at the given conditions is confirmed to be quasi first-order reaction, with the apparent activation energy of 53.44 kJ·mol−1 and TOF value of 47.04 min−1. The Pd@Ag-NWs catalyst behaves satisfactory stability, with 87.8 % initial catalytic activity retained after five cyclic use.

The role of ligament gap in electrocatalytic activity of reduced graphene oxide/NiO mesoporous in hydrogen evolution reaction

This work investigates the role of ligament gap of NiO mesoporous prepared with different template in the activity of rGO/NiO in alkaline hydrogen evolution reaction. The activity of electrocatalyst was found to be highly dictated by the size of ligament gap rather than surface area. Result showed that rGO/NiO made with KCC-1 exhibited a superior activity due to its large ligament gap, even though its surface area was the smallest. It is believed that the evolved hydrogen gas built-up inside NiO mesoporous bulk structure could increase the internal electrode resistance and decrease overall catalytic activity.

Stable Immobilization of Nickel Ions on Covalent Organic Frameworks for Panchromatic Photocatalytic Hydrogen Evolution.

Post-coordination design on covalent organic frameworks (COFs) is an efficient strategy for elevating the photocatalytic activity of organic moiety. However, the rigid skeletons and densely layered stacking of two-dimensional (2D) COFs cannot be flexibly adapted for specific conformations of metal complexes, thereby impairing the metal-COF cooperation. Here, we adopt a solvothermal method to immobilize nickel(II) ions into a 2,2'-bipyridine-containing 2D COF, forming a stable coordination motif. Such the complex remarkably enhances the photocatalytic performance, giving an optimized H2 evolution rate of as high as 51 300 μmol h-1 g-1 , 2.5 times higher than the pristine COF. The evolved hydrogen gas can also be detected upon 700-nm light irradiation, while its analog synthesized by the traditional coordination method is photo-catalytically inert. This work provides a strategy for optimizing the metal-COF coordination system and strengthening a synergy for electronic regulation in photocatalysis.

Stable Immobilization of Nickel Ions on Covalent Organic Frameworks for Panchromatic Photocatalytic Hydrogen Evolution

AbstractPost‐coordination design on covalent organic frameworks (COFs) is an efficient strategy for elevating the photocatalytic activity of organic moiety. However, the rigid skeletons and densely layered stacking of two‐dimensional (2D) COFs cannot be flexibly adapted for specific conformations of metal complexes, thereby impairing the metal‐COF cooperation. Here, we adopt a solvothermal method to immobilize nickel(II) ions into a 2,2′‐bipyridine‐containing 2D COF, forming a stable coordination motif. Such the complex remarkably enhances the photocatalytic performance, giving an optimized H2 evolution rate of as high as 51 300 μmol h−1 g−1, 2.5 times higher than the pristine COF. The evolved hydrogen gas can also be detected upon 700‐nm light irradiation, while its analog synthesized by the traditional coordination method is photo‐catalytically inert. This work provides a strategy for optimizing the metal‐COF coordination system and strengthening a synergy for electronic regulation in photocatalysis.

The impact of in-situ hydrogen evolution on the flow resistance of electrolyte flowing through the carbon felt electrode in a redox flow battery

The parasitic hydrogen evolution reaction (HER) leads to capacity fade of aqueous redox flow batteries. In addition, the evolved hydrogen gas bubbles stagnating inside the porous electrode may block the flow of electrolyte, increase the flow resistance, and reduce the battery performance. By precisely controlling the HER and electrolyte flow rates, we explore the impact of the mA cm−2 scale HER on the relative permeability of HCl-based aqueous electrolyte flowing through a carbon felt electrode. Experimental results show that the HER with a current density of 2 mA cm−2 reduces the quasi-steady two-phase flow relative permeability in the negative half-cell from 1.0 to 0.84, even at a high electrolyte flow velocity of 16 mm s−1. With an ultrasonic gas sensor, the delay of gas release out of the cell from the beginning of HER has been measured. After the halt of HER, the recovery of the liquid permeability lasts for more than an hour if the electrolyte velocity is maintained at 8 mm s−1. Moreover, significant instability of pressure drop is observed at a low electrolyte velocity of 2 mm s−1.

Self-Enclosed Bio-Photoelectrochemical Cell in Succulent Plants.

Harvesting an electrical current from biological photosynthetic systems (live cells or isolated complexes) is typically achieved by immersion of the system into an electrolyte solution. In this study, we show that the aqueous solution found in the tissues of succulent plants can be used directly as a natural bio-photo electrochemical cell. Here, the thick water-preserving outer cuticle of the succulent Corpuscularia lehmannii serves as the electrochemical container, the inner water content as the electrolyte into which an iron anode and platinum cathode are introduced. We produce up to 20 μA/cm2 bias-free photocurrent. When 0.5 V bias is added to the iron anode, the current density increases ∼10-fold, and evolved hydrogen gas can be collected with a Faradaic efficiency of 2.1 and 3.5% in dark or light, respectively. The addition of the photosystem II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea inhibits the photocurrent, indicating that water oxidation is the primary source of electrons in the light. Two-dimensional fluorescence measurements show that NADH and NADPH serve as the major mediating electron transfer molecules, functionally connecting photosynthesis to metal electrodes. This work presents a method to simultaneously absorb CO2 while producing an electrical current with minimal engineering requirements.

Characterization of the Reduction Mechanism of Chromium(III) By in Situ Microgravimetry and Volumetric Determination of Hydrogen

Processes for chromium electrodeposition based on hexavalent chromium compounds are more and more restricted by governmental laws1 due to the toxic and carcinogenic nature of Cr(VI) compounds. The most promising alternatives to replace hexavalent chromium solutions are trivalent chromium electrolytes considering process management, quality of the deposits and cost issues.2 However, many of these electrolytes suffer from low current efficiencies and reduced process stability compared to hexavalent chromium electrolytes. Organic additives are used to reduce the overvoltage of Cr(III) reduction and, hence, reach an acceptable current efficiency.3 In order to improve performance and reliability of the deposition process, a profound knowledge of the deposition mechanism and the effect of additives is crucial.In this work the stepwise reduction process of Cr(III) to metallic chromium is investigated by gravimetric and volumetric in-situ methods under variation of current density. Electrochemical quartz crystal microbalance (EQCM) was used to quantify the mass of deposited chromium metal.4 The amount of evolved hydrogen gas was determined with a gas burette in combination with a purpose-built setup for collecting the gas. Based on the results, the partial current densities of the two reduction steps of Cr(III) and the hydrogen evolution were calculated. A shift in the ratio of the partial current densities and an increased current efficiency of metal deposition was observed after the addition of saccharin, which is used as additive in chromium electrolytes for decorative applications.5 A mechanism on the mode of action of saccharin during chromium electrodeposition is proposed. European Chemicals Agency, Authorisation List, EC No. 215-607-8, 231-801-5, 231-889-5, 231-906-6, 232-140-5, 232-143-1, 234-190-3, 236-881-5. Z. X. Zeng, A. M. Liang, and J. Y. Zhang, Recent Pat. Mater. Sci., 2 (1), 50-57 (2009). D. Del Pianta, J. Frayret, C. Gleyzes, C. Cugnet, J. C. Dupin, and I. Le Hecho, Electrochim. Acta, 284, 234-241 (2018). M. Leimbach, C. Tschaar, U. Schmidt, and A. Bund, Electrochim. Acta, 270, 104-109 (2018). R. Katirci, Int. J. Surf. Sci. Eng., 10 (1), 73-85 (2016).

Safety Considerations of Lithium Metal Solid State Batteries

The advancements in Lithium Ion Batteries (LIBs) over the last three decades has significantly altered the modern world. The availability of efficient, portable electrical energy storage has enabled the proliferation of personal electronics, improved the viability of renewal energy sources such as wind and solar, and begun to transform the transportation sector.Most next generation battery technologies, such as Lithium Metal Solid State Batteries (LMSSB), rely on the adoption of lithium metal for their improved energy storage density. The large-scale adoption of batteries using lithium metal anodes may raise safety concerns, with the properties of lithium making it unstable in the room environment. Proponents of LMSSBs often list improved safety over LIB technology due to the replacement of the flammable liquid electrolyte with an inflammable solid. This view largely ignores the impact on safety of adding lithium metal, which exothermically reacts with water to evolve hydrogen gas. This potential safety consideration as well as others from a fault tree analysis of LMSSB will be introduced and explored.

Hydrogen storage using liquid organic carriers: Equilibrium simulation and dehydrogenation reactor design

Liquid organic hydrogen carriers (LOHC) are unsaturated organic compounds used for chemical hydrogen storage. Using an equilibrium model of the LOHC N-ethylcarbazole, we discuss potential efficiency increases of hydrogen storage systems based on N-ethylcarbazole by the integration of low-temperature waste heat. N-ethylcarbazole is well suited for pressure swing operation with heat exchange between hydrogenation and dehydrogenation. We present and discuss kinetic data of the dehydrogenation reaction gathered in a tubular reactor that was mounted in different orientations and flow configurations. Similar maximum values of power density are reached in vertical and in horizontal orientation. Vertical orientation allows the favorable operation with counter-flow of the liquid carrier and the evolved hydrogen gas and radial heat transfer is significantly better than in horizontal orientation. In vertical reactor configurations, catalyst efficiency and operational stability are impaired at high void fractions. This issue can be reduced by dehydrogenation at elevated pressure and intermediate gas separation from the catalyst bed.

Preparation of CoB catalysts supported on raw and Na-exchanged bentonite clays and their application in hydrogen generation from the hydrolysis of NaBH4

The aim of this work is to prepare CoB catalysts supported on raw bentonite (CoB/bentonite) and Na-exchanged bentonite (CoB/Na-bentonite) by the impregnation and chemical reduction method. The prepared catalysts were characterized using X-ray diffractometry (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques. The activities of the catalysts were tested in the hydrolysis reaction of sodium borohydride (NaBH4) in a semi-batch system. The volume of the evolved hydrogen gas was determined by a water displacement method. The effects of catalyst amount, NaOH (a base stabilizer) concentration, NaBH4 concentration and solution temperature on the hydrogen generation rate were investigated. The maximum hydrogen generation rates were determined as 921.94 mL/min.gcat for CoB/bentonite and 1601.45 mL/min.gcat for CoB/Na-bentonite when the 5 wt % NaBH4 and 10 wt % NaOH solutions were used at 50 °C. The activation energies (Ea) of the hydrolysis reaction over CoB/bentonite and CoB/Na-bentonite were determined as 55.76 and 56.61 kJ/mol, respectively.

Isotope Effect between H2O and D2O in Hydrothermal Synthesis

Synthetic chemists can use different solvents (for example, polar vs nonpolar) to affect solute–solvent interactions and therefore favor a particular reaction product. Using a different isotope of the same solvent to select the product, however, is uncommon. We find that water and heavy water (D2O) can select different products in the hydrothermal syntheses of iron-containing solids. Under hydrothermal and anaerobic conditions, water oxidizes iron to evolve hydrogen gas and a mixture of Fe2+- and Fe3+-containing solids. When we replace D2O for H2O under identical hydrothermal conditions, we can select thermodynamic products in our syntheses of iron-containing solids, whether it be oxides or chalcogenides. To explain this remarkable difference in product selectivity, we discover an unexpected difference in a fundamental property between H2O and D2O: their standard reduction potentials. Through electrochemical measurements and under strongly basic conditions (pH = 14), we find that the reduction potential o...

Bioactivity enhancement by Sr doped Zn-Ca-P coatings on biomedical magnesium alloy

Abstract The effect of strontium doped Zn-Ca-P (ZCP) coating by chemical conversion technique on the biodegradation of AZ31 alloy was evaluated. The coating formed with 1.5 wt.% Sr and 20 min phosphating time at 50 °C with pH 2.5 completely covers the alloy surface. The Sr doped coated sample also showed very low evolved hydrogen gas and pH change than the ZCP coatings suggested that the degradation of the alloy was extremely controlled. The in vitro bioactivity studies in simulated body fluid exhibits deposition of calcium phosphate phases with Ca/P ratio of 1.55 which is close to that of hydroxyapatite, mineral component of bone. Cytotoxicity evaluation with L929 cells showed higher cell viability of the Sr doped coatings compared to ZCP coatings.

Converting glycerol aqueous solution to hydrogen energy and dihydroxyacetone by the BiVO4 photoelectrochemical cell

Replacement of oxygen evolution reaction (OER) by the more readily oxidized biomass derivatives is considered to be a promising strategy for photoelectrocatalytic water splitting hydrogen production. In this work, a biodiesel industrial waste by-product, glycerol, played the critical role for the efficient hydrogen production as well as the highly valuable dihydroxyacetone (DHA) and industrial useful formic acid production. As the glycerol was introduced, a remarkable cathodic shift of the onset potential was observed (∼300 mV) while the current density was 4 times higher compared to the water oxidation. The incident photon-to-current efficiency (IPCE) of BiVO4 photoanode for glycerol oxidation reached about 55%, which was 3 times higher than the system without glycerol. More importantly, during the photoelectrochemical water splitting in glycerol aqueous solution, in addition to the evolved hydrogen gas, glycerol was oxidized to valuable products with 15% dihydroxyacetone (DHA) and 85% formic acid. This strategy not only boosts the hydrogen production efficiency, keeps the photoanode very stable but also makes the biodiesel production more profitable and sustainable.

Communication—Deuterium Isotope Separation by Solid Polymer Electrolyte Water Electrolysis

Electrolytic deuterium (D) separation from protium-containing solution has been investigated. Proton (PEM) and anion exchange membrane (AEM) electrolysis were performed at constant current. The mass analysis of hydrogen gas and water vapor was carried out. For both PEM and AEM electrolysis, the D concentration in the evolved hydrogen gas was lower than that of the initial electrolytic solution. The D concentration in the water vapor was unchanged by PEM electrolysis, but was increased by AEM. The separation factor of PEM was smaller than that of AEM, which was attributed to the humidification state on platinum catalyst.

Real-Time Monitoring of Atmospheric Magnesium Alloy Corrosion

The atmospheric corrosion progress of Mg alloys is traditionally tracked by determining mass loss of the samples after exposure. This method provides only an average corrosion rate over the exposure time and is destructive. The work presented introduces a new non-destructive method for real-time monitoring of atmospheric Mg alloy corrosion rates based on the evolved hydrogen gas. This is realized with an adaption of the gravimetric hydrogen collection method. The effect of temperature and atmospheric pressure variations during the experiment can be compensated and reliable atmospheric hydrogen evolution rates can be measured. The new technique was applied to monitor real-time atmospheric corrosion rates of Mg alloys AZ31 and AZ91 with different amounts of NaCl contamination. Comparing the results of the gravimetric hydrogen method with mass loss experiments reveals a good correlation of the consumed charge over the total exposure time, thus validating the new technique. Evidence for the contribution of O2 reduction reaction to cathodic processes on Mg alloy atmospheric corrosion is presented.

Novel Electrochemical Sensor Concept for the Detection of Lead Contamination in Drinking Water

Lead contamination of drinking water is a widespread problem affecting people in developing as well as developed countries. While lead contamination levels can be monitored at water treatment facilities, drinking water may get contaminated with lead during its distribution. To ensure that drinking water ‘at the tap’ is not lead contaminated, it is essential to develop a low-cost, portable sensor for use in homes and offices. In the present talk, a novel electrochemical sensor concept which enables accurate detection of ppb-levels of Pb2+ in water will be outlined. The sensor works on the principle of underpotential deposition of lead (Pbupd) onto a Cu electrode followed by quantitative measurement of the hydrogen evolution reaction (HER) current on the partially Pbupd-modified Cu electrode surface. The basic operation of the electrochemical sensor involves the following steps (Figure 1): (i) A copper working electrode is immersed in a Pb2+-contaminated sample, and a suitable electrode potential is applied to it which facilitates the underpotential deposition of lead onto the copper surface. Depending on the Pbupd time and the Pb2+ concentration in the sample, the Pbupd coverage of the Cu surface increases gradually; (ii) The kinetics of electrochemical splitting of water to evolve hydrogen gas depends on the Pbupd coverage on the Cu electrode – higher the Pb coverage during step i, more sluggish is the hydrogen gas evolution during step ii. The degree of suppression of the HER kinetics (i.e., current) is measured, which then provides the Pbupd coverage (for a known deposition time) and thus the Pb2+ concentration in solution. In this presentation, we will demonstrate the feasibility of the above electrochemical sensor concept to achieve a detection limit of 10 ppb Pb2+ in water samples. Furthermore, we will present detailed analysis of the sensor response time using a mathematical diffusion-reaction model. Techniques to minimize interference effects due to other contaminants, and comparison between the sensor performance and standardized spectroscopic measurements of lead concentration will also be discussed. Ongoing work on building a portable electrochemical sensor prototype will be outlined. Figure 1

New Method for Monitoring Hydrogen Evolution of Magnesium Alloys Under Atmospheric Exposure

Magnesium (Mg) alloys are attractive lightweight materials for the automotive industry due to their low density and high specific strength [1]. However, widespread use of Mg alloy components is hindered by their corrosion properties. Full immersion conditions are frequently used to study the corrosion behavior, although Mg alloys are typically subjected to atmospheric corrosion environments in most applications. With a limited amount of electrolyte, the corrosion mechanism can be different [2]. For example, corrosion products that partly dissolve in a bulk electrolyte can remain at the surface and block active sites in the case of atmospheric conditions [3]. Effects of micro-galvanic coupling of secondary phases can be reduced with thin electrolyte films [4]. In addition, atmospheric concentrations of CO2 can influence the surface pH and change the composition of the corrosion products [3]. As a result, corrosion rates in atmospheric environments are smaller and cannot be directly compared to results obtained under immersion conditions. The atmospheric corrosion progress is traditionally tracked gravimetrically by determining mass gain or mass loss of the samples after exposure. This work introduces a new method that makes it possible to monitor the real time atmospheric corrosion rate of Mg alloys during exposure. The idea is to measure the amount of hydrogen evolved during atmospheric corrosion. This is realized with an adaption of the gravimetric hydrogen collection method, originally developed by Curioni [5]. The change in buoyancy exerted by the evolved hydrogen gas can be accurately measured. Therefore, it is possible to monitor the instant atmospheric corrosion rate even at the initial stages of corrosion where mass loss measurements are difficult. Different exposure conditions like relative humidity, temperature or CO2 content can be studied. The possible contribution of the oxygen reduction reaction to the cathodic processes will be discussed.

Combined Structure Geometry and Anode Placement Effects on Cathodic Protection Effectiveness

Abstract An impressed current cathodic protection system was applied to an uncoated test sample. The test sample was chosen to represent an essential right angle feature of a common structure. Anode placement was quantitatively shown to affect the resulting surface polarization distribution. Two distinct types of local polarization depletion zones have been demonstrated. These regions of lesser polarization represent a locally insufficient amount of cathodic protection compared to criteria designated values. Conversely, for geometrically complex structures containing sharp features, the possibility of locally evolving hydrogen gas is also discussed.

(Invited) Photoelectrocatalysis: Solar-Assisted Hydrogen Production in Microgravity Environments

Artificial photosynthesis systems, which follow the concept of the Z-scheme of natural photosynthesis, are presently being realized as catalyst-functionalized photovoltaic tandem devices for the photoelectrochemical oxidation of water and the simultaneous generation of hydrogen as a so-called “solar fuel”. The successful implementation of an efficient photoelectrochemical (PEC) water splitting cell is not only a highly desirable approach to solving the energy challenge on earth: an effective air revitalization system generating a constant flux of O2 while simultaneously recycling CO2 and providing a sustainable fuel supply is also essential for the International Space Station and long-term space missions, where a regular resupply from earth is not possible. Here, we present the photoelectrochemical production of hydrogen in microgravity environments on p-type indium phosphide electrodes with deposited rhodium electrocatalysts. Our findings indicate that microgravity has a significant impact on the gas bubble evolution behaviour and the mass transfer rate of the evolved hydrogen gas on the electrode surface. Furthermore, microgravity influences the current-voltage characteristics and the overall solar-to-hydrogen efficiency of the catalyst functionalized semiconductor-based half-cell. Further experiments with nanostructured rhodium catalysts fabricated by shadow nanosphere lithography on the InP surface suggest that the structure of the electrode surface plays a significant role for the gas bubble evolution behaviour and for the further the development of efficient prototypes for solar-assisted water splitting and hydrogen production that operate in micro- and hypergravity environments.

A highly efficient pn junction nanocomposite solar-energy-material [nano-photovoltaic] for direct conversion of water molecules to hydrogen solar fuel

Abstract: Besides their application in photovoltaics, semiconductor solar-energy-materials can be directly employed as photocatalysts of hydrogen fuel production using sunlight and water feedstock. In this paper, through a facile hydrothermal route, we synthesized a CuO-ZnO pn junction nanocomposite in the absence and presence of carbon nanotube (CNT), and applied them in a water photosplitting setup to evolve hydrogen gas. The investigation revealed that in the presence of CNT, the photocatalyst performance increases significantly–becomes approximately twice. The superior activity witnessed here for the ternary nanocomposite (CuO-ZnO/CNT) was explained in terms of the ability of CNT to enlarge the photocatalyst surface area, enhance the absorption of photons, and prohibit the recombination of photogenerated e/h pairs. Finally, quantum yield and energy efficiency analyses were performed on both binary and ternary nanocomposite materials as well as on their semiconductor components, and the results were discussed in detail from physicochemical viewpoint.