Molybdenum electrodes for hydrogen production by water electrolysis using ionic liquid electrolytes

The hydrogen production by water electrolysis was tested with different electrocatalysts (molybdenum, nickel, iron alloys containing chromium, manganese and nickel) using aqueous solutions of ionic liquid (IL) like 1-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF₄). The hydrogen evolution reaction (HER) was performed at room temperature in a potential of −1.7 V (PtQRE). A Hoffman cell apparatus was used to water electrolysis with current density values, j, between 14.6 mA cm⁻² (for Ni electrode) and 77.5 mA cm⁻² (for Mo electrode). The system efficiency was very high for all electrocatalysts tested, between 97.0% and 99.2%. The energy activation values of HER was determined in an aqueous solution of BMI.BF₄ 10 vol.%, using platinum (23.40 kJ mol⁻¹) and Mo (9.22 kJ mol⁻¹) as electrocatalysts. The results show that the hydrogen production in IL electrolyte can be carried out with cheap material at room temperature, which makes this method economically attractive.     

Ether-based electrolyte enabled Na/FeS2 rechargeable batteries

We demonstrate for the first time that by simply substituting ether-based electrolyte (1.0 M NaCF₃SO₃ in diglyme) for the commonly used carbonate-based electrolyte, the cyclability of FeS₂ towards sodium storage can be significantly improved. A sodiation capacity over 600 mAh/g and a discharge energy density higher than 750 Wh/kg are obtained for FeS₂ at 20 mA/g. When tested at 60 mA/g, FeS₂ presents a sodiation capacity of 530 mAh/g and retains 450 mAh/g after 100 cycles, much better than the cycling performance of Na/FeS₂ tested in carbonate-based electrolyte.     

Enhancement of hydrogen evolution activities of low-cost transition metal electrocatalysts in near-neutral strongly buffered aerobic media

The advantages of hydrogen evolution reaction (HER) in strongly buffered neutral pH are manifold including enhanced stability of the electrocatalysts, oxygen tolerance, safer and environmental friendly devices, etc., yet, not much research effort has been devoted on the subject. HER activities of several low-cost electrocatalysts like Mo₂C, MoS₂, CoSe₂ and NiSe₂ have been studied in sodium phosphate buffer solution of pH 5. An optimal buffer concentration of 1.75 M was observed for the electrocatalysts. Compared to un-buffered electrolyte, a reduction of about 100 mV in the onset overpotential has been achieved. The electrocatalysts are highly oxygen tolerant with more than 90% HER selectivities. Furthermore, electrochemical surface area of Mo₂C was evaluated by capacitance and surface oxidation methods to obtain an insight on the specific adsorption of buffer electrolytes.     

Enhanced stability and activity of PtRu nanotubes for methanol electrooxidation

PtRu 1D nanostructures on titanium are prepared and analysed as electrocatalysts for methanol electrooxidation. The morphology and composition of the 1D nanostructure are characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The electrocatalytic properties of such catalysts for methanol oxidation are investigated by cyclic voltammetry (CV) and chronoamperometry (CA) in 1.0 M CH₃OH + 0.5 M H₂SO₄ aqueous solution. The results show that Pt₄₆Ru₅₄ nanotubes yields to a five-fold improvement of the mass specific activity and to a three-fold improvement of the long-term poisoning rate as compared to PtRu black of similar composition.     

Enhancement of electrochemical and catalytic properties of MoS2 through ball-milling

MoS₂ nanosheets of one to few layer thickness present novel electronic and enhanced catalytic properties with respect to the bulk material. Here we show that a simple and highly scalable ball-milling procedure can lead to significant improvements of the electrochemical and catalytic properties of the bulk natural MoS₂. We characterized the material before and after the milling process by means of scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy in order to evaluate morphological and chemical features. We investigated the electrochemical properties by means of voltammetry techniques to monitor the electron transfer with [Fe(CN)₆]^{4 −/3 −} redox probe and the catalytic properties by monitoring the electrochemical hydrogen evolution reaction (HER). A significant overpotential lowering of about 210 mV is obtained for the HER by the ball-milled material when compared to bulk materials. This has a huge potential for the lowering of the energy consumption during hydrogen evolution. Ball-milling offers highly scalable dry method for large scale production of electrocatalyst with enhanced properties.     

Electrochemical kinetics of the hydrogen reaction on platinum in concentrated HCl(aq)

The hydrogen reaction in concentrated HCl(aq) solutions is a key reaction for the CuCl(aq)/HCl(aq) electrolytic cell. Here, electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) were used to obtain new data for the hydrogen reaction on platinum submerged in highly concentrated acidic solutions at 25 °C and 0.1 MPa. LSV and EIS data were collected for Pt in 0.5 mol/L H₂SO₄(aq), 1 mol/L HCl(aq) and 7.71 mol/L HCl(aq) solutions. It was found that exchange current density (j₀) values varied between 1 and 2 mA/cm². An equivalent circuit model was used to obtain comparable j₀ and limiting current density values from EIS data relative to values obtained with LSV data. It was found that as the concentration of acid increased, a noticeable decrease in the performance was observed.     

pH effect on electrocatalytic reduction of CO2 over Pd and Pt nanoparticles

Adsorbed hydrogen participates in electrocatalytic reduction of CO₂ and competitive hydrogen evolution reaction (HER) simultaneously, and its reaction pathway greatly affects the activity and selectivity of CO₂ reduction. In this work, we investigate pH effect on electrocatalytic reduction of CO₂ over Pd and Pt nanoparticles (NPs) with a similar size in a pH range from 1.5 to 4.2. Pt NPs completely contribute to HER in the pH range. Over Pd NPs, Faradaic efficiency for CO production at − 1.19 V (vs. reversible hydrogen electrode) varies from 3.2% at pH of 1.5 to 93.2% at pH of 4.2, and current density for CO production reaches maximum at pH of 2.2. The significant enhancement of Faradaic efficiency and current density for CO production over Pd NPs at high pH values is attributed to decreased kinetics of hydrogen evolution reaction by increasing hydrogen binding energy and lowered adsorption affinity of CO-like intermediate compared to Pt.     

Combining phosphate species and stainless steel cathode to enhance hydrogen evolution in microbial electrolysis cell (MEC)

Microbial electrolysis cells (MEC) must work around neutral pH because of microbial catalysis at the anode. To develop a hydrogen evolution cathode that can work at neutral pH remains a major challenge in MEC technology. Voltammetry performed at pH 8.0 on rotating disk electrodes showed that the presence of phosphate species straightforwardly multiplied the current density of hydrogen evolution, through the so-called cathodic deprotonation reaction. The mechanism was stable on stainless steel cathodes whereas it rapidly vanished on platinum. The phosphate/stainless steel system implemented in a 25 L MEC with a marine microbial anode led to hydrogen evolution rates of up to 4.9 L/h/m² under 0.8 V voltage, which were of the same order than the best performance values reported so far.     

Environment friendly hydrothermal synthesis of carbon–Co_3O_4 nanorods composite as an efficient catalyst for oxygen evolution reaction

The design of cost-effective, highly active catalysts for hydrogen energy production is a vital element in the societal pursuit of sustainable energy. Water electrolysis is one of the most convenient processes to produce high purity hydrogen. Cobalt-based catalysts are well-known electrocatalysts for oxygen evolution reaction(OER). In this article, all these merits indicate that the present cobalt nanocomposite is a promising electrocatalyst for OER. C–Co_3O_4-nanorods catalyst with nanorod structure was synthesized by hydrothermal treatment of CoCl_2·6H_2O/dextrose/urea mixture at 180 °C for 18 h and then calcined at400 °C for 3.5 h. The role of dextrose percentage in solution to achieve the uniform coating of carbon on the surface of Co_3O_4-nanorods has been demonstrated. The prepared materials were characterized by X-ray diffraction(XRD), X-ray photoelectron spectrum(XPS), field emission scanning electron microscopy(FE-SEM), high-resolution transmission electron microscopy(HR-TEM), and Brunauer–Emmett–Teller instrument(BET). Due to its unique morphology, the C–Co_3O_4-nanorods catalyst exhibited better activity than Co_3O_4-microplates catalyst for OER in 1 M KOH aqueous solution. The results showed a highly efficient, scalable, and low-cost method for developing highly active and stable OER electrocatalysts in alkaline solution.     

Utilization of Low-grade Iron Ore in Ammonia Decomposition

Due to its cleanliness, fast energy cycle, and convenience of energy conversion, hydrogen has been regarded as the new energy source. Conventional process to produce hydrogen yield large amount of CO as byproduct. Moreover, the hydrogen storage and transportation have become the drawbacks in hydrogen economy. Thus, there has been increased interest in the hydrogen transportation medium as alternatives from the conventional process to produce and transport hydrogen. Ammonia has drawn worldwide attention as the most reliable hydrogen transportation medium. Through the decomposition of ammonia, hydrogen and nitrogen gas were produces as the byproduct without any CO or CO₂ emission. In this experiment, the ore were introduced as the medium for ammonia decomposition. The ore were put into quartz tube reactor and were dehydrated at 400 °C for 1 hour, then hydrogen reduced for 2 hours before and undergone ammonia decomposition at 500-700 °C for 3 hours. The effects of temperature to the % conversion of ammonia decomposition were also studied. Ammonia decomposition at higher temperature gives higher conversion. As seen in the results, the NH₃ conversion decreased with increasing time and the value after 3 hours of reaction increased in the sequence of 500 °C<600 °C< 700 °C. During ammonia decomposition, nitriding of iron occurred. The relation between temperature and the nitriding potential, K_N is also investigated. The purpose of this study is to investigate the utilization of low-grade ore as medium for ammonia decomposition to produce hydrogen.     

High oxygen-reduction activity of silk-derived activated carbon

Activated carbon prepared from silk fibroin, which is free of metal elements, showed a high catalytic activity for the oxygen-reduction reaction (ORR). The activated carbon had a very high onset potential of E_onset = 0.83 V (vs. RHE) in oxygen-saturated 0.5 M H₂SO₄ at 60 °C. The ORR on the activated carbon proceeded by a four-electron process in the high-electrode-potential region; this gradually decreased to a 3.5-electron reaction below about 0.6 V (vs. RHE). Only about 1% of nitrogen atoms (mostly quaternary) remained in the activated carbon by heat-treatment at up to 1200 °C are responsible for the high catalytic activity. The open circuit voltage of a polymer electrolyte fuel cell using the activated carbon as the cathode and a platinum/carbon black anode under pure oxygen and hydrogen gases, respectively, both at one atmosphere, was 0.96 V at 27 °C.     

Pd Nanostructures with High Tolerance to CO Poisoning in the Formic Acid Electrooxidation Reaction

Pd architectures such as nanobars and nanoparticles were synthetized by the polyol method using di-ethylene glycol as reaction media. The morphology, composition and electrocatalytic properties were investigated by transmission electronmicroscopy (TEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and electrochemical measurements. The electrocatalytic activity of Pd nanostructures was tested in terms of formic acid electrooxidation reaction (FAOR) in acid media (0.5 M H₂SO₄) and compared with commercial Pd/XC-72 (Pd/C). Results from the electrochemical studies showed that Pdnanobars (PdNB/C) presented higher tolerance to the CO and CO₂ poisoning effect compared with Pd nanoparticles (PdNP/C) and commercial Pd/C. Furthermore, the onset potential toward formic acid electrooxidation at high concentration (1 M) on PdNB/C exhibited a negative shift ca. 100 mV compared with commercial Pd/C. Finally, PdNB/C in the presence of 1 M FA showed a lower poisoning degree compared with commercial Pd/C and PdNP/C.     

Electrochemical noise analysis of the effects of a magnetic field on cathodic hydrogen evolution

The effect of a static magnetic field on the evolution of hydrogen gas from a small platinum electrode in an aqueous electrolyte has been studied by recording the noise spectrum of overpotential voltage fluctuations at a constant current density of ?50 mA mm^?2. A 1/f² variation of the power spectrum characteristic of droplet coalescence is found for frequencies >10 Hz. The overpotential for hydrogen evolution decreases with applied field. When the production of gas bubbles is quasiperiodic, there is a threshold field of 0.5 T beyond which the size of the bubbles released is approximately doubled. This is explained by enhanced coalescence of small bubbles swept across the electrode surface by forced convection due to the Lorentz force.     

Adsorption of hydrogen on Pt(1 1 1) and Pt(1 0 0) surfaces and its role in the HOR

Hydrogen adsorption isotherms, evaluated by combination of cyclic voltammetry and chronoamperometry, are reported on Pt(1 1 1) and Pt(1 0 0) surfaces in 0.1 M HClO₄. We found that at E > 0.05 V Pt(1 1 1) and Pt(1 0 0) are only partially covered by the adsorbed hydrogen (H_ad). On both surfaces, a full monolayer of the adsorbed hydrogen is completed at −0.1 V, i.e. the adsorption of atomic hydrogen is observed in the hydrogen evolution potential region. We also found, that the activity of the hydrogen oxidation reaction is mirrored by the shape of the hydrogen adsorption isotherms, implying that H_ad is in fact a spectator in the HOR.     

Visible light active hydrogen modified (HM)-n-TiO2 thin films for photoelectrochemical splitting of water

Visible light active hydrogen modified n-type titanium oxide (HM-n-TiO₂) thin films were synthesized by thermal oxidation of Ti metal sheet (Alfa Co. 0.25 mm thick) in an electric oven followed by incorporation of hydrogen electrochemically under cathodic polarization at ?1.6 V vs Pt. The photoresponse of the HM-n-TiO₂ was evaluated by measuring the rate of water splitting reaction to hydrogen and oxygen in terms of photocurrent density, J_p. The optimized electric oven-made n-TiO₂ and HM-n-TiO₂ photoelectrodes showed photocurrent densities of 0.2 mA cm^?2 and 1.60 mA cm^?2, respectively, at a measured potential of ?0.4 V vs Pt at illumination intensity of 100 mW cm^?2 from a 150 W xenon lamp. This indicated an eightfold increase in photocurrent density for HM-n-TiO₂ compared to oven-made n-TiO₂ at the same measured electrode potential. The band-gap energy of HM-n-TiO₂ was found to be 2.7 eV compared to 2.82 eV for electric oven-made n-TiO₂ and a mid-gap band at 1.67 eV above the valence band was also observed. The HM-n-TiO₂ thin film photoelectrodes were characterized using photocurrent density under monochromatic light illumination and UV–Vis spectral measurements.     

New power source from fractional quantum energy levels of atomic hydrogen that surpasses internal combustion

Extreme ultraviolet (EUV) spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 or these lines inelastically scattered by helium atoms wherein 21.2 eV was absorbed in the excitation of He (1s²) to He (1s¹2p¹). These lines were identified as hydrogen transitions to electronic energy levels below the ‘ground’ state corresponding to fractional quantum numbers. Significant line broadening corresponding to an average hydrogen atom temperature of 33–38 eV was observed for helium–hydrogen discharge plasmas; whereas pure hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of ≈3 eV. Since a significant increase in H temperature was observed with helium–hydrogen discharge plasmas, and energetic hydrino lines were observed at short wavelengths in the corresponding microwave plasmas that required a very significant reaction rate due to low photon detection efficiency in this region, the power balance was measured on the helium–hydrogen microwave plasmas. With a microwave input power of 30 W, the thermal output power was measured to be at least 300 W corresponding to a reactor temperature rise from room temperature to 900 °C within 90 s, a power density of 30 MW/m³, and an energy balance of about −4×10⁵ kJ/mol H₂ compared to the enthalpy of combustion of hydrogen of −241.8 kJ/mol H₂.     

Preparation of palladium membranes from the reaction of Pd(C3H3)(C5H5) with H2: wet-impregnated deposition

A new technique to prepare a palladium membrane for high-temperature hydrogen permeation was developed: Pd(C₃H₃)(C₅H₅) an organometallic precursor reacted with hydrogen at room temperature to decompose into Pd crystallites. This reaction together with sintering treatment under hydrogen and nitrogen in sequence resulted in the formation of dense films of pure palladium on the surface of the mesoporous stainless steel (SUS) support. Under H₂ atmosphere the palladium membrane could be sintered at 823 K to form a skin layer inside the support pores. The hydrogen permeance was 5.16×10⁻² cm³ cm⁻² cm Hg⁻¹ s⁻¹ at 723 K. H₂/N₂ selectivity was 1600 at 723 K.     

Comparative study of the catalytic hydroconversion of cyclopentane over iridium and platinum single-crystal surfaces

In the context of fuel upgrading by selective ring opening of naphthenes, we have investigated the catalytic conversion of cyclopentane in large hydrogen excess over iridium and platinum single-crystal surfaces. Both (111) and (112) orientations have been considered. The catalytic tests have been performed at 1 kPa and 25–600 °C using a recently developed surface reactor equipped with laser heating and online gas chromatography. Only cyclopentene and C₁–C₄ cracking products are formed on iridium, while platinum additionally catalyzes the formation of pentane around 200 °C, which dehydrogenates to pentene at 250 °C. Noticeably, on both metals, the surface steps prevent hydrocarbon cracking (up to 400 °C) at the benefit of dehydrogenation. In all cases, a carbon overlayer is formed on the surfaces in the course of the reaction.     

Platinum-like oxidation of nickel surfaces by rapidly switching voltage to generate highly active bifunctional catalysts

Recently the importance of catalyzing the water splitting step of the hydrogen evolution reaction (HER) was highlighted. We demonstrate here a treatment to modify a nickel surface into a highly effective bifunctional HER catalyst (i₀ = 0.18 A/m², Tafel Slope = 106 mV/dec) that has a good distribution of both water splitting sites and H_ads combination sites. The resulting surface is characterized electrochemically, and with SEM, EDX, XPS and AFM. The data is found to be consistent with the treatment oxidizing the Ni surface in a novel way creating the hypothesized “Ni(OH)_x” structure (x between 0 and 2).     

A time-dependent wave packet study of the H4 four-center reaction

A quantum model based on the time-dependent initial state selected wave packet approach was developed to study the four-center (4C) reaction, A₂ + B₂ → 2AB, and the competing collision induced dissociation (CID), A₂ + B₂ → A + B₂ + A, as applied to the H₂(v₁) + H₂(v₂) system important in combustion. A reduced three-dimensional model of the reaction with the atoms constrained to an isosceles trapezium and a realistic global potential energy surface of Aguado et al. [J. Chem. Phys. 101 (1994) 2742], following Hernández and Clary [J. Chem. Phys. 104 (1996) 8413], was used. A method to analyse the reaction flux for 4C and CID reaction probabilities is presented. The initial A₂ vibrational excitation is not only more efficient than translational energy in facilitating the 4C and CID processes, it also reduces the threshold energy. Both the 4C and CID processes exhibit similar threshold energy behavior. For low vibrational excitation in the A₂ diatom, the 4C process is dominant; as the A₂ diatom becomes highly excited the CID process becomes more important at low collision energies with B₂, but as the collision energy increases the 4C process is favored again.