Improved electrochemical hydrogen storage properties of Ti49Zr26Ni25 quasicrystal alloy by doping with Pd and MWCNTs

Ti₄₉Zr₂₆Ni₂₅ quasicrystal was fabricated via mechanical alloying and subsequent annealing. The mixtures containing different amounts of Pd and MWCNTs were doped into the Ti₄₉Zr₂₆Ni₂₅ alloy by ball-milling method. The icosahedral quasicrystal and Ti₂Ni-type phases were the main phase compositions for the composite alloys. The composite alloy combined the large specific surface area and high conductivity of MWCNTs in conjunction with the excellent electrocatalysis ability of Pd, thus improving the discharge capacity and cycle stability of the matrix alloy. The Ti₄₉Zr₂₆Ni₂₅ + MWCNTs + Pd electrode possessed a maximum discharge capacity of 281.6 mAh/g, outstandingly higher than those for Ti₄₉Zr₂₆Ni₂₅ (206.1 mAh/g), Ti₄₉Zr₂₆Ni₂₅ + MWCNTs (248.4 mAh/g) and Ti₄₉Zr₂₆Ni₂₅ + Pd (259.3 mAh/g). The cycle stability and high-rate dischargeability were also enhanced. Furthermore, the studies on electrochemical reaction kinetics demonstrated that doping of Pd and MWCNTs accelerated the charge-transfer process, the two active materials played synergistic effect in enhancing the electrochemical activity and reaction kinetics for the Ti₄₉Zr₂₆Ni₂₅ electrode.     

Two operating modes of palladium film hydrogen sensor based on suspended micro hotplate

Palladium film hydrogen sensor based on suspended micro hotplate has been fabricated to operate at elevated temperature with low power consumption. Below 150 °C, the response of the sensor to H₂ is represented by an increase in resistance. At higher temperature, the phenomenon of resistance reduction appears when it comes into contact with H₂. We have researched the reasons for this phenomenon and proposed that the sensitive mechanism is the redox reaction of Pd film on the suspended structure. The suspended substrate can affect the temperature at which redox of the Pd film occurs, and be sensitive to the changes of the surrounding gas stream. When the working temperature is 400 °C, the magnitude of response (S) changes to −0.4% within 2 s for 200 ppm H₂, and S changes to −3% within 10 s for 4000 ppm H₂. This micro hotplate based hydrogen sensor can control the range of operating temperature according to the performance requirements.     

Direct synthesis of hydrogen peroxide over Pd nanoparticles embedded between HZSM-5 nanosheets layers

Direct synthesis of hydrogen peroxide (DSHP) was studied over Pd loaded on HZSM-5 nanosheets (Pd/ZN). Pd nanoparticles with average size of ca. 4.3 nm were introduced into the adjacent nanosheet layers (thickness of ca. 2.9 nm) by impregnation method. Pd/ZN with theoretical Si/Al molar ratio of 25 showed the highest selectivity for H₂O₂ among the prepared catalysts, together with highest formation rate of H₂O₂ (38.0 mmol·(g cat)⁻¹·h⁻¹), 1.9 times than that of Pd supported on conventional HZSM-5 zeolite (Pd/CZ-50). Better catalytic performance of nanosheet catalysts was attributed to the promoted Pd dispersion which promoted H₂ dissociation, more Brønsted acid sites and stronger metal-support interaction which inhibited the dissociation of OO bond in H₂O₂. The embedded structure sufficiently protected the Pd nanoparticles by space confinement which restrained the Pd leaching, leading to a better catalytic stability with 90% activity retained after 3 cycles, which was almost 3 times than that of Pd/CZ-50 (30.4% activity retained).     

Evaluation of Pd-TiO2/ZSM-5 catalysts composition effects on hydrogen production by photocatalytic water splitting

The photocatalyst composition can significantly affect their physicochemical properties that are directly related to their photocatalytic activity. In this work, the influence of the Pd-TiO₂/ZSM-5 catalyst composition on hydrogen production by photocatalytic water splitting was studied. The ZSM-5 zeolite was use as support for the active phase of titanium dioxide; palladium was also incorporated as a metallic co-catalyst. The concentrations of TiO₂ and Pd were varied during catalyst synthesis according to a factorial rotational experimental design. The catalysts were characterized and employed in hydrogen production under ultraviolet radiation. Empirical models were obtained for relating physicochemical properties and hydrogen production as functions of palladium and titanium dioxide content. Relative crystallinity of the support and specific surface area were affected only by the titanium dioxide contend while band gap energy and hydrogen production were affected by nominal percentage of metallic co-catalyst and active phase. The most active catalyst was the 1.5%Pd-28%TiO₂/ZSM-5, which promoted hydrogen production rate of 1148 μmol g_cat^?1 h^?1 under low power irradiation font.     

Electroless platinum and palladium deposition over alumina coated stainless steel plates and their catalytic activity for hydrogen mitigation in severe nuclear accidents

This work focused on platinum and palladium-based autocatalytic plates, which used to remove hydrogen. The six sandblasted stainless steel plates were coated with platinum and palladium metals using the electroless coating method. The three plates A-01, A-02, A-03 were first coated with alumina using the sol-gel dip method, and after that, different ratios of platinum and palladium were deposited on them. The three other plates, B-01, B-02, B-03 (without alumina coated), were coated directly with different ratios of platinum and palladium. The platinum and palladium ratio used for coating these plates were Pt 80%: Pd 20%; Pt 90%: Pd 10%, and Pt 70%: Pd 30. The coating of these plates was characterized using Scanning Electron Microscopy, X-rays Fluorescence Spectroscopy, and their catalytic efficiency was measured by the Passive Autocatalytic Recombiner testing rig method. It was found that the plates coated with alumina using two dipping cycles are suitable for different coating of mixed metals by electroless coating method compared to three dipping cycles. It was observed that the alumina-coated catalytic plates (A-01, A-02, A-03) exhibited excellent catalytic efficiency as compared to those without alumina-coated plates (B-01, B-02, B-03). Furthermore, the catalytic efficiency of A-03 and B-03 is higher than other plates. It was also found that the catalytic efficiency of A-03 is higher than B-03. The best coating ratio is Pt 90%: Pd10%, and alumina-coated plates give excellent results.     

Palladium nanoparticles grown on β-Mo2C nanotubes as dual functional electrocatalysts for both oxygen reduction reaction and hydrogen evolution reaction

Developing efficient dual functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is critical for boosting the performance of fuel cells and metal air batteries, as well as production of clean and sustainable energy source. Herein, Pd nanoparticles grown on Mo₂C nanotubes were prepared as dual functional electrocatalysts for both ORR and HER. A series of samples with different Pd loadings were fabricated, while the morphology and the structural features were well examined by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Interestingly, both the ORR activity and HER activity first increased then decreased with the increasing of Pd loading, and the sample of Mo₂C-Pd-9% exhibited the best performance among the series, superior than commercial Pd/C in both ORR and HER tests. Furthermore it also exhibited markedly higher long-term stability than Pd/C for both electrocatalytic reactions. The results may shed light on rational design of novel bi-functional electrocatalysts in the renewable energy field.     

Process analysis of hydrogen production from biomass gasification in fluidized bed reactor with different separation systems

Gasification is one of the most effective and studied methods for producing energy and fuels from biomass as different biomass feedstock can be handled, with the generation of syngas consisting of H₂, CO, and CH₄, which can be used for several applications. In this study, the gasification of hazelnut shells (biomass) within a circulating bubbling fluidized bed gasifier was analyzed for the first time through a quasi-equilibrium approach developed in the Aspen Plus environment and used to validate and improve an existing bubbling fluidized bed gasifier model. The gasification unit was integrated with a water-gas shift (WGS) reactor to increase the hydrogen content in the outlet stream and with a pressure swing adsorption (PSA) unit for hydrogen separation. The amount of dry H₂ obtained out of the gasifier was 31.3 mol%, and this value increased to 47.5 mol% after the WGS reaction. The simulation results were compared and validated against experimental data reported in the literature. The process model was then modified by replacing the PSA unit with a palladium membrane separation module. The final results of the present work allowed comparison of the effects of the two conditioning systems, PSA and palladium membrane, indicating a comparative increase in the hydrogen recovery ratio of 28.9% with the palladium membrane relative to the PSA configuration.     

Performance and durability of an anode-supported solid oxide fuel cell with a PdO/ZrO2 engineered (La0.8Sr0.2)0.95MnO3-δ-(Y2O3)0.08(ZrO2)0.92 composite cathode

PdO/ZrO₂ co-infiltrated (La_0.8Sr_0.2)_0.95MnO_3-δ-(Y₂O₃)_0.08(ZrO₂)_0.92 (LSM-YSZ) composite cathode (PdO/ZrO₂+LSM-YSZ), which adsorbs more oxygen than equal amount of PdO/ZrO₂ and LSM-YSZ, is developed and used in Ni-YSZ anode-supported cells with YSZ electrolyte. The cells are investigated firstly at temperatures between 650 and 750 °C with H₂ as the fuel and air as the oxidant and then polarized at 750 °C under 400 mA cm^?2 for up to 235 h. The initial peak power density of the cell is in the range of 438–1207 mW cm^?2 at temperatures from 650 to 750 °C, corresponding to polarization resistance from 1.04 to 0.35 Ω cm². This result demonstrates a significant performance improvement over the cells with other kinds of LSM based cathode. The cell voltage at 750 °C under 400 mA cm^?2 decreases from initial 0.951 to 0.89 V after 170 h of current polarization and remains essentially stable to the end of current polarization. It is identified that the self-limited growth of PdO particles is responsible for the cell voltage decrease by reducing the length of triple phase boundary affecting the high frequency steps involved in oxygen reduction reaction in the cathode.     

High-temperature close coupled catalysts Pd/Ce-Zr-M/Al2O3 (M = Y, Ca or Ba) used for the total oxidation of propane

A series of high-temperature close coupled catalysts Pd/Ce-Zr-M/Al₂O₃ (M = Y, Ca or Ba) were prepared by ultrasonic-assisted successive impregnation. The catalysts were subjected to a series of characterization measurements. The results of activity evaluation show that Y is the best promoter for propane total oxidation, especially at the calcination temperature of 1100 °C. It is interesting that although the BET specific surface areas and the dispersion of Pd species decrease, the Y-promoted catalyst calcined at 1100 °C shows higher catalytic activity than the corresponding one calcined at 900 °C and better sulfur-resisting performance. The results of TEM, TPHD and CO chemisorption indicate that Y can remarkably increase the dispersion of Pd species. However, the dispersion is hard to be connected with the activity increase as the calcination temperature is elevated from 900 to 1100 °C. The change of active phases and the interaction between Pd species and the supports may account for the activity enhancement. Combined with XRD, H₂-TPR and O₂-TPD results, it is deduced that the coexistence of metallic Pd and PdO species in the catalysts calcined at 1100 °C may be also favorable to C₃H₈ oxidation. In a word, Pd/Ce-Zr-Y/Al₂O₃ is indeed a promising high-temperature close coupled catalyst applicable to high temperature.     

Electrochemical and structural characterization of carbon-supported Pt-Pd bimetallic electrocatalysts prepared by electroless deposition

Electrochemical and structural characteristics of various Pt-Pd/C bimetallic catalysts prepared by electroless deposition (ED) methods have been investigated. Structural analysis was conducted by X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDS). Monometallic Pt or Pd particles were not detected by EDS, indicating the ED methodology formed only bimetallic particles. The size of the Pt-Pd bimetallic particles was smaller than those of a commercially available Pt/C catalyst. The morphology of the Pt on Pd/C catalysts was identified and corresponded to Pd particles partially encapsulated by Pt.The electrochemical characteristics of the lowest Pd loading catalyst (7.0% Pt on 0.5% Pd/C) for the oxygen reduction reaction (ORR) have been investigated by the rotating ring disk electrode technique. The electrochemical activity was equal or lower than the commercially available Pt/C catalyst; however, the amount of hydrogen peroxide observed at the ring was reduced by the Pd, suggesting that such a catalyst has the potential to decrease ionomer degradation in applications. The Pt on Pd/C catalysts also show a higher tolerance to ripening induced by potential cycling. Therefore, catalyst suitability cannot be judged solely by its initial performance; information related to specific degradation mechanisms is also needed for a more complete assessment.