Effect of H2O2 on Pt electrode dissolution in H2SO4 solution based on electrochemical quartz crystal microbalance study

The effect of H₂O₂ on the Pt dissolution in 0.5 mol dm⁻³ H₂SO₄ was investigated using an electrochemical quartz crystal microbalance (EQCM). For the potential cycling at 50 mV s⁻¹, the Pt weight irreversibly decreases in a N₂ atmosphere with H₂O₂, while only a negligible Pt weight-loss is observed in the N₂ and O₂ atmospheres without H₂O₂. The EQCM data measured by the potential step showed that the Pt dissolution in the presence of H₂O₂ depends on the electrode potential and the H₂O₂ concentration. For the stationary electrolysis, the Pt dissolution occurs at 0.61–1.06 and 1.06–1.36 V vs. RHE. It should be noted that the Pt dissolution phenomenon in the presence of H₂O₂ is also affected by the potential scanning time. Based on these results, H₂O₂ is considered not only to contribute to the formation of Pt-oxide causing the cathodic Pt dissolution, but also to participate in the anodic Pt dissolution and the chemical Pt dissolution.     

Li ion exchange in CeO2-TiO2 sol-gel layers studied by electrochemical quartz crystal microbalance

The paper reports first on the electrochemical behavior in liquid Li⁺ electrolytes of 200 nm thick single sol-gel (CeO₂)_0.81-TiO₂ electrochromic (EC) layers deposited by the dip-coating process. The electrolytes were solutions of 1 M LiClO₄ dissolved in dry propylene carbonate (PC) (containing 0.03 wt% of water) and wet PC containing up to 10 wt% of water, respectively. Then an electrochemical quartz crystal microbalance was used as a sensitive detector to analyze the mass changes occurring during the Li⁺ ion exchange processes. These electrochemical processes were studied for 370 nm thick double layers, deposited on gold-coated quartz crystal electrodes and sintered at 450 °C in air. The electrolytes were the same solutions with water content varying from 0.03 up to 3 wt% of water. The processes have been studied in the potential range from −2.0 to +1.0 V vs. Ag/AgClO₄ during 100 voltammetry cycles. The composition of the (CeO₂)_0.81-TiO₂ layers was found to change during the early cycles, mainly because of an irreversible Li⁺ intercalation. It was found, however, that the mass change observed during cycling is not due only to a pure Li⁺ ion exchange process but also involves the adsorption/desorption or exchange of other cations and anions contained in the electrolyte. These ions are Li⁺ and ClO₄⁻ in dry electrolyte and Li⁺, hydrated Li(H₂O)_n⁺ and ClO₄⁻ in wet electrolyte. The improvement of the reversibility of the intercalation and deintercalation processes as well as the faster kinetics observed in wet electrolytes are finally discussed in terms of a model in which the formation of hydrated Li⁺ ions takes an important role.     

Corrosion of carbon support for PEM fuel cells by electrochemical quartz crystal microbalance

During the voltammetry of carbon supports for proton exchange membrane fuel cells (PEMFCs), including commercial carbon blacks, graphitized carbon black and multi-wall carbon nanotubes (MWNTs), in deaerated 0.5 M H₂SO₄ solution results in mass changes as observed by using in situ electrochemical quartz crystal microbalance (EQCM). The mass change and corrosion onset potential during electrochemical carbon corrosion indicate that oxides are formed and accumulated on the carbon surface, leading to an increase in mass. A decrease in the mass is associated with carbon loss from the gasification of carbon surface oxides into carbon dioxide. High BET surface area carbon blacks ECP600 and ECP 300 have a carbon loss of 0.0245 ng cm⁻² s⁻¹ and 0.0144 ng cm⁻² s⁻¹ and as compared to 0.0115 ng cm⁻² s⁻¹ for low surface area support XC-72 and so they are less resistant to corrosion. Graphitized XC-72 and MWNTs, with higher graphitization have higher carbon corrosion onset potential at 1.65 V and 1.62 V and appear to be more intrinsically resistant to corrosion.     

H2SO4 stability of PBI-blend membranes for SO2 electrolysis

For hydrogen to become a serious contender for replacing fossil fuels, the manufacturing thereof has to be further investigated. One such process, the membrane based Hybrid Sulfur (HyS) process, where hydrogen is produced from the electrolysis of SO₂, has received considerable interest recently. Since H₂SO₄ is formed during SO₂ electrolysis, H₂SO₄ stability is a prerequisite for any membrane to be used in this process. In this study, pure as well as blended polybenzimidazole (PBI), partially fluorinated poly(arylene ether) (sFS) and nonfluorinated poly(arylene ethersulfone) (sPSU) membranes were investigated in terms of their acid stability as a function of acid concentration. Membranes were characterized using weight change, TGA, GPC, SEM/EDX and IEC. While a general stability was observed at 30 and 60 wt% H₂SO₄, the blended sFS-PBI and sPSU-PBI showed the highest stability throughout. According to the VI curve obtained for the SO₂ electrolysis, the sPSU-PBI blend membrane performed slightly better than Nafion^®117.     

Photocatalytic properties of redox-treated Pt/TiO2 photocatalysts for H2 production from an aqueous methanol solution

The influence of redox-treated Pt/TiO₂ photocatalysts on H₂ production is investigated. Catalyst characterizations are performed by TEM, XPS, XRD, BET, and UV–vis/DR spectroscopy techniques. In terms of production rate, the oxidation treatment shows higher reactivity than the reduction treatment. The reduction treatment allows the formation of metallic Pt(0), which more easily catalyzes the transition of TiO₂ from the anatase to the rutile phases. Reduction-treated Pt/TiO₂ photocatalysts have lower S_BET values than oxidation-treated Pt/TiO₂ photocatalysts due to the higher percentage of TiO₂ in the rutile phase. Combining the results of XPS and optical analyses, PtO/TiO₂ shows a higher energy band gap than metallic Pt(0)/TiO₂, indicating that oxidation-treated Pt/TiO₂ is more capable of achieving water splitting for H₂ production. According to the results of this study, the oxidation treatment of Pt/TiO₂ photocatalysts can significantly enhance the reactivity of photocatalytic H₂ production because of their homogenous distribution, lower phase transition, higher S_BET, and higher energy band gap.     

Enhancement of the H2 desorption properties of LiAlH4 doping with NiCo2O4 nanorods

Lithium aluminum hydride (LiAlH₄) is considered as an attractive candidate for hydrogen storage owing to its favorable thermodynamics and high hydrogen storage capacity. However, its reaction kinetics and thermodynamics have to be improved for the practical application. In our present work, we have systematically investigated the effect of NiCo₂O₄ (NCO) additive on the dehydrogenation properties and microstructure refinement in LiAlH₄. The dehydrogenation kinetics of LiAlH₄ can be significantly increased with the increase of NiCo₂O₄ content and dehydrogenation temperature. The 2 mol% NiCo₂O₄-doped LiAlH₄ (2% NCO–LiAlH₄) exhibits the superior dehydrogenation performances, which releases 4.95 wt% H₂ at 130 °C and 6.47 wt% H₂ at 150 °C within 150 min. In contrast, the undoped LiAlH₄ sample just releases <1 wt% H₂ after 150 min. About 3.7 wt.% of hydrogen can be released from 2% NCO–LiAlH₄ at 90 °C, where total 7.10 wt% of hydrogen is released at 150 °C. Moreover, 2% NCO–LiAlH₄ displayed remarkably reduced activation energy for the dehydrogenation of LiAlH₄.     

CuCr2O4/TiO2 heterojunction for photocatalytic H2 evolution under simulated sunlight irradiation

CuCr₂O₄/TiO₂ heterojunction has been successfully synthesized via a facile citric acid (CA)-assisted sol-gel method. Techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectrum (UV-vis DRS) have been employed to characterize the as-synthesized nanocomposites. Furthermore, photocatalytic activities of the as-obtained nanocomposites have been evaluated based on the H₂ evolution from oxalic acid solution under simulated sunlight irradiation. Factors such as CuCr₂O₄ to TiO₂ molar ratio in the composites, calcination temperature, photocatalyst mass concentration, and initial oxalic acid concentration affecting the photocatalytic hydrogen producing have been studied in detail. The results showed that the nanocomposite of CuCr₂O₄/TiO₂ is more efficient than their single part of CuCr₂O₄ or TiO₂ in producing hydrogen. The optimized composition of the nanocomposites has been found to be CuCr₂O₄·0.7TiO₂. And the optimized calcination temperature and photocatalyst mass concentration are 500 °C and 0.8 g l⁻¹, respectively. The influence of initial oxalic acid concentration is consistent with the Langmuir model.     

Effect of H2O2 on Nafion properties and conductivity at fuel cell conditions

During PEM fuel cell operation, formation of H₂O₂ and material corrosion occurs, generating trace amounts of metal cations (i.e., Fe²⁺, Pt²⁺) and subsequently initiating the deterioration of cell components and, in particular, PFSA membranes (e.g., Nafion). However, most previous studies of this have been performed using conditions not relevant to fuel cell environments, and very few investigations have studied the effect of Nafion decomposition on conductivity, one of the most crucial factors governing PEMFC performance. In this study, a quantitative examination of properties and conductivities of degraded Nafion membranes at conditions relevant to fuel cell environments (30-100%RH and 80 °C) was performed. Nafion membranes were pre-ion-exchanged with small amounts of Fe²⁺ ions prior to H₂O₂ exposure. The degradation degree (defined as loss of ion-exchange capacity, weight, and fluoride content), water uptake, and conductivity of H₂O₂-exposed membranes were found to strongly depend on Fe content and H₂O₂ treatment time. SEM cross-sections showed that the degradation initially took place in the center of the membrane, while FTIR analysis revealed that Nafion degradation preferentially proceeds at the sulfonic end group and at the ether linkage located in the pendant side chain and that the H-bond of water is weakened after prolonged H₂O₂ exposure.     

Thermal decomposition of (NH4)2SO4 in presence of Mn3O4

The main objective of this work is to develop a hybrid water-splitting cycle that employs the photon component of sunlight for production of H₂ and its thermal (i.e. IR) component for generating oxygen. In this paper, (NH₄)₂SO₄ thermal decomposition in the presence of Mn₃O₄, as an oxygen evolving step, was systematically investigated using thermogravimetric/differential thermal analyses (TG/DTA), temperature programmed desorption (TPD) coupled with a mass spectrometer (MS), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) techniques. Furthermore, thermolysis of ammonium sulfate, (NH₄)₂SO₄, in the presence of Mn₃O₄ was also investigated by conducting flow reactor experiments. The experimental results obtained indicate that at 200-450 °C, (NH₄)₂SO₄ decomposes forming NH₃ and H₂O and sulfur trioxide that in the presence of manganese oxide react to form manganese sulfate, MnSO₄. At still higher temperatures (800∼900 °C), MnSO₄ further decomposed forming SO₂ and O₂.     

Improvement in electrochemical performance of V2O5 by Cu doping

Cu_0.04V₂O₅ was prepared by a precipitation method followed by heat treatment at 300 and 600 °C. The material prepared at 300 °C showed porous morphology, whereas that prepared at 600 °C was highly crystalline. X-ray diffraction, Raman scattering and Fourier transform infrared spectroscopy showed both materials exhibiting the same structure as that of V₂O₅, with a slight lattice expansion. X-ray absorption spectroscopy confirmed the presence of V⁴⁺ cations in Cu_0.04V₂O₅, which would increase the electronic conductivity of V₂O₅. Cu_0.04V₂O₅ showed better electrochemical performance than V₂O₅ because of its high electronic conductivity and good structural stability. The material prepared at 600 °C delivered a reversible discharge capacity over 160 mAh g⁻¹ after 60 cycles at a C rate of C/5.6. The material prepared at 300 °C showed good high-rate performance, which delivered a reversible capacity ∼100 mAh g⁻¹ when cycled at C/1.9. The discrepancy in the rate performance of Cu_0.04V₂O₅ was attributed to the morphology of materials.     

Electrospun Pt/TiO2 hybrid nanofibers for visible-light-driven H2 evolution

One-dimensional (1D) Pt/TiO₂ hybrid nanofibers (HNFs) with different concentrations of Pt were fabricated by a facile two-step synthesis route combining an electrospinning technique and calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) results showed that the Pt nanoparticles (NPs) with the size of 5–10 nm were well dispersed in the TiO₂ nanofibers (NFs). Further investigations from the UV–Vis diffuse reflectance (DR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that some Pt ions were incorporated into the TiO₂ lattice as Pt⁴⁺ state, which contributed to the visible light absorption of TiO₂ NFs. Meanwhile, the Pt²⁺ ions existing on the surface of Pt NPs resulted in the formation of Pt–O–Ti bond at Pt NPs/TiO₂ NFs interfaces that might serve as an effective channel for improving the charge transfer. The as-electrospun Pt/TiO₂ HNFs exhibited remarkable activities for photocatalytic H₂ evolution under visible light irradiation in the presence of l-ascorbic acid as the sacrificial agent. In particular, the optimal HNFs containing 1.0 at% Pt showed the H₂ evolution rate of 2.91 μmol h⁻¹ and apparent quantum efficiency of 0.04% at 420 nm by using only 5 mg of photocatalysts. The higher photocatalytic activity could be ascribed to the appropriate amount of Pt ions doping and excellent electron-sink effect of Pt NPs co-catalysts.     

Ti/PbO2 + nano-Co3O4 composite electrode material for electrocatalysis of O2 evolution in alkaline solution

Ti/PbO₂ + nano-Co₃O₄ composite electrode materials with different compositions were prepared by anodic composite electrodeposition on Ti substrate, with a SnO₂-Sb₂O₅ intermediate layer in Pb²⁺ plating solution containing suspended nano-Co₃O₄ particles. The composition, structure, and morphology of the composite materials were investigated by XRD, XPS, and SEM analyses. The composite electrodes were studied as anodes for oxygen evolution reaction (OER) in 1 mol/L NaOH solution. The activities for the OER of the composites were explained by recording linear scanning voltammograms and Tafel plots. Results indicate that the onset potential of oxygen evolution at the composite electrode was lowered by approximately 160 mV compared to the PbO₂ electrode without nano-Co₃O₄. The catalytic activity of the composite electrode towards OER was improved significantly.     

Selective CO oxidation on Cu promoted Pt/Al2O3 and Pt/Nb2O5 catalysts

Pt–Cu catalysts supported on Al₂O₃ and Nb₂O₅ were studied for use in selective CO oxidation. The addition of copper enhanced the activity and selectivity of Pt–Cu/Nb₂O₅ at lower temperatures when compared to Pt/Nb₂O₅. On the other hand, copper addition was not beneficial in the case of Al₂O₃ supported catalysts.     

Solvothermal synthesis of SnNb2O6 nanoplates and enhanced photocatalytic H2 evolution under visible light

Well-defined SnNb₂O₆ nanoplates are synthesized here by a facile template-free solvothermal route in a mixed solvent of water and ethanol without an organic surfactant. The synthesized nanoplates have widths ranging from 200 to 400 nm and thicknesses in a range of 20–30 nm. The nanoplates were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–Vis spectroscopy, Raman spectrometry, and by the Brunauer–Emmett–Teller method. The variation of the lattice parameters and the optical properties of the nanoplates were discussed in detail based on the crystal and electronic structure. The SnNb₂O₆ nanoplates exhibited greatly enhanced photocatalytic activity in terms of the reduction of water for H₂ generation under visible light irradiation as compared to the same compound prepared by a solid–state reaction method. This was mainly attributed to its higher surface area and extremely high two-dimensional anisotropy, which provided a short migration distance along the thickness direction.     

Catalytic effect of Gd2O3 and Nd2O3 on hydrogen desorption behavior of NaAlH4

This study investigated the effect of Nd₂O₃ and Gd₂O₃ as catalyst on hydrogen desorption behavior of NaAlH₄. Pressure-content-temperature (PCT) equipment measurement proved that both two oxides enhanced the dehydrogenation kinetics distinctly and increasing Nd₂O₃ and Gd₂O₃ from 0.5 mol% to 5 mol% caused a similar effect trend that the dehydrogenation amount and average dehydrogenation rate increased firstly and then decreased under the same conditions. 1 mol% Gd₂O₃–NaAlH₄ presented the largest hydrogen desorption amount of 5.94 wt% while 1 mol% Nd₂O₃–NaAlH₄ exerted the fastest dehydrogenation rate. Scanning Electron microscopy (SEM) analysis revealed that Gd₂O₃–NaAlH₄ samples displayed uniform surface morphology that was bulky, uneven and flocculent. The difference of Nd₂O₃–NaAlH₄ was that with the increasing of Nd₂O₃ content, the particles turned more and more big. Compared to dehydrogenation behavior, this phenomenon demonstrated that small particles structure were beneficial to hydrogen desorption. Besides, the further study found that different catalysts and addition amounts had different effects on the microstructure of NaAlH_4.     

Influence of H2SO4 concentration on the performance of lead-acid battery negative plates

The influence of sulfuric acid concentration on negative plate performance has been studied on 12 V/32 Ah lead-acid batteries with three negative and four positive plates per cell, i.e. the negative active material limits battery capacity. Initial capacity tests, including C20 capacity, cold cranking ability and Peukert tests, have been carried out in a wide range of sulfuric acid concentrations (from 1.18 to 1.33 sp.gr.). High initial capacity and good CCA performance were registered for batteries with acid concentration between 1.24 and 1.30 sp.gr. The charge acceptance depends on acid concentration as well as on battery state of charge. Batteries with high SoC exhibit high charge acceptance at low acid concentrations. The cycle life tests at two discharge rates (10 and 3 h discharge) evidence that sulfuric acid concentration exerts a strong effect on negative plate performance. The cycle life of batteries decreases with increase of acid concentration. The obtained results demonstrate the high impact of lead sulfate solubility on the cycle life and charge efficiency of lead-acid batteries.     

Temperature and humidity dependence of the electrode polarization in intermediate-temperature fuel cells employing CsH2PO4/SiP2O7-based composite electrolytes

The polarization behaviors of platinum electrode were investigated with a single cell employing CsH₂PO₄/SiP₂O₇-based composite electrolyte. The electrochemical measurements were conducted in the temperature range of 180–240 °C under various humidity conditions. The cell performance was enhanced during several discharge cycles, and then the steady state was attained. The active triple phase boundary (TPB) appears to be spontaneously formed. The polarization behaviors for both anode and cathode were strongly affected by the electrolyte conductivity due to its humidity dependence. In accordance with this tendency, the maximum performance was achieved at 220 °C in 30% humidified condition whereas the deterioration was observed at 240 °C. Throughout the analysis, however, the performance limitation was mainly due to cathodic polarization at every condition. The cathodic overpotential showed a linear dependence against the log of current density at each temperature, which can be expressed as a Tafel equation. Then, the influence of steam concentration and temperature on the electrochemical kinetics was also discussed.     

Hybrid supercapacitor based on MnO2 and columned FeOOH using Li2SO4 electrolyte solution

The nano-sized columned β-FeOOH was prepared by the hydrolysis process and its electrochemical capacitance performance was evaluated for the first time in Li₂SO₄ solution. A hybrid supercapacitor based on MnO₂ positive electrode and FeOOH negative electrode in Li₂SO₄ electrolyte solution was designed. The electrochemical tests demonstrated that the hybrid supercapacitor has a energy density of 12 Wh kg⁻¹ and a power density of 3700 W kg⁻¹ based on the total weight of the electrode active materials with a voltage range 0–1.85 V. This hybrid supercapacitor also exhibits a good cycling performance and keeps 85% of initial capacity over 2000 cycles.     

High-rate performance of all-solid-state lithium secondary batteries using Li4Ti5O12 electrode

The all-solid-state Li–In/Li₄Ti₅O₁₂ cell using the 80Li₂S·20P₂S₅ (mol%) solid electrolyte was assembled to investigate rate performances. It was difficult to obtain the stable performance at the charge current density of 3.8 mA cm⁻² in the all-solid-state cell. In order to improve the rate performance, the pulverized Li₄Ti₅O₁₂ particles were applied to the all-solid-state cell, which retained the reversible capacity of about 90 mAh g⁻¹ at 3.8 mA cm⁻². The 70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic, which exhibits the higher lithium ion conductivity than the 80Li₂S·20P₂S₅ solid electrolyte, was also used. The Li–In/70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic/pulverized Li₄Ti₅O₁₂ cell was charged at a current density higher than 3.8 mA cm⁻² and showed the reversible capacity of about 30 mAh g⁻¹ even at 10 mA cm⁻² at room temperature.