Influence of Ionomer Content in the Catalytic Layer of MEAs Based on Aquivion® Ionomer

Perfluorinated sulfonic acid (PFSA) polymers such as Nafion® are widely used for both electrolyte membranes and ionomers in the catalytic layer of membrane-electrode assemblies (MEAs) because of their high protonic conductivity, σH, as well as chemical and thermal stability. The use of PFSA polymers with shorter side chains and lower equivalent weight (EW) than Nafion®, such as Aquivion® PFSA ionomers, is a valid approach to improve fuel cell performance and stability under drastic operative conditions such as those related to automotive applications. In this context, it is necessary to optimize the composition of the catalytic ink, according to the different ionomer characteristics. In this work, the influence of the ionomer amount in the catalytic layer was studied, considering the dispersing agent used to prepare the electrode (water or ethanol). Electrochemical studies were carried out in a single cell in the presence of H2-air, at intermediate temperatures (80–95 °C), low pressure, and reduced humidity (50% RH. %). The best fuel cell performance was found for 26 wt.% Aquivion® at the electrodes using ethanol for the ink preparation, associated to a maximum catalyst utilization.

Mechanical Stability Is Key for Large-Scale Implementation of Photocatalytic Surface-Attached Film Technologies in Water Treatment

Replacement of classical tertiary water treatment by chemical-free sunlight-driven photocatalytic units has been often proposed. Photocatalysts are required to be cost-effective, inert, chemically stable, reusable, and easy to separate and also that they are mechanically stable. The effect of mechanical stress on a photoactive TiO2 layer, and on its effectivity for degradation of phenol as a model pollutant, has been studied during photocatalytic water treatment using NUV–vis light. Sol–gel (SG) and liquid phase deposition (LPD) methods have been used to coat spherical glass beads with the photocatalyst (TiO2). Physicochemical characterization of coated glass beads has been performed by N2 adsorption–desorption isotherms, SEM, EDXS, and AFM. Phenol photocatalyzed degradation was carried out both in stirred batch and flow reactors irradiated with a medium-pressure Hg-vapor lamp (λ > 350 nm). Phenol concentration was determined by HPLC, and its photoproducts were identified using HPLC/MS. In the stirred batch reactor, all LPD-coated glass beads displayed higher catalytic activity than SG-coated ones, which increased with calcination temperature, 700°C being the most efficient temperature. Preliminary etching of the glass beads surface yielded dissimilar results; whereas, phenol photodegradation with SG-coated etched glass beads is twice faster than with unetched SG ones, the rate reduces to one-third using LPD etched instead of unetched LPD glass beads. Phenol photodegradation using LPD is similar both in stirred batch and flow reactors, despite the latter uses a lower catalyst load. LPD-etched catalyst was recovered and reused in the stirred batch reactor; its activity reduced sharply after the first use, and it also lost activity in successive runs, ca. 10% of activity after each “use and recover” cycle. In the flow reactor, activity loss after the first experiment and recycling (ca. 30%) was much larger than in the following runs, where the activity remained rather constant through several cycles. LPD is more adequate than SG for TiO2 immobilization onto glass beads, and their calcination at 700°C leads to relatively strong and reactive photocatalytic films. Still, TiO2-coated glass beads exhibited very low photoactivity compared to TiO2-P25 nanoparticles, though their separation is much easier and almost costless. The durability of the catalytic layer increases when using a flow reactor, with the pollutant solution flowing in a laminar regime through the photocatalyst bed. In this way, the abrasion of the photocatalytic surface is largely reduced and its photoactivity is better maintained.

THE KINETICS AND MECHANISM OF THE SELECTIVE OXIDATIVE DEHYDROGENATION REACTİON OF METHYLCYCLOPENTANE

The oxidative dehydrogenation of alicyclic diene hydrocarbons refers to scarcely studied heterogeneous catalytic reactions which proceed with the participation of oxygen. The dehydrogenation of methylcyclopentane is an endothermic reaction. To improve the reaction kinetics, this research was to develop a structured catalyst by conductive metals (Cu, Zn, Co, Cr) support which could hold an adherent catalytic layer. The active phase was impregnated onto these support metals and the developed catalyst was tested for the dehydrogenation of methylcyclopentane. The catalyst preparation involved three main key steps which were support oxidative reaction, loading of active particles on the catalyst surface, preparation of an active catalyst layer on the surface finally bringing the catalyst into the active phase. Different types of catalyst activation and deactivation mechanisms stability have been studied in this investigation. The advantage of this works, the oxidative dehydrogenation of methylcyclopentane is that it occurs at the expense of oxygen in the air. The zeolite structure study helped identify the effect of the combination of catalysts, and adsorption of metals on clinoptilolite and dispersion on the selectivity of the catalyst particles. Numerical values of the kinetic parameters were calculated

Improvement of stability and reduction of energy consumption for Ti-based MnOx electrode by Ce and carbon black co-incorporating in electrochemical degradation of ammonia nitrogen

Ti-based electrode coated with MnOx catalytic layer has presented superior electrochemical activity for degradation of organic pollution in wastewater, however, the industrial application of Ti-based MnOx electrode is limited by the poor stability of electrode. In this study, the novel Ti-based MnOx electrodes co-incorporated with rare earth (Ce) and conductive carbon black (C) were prepared by spraying-calcination method. The Ti/Ce:MnOx-C electrode, with uniform and integrate surface and enhanced Mn(IV) content by C and Ce co-incorporating, could completely remove ammonia nitrogen (NH4+-N) with N2 as the main product. The cell potential and energy consumption of Ti/Ce:MnOx-C electrode during the electrochemical process was significantly reduced compared with Ti/MnOx electrode, which mainly originated from the enhanced electrochemical activity and reduced charge transfer resistance by Ce and C co-incorporating. The accelerated lifetime tests in sulfuric acid showed that the actual service lifetime of Ti/Ce:MnOx-C was ca. 25 times that of Ti/MnOx, which demonstrated the significantly promoted stability of MnOx-based electrode by Ce and C co-incorporating.

Influence of PtCu/C Catalysts Composition on Electrochemical Characteristics of Polymer Electrolyte Fuel Cell and Properties of Proton Exchange Membrane

The present work aimed to investigate the influence of “weakly bound“ copper dissolution from the surface of bimetallic PtCux/C catalysts on the properties of proton exchange membrane and the membrane electrode assembly (MEA) in general. A number of PtCux/C materials have been obtained by the simultaneous reduction in copper and platinum precursors in the course of liquid-phase synthesis with a varying ratio of metals from PtCu2.0/C to PtCu0.3/C. All bimetallic PtCux/C electrocatalysts after the activation stage exhibit high activity in the oxygen electroreduction reaction. The PtCux/C catalysts in “as prepared” state were tested in MEA. The increase in Cu content in PtCux/C catalysts led to a decrease in current density of MEA while its resistance was almost independent of the Cu fraction in the catalyst. The membrane saturation degree by Cu2+-ions after MEA testing did not exceed 40%, even in the case of the PtCu2.0/C material. The main reason for the degradation of membrane electrode assembly with PtCux/C materials is the transport limitation caused by the contamination of Nafion in three catalytic layer by “weakly bound” copper ions.

In Situ Regeneration of Copper-Coated Gas Diffusion Electrodes for Electroreduction of CO2 to Ethylene

A key challenge for carbon dioxide reduction on Cu-based catalysts is its low faradic efficiency (FE) and selectivity towards higher-value products, e.g., ethylene. The main factor limiting the possibilities of long-term applications of Cu-based gas diffusion electrodes (GDE) is a relatively fast drop in the catalytic activity of copper layers. One of the solutions to the catalyst stability problem may be an in situ reconstruction of the catalyst during the process. It was observed that the addition of a small amount of copper lactate to the electrolyte results in increased Faradaic efficiency for ethylene formation. Moreover, the addition of copper lactate increases the lifetime of the catalytic layer ca. two times and stabilizes the Faradaic efficiency of the electroreduction of CO2 to ethylene at ca. 30%. It can be concluded that in situ deposition of copper through reduction of copper lactate complexes present in the electrolyte provides new, stable, and selective active sites, promoting the reduction of CO2 to ethylene.

APPLICATION OF PLASMA-ELECTROLYTE COATINGS ON TITANIUM WITH REFRACTORY METALS FOR DETOXIFICATION OF ENVIRONMENTS FROM POLLUTING SUBSTANCES

Based on the review of the peculiarities of the photocatalytic processes, the peculiarities of the catalytic action of oxide systems based on titanium dioxide are determined. It is shown that TiO2 is one of the most chemically and thermally stable and non-toxic inorganic oxides of semiconductors, whose photocatalytic activity is manifested by irradiation with ultraviolet part of the spectrum (λ 320–400 nm) and allows the oxidation of a significant amount of toxic agents to water and carbon dioxide. The essence of the photocatalytic process of oxidation of toxicants under the action of UV radiation on the TiO2 surface is considered. The proposed technology of photocatalytic detoxification of contaminants is economically available, environmentally friendly and allows its widespread use, in particular for autonomous systems, including dual purpose. It is established that the main requirements for materials for photocatalysis are their chemical and biological inertness, photocatalytic stability and activity, low cost. It is shown that the most rational technological form of the photocatalyst is the application (synthesis) of the catalytic layer on structured metal substrates, in particular titanium alloys. It is proved that these catalytic oxide systems can be effectively formed by the method of plasma-electrolyte oxidation in aqueous electrolytes with the addition of dopant metal compounds that increase the photocatalytic activity of the obtained heterooxide systems. It is proposed to use tungsten oxides of variable valence as the target additive. The kinetic regularities of the process of plasma-electrolytic oxidation of titanium VT1-0 in a diphosphate-borate electrolyte with the addition of tungstates have been studied. It is shown that in an electrolyte of this type at a current density of 1.0 A/dm2 in the galvanostatic mode for 30 min a uniform coating of TiO2·WxOy with a tubular torus-like structure and tungsten content of 2.5–7.5 wt.% is formed. The predicted quantitative composition of the heteroxide layer in combination with the surface morphology creates the preconditions for high catalytic activity of the synthesized coating for detoxification of media from anthropogenic pollutants.

A Trilaminar-Catalytic Layered MEA Structure for a Passive Micro-Direct Methanol Fuel Cell

A membrane electrode assembly (MEA) with a novel trilaminar-catalytic layered structure was designed and fabricated for a micro-direct methanol fuel cell (μ-DMFC). The trilaminar-catalytic layer comprises three porous layers. The medial layer has a lower porosity than the inner and outer layers. The simulation results predicted a lower water content and a higher oxygen concentration in the trilaminar-catalytic layer. The novel trilaminar-catalytic layer enhanced the back diffusion of water from the cathode to the anode, which reduces methanol crossover and improves oxygen mass transportation. The electrochemical results of the half-cell test indicate that the novel MEA has a greatly increased cathode polarization and a slightly increased anode polarization. Thus, this novel μ-DMFC structure has a higher power density and a longer discharging time, and hence may be used in portable systems.

Surface passivated halide perovskite single-crystal for efficient photoelectrochemical synthesis of dimethoxydihydrofuran

Halide perovskite single-crystals have recently been widely highlighted to possess high light harvesting capability and superior charge transport behaviour, which further enable their attractive performance in photovoltaics. However, their application in photoelectrochemical cells has not yet been reported. Here, a methylammonium lead bromide MAPbBr3 single-crystal thin film is reported as a photoanode with potential application in photoelectrochemical organic synthesis, 2,5-dimethoxy-2,5-dihydrofuran. Depositing an ultrathin Al2O3 layer is found to effectively passivate perovskite surface defects. Thus, the nearly 5-fold increase in photoelectrochemical performance with the saturated current being increased from 1.2 to 5.5 mA cm−2 is mainly attributed to suppressed trap-assisted recombination for MAPbBr3 single-crystal thin film/Al2O3. In addition, Ti3+-species-rich titanium deposition has been introduced not only as a protective film but also as a catalytic layer to further advance performance and stability. As an encouraging result, the photoelectrochemical performance and stability of MAPbBr3 single-crystal thin film/Al2O3/Ti-based photoanode have been significantly improved for 6 h continuous dimethoxydihydrofuran evolution test with a high Faraday efficiency of 93%.