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1.
The research reports on the electrocatalytic properties of IrOx, Pt, and composite IrOx-Pt-IrOx thin films prepared by physical vacuum deposition technique of dc magnetron sputtering. The efficiency toward the oxygen evolution in aqueous solutions and in a laboratory electrolyser with polymer proton conductive electrolyte has been investigated using the conventional electrochemical methods of cyclic voltammetry and steady state polarisation curves. The sputtered films have demonstrated excellent catalytic properties, mechanical stability, and high corrosion resistance under intensive oxygen evolution. The best performance (anodic current density of 0.84 A cm−2 at potential of 1.8 V) has shown the IrOx film with loading of 0.2 mg cm−2. Some data on the catalytic activity toward oxygen reduction reaction in aerated 0.5 M H2SO4 solution and the possibility to use the method of magnetron sputtering for preparation of cost effective composite catalytic films with bifunctional properties are also presented and discussed.  相似文献   

2.
The arrays of vertically aligned carbon nano-filaments (VACNF) were synthesized by catalytic chemical vapor deposition on TiOx substrates, obtained via oxidative treatment of polycrystalline Ti and Ti thin films on Si(1 0 0). VACNF were studied using scanning and transmission electron microscopies. The Pt deposition on VACNF was utilized to prepare a set of model catalysts, which were investigated in two fuel cell related reactions: the oxygen reduction (ORR) and the hydrogen oxidation (HOR) reactions. The experimental data were compared with the results of mathematical modeling performed for a fast (quasi)reversible and a slow irreversible electrochemical reaction. The approach made it possible to study electrochemical reactions (HOR, ORR) on nano-materials under well defined mass transport conditions. The influence of the catalytic layer thickness and the Pt coverage on the penetration depth of the reactive species inside the layer and consequently on the performance and on the Pt effectiveness factor were analyzed.  相似文献   

3.
The oxygen reduction reaction (ORR) was studied at carbon supported MoOx-Pt/C and TiOx-Pt nanocatalysts in 0.5 mol dm−3 HClO4 solution, at 25 °C. The MoOx-Pt/C and TiOx-Pt/C catalysts were prepared by the polyole method combined by MoOx or TiOx post-deposition. Home made catalysts were characterized by TEM and EDX techniques. It was found that catalyst nanoparticles were homogenously distributed over the carbon support with a mean particle size about 2.5 nm. Quite similar distribution and particle size was previously obtained for Pt/C catalyst. Results confirmed that MoOx and TiOx post-deposition did not lead to a significant growth of the Pt nanoparticles.The ORR kinetics was investigated by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. These results showed the existence of two E − log j regions, usually observed with polycrystalline Pt in acid solution. It was proposed that the main path in the ORR mechanism on MoOx-Pt/C and TiOx-Pt/C catalysts was the direct four-electron process with the transfer of the first electron as the rate-determining step. The increase in catalytic activity for ORR on MoOx-Pt/C and TiOx-Pt/C catalysts, in comparison with Pt/C catalyst, was explained by synergetic effects due to the formation of the interface between the platinum and oxide materials and by spillover due to the surface diffusion of oxygen reaction intermediates.  相似文献   

4.
Oxygen reduction reaction (ORR) on Pt microelectrode was used for developing a micro pH sensor for scanning electrochemical microscopy (SECM) study in this work. When the potential of Pt microelectrode was held constant in ORR region, the ORR current (cathodic current) increased with decreasing solution pH and vice versa. The response time of the ORR current to pH changes was measured to be ca. 30 ms which implies that the pH response is fast enough for monitoring the temporal pH changes. Furthermore, a fine linear relationship was found to exist between the half wave potential of ORR (E1/2) and the solution pH value, and the slope is −46 mV/pH. The Pt micro pH sensor was located 1 μm above the LaNi5−xAlx (x = 0, 0.3) substrate electrode surface in pH = 9 KOH solution to perform the tip-substrate voltammetry of SECM. In tip voltammogram, the ORR tip current qualitatively reflects the transit solution pH changes during LaNi5−xAlx discharge reaction. Also, the minimum values of the solution pH near LaNi5 and LaNi4.7Al0.3 surface during the discharge reaction were quantitatively detected; they were 7.17 and 7.57, respectively. The result indicates that Al partial substitution for Ni degrades the maximum discharge ability of the alloy and decreases the hydrogen diffusion coefficient in alloy bulk.  相似文献   

5.
Yan Liu  Wei Chao 《Electrochimica acta》2010,55(20):5617-5623
We report a new nanocomposite catalytic cathode composed of iron phthalocyanine, platinum, carbon black and Nafion® (FePc-Pt/C-Nafion®) which exhibited enhanced catalytic activity for the oxygen reduction reaction (ORR) in the presence of methanol compared with usual Pt/C based electrodes. The catalytic cathode was prepared by depositing Pt colloidal nanoparticles (dav = 2.2 nm) on a FePc/C support to form a FePc-Pt/C powder and ultrasonically treating a mixture of Nafion® and the FePc-Pt/C powder in ethanol, followed by loading the mixture on a glassy carbon electrode and drying at 120 °C. In an O2-saturated H2SO4 solution (0.5 M) with methanol (0.5 M), the onset potential (0.92 V vs RHE) over the FePc-Pt/C-Nafion® electrode shifted by more than 240 mV toward positive relative to that over an electrode prepared with a commercial Pt/C catalyst and Nafion®. A new kind of catalytic sites constructed by FePc nanocrystals and Pt nanoparticles was found in the FePc-Pt/C-Nafion® electrode for the first time, which exhibited higher specific activity for ORR than Pt as calculated based on the hydrogen desorption charge.  相似文献   

6.
The performance of proton exchange membrane fuel cells (PEMFC) fed with CO-contaminated hydrogen was investigated for anodes with PtWOx/C and phosphotungstic acid (PTA) impregnated Pt/C electrocatalysts. A quite high performance was achieved for the PEMFC fed with H2 + 100 ppm CO with anodes containing 0.4 mg PtWOx cm−2 and also for those with 0.4 mg Pt cm−2 impregnated with ca. 1 mg PTA cm−2. A decay of the single cell performance with time is observed, and this was attributed to an increase of the membrane resistance due to the polymer degradation promoted by the crossover of the tungsten species throughout the membrane.  相似文献   

7.
The influence of poisoning of Pt catalyst by CO on the kinetics and mechanism of H2 oxidation reaction (HOR) at Pt/C electrode in 0.5 mol dm−3 HClO4, saturated with H2 containing 100 ppm CO, was examined with rotating disc electrode (RDE) at 22 °C. Commercial carbon black, Vulcan XC-72 was used as support, while Pt/C catalyst was prepared by modified polyol synthesis method in an ethylene glycol (EG) solution. The kinetically controlled current (Ik) for the HOR at Pt/C decreases significantly at CO coverage (ΘCO) > 0.6. For ΘCO < 0.6 the HOR takes place through Tafel-Volmer mechanism with Tafel reaction as rate-determining step at the low CO coverage, while Volmer step controls the overall reaction rate at the medium CO coverage. When CO coverage is higher then 0.6, Heyrovsky-Volmer mechanism is operative for the HOR with Heyrovsky as the rate-determining step (rds).  相似文献   

8.
Carbon-supported IrO2 and RuO2 were prepared using an incipient wetness method and were then calcinated at various temperatures. IrO2/C and RuO2/C are less expensive than the conventional Pt/C material and more stable than metal Ni in an acidic electrolyte. Moreover, IrO2/C and RuO2/C are not influenced by under potential deposition (UPD) and show lower sensitivity to poisoning by Ni or Fe impurities. The physical properties of IrO2/C and RuO2/C were investigated via XRD and TEM. Cyclic voltammograms (CV) and Tafel plots were used to provide information regarding surface redox reaction and electrocatalytic activity. The activity and durability of IrO2/C and RuO2/C were studied after prolonged potential cycling between −0.3 and 0.3 VSCE. After comparison of Tafel plots of Pt/C and IrO2/C after activation, it was observed that they have similar electrocatalytic activities in a hydrogen evolution reaction (HER). A single cell test with solid polymer electrolyte (SPE) proved that the performance of IrO2/C (0.5 mg cm−2) was similar to that of Pt/C (0.5 mg cm−2).  相似文献   

9.
This work reports on the kinetics of the hydrogen oxidation reaction (HOR) on model Pd nanoparticles supported on a low surface area carbon substrate. Two Pd/C samples, with the average particle size 2.6 and 4.0 nm were used. The structure of the catalysts was characterized with the ex situ (electron microscopy) and in situ (electrochemical) methods. We utilized the electrochemical impedance spectroscopy (EIS) and the rotating disk electrode (RDE) voltammetry to study the kinetics of the HOR on Pd/C. The relevance of these techniques for elucidating the kinetics and the mechanism of the HOR on Pd/C was explored. The experimental results suggest that the catalytic activity of Pd in the HOR is more than 2 orders of magnitude lower than that of Pt, and does not depend on the particle size in the range from 2.6 to 4.0 nm. Computational modeling of the experimental steady-state (RDE) and non-steady-state (EIS) data shows that the reaction kinetics can be adequately described within Heyrovsky-Volmer mechanism, with the rate constants υ0H = (8.8 ± 1.5) × 10−10 mol cm−2 s−1 and υ0V = (1.0 ± 0.3) × 10−8 mol cm−2 s−1. The model suggests that underpotentially deposited hydrogen HUPD is unlikely to be the active intermediate Had of the HOR. It is concluded that the surface coverage of Had deviates from that of HUPD with increasing overpotential, and the lateral interactions within Had adlayer are weak.  相似文献   

10.
Thin films of iridium oxide deposited by reactive magnetron sputtering have been investigated as catalysts for electrochemical water splitting in a polymer electrolyte membrane (PEM) cell. The sputtered films possess excellent mechanical stability and corrosion resistance at the high anodic potentials where oxygen evolution takes place. Their catalytic activity has been assessed using the conventional electrochemical methods of cyclovoltammetry and steady state polarisation techniques. A morphology factor assessing the catalyst active surface for a series of sputtered samples with varying thickness/loading has been determined and correlated to the catalytic efficiency. It has been proven that iridium oxide is a very efficient catalyst for oxygen evolution reaction (OER). The best performance with anodic current density of 0.3 A cm−2 at potential of 1.55 V (versus RHE) has shown the 500 nm thick film containing 0.2 mg cm−2 catalyst. The results obtained have also demonstrated the advantages of the reactive magnetron sputtering as simple and reliable method for deposition of efficient and cost effective catalysts for PEM electrolysis application.  相似文献   

11.
A comprehensive set of rotating disk electrode (RDE) tests has been developed to test the suitability of fuel cell catalyst candidates for use as either anode or cathode catalysts for transient conditions. The activity for Hydrogen Oxidation reaction (HOR), Oxygen Reduction reaction (ORR) and Oxygen Evolution reaction (OER) is tested together in one protocol. A total of 5 Pine Instruments RRDE test stations have been set up with automatic gas flow switching and computer software to control all aspects of the data collection process. The user simply sets up the electrochemical cell with a gas bubbler, reference electrode, counter electrode and sample and then selects a series of tests to be run. The software then switches gas flow, rotation rates and potentiostat set up files automatically. This infrastructure allows the rapid characterization of catalyst candidate materials. The series of tests is described, along with the purpose of each test in the protocol. As an example, the data collected from a Pt1−xHfx composition spread is presented. The optimal composition is found to be approximately 30 at.% Hf, when the ORR performance begins to decrease at a faster rate than the HOR performance and the OER current at 1300 mV is also a maximum. However, it was determined that from an applied point of view the drop in ORR performance was insufficient to adequately protect the cathode from the effects of the transient potentials during start-up of the fuel cell.  相似文献   

12.
Kinetics of RuxMoySez nanoparticles dispersed on carbon powder was studied in 0.5 M H2SO4 electrolyte towards the oxygen reduction reaction (ORR) and as cathode catalysts for a proton exchange membrane fuel cell (PEMFC). RuxMoySez catalyst was synthesized by decarbonylation of transition-metal carbonyl compounds for 3 h in organic solvent. The powder was characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. Catalyst is composed of uniform agglomerates of nanocrystalline particles with an estimated composition of Ru6Mo1Se3, embedded in an amorphous phase. The electrochemical activity was studied by rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. Tafel slopes for the ORR remain invariant with temperature at −0.116 V dec−1 with an increase of the charge transfer coefficient in dα/dT = 1.6 × 10−3, attributed to an entropy turnover contribution to the electrocatalytic reaction. The effect of temperature on the ORR kinetics was analyzed resulting in an apparent activation energy of 45.6 ± 0.5 kJ mol−1. The catalyst generates less than 2.5% hydrogen peroxide during oxygen reduction. The RuxMoySez nanoparticles dispersed on a carbon powder were tested as cathode electrocatalyst in a single fuel cell. The membrane-electrode assembly (MEA), included Nafion® 112 as polymer electrolyte membrane and commercial carbon supported Pt (10 wt%Pt/C-Etek) as anode catalyst. It was found that the maximum performance achieved for the electro-reduction of oxygen was with a loading of 1.0 mg cm−2 RuxMoySez 20 wt%/C, arriving to a power density of 240 mW cm−2 at 0.3 V and 80 °C.  相似文献   

13.
A systematic investigation of the influence of Ti/[IrO2-Nb2O5] electrode composition ([IrO2]=40, 45 and 50 mol%) on electrochemical ozone production (EOP), was conducted in 3.0 mol dm−3 H2SO4 in the presence and absence of 0.03 mol dm−3 KPF6. “In situ” characterisation revealed all oxide layer presented similar structures, except for the 50 mol% IrO2 nominal composition which showed a higher porosity/roughness. The introduction of KPF6 in the electrolyte resulted in an inhibition of the oxygen evolution reaction (OER) at high current densities, improving ozone generation efficiency at i > 0.4 A cm−2, while reducing overpotential for OER. When normalised for the area, the ozone current efficiency presented a good performance of the system. However, improvement of the electrode service life is necessary in order to support the drastic conditions observed during EOP.  相似文献   

14.
Cobalt based non-precious metal catalysts were synthesized using chelation of cobalt (II) by imidazole followed by heat-treatment process and investigated as a promising alternative of platinum (Pt)-based electrocatalysts in proton exchange membrane fuel cells (PEMFCs). Transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements were used to characterize the synthesized CoNx/C catalysts. The activities of the catalysts towards oxygen reduction reaction (ORR) were investigated by electrochemical measurements and single cell tests, respectively. Optimization of the heat-treatment temperature was also explored. The results indicate that the as-prepared catalyst presents a promising electrochemical activity for the ORR with an approximate four-electron process. The maximum power density obtained in a H2/O2 PEMFC is as high as 200 mW cm−2 with CoNx/C loading of 2.0 mg cm−2.  相似文献   

15.
Composite film electrodes containing mechanically mixed MnxCu1−xCo2O4 (0 ≤ x ≤ 1) particles, carbon black Vulcan XC72R and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) were formed on the glassy carbon disk surface of a rotating ring-disk electrode (RRDE) and studied for the oxygen reduction and evolution reactions (ORR and OER, respectively) in 1 M KOH solution. The electrocatalytic activities for both reactions were observed to depend strongly on the Mn content in CuCo2O4. An opposite trend was observed for the apparent and intrinsic electrocatalytic activities for the ORR; the simultaneous presence of Cu and Mn was found to be detrimental to the intrinsic charge density, but beneficial to the geometric charge density with a maximum for Mn0.6Cu0.4Co2O4. The latter was characterized by the highest total number of electrons exchanged per O2 molecule, n, close to 4, greater k1 (4e process)/k2 (2e process) ratios, and by a unique and low Tafel slope (−41 mV dec−1). The results obtained for the OER showed that the intrinsic electrocatalytic activity is determined by the number of active sites (Co4+) electrochemically formed at the oxide surface prior to the OER, from Co3+ cations. The partial substitution of Cu by Mn in CuCo2O4 was found to decrease the OER activity.  相似文献   

16.
The current study is concerned with the preparation and characterization of tantalum oxide-loaded Pt (TaOx/Pt) electrodes for hydrogen spillover application. XPS, SEM, EDX and XRD techniques are used to characterize the TaOx/Pt surfaces. TaOx/Pt electrodes were prepared by galvanostatic electrodeposition of Ta on Pt from LiF-NaF (60:40 mol%) molten salts containing K2TaF7 (20 wt%) at 800 °C and then by annealing in air at various temperatures (200, 400 and 600 °C). The thus-fabricated TaOx/Pt electrodes were compared with the non-annealed Ta/Pt and the unmodified Pt electrodes for the hydrogen adsorption/desorption (Hads/Hdes) reaction. The oxidation of Ta to the stoichiometric oxide (Ta2O5) increases with increasing the annealing temperature as revealed from XPS and X-ray diffraction (XRD) measurements. The higher the annealing temperature the larger is the enhancement in the Hads/Hdes reaction at TaOx/Pt electrode. The extraordinary increase in the hydrogen adsorption/desorption at the electrode annealed at 600 °C is explained on the basis of a hydrogen spillover-reverse spillover mechanism. The hydrogen adsorption at the TaOx/Pt electrode is a diffusion-controlled process.  相似文献   

17.
Values of open-circuit-potentials (OCP) have been determined for pairs of electrodes: Au and Pt, Ni-Ce0.8Sm0.2O1.9 cermet and Au, Pt and Sm0.5Sr0.5CoO3 composite at the YSZ electrolyte, in the uniform atmospheres of xCH4 + yO2 + (1 − x − y)Ar gas mixtures with variable x and y coefficients, at 600 °C. The determined dependencies of OCP values on the initial gas mixture compositions have been compared with the respective dependencies calculated for equilibrium or quasi-equilibrium compositions of these gas mixtures. The OCP values for the pair of Pt and Au electrodes have been measured also in the xH2 + yO2 + (1 − x − y)Ar uniform gas mixtures but no distinct difference of the OCP values has been observed in this atmosphere. For some pairs of electrodes investigated in xCH4 + yO2 + (1 − x − y)Ar atmospheres the measured OCP values have shown differences up to ca 0.9-1.0 V. These differences were stable within large range of compositions of this gas mixture. Within this gas composition range one of the electrodes conserves the potential of oxygen electrode determined by oxygen partial pressure in the initial gas mixture and is insensitive to reaction occurring in the gas phase. These results are discussed on the basis of equilibria or some quasi-equilibria, that establish in the C-H-O gas mixture and the solid carbon deposition is considered. For a given pair of dissimilar electrodes, their selective sensibility to the electrochemical process of oxygen electrode has been confirmed. Within large range of gas mixture concentrations, in the Pt-Au electrode pair Au has shown behavior of the oxygen electrode, whereas the OCP values of the Pt electrode are within the range of hydrogen electrode, also at gas compositions corresponding to the solid carbon stability. With this pair the OCP differences of ca. 600 mV have been obtained. Among three electrodes studied the cermet Ni-Ce0.8Sm0.2O1.9 electrode shows the best electrocatalytic properties resulting in the OCP values following exactly the respective equilibrium dependence. In the pair Ni-Ce0.8Sm0.2O1.9 and Au a stable potential difference of ca. 900 mV have been established. Unexpectedly, Pt electrode in the pair with the Sm0.5Sr0.5CoO3 composite electrode plays role of the oxygen electrode quite insensitive to other components of the equilibrated initial gas mixture. This surprising fact seems indicate that in conditions of the experiments performed the electrocatalytic behavior of the electrode depends not only of the material of this electrode but also on the properties of the second electrode in the given pairs of electrodes.  相似文献   

18.
Two different forms of rutile-type iridium oxide catalysts were prepared: IrO2-coated titanium plate electrocatalysts prepared by a dip-coating method (IrO2/Ti) and iridium oxide nanoparticles (IrO2) prepared by a wet method, the Adams fusion method. The catalytic behavior of the oxygen reduction reaction (ORR) was evaluated by cyclic voltammetry in 0.5 M H2SO4 at 60 °C. Both catalysts were found to exhibit considerable activity for the ORR; however, the former oxide electrodes showed higher activity than the latter ones. All the IrO2/Ti catalyst electrodes heat-treated at a temperature between 400 °C and 550 °C showed ca. 0.84 V (vs. RHE) of the onset potential for the ORR, EORR, where the reduction current of oxygen had begun to be observed during the cathodic potential sweep of the test electrodes. It has been confirmed clearly that IrO2, but neither metallic Ir nor the hydrated IrO2, behaves as an active catalyst for the ORR in an acidic solution. It was also demonstrated that the enlargement of the surface area of the IrO2/Ti with the help of lanthanum is effective for the enhancement of the catalytic activity in the reaction.  相似文献   

19.
Ag/C catalysts with different loading were prepared using a colloidal route to obtain well dispersed catalysts on carbon, with a particle size close to 15 nm. An amount of 20 wt.% Ag on carbon was found to be the best loading in terms of current density and mass activity. The 20 wt.% Ag/C catalyst was then studied and the kinetics towards ORR was determined and compared with that of a 20 wt.% Pt/C catalyst. The number of exchanged electrons for the ORR was found to be close to four with the rotating disk electrode (RDE) as well as with the rotating ring disc electrode (RRDE) techniques. From the RDE results, the Tafel slopes b, the diffusion limiting current density inside the catalytic film (jlfilm) and the exchange current density (j0) were evaluated. The Tafel slopes b and diffusion limiting current densities inside the catalytic film (jlfilm) were found to be in the same order for both catalysts, whereas the exchange current density (j0), which is a suitable estimation of the activity of the catalyst, was at least 10 times higher at the Pt/C catalyst than at the Ag/C catalyst. The behavior of both catalysts in methanol containing electrolyte was investigated and it was found that at a low methanol concentration, the Pt/C catalyst was quasi-tolerant to methanol. But, at a high methanol concentration, the ORR at a Pt/C was affected. However, the Pt/C catalyst showed in each case better activity towards ORR than the Ag/C catalyst, even if the latter one was less affected by the presence of methanol than the former one.  相似文献   

20.
In this paper is described the preparation of new platinum-free Pd-Co carbon-nitride electrocatalysts (Pd-Co-CNs) for application in low-temperature fuel cells. Two groups of materials with formula Kn[PdxCoyCzNlHm] were synthesized, which are grouped in two ensembles: the first is characterized by a molar ratio y/x > 1 (I), and the second by y/x < 1 (II). Kn[PdxCoyCzNlHm] materials were prepared through a two-step synthesis protocol. The effect of the Pd/Co molar ratio and of the temperature of the thermal treatments on the structure and properties of the products were studied extensively by thermogravimetry, scanning electron microscopy, and vibrational (FT-IR and micro-Raman) and XPS spectroscopy. Vibrational studies revealed that I and II systems consist of two polymorphs of α- and graphitic-like carbon-nitride nanomaterials. The electrochemical activity towards the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) was measured by cyclic voltammetry measurements with thin-film rotating disk electrode (CV-TF-RDE). The electrochemical performance of Pd-Co-CNs of group I obtained at tf ≥ 700 °C resulted higher than that measured for a platinum-based commercial electrocatalyst in terms of both the activity towards the ORR and the HOR and of the resistance towards the poisoning effect of methanol towards the ORR.  相似文献   

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