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1.
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
2.
The coverage of Sn on Pt(1 1 1) which is obtained by electrochemical deposition from 5×10−5 M Sn2+ in 0.5 M H2SO4 has been determined by XPS for different deposition times. Complete suppression of hydrogen adsorption corresponds to a coverage of ?max=0.35 (Sn to surface Pt atoms).Co-adsorption of CO with Sn on Pt(1 1 1) has been studied by FTIR spectroscopy. The IR spectra of the stretching vibration of CO can be interpreted in terms of the vibrational signature of the Pt(1 1 1)/CO system and no vibrational bands associated with CO on Sn are detected. At high Sn coverages, the 1840 cm−1 band associated with bridge-bonded CO and the 2070 cm−1 band assigned to on-top CO are present, however, no hollow site adsorption which is characterized by the 1780 cm−1 band is revealed within the resolution of the experiment. This vibrational signature corresponds to a less compressed adlayer compared to the (2×2)-3CO saturation structure on Pt(1 1 1). At lower Sn coverages, signatures from both the compressed and the less compressed CO adlayer structures are seen in the spectra. From earlier structural and electrochemical studies it is known that Sn is adsorbed in 2D islands and influences CO molecules in its neighbourhood electronically. This leads to a disappearance of the IR band from CO adsorbed in the hollow site at high Sn coverages and to higher population of the weakly adsorbed state of CO for all Sn-modified surfaces, i.e. a relative increase of the amount of CO oxidised at low potentials. In addition to this electronic effect, Sn also exerts a co-catalytic effect at low Sn coverages on that part of CO which is adsorbed at a larger distance from Sn due to a bi-functional mechanism. The IR spectra shows for the Sn-modified Pt(1 1 1) surface that the transition from the compressed CO adlayer which is characterized by the hollow site adsorption of CO to the less compressed one which exhibits a characteristic band associated with bridge-bonded CO occurs already at 250 mV instead of 400 mV. 相似文献
3.
This work describes the utilization of a Pt UME in the study of the hydrogen evolution reaction in 0.5 M H2SO4. A non-linear fitting procedure was employed in order to analyze polarization curves obtained at several temperatures (25–75 °C). The results revealed that the traditionally accepted model described by a Volmer–Tafel route fails to fit the obtained experimental data. In this sense, a new model was proposed involving the Volmer–Heyrovsky mechanism, being the Heyrovsky reaction rate determining step. To achieve the best fit between experimental and calculated data, the kinetic equations had to be proposed with a small value of the transfer coefficient (β<0.2). This unusual value was associated with an activationless process, which can also justify the limiting kinetic current (not diffusional) observed. Trying to get further insight into this possibility, the polarization studies were also performed on a surface modified by underpotentially deposited copper. With a degree of coverage as high as 0.8, the only observed effect on the polarization curves was a shift towards minor current values. This shift can be completely justified by the blocking of surface area. A change in mechanism was not observed albeit the Cu UPD eliminated the pairs of neighbor active sites necessary to the Volmer–Tafel pathway. 相似文献
4.
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
5.
P.M. Quaino 《Electrochimica acta》2007,52(25):7396-7403
6.
Svetlana Strbac 《Electrochimica acta》2011,(3):1597
Oxygen reduction (ORR) and hydrogen peroxide reduction (HPRR) reactions were studied on polycrystalline Pt by the rotating disc electrode technique in sulphate solutions over the entire pH range. Initial potentials for both ORR and HPRR coincide with the potential region of PtOH formation and shift negatively with the increase of the pH of the solution. For pHs lower than 3.0 and higher than 10.0, the ORR takes place through 4e-series pathways from acid and alkaline solutions, respectively. For 3.0 < pH < 6.0, the overall number of electrons exchanged depends on the potential and falls below 4 for ORR and below two for HPRR. This indicates that both reactions occur in a limited extent due to the changes of the local pH in the course of these reactions which gives rise to the double wave in the polarization curves (as observed for ORR for pH 3.5 and pH 4.0 and for HPRR for pH 4.0). The change of the Tafel slopes with potential indicate the change in reaction pathway from one that takes place in acid – to one that takes place in alkaline solution. 相似文献
7.
Xiaoyan Yuan Wenrui Huang Dan Zhao Xiaofei Wang Shouwu Guo 《Ceramics International》2021,47(9):12228-12233
Development of economical noble-metal-free electrocatalysts is important for hydrogen evolution reaction (HER). Herein, phase-pure ditungsten carbide (W2C) nanocrystallines covered with thin carbon layer were fabricated via simple pyrolysis of urea and WO3 wires under catalyst-free condition at 700 °C. Phase composition of as-prepared samples, including W2N, W2C or WC, could be modulated by changing the amount of urea. Moreover, urea not only regulated their phase composition and carbon content, but also acted as a reducing agent for facilitating the formation of phase-pure W2C. Under optimized phase composition, the sample displayed excellent HER activity and remarkable stability in acid-solution. These prominent electrocatalytic performances could be attributed to phase-pure W2C dispersed in thin carbon layer with high conductivity, leading to enhanced the activity area. This study exhibits simple route for the fabrication of economical electrocatalysts under mild reaction conditions. 相似文献
8.
FTIR spectroscopy was employed to investigate high molecular weight substances formed on a platinum electrode surface during the electrochemical oxidation of phenol and its chlorinated derivatives. Potentiodynamic (potential range from –0.80 V to 0.85 V vs SHE; scan rate 200 mV s–1) and potentiostatic (at 0.78 V vs SHE) electropolymerization was used in alkaline solutions (1 M NaOH) containing 0.1 M of phenol, monochlorophenols, dichlorophenols, trichlorophenols and pentachlorophenol. The IR spectra of the corresponding monomers were recorded for the comparison. The FTIR spectroscopy studies revealed that the polymers formed under potentiodynamic and potentiostatic conditions are of aromatic nature (–C=C– stretching vibrations at 1450–1600 cm–1), they have ether-linkages (=C—O—C= stretching vibrations at 1100–1300 cm–1) and quinone groups (–C=O stretching vibrations at 1630–1800 cm–1 and –C—H out-of-plane bending at 760 cm–1). The intensities of the hydroxyl group bands in most of the polymers are rather weak compared to those in the corresponding monomers. Vibrations at 2850–2960 cm–1, which are present in most of the IR spectra of polymers formed under cyclic voltammetry conditions, correspond to the stretching vibrations of the sp3 hybridized C—H bond and suggest that the cleavage of the benzene ring occurs to some extent during electrooxidation–electropolymerization of phenol and its chlorinated derivatives when reaching the potential of oxygen evolution (0.85 V vs SHE). 相似文献
9.
《Ceramics International》2022,48(13):18645-18650
Novel and efficient catalytic materials with enhanced electrocatalytic properties are needed for hydrogen production from water through electrochemical water splitting. In this study, novel lanthanum oxide rods were prepared using a facile, soft chemical process. These lanthanum oxide rods were used for electrocatalytic hydrogen and oxygen evolution reactions. Electrochemical studies of the catalyst at 100 mA cm?2 indicated overpotentials of ~340 and ~405 mV for hydrogen and oxygen evolution reactions, respectively. In addition, the lanthanum oxide rods demonstrated good stability. Finally, lanthanum oxide rods were used as the cathode and anode to fabricate the electrolyzer in a two-electrode configuration. This electrolyzer required 1.6 V to drive 10 mA cm?2, and its performance did not change significantly during durability testing. To the best of our knowledge, this is the first study demonstrating the use of lanthanum oxide rods in electrocatalysis. The prepared lanthanum oxide rods have good electrocatalytic activity, and therefore, they are promising materials for the development of alkaline electrolyzers. 相似文献
10.
Ternary nickel-iron-carbon (Ni-Fe-C) alloys have been characterized by means of microstructural and electrochemical techniques in view of their possible applications as electrocatalytic materials for hydrogen evolution reaction (HER). The electrochemical efficiency of the electrodes has been evaluated on the basis of electrochemical data obtained from the steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) in 1 M NaOH solution at 298 K in the absence and presence of cyanide ion as the poison. Steady-state polarization Tafel curves showed that the Ni-Fe-C electrodes were apparently active for the HER. Therefore, the EIS studies were performed to obtain more precise data and find the source of activity. A surface roughness of more than three orders of magnitude was observed for Ni62Fe35C3 electrode. The rate constants of the forward and backward reactions of Volmer and Heyrovský steps were estimated by using Tafel-impedance data. A comparison between the values obtained for Rf by the EIS and the values obtained for k2 by approximation of Tafel-impedance data revealed that the increase in activity of Ni62Fe35C3 electrode toward the HER was partially (20%) originated from increase in the surface roughness, and mostly (80%) from increase in the intrinsic activity. 相似文献
11.
In this communication we demonstrate that tungsten carbide, WC, is a promising electrocatalyst for the hydrogen evolution reaction in pH neutral electrolytes. In a systematic investigation of mixed catalysts containing different fractions of WC, W2C, W and WO2 we show that the performance of the catalyst is proportional to its WC content, whereas W2C, W and WO2 play only a minor role. The relationship between WC content and electrocatalytic activity indicates that hydrogen evolution and oxidation are related to similar surface sites preferentially formed on WC. In contrast to anodic conditions, the cathodic polarization diminishes corrosion processes and thus increases the long term stability. 相似文献
12.
Hugues Duncan 《Electrochimica acta》2008,53(23):6845-6850
Hydrogen sorption at Pd films of 20-80 nm deposited on a polycrystalline gold electrode was studied in sulfuric and perchloric acid. Assuming that the hydrogen adsorption does not vary with the Pd films thickness, hydrogen adsorption/absorption charges in Pd were separated in the two contributions in the hydrogen-poor α-Pd-H phase. The results are compared to those obtained at Pd monolayers on Au(1 1 1). The adsorption on polycrystalline Pd begins at potentials more negative than on 0.8 ML Pd on Au(1 1 1) and is not much affected by the nature of anion (sulfate or perchlorate), contrary to the thin layers on Au(1 1 1). The absorption charge in α-PdH phase in the potential range of 0.08-0.15 V was found to be similar to that at a 25 μm Pd foil in this potential range while at more positive potentials it is larger. In the presence of crystal violet which adsorbs at the electrode surface it was found that some residual H adsorption exists. There is more hydrogen absorbed in Pd in the presence of crystal violet in the hydrogen-poor α phase but in the hydrogen-rich β phase the amount of hydrogen is the same. 相似文献
13.
Porous metals are of interest for their high surface area and potential for enhanced catalytic behavior. Electrodeposited NiCu thin films with a range of compositions were electrochemically dealloyed to selectively remove the Cu component. The film structure, composition, and reactivity of these samples were characterized both before and after the dealloying step using scanning electron microscopy, energy-dispersive spectroscopy, and electrochemical measurements. The catalytic behavior of the dealloyed porous Ni samples towards the hydrogen evolution reaction was measured and compared to that of the as-deposited samples. The dealloyed samples were generally more reactive than their as-deposited counterparts at low overpotentials, making the dealloying procedure a promising area of exploration for improved hydrogen evolution catalysts. 相似文献
14.
M. Heinen 《Electrochimica acta》2007,53(3):1279-1289
Using a novel combined spectro-electrochemical DEMS/ATR-FTIRS technique, the CO adsorption kinetics on a Pt film electrode were studied, performing transient CO adsorption experiments at different constant potentials (0.06-0.6 V). CO adsorption rate and COad coverage were determined continuously from the CO consumption measured by on-line differential electrochemical mass spectrometry (DEMS). Simultaneously measured FTIR spectra, recorded in situ in an attenuated total reflection (ATR) configuration, allow a direct correlation of the IR band intensity and frequency with COad surface coverage at different constant potentials. The data show that (i) the CO adsorption kinetics are independent of the adsorption potential up to 0.5 V, (ii) a significant potential dependence of the ratio between COL and COM for the same coverage, (iii) in the regime of very high COad coverages there is no proportional relation between COad coverage and COL,M intensity, and (iv) a distinct tendency for COad island formation at Eads < 0.2 V and > 0.4 V, most likely due to coadsorption of H-upd at the lower potentials and (bi-)sulfate at higher potentials. Finally, at 0.6 V, COad oxidation follows a Langmuir-Hinshelwood mechanism with the highest CO2 formation rate at a relative COad coverage of ∼0.4. 相似文献
15.
The experimental evidence and mechanism of ‘hydrogen spill-over’ on Pt/WO3 is reviewed and the application of this catalyst system for the evolution of hydrogen, anodic oxidation, hydrogenation and the anodic oxidation of small molecules and impure H2 is discussed. It is suggested that further work on preparation techniques to ensure the maximisation of Pt/WO3 interfaces and other analogous systems should lead to even higher catalyst activity and applications. 相似文献
16.
The electro-oxidation of CO adlayer on Pt electrode in Cl−-containing 0.1 M HClO4 has been investigated with in situ attenuated-total-reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Two potentials were selected for predosing CO on the Pt electrode: one is in the H-UPD region, i.e., 0.1 V (vs. RHE) and the other is in the double-layer region, i.e., 0.45 V (vs. RHE). The broadening of the prewave and the main peak for the CO oxidation is observed, in addition to the positively shifted oxidation potentials. The spectroelectrochemical data suggest the specific adsorption of Cl− starts at a potential as negative as 0.1 V which may compete with the adsorption of OH at CO-unoccupied sites (including but not limited to defect sites) and/or hinder the diffusion of CO to OH adsorption sites on Pt electrode, slowing down the CO oxidation. This competitive Cl− adsorption at lower potentials disrupts the interfacial free H2O structure on the top of CO adlayer, signaled by a reduced OH stretching band intensity. 相似文献
17.
ATR-FTIRAS measurements combined with linear potential sweep voltammetry were conducted to perform detailed analysis of CO adsorption/oxidation processes on a chemically deposited Pt film on Si ATR prism. Roles of terrace and step edge sites were clearly demonstrated based on the band analyses of the atop, CO(L), and bridge bonded CO, CO(B), spectra during the adsorption/oxidation processes. In the main current peak region above 0.45 V, a direct spectroscopic evidence was obtained to show oxidation of CO(L) and its diffusion to the step edge sites, where local coverage of CO(L) and CO(B) increases between 0.5 V and 0.64 V. This triggers further oxidation of the overall CO adlayer. 相似文献
18.
The surface melting and crystallization behavior of two biodegradable polyesters, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-co-HHx)) (HHx=12 mol%) and poly(3-hydroxybutyrate) (PHB), were investigated by using attenuated total reflection (ATR) and transmission infrared (IR) spectroscopy coupled with the generalized two-dimensional (2D) correlation analysis. IR bands in the CO stretching vibration region were analyzed to explore the changes in crystallinity at the surface and those in the bulk of the polymer film samples during the melting and crystallization processes. Due to the intrinsic sub-micrometer sampling depth of the ATR technique, spectral information attributed to the chemical moieties situated at the surface region of the film samples can be observed. The present study revealed that the surface melting of P(HB-co-HHx) takes place through an intermediate state. The distribution of crystalline phase detected by the ATR technique and that detected by the transmission technique suggested that the polymer crystals tend to grow at the surface in a manner different from that in the bulk. It is very likely that the population of polymer crystals at the surface is higher than that in the bulk for both P(HB-co-HHx) and PHB. The time-dependent IR spectral variations for P(HB-co-HHx) and those for PHB indicated that P(HB-co-HHx) crystallizes much slower than PHB. This observation suggested that the HHx units incorporated in P(HB-co-HHx) markedly reduce not only the degree of crystallinity but also the crystallization rate of PHB homopolymer. 相似文献
19.
20.
采用温和化学镀法在非导电基底材料聚氨酯海绵(PU)上成功制备了NiB@Fe–B/PU催化电极,并通过掺杂少量第三种元素,如钴、钼等金属元素制备了NiB@Fe–Co–B/PU和NiB@Fe–Mo–B/PU催化电极。结果表明,掺杂钴、钼可明显提升NiB@Fe–B/PU催化电极的析氢性能,其中掺杂钴的性能更优。在0.5 mol/L缓冲液(磷酸缓冲盐溶液,PBS)中,NiB@Fe–Co–B/PU电极的析氢反应(HER)过电位仅为161 mV(电流密度, j=50 mA/cm2),塔菲尔斜率为68.24 mV/dec,且在过电位为61 mV下能够稳定工作24 h以上,电化学稳定性良好。 相似文献