High efficient electrocatalytic oxidation of formic acid on Pt/polyindoles composite catalysts

Four novel composite catalysts have been developed by the electrodeposition of Pt onto glassy carbon electrode (GCE) modified with polyindoles: polyindole, poly(5-methoxyindole), poly(5-nitroindole) and poly(5-cyanoindole). As-formed composite catalysts are characterized by SEM, XRD and electrochemical analysis. Compared with Pt nanoparticles, respectively, deposited on the bare GCE and on the GCE modified with polypyrrole, the four newly developed composite catalysts exhibit higher catalytic activity towards formic acid electrooxidation by improving selectivity of the reaction via dehydrogenation pathway and thus mostly suppressing the generation of poisonous CO_ads species. The enhanced performance is proposed to come from the synergetic effect between Pt and polyindoles and the increase of electrochemical active surface area (EASA) of Pt on polyindoles.     

Investigation of formic acid oxidation on Ti/IrO2 electrodes

A model has been proposed according to which the voltammetric charge involved in the Ti/IrO₂ electrodes is due to two contributions: a faradaic contribution due to surface redox activities at the IrO₂ coating and a non-faradaic contribution due to the charging of electrical double layer (). The later has been proposed as a tool for the estimation of the relative surface area of the Ti/IrO₂ electrodes.Differential electrochemical mass spectrometry (DEMS) measurements using H₂¹⁸O has demonstrated that we are dealing with an active electrode in which the surface redox couple IrO₃/IrO₂ acts as mediator in the oxidation of formic acid (FA).From the voltammetric measurements using different IrO₂ loading and FA concentrations, the kinetic parameters of FA oxidation via the surface redox couple IrO₃/IrO₂ have been determined.Finally a model has been proposed considering that FA oxidation at Ti/IrO₂ anodes is controlled by mass transfer. The good agreement between the experimental results and the model indicates that the surface reaction between FA and the electrogenerated IrO₃ is a fast reaction.     

钛基纳米多孔钯电极的制备及对甲酸氧化的电活性

采用水热法,通过改变溶液组成制备了5种不同的钛基纳米多孔钯电极(Pd/PEG、Pd-EDTA/PEG、Pd-EDTA/HCHO、Pd/EG和Pd/HCHO)。扫描电镜图(SEM)分析表明,加入络合剂乙二胺四乙酸(EDTA)后,钯颗粒均匀,粒径明显减小,仅有60 nm左右。利用循环伏安法研究了甲酸在这些电极上的电催化氧化,发现在1.0 mol/L NaOH+0.5 mol/L HCOOH溶液中,加入EDTA且以甲醛作还原剂的电极(Pd-EDTA/HCHO)对甲酸氧化电流密度达132.00 mA/cm2,甲酸氧化的起始电位为-0.85 V,表明电催化活性优于其他电极。同时研究了Pd-EDTA/HCHO电极对不同浓度甲酸电催化氧化,结果表明,在一定甲酸浓度范围内,甲酸氧化的阳极电流密度随浓度的增加而增大。     

Polythiophene, polyaniline and polypyrrole electrodes modified by electrodeposition of Pt and Pt+Pb for formic acid electrooxidation

The electrosynthesis of polythiophene (PTh), polyaniline (PANI) and polypyrrole (PPy) films modified by dispersion of Pt or Pt+Pb and its employment in the electrocatalytic oxidation of HCOOH are studied and compared. The influence of parameters such as polymer film thickness, the number of dispersed Pt particles, the amount of Pb deposited and the presence of Pb2+ in the electrolyte on the electrooxidation of HCOOH is investigated. Electrode systems including the polymer and a mixture of Pt and Pb particles show a better electrocatalytic activity than electrodes having a polymer–Pt combination or bulk Pt electrodes. Furthermore, during the electrooxidation of HCOOH using polymer–(Pt+Pb) electrodes the presence of fewer poisoning species is observed, indicating that the role of Pb in these electrode systems is in agreement with the Pb adatom effect observed when bulk Pt electrodes are used. However, the presence of Pb(ii) in the electrolyte is not required for the PTh–(Pt+Pb) electrode system and, in addition, a better electrocatalytic effect is obtained in this case. With application of an appropriate E/t program the activity is unchanged over a long time.     

Giant multilayer electrocatalytic effect investigation on Pt/Bi/Pt nanostructured electrodes towards CO and methanol electrooxidation

This work describes CO and methanol electrooxidation over Bi/Pt 1.2:1.2 or 10:10 ML electrodeposited on a bulk platinum substrate. It could be observed in a blank solution that the same features for bulk Pt and Pt/Bi/Pt MM and the hydrogen region were overlaid. The electroactive areas, calculated using the hydrogen desorption method, are the same for both bulk Pt and Pt/Bi/Pt MM electrodes. This is in agreement with AFM images and RMS values, which were the same for bulk Pt and Pt/Bi/Pt MM electrodes. CO stripping voltammograms showed a shift in the anodic peak potential towards the negative direction of 138 and 197 mV for Pt/Bi/Pt 10:10 and 1.2:1.2 ML, respectively, in comparison to bulk Pt. Moreover, for methanol electrooxidation the Pt/Bi/Pt 1.2:1.2 ML electrodes presented an enhancement of 315% and 22 times in the peak current density compared to bulk Pt using cyclic voltammetry and chronoamperometry techniques respectively. Using electrochemical impedance spectroscopy, it was possible to observe the lowest resistance charge transfer for Pt/Bi/Pt 1.2:1.2 ML compared to Pt/Bi/Pt 10:10 ML and bulk Pt respectively. We designate the Pt/Bi/Pt MM electrodes as a giant multilayer electrocatalytic (GME) system, due to their enhanced electrocatalytical properties.     

Electrochemical characterization of the electrooxidation of methanol,ethanol and formic acid on Pt/C and PtRu/C electrodes

Methanol, ethanol and formic acid electrooxidations in acid medium on Pt/C and PtRu/C catalysts were investigated. The catalysts were prepared by a microwave-assisted polyol process. Cyclic voltammetry and chronoamperometry were employed to provide quantitative and qualitative information on the kinetics of methanol, ethanol and formic acid oxidations. The PtRu/C catalyst showed higher anodic current densities than the Pt/C catalyst and the addition of Ru reduced the poisoning effect.     

Impedance study of formic acid oxidation on platinum electrodes

The electrooxidation of formic acid on polycrystalline platinum electrodes in sulphuric acid is studied by a dynamic impedance method. Impedance spectra in the frequency range 0.7 Hz to 20 kHz, assembled from ac voltammograms, are interpreted in terms of a mechanism with three adsorbed species, although one of these may be free sites. The spectra show evidence for incipient oscillations in two potential regions, and observed oscillations were related to these spectra. The zeroes of the interfacial impedance were directly extracted from suitable equivalent circuits in distinct potential regions where oscillations may be triggered. The observation of only real zeroes of the interfacial impedance eliminates the possibility of pure potentiostatic oscillations arising from chemical reasons alone, and therefore potential is an essential variable.     

Electrosynthesis of Pd/Au hollow cone-like microstructures for electrocatalytic formic acid oxidation

Pd/Au hollow cone-like microstructures (HCMs) have been electrodeposited on indium tin oxide (ITO) using a two-step protocol, which involves the nucleation pulse and succedent constant potential reduction in the presence of metal precursors and polyvinylpyrrolidone (PVP). Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) were used to characterize the Pd/Au HCMs. The electrochemical results (cyclic voltammetry and chronoamperometry) testify that the Pd/Au HCMs exhibit significantly higher electrocatalytic activity and stability for the oxidation of formic acid than that of Pd/Au solid microhemispheres (SMHs). These attractive features are attributable to the unique hollow structures of Pd/Au with much higher electrochemical active surface areas and the exposure of favorable planes. Our work points to a new path for the preparation of Pd/Au HCMs, which are promising as electrocatalysts in direct formic acid fuel cell (DFAFC).     

Improvements of electrocatalytic activity of PtRu nanoparticles on multi-walled carbon nanotubes by a H2 plasma treatment in methanol and formic acid oxidation

A H₂ plasma has been used to treat the PtRu nanoparticles supported on the plasma functionalized multi-walled carbon nanotubes (PtRu/PS-MWCNTs). The plasma treatment does not change the size and crystalline structure of PtRu nanoparticles, but reduces the fraction of the oxidized species at the outermost perimeter of particles. The electrochemical results show that these plasma treated PtRu/PS-MWCNTs exhibit increased electrochemically active surface area, improved electrocatalytic activity and long term stability toward methanol and formic acid oxidation, and enhanced tolerance to carbonaceous species relative to the sample untreated with the H₂ plasma. The electrocatalytic activities of the plasma treated PtRu/PS-MWCNTs are found to be dependent upon the Pt:Ru atomic ratios of PtRu nanoparticles. The catalysts with a Pt:Ru atomic ratio close to 1:1 show superior properties in the electrooxidation of methanol and formic acid at room temperature and better tolerance to carbonaceous species.     

Electrodeposited porous Pb electrode with improved electrocatalytic performance for the electroreduction of CO2 to formic acid

A porous Pb foam was fabricated electrochemically at a copper substrate and then used as the cathode for the electroreduction of CO₂. The surface morphology and composition of the porous Pb electrode was characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and selected area electron diffraction. The honeycomb-like porous structure was composed of needle-like Pb deposits. Cyclic voltammetry studies demonstrated that the porous Pb electrode had better electrocatalytic performance for the formation of formic acid from CO₂ compared with a Pb plate electrode. The increase in current density was due to the large surface area of the porous Pb electrode, which provides more active sites on the electrode surface. The improved formic acid selectivity was due to the morphology of the roughened surface, which contains significantly more low-coordination sites which are more active for CO₂ reduction. The highest current efficiency for formic acid was 96.8% at -1.7 V versus saturated calomel electrode at 5 °C. This porous Pb electrode with good catalytic abilities represents a new 3D porous material with applications for the electroreduction of CO₂.     

Kinetic study of formic acid oxidation on Ti/IrO2 electrodes prepared using the spin coating deposition technique

In the first part of this paper, IrO₂ electrodes produced by thermal decomposition of H₂IrCl₆ precursor were manufactured using the spin coating deposition technique, where centrifugal forces spread the precursor solution with simultaneous evaporation of the solvent on the rotating Ti substrate. It was found using this technique, that it is possible to obtain thin and uniform IrO₂ coatings with controlled loadings. The influence of the concentration of iridium salt in the precursor solution (c₀) as well as the influence of the rotation speed at which the substrate spins (ω) on the IrO₂ loading have been studied using voltammetric charge measurements. From these results, a simple relation has been proposed for the estimation of the IrO₂ loading for a given c₀ and ω.In the second part of this paper and from measurements performed using different IrO₂ loadings and formic acid concentrations, the kinetic parameters of the oxidation of formic acid have been quantitatively determined using a model that involves the redox couple IrO₃/IrO₂ as mediator of this reaction. Furthermore, using the kinetic parameters obtained together with the Nernst equation and the I-V curves of the supporting electrolyte (1 M HClO₄), theoretical I-V curves could be constructed for different concentrations of formic acid and different IrO₂ loadings.     

Stability of carbon monoxide adsorbed on nanoparticle Pt and Pt/Ru electrodes in sulfuric acid media

Pt and Pt/Ru nanoparticle electrodes were used as substrates for studies of stability of chemisorbed CO and its interactions (exchange) with carbon monoxide and hydrogen gas admitted to sulfuric acid solution, which served as the supporting electrolyte for these measurements. The surface bound, radioactive CO was obtained after decomposition of ¹⁴C labeled methanol or formic acid from the same solution. The stability and/or exchange of the surface bound CO was examined after (i) the ¹⁴CCO containing electrolyte was replaced by the clean supporting electrolyte (to remove the CO solute from the bulk) and (ii) after hydrogen and, separately, non-radioactive CO was admitted to the cell. We found no displacement of adsorbed CO due to the exchange of electrolyte or introduction of hydrogen to the cell. However, non-radioactive CO rapidly displaced the adsorbed ¹⁴CCO on the surface leaving behind a monolayer of chemisorbed but non-radioactive CO. Both results were independent of the electrode potential applied and they neither dependent on the source of surface CO, that is, whether it was deposited from methanol or formic acid solutions.     

Enhancement of electrodes modified by electrodeposited PEDOT‐nanowires with dispersed Pt nanoparticles for formic acid electro‐oxidation

Preparation of electrodes modified with poly(3,4‐ethylenedioxythiophene) nanowires, PEDOT‐nw, was optimized using nanoparticles of dispersed Pt, Pt‐np, to be tested for HCOOH electro‐oxidation. The PEDOT‐nw is electrosynthesized directly on the working electrode, using mesoporous silica as template, by cyclic voltammetry from a 0.01 mol L^?1 monomer + 0.1 mol L^?1 tetrabutylammonium hexafluorophosphate solution in acetonitrile, on the Pt|PEDOT|mesoporous silica template previously modified electrodes. Using SEM, the presence of PEDOT nanowires with 20 to 25 nm in diameter was verified. In addition, its p ‐doping response is about 500 times larger than that obtained on the bulk polymer, maintaining full reversibility of the process. The subsequent electrochemical insertion of Pt‐np and formation of Pt‐np with average diameter of about 20 nm, checked by TEM, demonstrated that the catalytic activity of this nanostructured electrode remarkably enhanced HCOOH electro‐oxidation. The obtained current is up to 2 orders of magnitude higher than previously reported in similar studies, using a much smaller amount of Pt and with a potential decrease greater than 100 mV. Thus, we have at our disposal a simple, inexpensive, and highly reproducible way to prepare in situ nanostructured electrodes using just electrochemical techniques, which can be useful on all the applications of these devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44723.     

CO and methanol electrooxidation on Pt/Ir/Pt multilayers electrodes

This work describes the CO and methanol electrooxidation over an Ir/Pt bilayer electrodeposited on a platinum polycrystalline substrate. In the blank acidic solution it was observed that the electrochemical behavior of both the polycrystalline Pt and Pt/Ir/Pt nanostructured electrodes were very similar. The electroactive area, calculated using the hydrogen desorption method, are the same for both materials. In order to investigate the effect of the thickness change of Ir interlayer, two different samples were prepared. One with 1 Ir monolayer and the second with 3 monolayers thick. CO stripping voltammograms showed a shift in the anodic peak potential towards the negative direction of 160 and 180 mV for Pt/Ir/Pt 3:1 and 1:1 ML, respectively, compared to polycrystalline Pt. Besides, for methanol electrooxidation, the Pt/Ir/Pt electrodes presented an increase of 170% in the peak current density compared to polycrystalline Pt. These results are in agreement with the calculated activation energies which were 31.5, 39.0 and 43.5 kJ mol⁻¹ for Pt/Ir/Pt 1:1, 3:1 ML and polycrystalline Pt electrodes, respectively. Using the electrochemical impedance spectroscopy, surprisingly, the Pt/Ir/Pt electrodes, did not exhibit the inductive arc which means that the poisoning of the electrode surface is not important in this case.     

Oxidation of dilute H2 and H2/O2 mixtures by hydrogenases and Pt

Hydrogenase enzymes that allow micro-organisms to gain energy from oxidation of H₂ undergo efficient electrocatalysis of H₂ oxidation or production when adsorbed on a graphite rotating disk electrode [K.A. Vincent, A. Parkin, F.A. Armstrong, Chem. Rev. 107 (2007) 4366]. Combining potential sweeps or steps with precisely controlled gas exchanges is enabling us to build up a detailed understanding of the many factors that control the chemistry of nickel-iron membrane-bound hydrogenase (MBH) enzymes. The observation that the MBH enzymes from Ralstonia strains have extremely high affinity for H₂ and continue oxidising H₂ in the presence of O₂ and CO has relevance for selective fuel cell catalysis [K.A. Vincent, J.A. Cracknell, J.R. Clark, M. Ludwig, O. Lenz, B. Friedrich, F.A. Armstrong, Chem. Commun. (2006) 5033; K.A. Vincent, J.A. Cracknell, O. Lenz, I. Zebger, B. Friedrich, F.A. Armstrong, Proc. Natl. Acad. Sci. U.S.A. 102 (2005) 16951], and this has led us to compare the ability of hydrogenases and platinum to oxidise low levels of H₂ and mixtures of H₂ and O₂. We show that Pt is a poor catalyst for oxidation of sub-atmospheric levels of H₂ compared to the MBH from Ralstonia eutropha H16, and that at a platinised electrode, H₂ oxidation competes less favourably with reduction of O₂ compared to the situation at hydrogenase-modified graphite. This should have implications for development of future selective energy catalysts able to concentrate the energy available from dilute H₂.     

电化学二氧化碳还原制甲酸催化剂的研究进展

随着日益增长的能源需求,人类社会对于传统碳基化石能源过度依赖,不仅加速了地球上有限能源储备的消耗,还导致大气中二氧化碳(CO₂)不断累积。如何对二氧化碳进行可持续的捕获再利用,实现高效的零碳网络循环,已成为人类亟需解决的重大挑战之一。近年来,使用绿色可持续电力的电化学二氧化碳还原反应(CO₂RR)生产增值化学品成为研究热点。本文首先介绍了CO₂RR的基本电化学反应原理;然后总结了电化学还原CO₂制备甲酸/甲酸盐的主要金属基催化剂,着重介绍了Bi、Sn、In三类金属基催化剂的设计调控策略;进一步概括了电化学相关的原位表征手段,分别介绍了原位光谱技术和原位X射线表征技术;最后对电催化二氧化碳还原研究领域的未来发展进行了展望。     

Pb and Sb modified Pt/C catalysts for direct formic acid fuel cells

PtPb/C and PtSb/C bi-metallic catalysts were synthesized by chemical deposition of Pb or Sb on a commercial 40% Pt/C catalyst. The performances of catalysts with a range of compositions were compared in a multi-anode direct formic acid fuel cell in order to optimize compositions and evaluate the statistical significance of differences between catalysts. The catalytic activity for formic acid oxidation increased approximately linearly with adatom coverage for both PtPb/C and PtSb/C, to maxima at fractional coverages of ca. 0.7. At a cell voltage of 0.5 V, the currents at the optimum Pb or Sb coverages were ca. 8 times higher than at unmodified Pt/C. CO-stripping results indicate that the presence of Pb or Sb facilitates the oxidation of adsorbed CO. In addition, both metals appear to produce electronic effects that inhibit poison formation on the modified Pt surface.     

Electrochemical degradation of Ibuprofen on Ti/Pt/PbO2 and Si/BDD electrodes

The electrochemical oxidation of Ibuprofen (Ibu) was performed using a Ti/Pt/PbO₂ electrode as the anode, prepared according to literature, and a boron doped diamond (BDD) electrode, commercially available at Adamant Technologies. Tests were performed with model solutions of Ibu, with concentrations ranging from 0.22 to 1.75 mM for the Ti/Pt/PbO₂ electrode and 1.75 mM for the BDD electrode, using 0.035 M Na₂SO₄ as the electrolyte, in a batch cell, at different current densities (10, 20 and 30 mA cm⁻²). Absorbance measurements, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) tests were conducted for all samples. The results have shown a very good degradation of Ibu, with COD removals between 60 and 95% and TOC removals varying from 48 to 92%, in 6 h experiments, with higher values obtained with the BDD electrode. General Current Efficiency and Mineralization Current Efficiency, determined for both electrodes, show a similar behaviour for 20 mA cm⁻² but a very different one at 30 mA cm⁻². The combustion efficiency was also determined for both anodes, and found to be slightly higher with BDD at lower current density and equal to 100% for both anodes at 30 mA cm⁻².     

Pt/MnOx-FeOy催化氧化甲醛的性能研究

以MnOx-FeOy为载体,采用浸渍法负载不同质量分数的Pt,制备了一系列x％Pt/MnOx-FeOy催化剂(x=0.1％、0.3％、0.5％,质量分数),考察了Pt质量分数对催化剂催化氧化甲醛性能的影响.当Pt质量分数为0.3％时,0.3％Pt/MnOx-FeOy催化剂性能最优,在60℃可将甲醛完全转化成H2O和CO...