Electrocatalytic Oxidation Of Formic Acid Research Articles

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.

Iron(ii) tetrakis(diaquaplatinum)octacarboxyphthalocyanine supported on multi-walled carbon nanotube platform: an efficient functional material for enhancing electron transfer kinetics and electrocatalytic oxidation of formic acid

A novel platinum-based macrocycle, iron(II) tetrakis(diaquaplatinum)octacarboxyphthalocyanine (PtFeOCPc), was synthesised and characterised. The heterogeneous electron transfer and electrocatalytic properties of this functional material towards the oxidation of formic acid have been explored on a graphite electrode platform pre-modified with or without acid-functionalised multi-walled carbon nanotubes (MWCNTs). We prove that PtFeOCPc supported on a MWCNT platform (MWCNT–PtFeOCPc) exhibits enhanced electrochemical response in terms of (i) electron transfer towards outer-sphere redox probe, (ii) catalytic rate constant, and (iii) tolerance towards CO poisoning during formic acid oxidation. The results clearly suggest that the MWCNT–PtFeOCPc is a promising platform for potential application as an electrocatalyst for direct formic acid fuel cell.

Clean, efficient electrolysis of formic acid via formation of eutectic, ionic mixtures with ammonium formate

Formic acid is a promising compound with regard to hydrogen storage and generation, as it can be formed via the hydrogenation of CO2 and decomposed to form H2 and CO2. The electrochemistry of formic acid, aqueous solutions of ammonium formate, and ammonium formate/formic acid eutectic mixtures (1.0 : 1.25 mol/mol, respectively) have been investigated. The electrocatalytic oxidation of formic acid was observed in the eutectic mixtures, and bulk electrolysis at platinum electrodes demonstrated electrolysis of the formic acid to form H2 and CO2.

Electrocatalytic oxidation of formic acid on functional MWCNTs supported nanostructured Pd–Au catalyst

In this work, PdAu nanocatalysts with different weight ratio of Pd and Au supported on functional multi-walled carbon nanotubes (f-MWCNTs) were prepared, and their electrocatalytic activity for the oxidation of formic acid was also studied. The electrocatalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical results showed that the 4Pd1Au/f-MWCNTs (by weight) catalyst, exhibited distinctly higher activity and better stability in formic acid electrooxidation than the Pd/f-MWCNTs catalyst. The Nano-Au improves potentially the performance of Pd-based electrocatalysts for the direct formic acid fuel cells (DFAFCs).

Highly efficient electrocatalytic oxidation of formic acid by electrospun carbon nanofiber-supported Pt xAu 100−x bimetallic electrocatalyst

Electrospun carbon nanofiber-supported bimetallic Pt x Au 100− x electrocatalysts (Pt x Au 100− x /CNF) were prepared by electrochemical codeposition method. The composition of PtAu bimetallic nanoparticles could be controlled by varying the ratio of H 2PtCl 6 and HAuCl 4. Scanning electron microscopy images showed that bimetallic nanoparticles had coarse surface morphology with high electrochemically active surface areas. X-ray diffraction analysis testified the formation of PtAu alloys. Pt x Au 100− x /CNF electrocatalysts exhibited improved electrocatalytic activities towards formic acid oxidation by providing the selectivity of the reaction via dehydrogenation pathway and suppressing the formation/adsorption of poisoning CO intermediate, indicating that Pt x Au 100− x /CNF is promising electrocatalyst in direct formic acid fuel cells.

Enhanced electrocatalytic oxidation of formic acid by platinum deposition on ruthenium nanoparticle surfaces

PtRu alloy nanoparticles were prepared by the spontaneous adsorption of Pt(acac) 2 on the surface of freshly prepared octanethiolate-protected ruthenium (RuSC8) nanoparticles. UV–vis spectroscopic measurements suggested that the adsorption was facilitated by the strong affinity of the platinum metal center to the ruthenium surface. Scanning tunneling spectroscopic studies showed that the resulting PtRu nanoparticles exhibited enhanced conductance as compared to the original ruthenium nanoparticles, where the adsorbed Pt centers might serve as the effective sites for electron-tunneling across the tip/particle/substrate junction. The nanoparticles were then loaded onto a glassy carbon (GC) electrode and their catalytic activities in the electro-oxidation of formic acid were examined and compared. Remarkably, despite the presence of an organic protecting monolayer on the particle surface, apparent electrocatalytic activity was observed. Voltammetric measurements suggested that a Pt skin layer was formed on the Ru nanoparticle surface, most likely as a result of electro-reduction of the adsorbed Pt(acac) 2. On the basis of the onset potential and current density in the electro-oxidation of HCOOH, the resulting PtRu nanoparticles displayed much higher electrocatalytic activity than the Ru counterparts and commercial PtRu nanoparticle catalysts from BASF. It was also found that the electrocatalytic activity of the PtRu nanoparticles was comparable to that of FePt alloy nanoparticles and PtRu bulk electrocatalysts, despite a minimal loading of Pt in the catalysts. Consistent responses were observed in electrochemical impedance spectroscopic measurements, where the charge-transfer resistance on PtRu/GC was found to be at least an order of magnitude smaller than that on Ru/GC and commercial PtRu catalysts. These measurements suggest that the PtRu thin-layer nanoparticles might be used as a promising candidate for the electrocatalytic oxidation of formic acid.

Shil’nikov chaos in the oxidation of formic acid with bismuth ion on Pt ring electrode

We report experimental observations of potential oscillations in electrocatalytic oxidation of formic acid with bismuth ion on the Pt ring electrode. Potential oscillations were investigated under galvanostatic conditions. The presence of bismuth ion enables to get the low and stable potential values at larger current range. Periodic and Shil’nikov chaotic potential oscillations were observed at fixed current. To extract information from the oscillation pattern, we used time series, reconstructed attractor, next-maximum map, pattern formation of interfacial potential above ring electrode.

Electrocatalytic oxidation of formic acid and formaldehyde on nanoparticle decorated single walled carbon nanotubes

A potent catalyst has been prepared consisting of platinum (Pt), and platinum–palladium (Pt–Pd) nanoparticles supported on purified single-walled carbon nanotubes (Pt/CNT and Pt–Pd/CNT). Electrochemical characteristics of formic acid and formaldehyde oxidation on these catalysts are investigated via cyclic voltammetric analysis in mixed 0.5 M HCOOH (or 0.5 M HCHO) and 0.5 M H 2SO 4 solutions. The results imply that the Pt–Pd/CNT electrodes exhibit a better activity than the corresponding Pt nanoparticles modified SWCNT electrodes. The modified electrode exhibits significant electrocatalytic activity towards formic acid and formaldehyde oxidation, which may be attributed due to the uniform dispersion of nanoparticles on SWCNTs and the efficacy of Pd species in Pt–Pd system. Such nanoparticles modified CNT electrodes exhibit better catalytic behavior towards formic acid and formaldehyde than the corresponding carbon electrodes, indicating that the system studied in the present work is the more promising system for use in fuel cells.

Effect of Adding Fe on the Performances of Pd/C Catalyst

Pd-Fe/C catalysts were prepared by the impregnation-reduction method.The ratios of Pd to Fe were 1:1,2:1,1:2,respectively.The catalysts were characterized by transmission electron microscope (TEM) and powder X-ray diffraction (XRD).The results indicate that the catalyst particles are homogeneously distributed in the carrier.The average particle sizes are less than 5nm.The influence of adding Fe on Pd/C catalyst crystal structure was also studied.Finally,the activation of Pd-Fe/C catalysts with different Pd/C ratios to the electrocatalytic oxidation of formic acid was investigated. The results show that the catalytic performances of Pd/C catalyst are improved by adding suitable Fe; the catalytic performance of the Pd-Fe/C catalysts reaches the best when the atom ration of Pd:Fe equal to 1:1.

Facile preparation of carbon-supported Pd nanoparticles for electrocatalytic oxidation of formic acid

A low-temperature approach via the complexing of PdCl 2 with EDTA followed by NaBH 4 reduction has been used to prepare Vulcan XC-72 carbon-supported Pd nanoparticles (Pd/C). The mean particle size of the Pd/C catalysts is found to increase from 3.3 to 9.2 nm with heat-treated temperature. TEM images demonstrated that the Pd nanoparticles are well dispersed on the support, with a relatively narrow particle size distribution. A correlation between the electrocatalytic activity of formic acid oxidation and the particle size of the Pd/C catalysts indicates that the highest activity of formic acid oxidation is found with a Pd mean particle size of ca. 4.7 nm. The preparation method used here is cost-effective and should be easily scaled for industrial production.

Localized Pd Overgrowth on Cubic Pt Nanocrystals for Enhanced Electrocatalytic Oxidation of Formic Acid

Binary Pt/Pd nanoparticles were synthesized by localized overgrowth of Pd on cubic Pt seeds for the investigation of electrocatalytic formic acid oxidation. The binary particles exhibited much less self-poisoning and a lower activation energy relative to Pt nanocubes, consistent with the single crystal study.

A facile preparation of carbon-supported Pd nanoparticles for electrocatalytic oxidation of formic acid

A low temperature approach via the complexing of PdCl 2 with EDTA followed by NaBH 4 reduction has been used to prepare Vulcan XC-72 carbon-supported Pd nanoparticles (Pd/C). The mean particle size of the Pd/C catalysts is found to increase from 3.3 to 9.2 nm with heat-treated temperature. TEM images demonstrated that the Pd nanoparticles are well dispersed on the support with a relatively narrow particle size distribution. A correlation between the electrocatalytic activity of formic acid oxidation and particle size of the Pd/C catalysts indicates that the highest activity of formic acid oxidation is found with a Pd mean particle size of ca. 4.7 nm. The preparation method used here is cost-effective and should be easily scaled for industrial production.

Activity of a novel titanium-supported bimetallic PtSn/Ti electrode for electrocatalytic oxidation of formic acid and methanol

Bimetallic platinum–tin nanoparticles were co-deposited on a titanium surface using a simple one step hydrothermal method process. The electrochemical catalytic activity of this titanium-supported nanoPtSn/Ti electrode towards the oxidation of formic acid and methanol in 0.5 M H2SO4 was evaluated by voltammetric techniques, chronoamperometric responses and electrochemical impedance spectra (EIS). According to the cyclic voltammograms of the oxidation of both formic acid and methanol, the nanoPtSn/Ti presents high anodic current densities and low onset potentials. Potential-time transient measurements show that the nanoPtSn/Ti exhibits high steady-state current densities for the oxidation of both formic acid and methanol. The EIS data indicate that the nanoPtSn/Ti presents very low electrochemical impedance values, showing that for the oxidation of both formic acid and methanol, low charge transfer resistances are present on the nanoPtSn/Ti catalyst. This confirms the high electrocatalytic activity of the nanoPtSn/Ti for the formic acid and methanol oxidation.

Mild Metal Mixing

CHEMISTRY Combining a second metal with platinum (Pt) to form an intermetallic can reduce costs, inhibit poisoning, and in certain cases improve the reactivity of this widely used catalyst. However, the need for particle annealing at high temperature causes sintering that reduces the particle surface area and introduces shape and size distortions. Bauer et al. present a milder technique whereby Pt nanoparticles synthesized with specific shape and size dispersity are treated in low-temperature solution with metal salts to form Pt-M intermetallics (M can be tin, lead, or several other metals). When stabilized by growth on a support such as alumina or ceria, the Pt particles did not aggregate. In the case of PtPb particles supported on Vulcan XC-72, a conductive carbon black pigment, the electrocatalytic oxidation of formic acid occurred at a lower onset potential in comparison with commercial PtRu particles on the same support. — MSL J. Mater. Chem. 18 , 275 (2008).

Catalytic and electro-catalytic oxidation of formic acid on the pure and Cu-modified Pd(1 1 1)-surface

The electrooxidation of formic acid, potentially important for future fuel cells, was investigated by means of cyclic voltammetry (CV) and in situ infrared reflection absorption spectroscopy (IRRAS) both on a pure and on a copper-modified Pd(111)-electrode in sulphuric acid solutions. In situ IR spectra recorded under open-circuit conditions exhibit several vibrational bands in the carbonyl region characteristic of “free” and adsorbed formic acid as well as of decomposition intermediates. A detailed analysis of the intensity of the bands as a function of time leads to a reaction mechanism for the mere “catalytic” oxidation of formic acid at the Pd(111)/electrolyte interface. The “electro-catalytic” oxidation of formic acid under potential control starting above 0.35V is investigated by following the evolution of carbon dioxide as a function of electrode potential. IR measurements at different but constant potentials point to an electronic structure of the solid/liquid interface in the open-circuit HCOOH/Pd(111)–H2SO4 system which resembles that at an electrode potential of about 0.4V. Modification of the Pd(111) surface is achieved by copper deposition from a Cu2+/HCOOH/H2SO4 solution. Simultaneously, the influence of the foreign metal on the electro-catalytic oxidation of formic acid is studied in dependence on the potential scan direction. In the positive-going scan copper deposited on Pd(111) at cathodic potential inhibits the electro-catalytic oxidation of formic acid below 0.45V by blocking catalytically active Pd sites. Conversely, during the negative-going scan the Cu2+/HCOOH/Pd(111)–H2SO4 system shows an increased oxidation activity between 0.6V and 0.2V due to a direct redox reaction between copper ions and formic acid. The amount of copper deposited on the surface was determined by ex situ Auger Electron Spectroscopy after a contamination free sample transfer into UHV.

Formic acid electrooxidation on Pd in acidic solutions studied by surface-enhanced infrared absorption spectroscopy

A mechanistic study of electrocatalytic oxidation of formic acid on Pd in sulfuric and perchloric acids is reported. Surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS) shows the adsorption of CO, bridge-bonded formate, bicarbonate, and supporting anions on the electrode surface. Poisoning of the Pd surface by CO, formed by dehydration of formic acid, is very slow and scarcely affects formic acid oxidation. The anions are adsorbed more strongly in the order of (bi)sulfate > bicarbonate > perchlorate, among which the most strongly adsorbed (bi)sulfate considerably suppresses formic acid oxidation in the double layer region. The oxidation is suppressed also at higher potentials in both acids by the oxidation of the Pd surface. Adsorbed formate is detected only when formic acid oxidation is suppressed. The results show that formate is a short-lived reactive intermediate in formic acid oxidation and is hence detected when its decomposition yielding CO(2) is suppressed. The high electrocatalytic activity of Pd can be ascribed to the high tolerance to CO contamination and also high catalytic activity toward formate decomposition.

Electrocatalytic Oxidation of Formic Acid and Methanol on Pt Deposits on Au(111)

This work presents characteristics of Pt deposits on Au(111) obtained by the use of spontaneous deposition and investigated by electrochemical scanning tunneling microscopy (EC-STM). On such prepared and STM characterized Au(111)/Pt surfaces, we studied electrocatalytic oxidation of formic acid and methanol. We show that the first monatomic layer of Pt displays a (square root 3 x square root 3)R30 degrees surface structure, while the second layer is (1 x 1). After prolonged deposition, multilayer Pt deposits are formed selectively on Au(111) surface steps and are 1-20 nm wide and one to five layers thick. On the optimized Au(111)/Pt surface, formic acid oxidation rates are enhanced by a factor of 20 compared to those of pure Pt(111). The (square root 3 x square root 3)R30 degrees-Pt yields very low methanol oxidation rates, but the rates increase significantly with further Pt growth.

The pattern formation under a condition of low conductivity of electrolyte

Decreasing the electrolytic conductivity leads to the formation of more plentiful patterns, in comparison to normal electrochemical system. In this experiment local standing wave, cluster pattern, modulated pulse, pulse failure, pulse reflection, standing wave and pulse have been observed during the electrocatalytic oxidation of formic acid on a platinum ring electrode in a system with a very low conductivity of electrolyte and discussed. The resistivity of electrolyte used in this article is 526 Ω cm. The potential ranges of existence of different types of patterns were analysed with the help of theoretical researches and it was found that the potential ranges where different types of patterns exist can superpose each other to some extent.

Synthesis and characterization of metal nanoparticles-decorated PPY–CNT composite and their electrocatalytic oxidation of formic acid and formaldehyde for fuel cell applications

Polymer composite films encompassed of polypyrrole (PPY) and multi-walled carbon nanotubes (MWCNT) [PPY–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1M HCl containing (NH4)S2O8 as oxidizing agent at 0–5°C. 2–4nm sized metal nanoparticles, viz. Pt and Pt–Pd were then deposited on the prepared polypyrrole/CNT composites by chemical reduction of the corresponding metal salts using HCHO as reducing agent at pH 11. The fabricated nanoparticles-decorated composite films were then used as a probe towards formic acid and formaldehyde oxidation. Furthermore, the addition of CNT to polypyrrole imparts a high activity, which might be due to the higher electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/carbon nanotubes interfaces allowing a higher dispersion and utilization of deposited Pt and Pt–Pd nanoparticles. Results from formic acid and formaldehyde oxidation showed that Pt–Pd nanoparticles-modified Ppy–CNT exhibits better catalytic activity and stability in contrast to Pt supported on Ppy–CNT. Pt and Pt–Pd nanoparticles are found homogeneously dispersed in Ppy–MWCNT composites ascertained from various analytical data like scanning electron microscopy (SEM), transmission electron microscopy (TEM). Energy dispersive X-ray analysis (EDAX) is used to characterize the nature of metal present in the nanoparticles-modified electrodes.

Mechanistic Study of Electrocatalytic Oxidation of Formic Acid at Platinum in Acidic Solution by Time-Resolved Surface-Enhanced Infrared Absorption Spectroscopy

Surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with cyclic voltammetry or chronoamperometry has been utilized to examine kinetic and mechanistic aspects of the electrocatalytic oxidation of formic acid on a polycrystalline Pt surface at the molecular scale. Formate is adsorbed on the electrode in a bridge configuration in parallel to the adsorption of linear and bridge CO produced by dehydration of formic acid. A solution-exchange experiment using isotope-labeled formic acids (H(12)COOH and H(13)COOH) reveals that formic acid is oxidized to CO(2) via adsorbed formate and the decomposition (oxidation) of formate to CO(2) is the rate-determining step of the reaction. The adsorption/oxidation of CO and the oxidation/reduction of the electrode surface strongly affect the formic acid oxidation by blocking active sites for formate adsorption and also by retarding the decomposition of adsorbed formate. The interplay of the involved processes also affects the kinetics and complicates the cyclic voltammograms of formic acid oxidation. The complex voltammetric behavior is comprehensively explained at the molecular scale by taking all these effects into account.