A remarkable activity of glycerol electrooxidation on gold in alkaline medium

In this paper, the activity and stability of glycerol oxidation on Au electrode have been investigated by cyclic voltametry, chronoamperometry and chronopotentiometry methods in alkaline medium. The glycerol shows a remarkable activity and better performance than methanol, ethanol, n-propanol, isopropanol and ethylene glycol on the Au electrode in alkaline medium. The activity and stability of glycerol oxidation on the Au electrode are higher than that of glycerol oxidation on Pd electrode. The stability of glycerol oxidation on the Au electrode is higher than that of methanol and glycerol oxidation on Pt electrode. The results show that glycerol is an excellent fuel applied in direct alcohol fuel cells with Au as anode catalyst.     

Ethylene glycol, 2-propanol electrooxidation in alkaline medium on the ordered intermetallic PtPb surface

The ethylene glycol and 2-propanol electrooxidation reaction was studied on carbon dispersed ordered intermetallic PtPb nanocatalysts in KOH solution. X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize ordered intermetallic PtPb/C catalysts. The electrochemical behaviors for the ethylene glycol and 2-propanol electrooxidation reaction were measured in a thin film electrode by cyclic voltammetry, Tafel curves and electrochemical impedance spectroscopy. The results showed that in contrast with PtRu/C and Pt/C catalyst, ordered intermetallic PtPb/C had better electroactivity, and kinetic mechanism of PtPb/C is complex. Although the activity of electrocatalysts depends on many factors, such as modification of geometric and electronic structure by Pt-Pb interaction, crystalline size and so on. But the key factor for each electrooxidation reaction was different. For ethylene glycol electrooxidation, the effect of formation and desorption of poisonous species on activity of catalyst was very significant. For 2-propanol electrooxidation, the modification of geometric and electronic structures may be play a decisive role in the enhance activity of electrocatalyst.     

Pt supported on highly graphitized lace-like carbon for methanol electrooxidation

A simple solvothermal method has been used to synthesize highly graphitized lace-like carbon (GLC) using ethanol as the carbon source and Mg as reducing agent. The GLC is characterized by transmission electron microscopy, X-ray diffraction, N₂ adsorption, Raman spectroscopy and electrochemical techniques. The GLC synthesized at optimized conditions shows interlaced structure with an average thickness of 3 nm. Platinum on GLC electrocatalysts were prepared for methanol oxidation in acidic media for the first time. They show extremely higher activity for methanol oxidation compared to Pt/C electrocatalyst for the same Pt loadings. GLCs act as structural units to form mesopores and channels in the catalyst layers, which lead to the increase of the electrochemical active surface area and improvement in the mass transport by reducing the liquid sealing effect.     

Indirect urea electrooxidation by nickel(III) in alkaline medium: From kinetic and mechanism to reactor modeling

This study consists in the determination of two kinetic laws of urea oxidation (UO) and electrooxidation (UEO) in alkaline media on nickel(III). Two kinds of active sites were examined, the first one derived from a Ni(OH)₂ powder and the second from a massive nickel electrode. Partial orders of nickel(III) (two for UO and five UEO) enable to conclude about (i) the urea adsorption on two nickel(III) sites and (ii) that a multistep oxidation of urea occurs involving five nickel(III) site electroregenerations. A multipathway mechanism is also proposed to explain UEO facilitated by the nickel(III)/nickel(II) mediation system, and to predict the by-products' formation previously identified ($\mathrm{N}{\mathrm{O}}_2^{-},\mathrm{N}{\mathrm{H}}_3,\mathrm{OC}{\mathrm{N}}^{-},\mathrm{C}{\mathrm{O}}_3^{2-}$). At last, a model combining the UEO kinetic law previously established, with diffusive and convective transport phenomena was developed. A consistent correlation (maximum deviation of 6%) between laboratory electrolysis results with the model' predictions was obtained under different operating conditions, enabling the validation of this model.     

Ethanol electrooxidation on novel carbon supported Pt/SnOx/C catalysts with varied Pt:Sn ratio

Novel carbon supported Pt/SnO_x/C catalysts with Pt:Sn atomic ratios of 5:5, 6:4, 7:3 and 8:2 were prepared by a modified polyol method and characterized with respect to their structural properties (X-ray diffraction (XRD) and transmission electron microscopy (TEM)), chemical composition (XPS), their electrochemical properties (base voltammetry, CO_ad stripping) and their electrocatalytic activity and selectivity for ethanol oxidation (ethanol oxidation reaction (EOR)). The data show that the Pt/SnO_x/C catalysts are composed of Pt and tin oxide nanoparticles with an average Pt particle diameter of about 2 nm. The steady-state activity of the Pt/SnO_x/C catalysts towards the EOR decreases with tin content at room temperature, but increases at 80 °C. On all Pt/SnO_x/C catalysts, acetic acid and acetaldehyde represent dominant products, CO₂ formation contributes 1-3% for both potentiostatic and potentiodynamic reaction conditions. With increasing potential, the acetaldehyde yield decreases and the acetic acid yield increases. The apparent activation energies of the EOR increase with tin content (19-29 kJ mol⁻¹), but are lower than on Pt/C (32 kJ mol⁻¹). The somewhat better performance of the Pt/SnO_x/C catalysts compared to alloyed PtSn_x/C catalysts is attributed to the presence of both sufficiently large Pt ensembles for ethanol dehydrogenation and C-C bond splitting and of tin oxide for OH generation. Fuel cell measurements performed for comparison largely confirm the results obtained in model studies.     

Electrochemical regeneration and porosity recovery of phenol-saturated granular activated carbon in an alkaline medium

The electrochemical regeneration of phenol-saturated activated carbon has been carried out in a filter-press electrochemical cell. The feasibility of the electrochemical regeneration has been assessed by monitoring the regeneration efficiency and the textural properties of a phenol-saturated granular activated carbon (GAC) electrolysed in NaOH medium. The influence of the following factors: (i) the electrolysis treatment (either anodic or cathodic); (ii) the separation of compartments; (iii) applied current and (iv) electrolysis time has been studied. Basing on the obtained results, an overall phenomenological mechanism for the electrochemical regeneration has been proposed. The general worse performance of anodic regenerations can be attributed to an important surface blockage of the GAC by reaction products such as quinones, phenolic oligomers and polymers coming from phenol electrooxidation. The cathodic regeneration in NaOH medium, where phenolate desorption is favoured, and in an undivided configuration, where surface blockage is minimized, produces a significant recovery of the porosity of the original GAC, in agreement with the highest RE values (close to 80%).     

中碳膨胀石墨的研究

以天然中碳鳞片石墨为原料,用浓H2SO4及浓HNO3作插层剂,在酸化阶段添加专门配制的H-L溶液,便可制备出膨胀倍率在280m l/g以上、含碳量在99%以上的膨胀石墨。     

Ethanol electrooxidation on platinum particles dispersed on poly(neutral red) film

The conductive polymer poly(neutral red) polymerized on a graphite electrode (PNR/graphite) as a support material was used for catalytic oxidation of ethanol in acidic solution and investigated by electrochemical methods. Pt particles loaded on the surface of PNR/graphite electrode exhibited higher electrocatalytic activity for ethanol oxidation in comparison with Pt particles supported directly on graphite. With the equivalent loading mass of Pt catalyst, the special activity (S _A ) at peak a of the Pt/PNR/graphite electrode polymerized for 10 cycles in 5 × 10⁻⁴ M NR + 0.5 M H₂SO₄ solution is 3,478 A C⁻¹ and about 2.20 times higher than that of the Pt/graphite electrode (1,582 A C⁻¹). The results show that the electrochemical performance of Pt catalyst for ethanol oxidation is improved by the addition of PNR     

Surface area loss of platinum supported on graphite

A study was conducted of the loss surface area of platinum when supported on both untreated and oxidized graphitized carbon black. The treatment of the graphite support was found to affect the rate of Pt area loss in a hot, concentrated H₃PO₄ solution with the support prepared using the iron oxide catalysed oxidation of the graphite resulting in the least loss of Pt surface area. This surface area loss was found to be relatively insensitive to electrode operating potential. A t-plot analysis of the nitrogen adsorption data on the support was used to explain the beneficial effect of the catalytically oxidized graphite. This study demonstrates that crystallite migration is the mechanism of supported Pt surface area loss in H₃PO₄ electrolyte.     

Ethanol oxidation on carbon supported platinum-rhodium bimetallic catalysts

Platinum is the most investigated catalyst for the electrochemical oxidation of small organic molecules. This metal presents high overpotentials for the oxidation of organic compounds and the poisoning of active sites by strongly adsorbed intermediates, mainly CO, which decrease the efficiency of a direct alcohol fuel cell (DAFC). Ethanol is an ideal fuel for these DAFC systems due to its high energy density, but one of the problems with the electro-oxidation of this fuel is the low yield for the total oxidation to CO₂. The purpose of the work reported here was to study the influence of the composition of Pt-Rh/C catalysts on the CO₂ yields. In addition, using the differential electrochemical mass spectrometry (DEMS) technique, it is shown that Pt-Rh/C catalysts enhance the total ethanol oxidation with respect to pure Pt/C by driving the reaction via the CO₂ route. The faradaic current efficiency for the oxidation of ethanol to CO₂ increased from 0.08 on pure Pt/C to 0.5 on the Pt₄₇Rh₅₃/C catalyst at 0.7 V vs. RHE. It was concluded that electronic effects play a key role in the mechanism of ethanol oxidation on Pt-Rh/C electrodes.     

Pt-decorated nanoporous gold for glucose electrooxidation in neutral and alkaline solutions

Exploiting electrocatalysts with high activity for glucose oxidation is of central importance for practical applications such as glucose fuel cell. Pt-decorated nanoporous gold (NPG-Pt), created by depositing a thin layer of Pt on NPG surface, was proposed as an active electrode for glucose electrooxidation in neutral and alkaline solutions. The structure and surface properties of NPG-Pt were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and cyclic voltammetry (CV). The electrocatalytic activity toward glucose oxidation in neutral and alkaline solutions was evaluated, which was found to depend strongly on the surface structure of NPG-Pt. A direct glucose fuel cell (DGFC) was performed based on the novel membrane electrode materials. With a low precious metal load of less than 0.3 mg cm^-2 Au and 60 μg cm^-2 Pt in anode and commercial Pt/C in cathode, the performance of DGFC in alkaline is much better than that in neutral condition.     

PtRu nanoparticles supported on nitrogen-doped multiwalled carbon nanotubes as catalyst for methanol electrooxidation

Nitrogen-doped carbon nanotubes (N-CNT) obtained by plasma treatment were compared to the conventional acid-treated carbon nanotubes (O-CNT) as catalyst support for platinum-ruthenium (PtRu) nanoparticles in the anodic oxidation of methanol in direct methanol fuel cells. PtRu catalysts were prepared by an impregnation-reduction method from chloride precursors with metal loadings of 20 wt.%, and were characterised by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical methods. Voltammetry and chronoamperometry studies showed that the performance of PtRu/N-CNT was significantly higher compared to PtRu/O-CNT and also to the commercial E-TEK PtRu/C catalyst, indicating that N-CNT are an interesting support material for fuel cell electrocatalyst. Nitrogen plasma treatment produced pyridinic and pyrrollic species on the CNT surface, which acts as the anchoring sites for the deposition of PtRu particles. A mechanism for the deposition of PtRu on N-CNT is tentatively proposed and discussed.     

In situ FTIR spectroscopic studies of electrooxidation of ethanol on Pd electrode in alkaline media

Electrooxidation of ethanol on a polycrystalline Pd disk electrode in alkaline media was studied by in situ Fourier transform infrared (FTIR) reflection spectroscopy. The emphasis was put on the quantitative determination of intermediates and products involved in the oxidation. It has revealed that most of ethanol was incompletely oxidized to acetate. The selectivity for ethanol oxidation to CO₂ (existing as CO₃²⁻ in alkaline media) was determined as low as 2.5% in the potential region where Pd electrode exhibited considerable electrocatalytic activity (−0.60 to 0.0 V vs. SCE). Nevertheless, the ability of Pd for breaking C-C bond in ethanol is still slightly better than that of Pt under the same conditions. Besides, a very weak band of adsorbed intermediate, bridge-bonded CO (CO_B) was identified on the Pd electrode for the first time, suggesting that CO₂ and CO₃²⁻ species may also be generated through CO pathway (i.e., indirect pathway).     

In situ fabricated iodine-adlayer assisted selective electrooxidation of uric acid in alkaline media

This work presents the electrooxidation of uric acid (UA) at an iodine-adlayer-modified gold, Au (I|Au (poly)) electrode in 0.1 M NaOH solution using cyclic voltammetric, amperometric and open-circuit potential measurement techniques. A tremendous enhancement of the electrode activity towards the electrooxidation of UA was achieved by virtue of the simple modification of the Au (poly) electrode surface with a neutral iodine-adlayer, fabricated in situ through the spontaneous oxidative chemisorption of iodide present in the sample solution. The cyclic voltammetric peak current increases remarkably for the oxidation of UA and the peak potential shifts by 365 mV to the negative direction of potential compared to the bare Au (poly) electrode. Oxidation of ascorbic acid (AA) at the I|Au (poly) electrode takes place at the same potential as that at the bare electrode, but the peak current intensity is almost twice at the bare Au (poly) electrode as compared to the modified one. In the mixture of the AA and UA, the cyclic voltammetric signals corresponding to the oxidations of AA and UA were resolved by 340 mV. The electrode response in the mixture was highly reproducible because of the inhibition of adsorption of oxidation products and UA.     

Anodic oxidation of copper cyanide on graphite anodes in alkaline solution

The anodic oxidation of copper cyanide has been studied using a graphite rotating disc with reference to cyanide concentration (0.05–4.00 M), CN:Cu mole ratio (3–12), temperature (25–60 °C) and hydroxide concentration (0.01–0.25 M). Copper had a significant catalytic effect on cyanide oxidation. In the low polarization region (about 0.4 V vs SCE or less), cuprous cyanide is oxidized to cupric cyanide complexes which further react to form cyanate. At a CN:Cu ratio of 3 and [OH^–] = 0.25 M, the Tafel slope was about 0.12 V decade^–1. Cu(CN)₃ ^2– was discharged on the electrode and the reaction order with respect to the predicted concentration of Cu(CN)₃ ^2– is one. With increasing CN:Cu mole ratio and decreasing pH, the dominant discharged species shifted to Cu(CN)₄ ^3–. Under these conditions, two Tafel slopes were observed with the first one being 0.060 V decade^–1 and the second one 0.17–0.20 V decade^–1. In the high polarization region (about 0.4 V vs SCE or more), cuprous cyanide complexes were oxidized to copper oxide and cyanate. Possible reaction mechanism was discussed.     

Anodic oxidation of sulphite ions on graphite anodes in alkaline solution

The anodic oxidation of sulphite ions in alkaline 1 M Na₂SO₄ solution on graphite rotating disc electrodes has been studied over the range from 25 to 60 °C. The reaction order with respect to sulphite ions is below 1 at low potentials and 1 at high potentials. The reaction order with respect to hydroxide ions is close to zero. Two Tafel slopes were observed, 0.060V decade^–1 at low potentials and 0.190.20V decade^–1 at high potentials. The reaction activation energy was calculated at different potentials. The results obtained, using the potential sweep method, are consistent with those realized using the rotating disc. A possible reaction mechanism has been proposed and the diffusion coefficients of sulphite ions and the diffusion activation energy have been calculated.     

Study of the electrooxidation of 1,3-propanediol on a gold electrode in basic medium

A study of the mechanism of electrooxidation of 1,3-propanediol on a gold electrode in basic medium has been made. The kinetic parameters measured, together with other experimental data, allow the formulation of a mechanism in which both 1,3-propanediol and OH^– ions adsorb on the gold surface and the rate determining step is an interaction between both coverages with the result of the formation of an adsorbed radical, whose oxidation leads to the formation of 3-hydroxypropanoic acid which has been identified by nuclear magnetic resonance (NMR).     

Enhanced activity of carbon-supported PdCo electrocatalysts toward electrooxidation of ethanol in alkaline electrolytes

Carbon-supported Pd and PdCo (1: 2, 1: 1, 2: 1 and 3: 1) catalysts were synthesized by chemical reduction with NaBH₄. Their electrochemical properties were investigated by cyclic voltammetry, chronoamperometry and CO stripping voltammetry in alkaline electrolytes, and compared with commercial Pt/C and PtRu(1: 1)/C catalysts. In electrochemical oxidation of ethanol in an alkaline electrolyte, marked improvements in the current density and onset potential were observed by incorporating Co into Pd/C to form PdCo/C alloy electrocatalysts. The best catalyst PdCo (1: 1)/C showed performance superior to the commercial Pt/C or PtRu/C catalysts. It is shown that the incorporated Co facilitates the oxidation of strongly-adsorbed carbonaceous intermediate species on the surface of Pd by forming OH^? group and reacts away the intermediates from Pd surface. Thus, PdCo(1: 1)/C catalyst is a promising anode catalyst for direct ethanol fuel cells with alkaline electrolytes.