Pd/Co Bimetallic Nanoparticles: Coelectrodeposition under Protection of PVP and Enhanced Electrocatalytic Activity for Ethanol Electrooxidation

A series of Pd–Co bimetallic nanostructures with Co compositions ranging from 0 to 13 at.% were fabricated on glassy carbon electrode by one step electrodeposition in the presence of polyvinylpyrrolidone (PVP). The roles of PVP and Co have been systematically investigated by using combined techniques such as scanning electron microscopy, energy dispersive spectrometry, cyclic voltammetry, X‐ray diffraction, and chronoamperograms. PVP was used as an additive to stabilize the Pd nanoparticles and inhibit agglomeration during their formation. The prepared Pd₁₀₀Co₁₀ bimetallic nanostructures exhibited great catalytic activity towards ethanol oxidation in alkaline, which implies that low Co doping can be a convenient way to enhance the electrocatalytic property of Pd. The present study shows that the Pd/Co bimetallic nanoparticulate can be a promising catalyst for portable applications in direct ethanol fuel cell in alkaline solution.     

Effects of alkaline treatment of hydrogen storage alloy on electrocatalytic activity for NaBH4 oxidation

Activation of the MmNi_4.03Co_0.42Mn_0.31Al_0.24 hydrogen storage alloy electrode is performed by immersing the electrode in a solution containing 6.0 mol dm⁻³ NaOH and 0.1 mol dm⁻³ NaBH_4. The effects of activation on the electrocatalytic activity of the electrode for NaBH₄ oxidation are investigated by cyclic voltammetry and chronoamperometry. Immersion activation greatly improves the electrocatalytic activity of the alloy electrode. Hydrogen was absorbed in the alloy during the immersion activation treatment and its electrooxidation is responsible for the high initial oxidation current. The stabilized current mainly results from the direct oxidation starting from the borohydride species. The effects of activation on structure and surface chemistry of the alloy are also discussed.     

Electrooxidation study of pure ethanol/methanol and their mixture for the application in direct alcohol alkaline fuel cells (DAAFCs)

Aliphatic alcohol mainly, ethanol, methanol and their mixture were subjected to electrooxidation study using cyclic voltammetry (CV) technique in a three electrodes half cell assembly (PGSTAT204, Autolab Netherlands). A single cell set up of direct alcohol alkaline fuel cell (DAAFC) was fabricated using laboratory synthesized alkaline membrane to validate the CV results. The DAAFC conditions were kept similar as that of CV experiments. The anode and cathode electrocatalysts were Pt-Ru (30%:15% by wt.)/Carbon black (C) (Alfa Aesar, USA) and Pt (40% by wt.)/High Surface Area Carbon (C_HSA) (Alfa Aesar, USA) respectively. The CV and single cell experiments were performed at a temperature of 30 °C. The anode electrocatalyst was in the range of 0.5 mg/cm² to 1.5 mg/cm² for half cell CV analysis. The cell voltage and current density data were recorded for different concentrations of fuel (ethanol or methanol) and their mixture mixed with different concentration of KOH as electrolyte. The optimum electrocatalyst loading in half cell study was found to be 1 mg/cm² of Pt-Ru/C irrespective of fuel used. The single cell was tested using optimum anode loading of 1 mg/cm² of Pt-Ru/C which was found in CV experiment. Cathode loading was kept similar, in the order of 1 mg/cm² Pt/C_HSA. In single cell experiment, the maximum open circuit voltage (OCV) of 0.75 V and power density of 3.57 mW/cm² at a current density of 17.76 mA/cm² were obtained for the fuel of 2 M ethanol mixed with 1 M KOH. Whereas, maximum OCV of 0.62 V and power density of 7.10 mW/cm² at a current density of 23.53 mA/cm² were obtained for the fuel of 3 M methanol mixed with 6 M KOH. The mixture of methanol and ethanol (1:3) mixed with 0.5 M KOH produced the maximum OCV of 0.66 V and power density of 1.98 mW/cm² at a current density of 11.54 mA/cm².     

Bromide ion mediated synthesis of carbon supported ultrathin palladium nanowires with enhanced catalytic activity toward formic acid/ethanol electrooxidation

Palladium nanowires with a diameter of about 5 nm and length of a few tens of nanometers can be synthesized in the presence of large amount of bromide ions, employing polyvinylpyrrolidone as protective reagent while sodium borohydride as reductant. The obtained Pd nanowires are well dispersed on Vulcan XC-72 carbon. The structure and composition of the as-prepared catalyst are analyzed by transmission electron microscope, X-ray diffraction, energy dispersive X-ray spectrum and inductively coupled plasma optical emission spectrometer. Electrochemical catalytic measurement results prove that the as-prepared catalyst exhibits superior electrocatalytic activity towards ethanol and formic acid electrooxidation.     

Electrooxidation of borohydride on platinum and gold electrodes: implications for direct borohydride fuel cells

The electrochemical oxidation of BH₄⁻ in 2 M NaOH on Pt and Au (i.e. catalytic and non-catalytic electrodes, respectively, for BH₄⁻ hydrolysis accompanied by H₂ evolution) has been studied by cyclic voltammetry, chrono-techniques (i.e., potentiometry, amperometry, coulometry) and electrochemical impedance spectroscopy. In the case of Pt the cyclic voltammetry behaviour of BH₄⁻ is influenced by both, the catalytic hydrolysis of BH₄⁻ yielding H₂ (followed by electrooxidation of the latter at peak potentials between −0.7 and −0.9 V versus Ag/AgCl, KCl_std) and direct oxidation of BH₄⁻ at more positive potentials, i.e., between −0.15 and −0.05 V. Thiourea (TU, 1.5×10⁻³ M) was an effective inhibitor of the catalytic hydrolysis associated with BH₄⁻ electrooxidation on Pt. Therefore, in the presence of TU, only the direct oxidation of BH₄⁻ has been detected, with peak potentials between −0.2 and 0 V. It is proposed that TU could improve the BH₄⁻ utilization efficiency and the coulombic efficiency of direct borohydride fuel cells using catalytic anodes. The electrooxidation of BH₄⁻ on Pt/TU is an overall four-electron process, instead of the maximum eight electrons reported for Au, and it is affected by adsorbed species such as BH₄⁻ (fractional surface coverage ∼0.3), TU and possibly reaction intermediates.     

Electrochemical-assisted photocatalytic degradation of textile washwater

Photocatalytic methods with TiO₂ catalyst were successfully applied to the decomposition of many organic contaminants. In this paper the performance of an electrochemical-assisted photocatalytic degradation of textile washwater containing procion blue dye was investigated. Several operational parameters to achieve optimum efficiency of this electrochemical-assisted photocatalytic degradation system have been done. The main objective was to determine the chemical oxygen demand (COD) and colour removal of the organic pollutant. The effects of pH, current density, supporting electrolyte, the irradiation time and photocatalyst on treatment efficiency were studied. The results showed that electrochemical-assisted photocatalytic process was used efficiently with 90% COD removal and complete colour removal after 7 h treatment.     

Electrooxidation of ethanol on a Pt electrode in acid solutions: in situ ATR-SEIRAS study

The electrooxidation of ethanol was investigated on a Pt thin film electrode in a HClO₄ solution using surface enhanced infrared absorption spectroscopy (SEIRAS) with the attenuated total reflection (ATR) technique. The spectra indicate that during this reaction acetate and CO adsorbates are formed. The intensity of symmetric OCO stretching band of adsorbed acetate correlates well with voltammetry in the potential range between −0.1 and 0.85 V. The CO stretching band for adsorbed acetaldehyde and/or acetyl also was observed; these compounds are the reaction intermediates whose oxidation generates CO_ad and acetic acid. We also explored the oxidation behavior of adsorbed residues. The oxidation of acetaldehyde was studied for comparison.     

Preparation and activity of mono- or bi-metallic nanoparticles for electrocatalytic reactions

Improvement of Pt activity for electrocatalytic reactions is possible by modifying Pt nanoparticles with other metals able to activate water. Selected examples are discussed with the electrooxidations of methanol and ethanol or the electroreduction of dioxygen. Nanoparticles electrodes of Pt-Ru (for methanol oxidation), of Pt-Sn (for ethanol oxidation) or of Pt-Cr (for oxygen reduction) supported on carbon powder can be prepared from colloidal precursors. This kind of preparation allows varying the composition and/or the structure of the electrode. The formulation of improved electrodes can be obtained after complete study of the reaction mechanism by “in situ” spectroscopic experiment.     

Synergistic effect of CeO2 modified Pt/C catalysts on the alcohols oxidation

The effect of the addition of CeO₂ to Pt/C catalysts on electrochemical oxidation of alcohols (methanol, ethanol, glycerol, ethylene glycol) was studied in alkaline solution. The ratios of Pt to CeO₂ in the catalysts were optimised to give the better performance. The electrochemical measurements revealed that the addition of CeO₂ into Pt-CeO₂/C catalysts could significantly improve the electrode performance for alcohols oxidation, in terms of the reaction activity and the poisoning resistance, due to the synergistic effect. The electrode with the weight ratio of Pt to CeO₂ equals 1.3:1 with platinum loading of 0.30 mg/cm² showed the highest catalytic activity for oxidation of ethanol, glycerol and ethylene glycol.     

Carbon-supported PdM (M = Au and Sn) nanocatalysts for the electrooxidation of ethanol in high pH media

Carbon-supported Pd₄Au- and Pd_2.5Sn-alloyed nanoparticles were prepared by a chemical reduction method, and characterized by a wide array of experimental techniques including mass spectrometry, transmission electron microscopy, and X-ray diffraction spectroscopy. Ethanol electrooxidation on the as-synthesized catalysts and commercial Pt/C was then investigated and compared in alkaline media by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy studies at room temperature. Voltammetric and chronoamperometric measurements showed higher current density and longer term stability in ethanol oxidation with the palladium alloy nanocatalysts than with the commercial one. Electrochemical impedance spectroscopy and Tafel plots were employed to examine the charge-transfer kinetics of ethanol electrooxidation. The results suggest that whereas the reaction kinetics might be somewhat more sluggish on the Pd-based alloy catalysts than on commercial Pt/C, the former appeared to have a higher tolerance to surface poisoning. Overall, the Pd-based alloy catalysts represent promising candidates for the electrocatalytic oxidation of ethanol, and Pd₄Au/C displays the best catalytic activity among the series for the ethanol oxidation in alkaline media.