Alkaline Alcohol Research Articles

Switching Carbon Nanodots from Single Emission to Dual Emission by One-Step Electrochemical Tailoring in Alkaline Alcohols: Implications for Sensing and Bioimaging

Fluorescent carbon nanodots (CNDs) capable of dual emission blue and red light (B-R-CNDs) (460 and 610 nm) have been synthesized by a simple and low cost electrochemical method of discharging indol...

One-step synthesis of fluorescent organic nanoparticles: The application to label-free ratiometric fluorescent pH sensor

In this work, we develop a facile one-step synthesis method of poly(3,4-dihydroxyphenylalanine) (poly(DOPA)) fluorescent organic nanoparticles (FONPs) by polymerization of DOPA in alkaline alcohol solution under ultrasonic radiation. The morphology and size of poly(DOPA)-FONPs are dependent on the synthesis conditions, such as solvent and alkali concentration. Under the optimized condition, the prepared poly(DOPA)-FONPs possess not only uniform size and morphology, but also strong green fluorescence, good solubility in water and organic solvents. Under excitation of single wavelength, two emission peaks can be clearly observed, which are pH-sensitive. Moreover, the intensity ratio of two emission peaks is linear against pH values from 4.0 to 8.0 in buffer solution. In addition, the pH-sensitive response of the poly(DOPA)-FONPs be free from the influence of various metal ions and biomolecules, indicating the excellent specificity to pH. Further, due to the excellent biocompatibility, the poly(DOPA)-FONPs might also be applied on biological imaging for monitoring intracellular pH. The as-prepared poly(DOPA)-FONPs would be promising to be applied on the low-cost, low-toxic and label-free ratiometric pH sensor.

The Alkaline Stability of Anion Exchange Membrane for Fuel Cell Applications: The Effects of Alkaline Media.

Alkaline alcohols (methanol, ethanol, propanol, and ethylene glycol) have been applied as fuels for alkaline anion exchange membrane fuel cells. However, the effects of alkaline media on the stability of anion exchange membranes (AEMs) are still elusive. Here, a series of organic cations including quaternary ammonium, imidazolium, benzimidazolium, pyridinium, phosphonium, pyrrolidinium cations, and their corresponding cationic polymers are synthesized and systematically investigated with respect to their chemical stability in various alkaline media (water, methanol, ethanol, and dimethyl sulfoxide) by quantitative 1H nuclear magnetic resonance spectroscopy and density functional theory calculations. In the case of protic solvents (water, methanol, and ethanol), the lower dielectric constant of the alkaline media, the lower is the lowest unoccupied molecular orbital (LUMO) energy of the organic cation, which leads to the lower alkaline stability of cations. However, the hydrogen bonds between the anions and protic solvents weaken the effects of low dielectric constant of the alkaline media. The aprotic solvent accelerated the SN2 degradation reaction of “naked” organic cations. The results of this study suggest that both the chemical structure of organic cations and alkaline media (fuels) applied affect the alkaline stability of AEMs.

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

Abstract 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 (CHSA) (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/CHSA. 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.

Hydroxide-ion selective electrolytes based on a polybenzimidazole/graphene oxide composite membrane

The objectives of this work are to prepare and characterize poly[2,2′-m-(phenylene)-5,5′-bibenzimidazole]/graphene oxide (PBI/GO) solid electrolyte for direct alcohol alkaline fuel cell (DAAFC) applications. GO nanosheets are coated onto a PBI surface using a spin coater to construct the PBI/GO composite membrane. The PBI/GO composite membrane exhibits an ionic conductivity of 2.53 × 10−2 S cm−1 at 80 °C, which is improved by 72–93% when compared with the pure PBI membrane. In addition, the methanol permeability is reduced by 18–25% by incorporating GO onto the PBI top surface. The peak power density (Pmax) of the PBI/GO electrolyte reaches 200 mW cm−2 when using alkaline methanol as fuel with Pt-based catalysts, or 120 mW cm−2 when fed with an ethanol and alkaline solution mixture at 80 °C. Replacing the Pt-based catalysts with Hypermec™ catalysts resulted in Pmax of 40 and 100 mW cm−2, for methanol and ethanol fuel cells, respectively. These superior DAAFC power outputs are ascribed to the improved anion conduction of the KOH doped GO and the suppressed methanol cross-over from high aspect ratio GO as the alcohol barrier layer.

Platinum–copper doped poly(sulfonyldiphenol/cyclophosphazene/benzidine)–graphene oxide composite as an electrode material for single stack direct alcohol alkaline fuel cells

Schematic representation of the preparation of a metal nanoparticle (Pt and Pt–Cu)-decorated poly(SDP/CP/BZ)–GO composite.

Electrodeposited cobalt oxide nanoparticles modified carbon nanotubes as a non-precious catalyst electrode for oxygen reduction reaction

Oxygen reduction electrode is one of the important electrode materials for energy technologies because of the technical importance of oxygen reduction reaction (ORR) in the development of fuel cells and batteries. In this work, a fast, simple and applicable electrodeposition process has been used to modify the oxygenated functionalized carbon nanotubes (FCNTs) with cobalt oxide nanoparticles (CoOx) for use as an active catalyst electrode for ORR in alkaline medium. The prepared electrodes were characterized with structural techniques (XRD and TEM) to confirm the deposition of CoOx nanoparticle on FCNTs surface. The electrocatalytic activity of the prepared electrodes towards ORR was evaluated using different electrochemical methods such as cyclic voltammetry, linear sweep voltammetry combined with rotating disk electrode technique and chronoamperometry. Based on RDE measurements, the CoOx/FCNTs showed higher electrocatalytic activity and the mechanism of ORR proceeds via the four-electron mechanism, the favourable mechanism shown by the noble metal catalysts. However, the CoOx electrode exhibited only the two-electron mechanism with formation of hydrogen peroxide, rather than the four-electron mechanism, while the FCNTs electrode exhibited the two parallel mechanisms favouring four-electron mechanism only at higher overpotential. These results indicate the synergistic effect of the coupling between FCNTs and CoOx nanoparticles catalyzing the ORR via the direct four-electron mechanism. Such a synergistic effect is assumed to be attributed to the formation of an active interface between the FCNTs and CoOx resulting in highly catalytic active sites that allow the adsorption of oxygen and simultaneous reduction and/or the chemical decomposition of the intermediates, mainly the peroxide intermediate formed during the two-electron pathway mechanism. Moreover, compared to the benchmarked catalyst (Pt/C), the non-precious CoOx/FCNTs electrode showed both the higher stability under continuous ORR at a fixed potential for 6 h and higher tolerance for methanol poisoning. The results reported in this work could contribute to the development of high stable and fuel poisoning tolerance cathode electrodes for direct alkaline alcohol fuel cells.

PERFORMANCE ASSESSMENT OF A POLYMER ELECTROLYTE MEMBRANE ELECTROCHEMICAL REACTOR UNDER ALKALINE CONDITIONS − A CASE STUDY WITH THE ELECTROOXIDATION OF ALCOHOLS

A novel polymer electrolyte membrane electrochemical reactor (PEMER) configuration has been employed for the direct electrooxidation of propargyl alcohol (PGA), a model primary alcohol, towards its carboxylic acid derivatives in alkaline medium. The PEMER configuration comprised of an anode and cathode based on nanoparticulate Ni and Pt electrocatalysts, respectively, supported on carbonaceous substrates. The electrooxidation of PGA was performed in 1.0M NaOH, where a cathode based on a gas diffusion electrode was manufactured for the reduction of oxygen in alkaline conditions. The performance of a novel alkaline anion-exchange membrane based on Chitosan (CS) and Poly(vinyl) alcohol (PVA) in a 50:50 composition ratio doped with a 5wt.% of poly (4-vinylpyridine) organic ionomer cross-linked, methyl chloride quaternary salt resin (4VP) was assessed as solid polymer electrolyte. The influence of 4VP anionic ionomer loading of 7, 12 and 20wt.% incorporated into the electrocatalytic layers was examined by SEM and cyclic voltammetry (CV) upon the optimisation of the electroactive area, the mechanical stability and cohesion of the catalytic ink onto the carbonaceous substrate for both electrodes. The performance of the 4VP/CS:PVA membrane was compared with the commercial alkaline anion-exchange membrane FAA −a membrane generally used in direct alcohol alkaline fuel cells- in terms of polarisation plots in alkaline conditions. Furthermore, preparative electrolyses of the electrooxidation of PGA was performed under alkaline conditions of 1M NaOH at constant current density of 20mAcm−2 using a PEMER configuration to provide proof of the principle of the feasibility of the electrooxidation of other alcohols in alkaline media. PGA conversion to Z isomers of 3-(2-propynoxy)-2-propenoic acid (Z-PPA) was circa 0.77, with average current efficiency of 0.32. Alkaline stability of the membranes within the PEMER configuration was finally evaluated after the electrooxidation of PGA.

Highly efficient electrocatalytic oxidation of glycerol by Pt-Pd/Cu trimetallic nanostructure electrocatalyst supported on nanoporous stainless steel electrode using galvanic replacement

In this work, glycerol electrooxidation in alkaline solution, as an interesting fuel in fuel cells, was studied at a modified Cu filled nanoporous stainless steel (NPSS) electrode decorated by Pt and Pd (Pt-Pd/Cu/NPSS). Firstly, nanopores were fabricated on the surface of a stainless steel support (NPSS) by anodizing and then Cu was filled into the pores by electrodeposition (Cu/NPSS) using multiple step potential. The Cu/NPSS electrode was decorated with Pt and Pd using galvanic replacement method by immersion into a precursor solution containing Pt and Pd. The surface morphology and composition characterization of the prepared electrode indicate the formation of the Pt and Pd nanoparticles with an average diameter of about 45nm. The electrochemical studies of the Pt-Pd/Cu/NPSS electrocatalyst revealed that the electrooxidation of glycerol in 1.0M KOH solution in compare to Pd/Cu/NPSS and Pt/Cu/NPSS, gives higher current density (J) by a factor of 4.2 which occurs at a lower onset potential (Eonset=−0.54V). It was found that the electrochemical active surface area (EASA) of the electrode in comparison with the Pd/Cu/NPSS and Pt/Cu/NPSS electrodes is more than 1.3 times and it was more resisting to the poisoning components. The proposed electrocatalyst demonstrates vastly superior electrocatalytic properties, indicating a great potential in direct alkaline alcohol fuel cells application.

Electrochemical conversion of alcohols for hydrogen production: a short overview

In the emerging hydrogen economy, one of the major objectives is the production of electricity using fuel cells, particularly proton exchange membrane fuel cells (PEMFC). In this perspective, high purity hydrogen is needed. Hydrogen is currently mainly produced from fossil fuels (natural gas, oil, and coal) by energy‐consuming and environmentally unfriendly industrial processes that also involve complicated clean up steps for the removal of carbon monoxide and carbon dioxide. Water electrolysis (particularly the proton exchange membrane electrolysis technology, which allows higher efficiency than alkaline technology) appears to be a good candidate for the production of clean hydrogen. The use of renewable primary energy sources, such as wind, solar, tidal, etc., makes this technology greener. However, the low kinetics of water oxidation, which implies high cell voltage (i.e. high energy consumption) even when using noble metal‐based catalysts (Pt, Ru, Ir), makes this technology expensive. Biosourced alcohols can be interesting alternatives as hydrogen carriers in an electrolysis cell; their reversible oxidation potentials are much lower than that of water, ca 0.1 V versus SHE (standard hydrogen electrode) against 1.23 V versus SHE, so that the cell voltages for hydrogen production are lower (and so is the energy consumption). However, the low kinetics of alcohol oxidation in acidic media requires high Pt‐based catalyst loadings at the anode. Direct alcohol alkaline electrolysis cells can be operated with low Pt loading and even non‐noble metals. In the case of glycerol, generation of hydrogen at the cathode can be performed simultaneously with the formation of value‐added products at the anode for a more profit‐making process. WIREs Energy Environ 2016, 5:388–400. doi: 10.1002/wene.193This article is categorized under: Bioenergy > Science and Materials Fuel Cells and Hydrogen > Science and Materials Energy Efficiency > Science and Materials

Carbon quantum dots directly generated from electrochemical oxidation of graphite electrodes in alkaline alcohols and the applications for specific ferric ion detection and cell imaging.

Carbon quantum dots (CQDs) are attracting tremendous interest owing to their low toxicity, water dispersibility, biocompatibility, optical properties and wide applicability. Herein, CQDs with an average diameter of (4.0 ± 0.2) nm and high crystallinity were produced simply from the electrochemical oxidation of a graphite electrode in alkaline alcohols. The as-formed CQDs dispersion was colourless but the dispersion gradually changed to bright yellow when stored in ambient conditions. Based on UV-Vis absorption, fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM), this colour change appeared to be due to oxygenation of surface species over time. Furthermore, the CQDs were used in specific and sensitive detection of ferric ion (Fe(3+)) with broad linear ranges of 10-200 μM with a low limit of detection of 1.8 μM (S/N = 3). The application of the CQDs for Fe(3+) detection in tap water was demonstrated and the possible mechanism was also discussed. Finally, based on their good characteristics of low cytotoxicity and excellent biocompatibility, the CQDs were successfully applied to cell imaging.

Fumed Silica Nanoparticles Incorporated in Quaternized Poly(Vinyl Alcohol) Nanocomposite Membrane for Enhanced Power Densities in Direct Alcohol Alkaline Fuel Cells

A nanocomposite polymer membrane based on quaternized poly(vinyl alcohol)/fumed silica (QPVA/FS) was prepared via a quaternization process and solution casting method. The physico-chemical properties of the QPVA/FS membrane were investigated. Its high ionic conductivity was found to depend greatly on the concentration of fumed silica in the QPVA matrix. A maximum conductivity of 3.50 × 10−2 S/cm was obtained for QPVA/5%FS at 60 °C when it was doped with 6 M KOH. The permeabilities of methanol and ethanol were reduced with increasing fumed silica content. Cell voltage and peak power density were analyzed as functions of fumed silica concentration, temperature, methanol and ethanol concentrations. A maximum power density of 96.8 mW/cm2 was achieved with QPVA/5%FS electrolyte using 2 M methanol + 6 M KOH as fuel at 80 °C. A peak power density of 79 mW/cm2 was obtained using the QPVA/5%FS electrolyte with 3 M ethanol + 5 M KOH as fuel. The resulting peak power densities are higher than the majority of published reports. The results confirm that QPVA/FS exhibits promise as a future polymeric electrolyte for use in direct alkaline alcoholic fuel cells.

Pd nanoparticles supported on three-dimensional graphene aerogels as highly efficient catalysts for methanol electrooxidation

Well-dispersed Pd nanoparticles supported on three-dimensional graphene aerogels (Pd/3DGA) were successfully prepared via a facile and efficient hydrothermal method without surfactant and template. The morphology and structure of the as-prepared Pd/3DGA nanocomposites were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM showed that the Pd nanoparticles with a small average diameter and narrow size distribution were uniformly deposited on the surface of the self-assembled three-dimensional graphene aerogels. Raman spectra revealed the surface properties of 3DGA and its interaction with metallic nanoparticles. Cyclic voltammetric (CV) and chronoamperometric (CA) experiments further exhibited its superior catalytic activity and stability for the electro-oxidation of methanol in alkaline media, making it a promising anodic catalyst for direct alkaline alcohol fuel cells (DAAFCs).

Novel quaternized polyvinyl alcohol/quaternized chitosan nano-composite as an effective hydroxide-conducting electrolyte

A novel polymer composite electrolyte consisting of quaternized polyvinyl alcohol (Q-PVA) and quaternized chitosan nano-particles (Q-chitosan) is synthesized for use in a direct alcohol alkaline fuel cell (DAAFC). The quaternization efficiencies of PVA and chitosan particles are 2.6% and 39%, respectively. Incorporation of 5% Q-chitosan nano-particles into the Q-PVA matrix results not only in an increased ion-exchange capacity but also a decreased polymer crystallinity and higher free volume hole density, which significantly enhance ion conduction. The shrunk polymer free volume size suppresses methanol permeability in the Q-PVA/Q-chitosan composite. In addition, the resulting nano-composite exhibited an inhibited in-plane swelling ratio without sacrificing the alkali uptake level. The KOH-doped Q-PVA/Q-chitosan was resistant to the Fenton reagent. In DAAFCs, a maximum power density of 73mWcm–2 is achieved using the Q-PVA/5%Q-chitosan electrolyte when fed with 2M methanol at 60°C or 59mWcm–2 with 3M ethanol at 60°C. The resulting maximum power densities are higher than most literature data. The alkaline fuel cell demonstrated stable long-term power output for at least 230h. This result confirms that the Q-PVA/Q-chitosan electrolyte exhibits great potential for future commercialization.

Hybrid NiCoOx adjacent to Pd nanoparticles as a synergistic electrocatalyst for ethanol oxidation

To improve the electrocatalytic activity of Pd for ethanol oxidation, hybrid NiCoOx adjacent to Pd catalyst (Pd-NiCoOx/C) is successfully synthesized. Physical characterization shows NiCoOx is closely adjacent to Pd nanoparticles in Pd-NiCoOx/C catalyst, which leads to Strong Metal-Support Interactions (SMSI) between the NiCoOx and Pd nanoparticles, in favor of the electrocatalytic properties. The Pd-NiCoOx/C catalyst is estimated to own larger electrochemically active surface area than Pd/C and Pd–NiO/C catalysts. Moreover, compared to Pd/C catalyst, the onset potential of Pd-NiCoOx/C catalyst is negative 40 mV for ethanol oxidation. Noticeably, the current density of Pd-NiCoOx/C catalyst is 2.05 and 1.43 times higher contrasted to Pd/C and Pd–NiO/C catalysts accordingly. Importantly, the Pd-NiCoOx/C catalyst exhibits better stability during ethanol oxidation, which is a promising electrocatalyst for application in direct alkaline alcohol fuel cells.

Comparative electrooxidation of C1–C4 alcohols on Pd|CC nanoparticle anode catalyst in alkaline medium

The comparative studies of methanol, ethanol, 2-propanol and 2-butanol electrooxidation were carried out on carbon-ceramic electrode (CCE) potentiostatically modified with Pd nano-particles. The Characterization of catalytic layer by Scanning electron microscope (SEM), Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) indicated that well-dispersed catalytic particles with high density have been formed on CC substrate. Voltammetry, Chronoamperometry (CA), Polarization study and electrochemical impedance spectroscopy (EIS) were used to investigate the alcohols oxidation reactions. The relevant parameters such as the Tafel slope and activation energy (Ea) were determined. This study upholds the fact that 2-propanol is a promising fuel candidate for a direct alkaline alcohol fuel cell.

Investigation of Nb2O5/Graphene Supported Platinum-Cobalt Nanocomposite as Electrocatalyst for the Alkaline Alcohols Fuel Cells

In this work Nb2O5/graphene supported PtCo catalyst with the Pt:Co molar ratio equal to 1:7 was fabricated by means of the rapid microwave heating method. The transmission electron microscopy (TEM) was used to detect the shape and size of catalyst particles. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was employed to characterize the composition of the synthesized catalysts. The electrocatalytic activity of the prepared catalysts towards the electro-oxidation of ethanol, methanol and ethylene glycol was investigated in an alkaline medium by means of cyclic voltammetry and chrono-techniques. It has been determined that the Nb2O5/graphene supported PtCo catalyst exhibits a higher electrocatalytic activity with respect to the electro-oxidation of all alcohols as compared to that at the commercial Pt/C catalyst.

Investigation of Nb2O5/Graphene Supported Platinum-Cobalt Nanocomposite as Electrocatalyst for the Alkaline Alcohols Fuel Cells

In the present work, niobium oxide/graphene supported PtCo catalyst with the Pt:Co molar ratio 1:7 (denoted as PtCo(1:7)Nb2O5/GR) was fabricated by means of the rapid microwave heating polyol method. The surface morphology, structure and composition of the synthesized catalyst were examined by transmission electron microscopy, X-ray diffraction and inductively coupled plasma optical emission spectroscopy. The electrocatalytic activity of the synthesized catalyst towards the oxidation of alcohols – ethanol, methanol and ethylene glycol in an alkaline medium was investigated by means of cyclic voltammetry and chronoamperometry.It has been determined that the Pt loadings was 0.285 mg Pt cm–2 in the synthesized PtCo(1:7)Nb2O5/GR catalyst. For comparison, the bare commercial Pt/C (Sigma-Aldrich) catalyst with 10% wt. Pt with the Pt loading of 0.385 mg Pt cm–2 was used. The electroactive surface areas (ESAs) of the prepared and commercial catalysts were determined from the cyclic voltammograms of PtCo(1:7)Nb2O5/GR and Pt/C catalysts recorded in a deaerated 0.5 M H2SO4 solution at a sweep rate of 50 mV s–1by calculating the charge associated with the hydrogen adsorption.According to the data of TEM analysis, the Pt nanoparticles of ca. 1-2 nm in size were successively deposited onto the surface of graphene nanosheets.It has been found that niobium oxide/graphene supported PtCo catalyst with the Pt:Co molar ratios 1:7 show an enhanced electrocatalytic activity towards the oxidation of alcohols in an alkaline medium as compared with that of 10% wt. Pt implicated commercial Pt/C catalyst. Alcohols oxidation current densities were found to be ca. 3 – 40 times higher at the PtCo(1:7)Nb2O5/GR catalyst in comparison with those at the commercial Pt/C catalyst. The prepared catalyst seem to be a promising anodic material for direct alcohols fuel cells. Acknowledgement Postdoctoral fellowship is being funded by European Union Structural Funds project ”Postdoctoral Fellowship Implementation in Lithuania”.

Ethylene Glycol Oxidation at Pt/TiO2/Carbon Hybrid Catalysts Modified Glassy Carbon Electrodes in Alkaline Media

Biomass-based fuels in conjunction with direct alcohol alkaline fuel cells are an emerging technology that may be able to wean us of our dependency of fossil fuels. However, their adoption is stalled by their high production costs (i.e., precious metal loading) and low electrocatalytic efficiencies. In this study, the platinum loading of 20 % Pt/C catalyst for use in ethylene glycol electrooxidation was reduced by mixing with TiO2 nanopowder in different mass ratios. This was followed by surface activation and cyclic voltammograms of the hydrogen adsorption and Pt oxide potential regions in 0.1 M KOH showed peak potential changes that are attributed to platinum interactions with TiO2. The catalysts were further tested for the electrochemical oxidation of ethylene glycol in alkaline media, where the titanium-modified catalysts showed a maximum increase in peak current density by 91 %, when compared to the commercial Pt/C catalyst. When the peak current was normalized by Pt surface area and mass, a maximum increase of 322 % was found. Tafel plot analysis showed increased exchange currents for the rate determining step of ethylene glycol oxidation at Pt/TiO2/C hybrid catalysts up to 7.35 × 10−7A/cm2. This is nearly 8.7 times larger than, 8.47 × 10-8A/cm2, the ethylene glycol exchange current density for the rate determining step in commercial Pt/C catalysts. Finally, chronoamperometric studies showed that the hybrid catalysts possessed increased stability and activity for ethylene glycol electrooxidation in 0.1 M ethylene glycol in 0.1 M KOH at an applied potential of −0.350 V vs. Ag/AgCl. This study shows that TiO2 can modify the platinum surface catalyst activity without the need of a TiO2 support. This avoids loss in electrical conductivity of the catalyst and lowers the total catalyst mass without sacrificing catalytic mass activity.

Operating Alkaline Alcohol Fuel Cell (ITAAFC) in Intermediate-Temperature Range

Direct alcohol fuel cells (DAFCs) possess obvious advantages over traditional hydrogen fuel cells in terms of hydrogen storage, transportation, and the utilization of existing infrastructure. However, the commercialization of this fuel cell technology based on the use of proton-conductive polymer membranes has been largely hindered by its low power density owing to the sluggish kinetics of both anode and cathode reactions in acidic media and high cost owing to the use of noble metal catalysts. These could be potentially addressed by the development of alkaline alcohol fuel cells (AAFCs). In alkaline media, the polarization characteristics of alcohol electrooxidation and oxygen electroreduction are far superior to those in acidic media. Another obvious advantage of using alkaline media is less-limitations of electrode materials. The replacement of Pt catalysts with non-Pt catalysts will significantly decrease the cost of catalysts. Recently, the AAFCs have received increased attention. However, these fuel cells are normally operated at temperature lower than 80 °C. In this low temperature range, both methanol electrooxidation and oxygen electroreduction reactions are not sufficiently facile for the development of high performance AAFCs. Considerable undergoing efforts are now focused on the development of highly active catalysts for accelerated electrode reactions.Alternatively, increasing temperature has been proven as an effective way to accelerate electrode reactions. The changes of the reaction rates with increasing temperature are strongly determined by the values of activation energy, as described by the Arrhenius equation. More obvious changes are expected for alcohol electrooxidation in alkaline media than in acidic media since reported values of the activation energy are higher in alkaline media. Additionally, increasing temperature may decrease concentration polarization, Ohmic polarization, and CO poisoning of the catalysts. All these advantages can contribute to the performance improvement of the AAFCs.In an intermediate temperature range of 80 to 200 oC, CO is likely to spontaneously react with OH- to give formate as follows [1]: (1)Because formate produced via Reaction I is soluble and more electrochemically active than CO on Pt, surface CO formed during alcohol oxidation would be readily removed, resulting in considerable decrease in the CO-poisoning of Pt-based catalysts. Moreover, the kinetics of the alcohol oxidation in alkaline media on Pt has been suggested to be largely determined by the reaction between the surface CO and surface oxygen-containing species (OH), following a Langmuir-Hinshinwood mechanism. Accordingly, accelerated electrooxidation of CO intermediate would increase the rate of the alcohol oxidation.Further finding of increasing temperature for the methanol oxidation is that methanol can be efficiently converted with water in the aqueous phase over appropriate heterogeneous catalysts at temperatures near 200 oC to produce primarily H2 and CO2 [2]. (2)During the methanol liquid-phase reforming, trace amount of methane is the side product and the use of more basic catalyst favors H2 production. The methanol reforming indicates that sluggish methanol oxidation reaction which has plagued low temperature DAFCs, could become highly facile in alkaline media at temperatures close to 200 oC where the reforming of methanol is triggered. Substantially accelerated electrooxidation of methanol would make it possible to achieve low anode overpotentials. Therefore, driving the electrooxidation of methanol in an intermediate-temperature range over the methanol-boiling temperature (around 80 oC) and the triggering temperature of the methanol reforming (about 200 oC) would be of academic and practical importance for the development of high performance a technology.We have investigated systematically the electrocatalysis associated with the ITAAFC and demonstrated high performance of this promising fuel cell technology. Our status-of-the-art ITAAFC operating with methanol at 120 oC demonstrated a peak power density of around 250 mW cm-2 at around 700 mA cm-2.