聚合物电解质膜燃料电池薄电极制备技术的研究

为降低聚合物电解质膜燃料电池 (PEMFC)电极中铂的载量 ,本文建立一种新的薄电极制备技术 (TEFT) ,制备了表面平滑、颗粒分布均匀的低铂载量电极 .结果表明当电极的铂载量为 1mg/cm2 ,用Nafion 117膜作电解质时 ,电池的最大功率密度达 0 30W·cm-2 .系统地考察了阴极中不同PTFE和Nafion含量对PEMFC性能的影响 .     

The Mass Transfer of Proton on Meniscus Nafion/Pt/HOPG Electrode

Proton-exchange membrane fuel cells (PEMFCs) recently have been studied extensively because of their high performance^[1-3]. Since a small contacting area between the platinum catalyst and polymer electrolyte in PEMFCs, the platinum utilization is very important for this kind of cells. In order to improve the platinum utilization, Nafion solution is often impregnated into the gas-diffusion electrodes of PEMFCs. We introduced a partially immersed Nafion-coated electrode, Nafion/Pt/HOPG(highly oriented pyrolytic graphite) as a model electrode in PEMFC, to examine the effects of Nafion coating on the mass transport of hydrogen and proton at the meniscus and supermeniscus formed on the electrodes.     

Mass transport and kinetics of electrochemical oxygen reduction at nanostructured platinum electrode and solid polymer electrolyte membrane interface

Oxygen reduction reaction (orr) at nanostructured Pt electrode in a flooded polymer electrolyte membrane fuel cell environment has been investigated using a nanoporous Pt–Nafion membrane composite microelectrode by means of steady-state voltammetry and chronoamperometry. The interfacial mass transport of dissolved oxygen is characterized by comparable diffusion coefficients and lower concentrations as compared with literature data obtained with a humidified membrane. The exchange current densities measured at the nanoporous Pt and membrane interface are higher than those reported for the orr in acidic solutions or at polycrystalline Pt and Nafion membrane interface, indicating the improvement of the orr kinetics. Increasing temperature substantially improves the orr kinetics and accelerates the diffusion of oxygen, as expected by their Arrhenius behavior. At the nanoporous Pt and membrane interface, the Tafel plot exhibits an unusual slope of around 240?mV?dec^?1 at high overpotentials. This Tafel slope doubling the value of 120?mV?dec^?1 normally reported for the orr in acidic media and at the polycrystalline Pt and membrane interface is a signature of non-uniform polarization of the nanoporous Pt electrode on the membrane which origins have been discussed.     

Operando 3D Visualization of Migration and Degradation of a Platinum Cathode Catalyst in a Polymer Electrolyte Fuel Cell

The three‐dimensional (3D) distribution and oxidation state of a Pt cathode catalyst in a practical membrane electrode assembly (MEA) were visualized in a practical polymer electrolyte fuel cell (PEFC) under fuel‐cell operating conditions. Operando 3D computed‐tomography imaging with X‐ray absorption near edge structure (XANES) spectroscopy (CT‐XANES) clearly revealed the heterogeneous migration and degradation of Pt cathode catalyst in an MEA during accelerated degradation test (ADT) of PEFC. The degradative Pt migration proceeded over the entire cathode catalyst layer and spread to MEA depth direction into the Nafion membrane.     

Optimizing Weights of Platinum in the Active Layer of the Cathode of a Hydrogen–Oxygen Fuel Cell with a Solid Polymer Electrolyte

The active layer of the cathode of a hydrogen–oxygen fuel cell with a solid polymer electrolyte is computer simulated. The active mass of the electrode consists of substrate grains (agglomerates of carbon particles with Pt particles embedded into them) and grains of a solid polymer electrolyte (Nafion). The substrate grains presumably contain hydrophobic pores, which facilitate the oxygen penetration into the active mass. A calculation of characteristics of such an electrode focuses on the optimization of platinum weights. The principal parameters of the system are concentration and size of grains of substrate and Nafion, Pt concentration in substrate grains, average diameter of hydrophobic pores in substrate grains, and the electrode polarization. The optimum, at a given electrode polarization, electrochemical activity of the active layer, its thickness, and the platinum weight are calculated. A link between these quantities and principal parameters of the active layer is revealed.     

FTIR spectroscopic characterization of Nafion®–polyaniline composite films employed for the corrosion control of stainless steel

Nafion?–polyaniline (PAn) composite films deposited by a two-step process on a stainless steel (SS) substrate were characterized in this study using Fourier transform infrared (FTIR) spectroscopy under various conditions employed to evaluate their anticorrosion properties. The SS|Nafion? electrode was first prepared by placing a certain amount of Nafion? on the SS substrate, and then polymerization of aniline was carried out potentiodynamically on the SS|Nafion? electrode. The SS|Nafion?–PAn electrodes subjected to both potentiodynamic polarization and open-circuit conditions in sulfuric acid solutions without and with chlorides appeared to have distinct differences in their FTIR spectra. It is proposed that under the electrochemical conditions used in this study, the PAn is mostly formed inside the Nafion? membrane with a high proportion of oligomers influencing the ionic transport through the membrane. The inhibition of pitting corrosion arises primarily from the enhanced permselectivity of the composite film due to the Nafion? membrane that prevents chloride transport. An essential beneficial effect comes also from the PAn redox properties on the growth of the passive oxide film. Even under severe corrosion conditions, Nafion???/em>PAn films retain their redox activity and chemical stability, whereas the membrane crystallinity seems to be enhanced.     

Electrodes supported on ion-exchange membranes as sensors in gases and low-conductivity solvents

An electroanalytical sensor is proposed that is suitable for the detection of electroactive analytes present in gases or low-conductivity solvents where supporting electrolytes cannot be introduced. It consists of a porous working electrode supported on one surface of a cationic ion-exchange membrane (Nafion 417), the other surface of which is in contact with an electrolyte solution containing the counter and reference electrodes. Such an ion-exchange membrane replaces a conventional supporting electrolyte dissolved in the analyte sample and can be regarded as a solid polymer electrolyte (SPE) confined in the close neighbourhood of the working electrode. Alternative procedures followed for coating SPE membranes with various materials (Pt, Au, C or Hg) are described, together with the general properties displayed by the resulting composite electrodes in analyte-free gaseous or liquid media. These assemblies have been used as both voltammetric and amperometric sensors for electroactive analytes present in gases and in aqueous or organic solvents with no supporting electrolyte. The results indicate that their performance is similar to that expected on conventional electrodes, the only difference being a slightly lower degree of reversibility for the electrode processes investigated. Detection limits for some analytes were calculated and the use of SPE electrodes as sensors suitable for the continuous monitoring of electroactive analytes dispersed in gases or non-conductive liquids is reported. Preliminary attempts to use these assemblies for the determination of trace metals in low-conductivity solvents by anodic stripping voltammetry are discussed.     

Improved Nafion-based amperometric sensor for hydrogen in argon

An improved polymer electrolyte membrane fuel cell-based amperometric hydrogen sensor has been developed. The sensor operates at room temperature, and the electrolyte used in the sensor is Nafion which is a proton-conducting solid polymer electrolyte. Platinum black is used as both anode and cathode. The sensor functions as a fuel cell, H₂/Pt//Nafion//Pt/O₂, and a mechanical barrier limits the supply of hydrogen to the sensing side electrode. The limiting current is found to be linearly related to the hydrogen concentration. The sensor can be used to measure hydrogen in argon in parts per million and percentage levels. The basic principle, details of assembly, and response behavior of the sensor are discussed.     

采用Nafion粘结剂的PEMFC氧电极研究

研究了聚合物电解质燃料电池（PEMFC）中以Nation溶液取代PTFE乳液作粘结剂的效果．并对催化剂层内Nafion含量进行了优化，同时探讨了气体工作压力和离子交换膜的影响，实验发现：1．使用Nafion溶液后显著提高电池性能，Nafion含量为2mg·cm－2时性能技好；2．气体压力增大改善了电池位能；3．使用Nafion115膜的电池性能优于使用Nafion117膜的电池．要进一步提高电池性能，减小欧姆控制区的斜率是必要的．     

直接甲醇燃料电池催化活性层的优化

本文考察了直接甲醇燃料电池 (DMFC)不同催化剂载量的膜电极性能 .对催化剂层中Nafion含量进行优化 ,研究了Nafion含量对电池的阻抗的影响 .实验发现 :DMFC适宜的阳极Pt_Ru/C载量为Pt 4mg/cm2 、Nafion质量百分含量为 2 1.4 % ;高电流密度下 ,阴极Pt/C载量为Pt4mg/cm2 、Nafion质量百分含量为 2 1.4 %时 ,有较好的放电性能 ,继续增加Nafion含量 ,阴极的欧姆极化和浓差极化增大 ,电池性能下降     

Influence of Analyte Flow Rate on Signal and Response Time of the Amperometric Gas Sensor with Nafion Membrane

This paper presents results of an investigation on influence of volumetric flow rate on the signal and response time of a prototype of sulfur dioxide gas sensor with Nafion membrane. The sensors differing in type of working electrode and composition of internal electrolyte were compared. We used Au and Pt working electrodes obtained via vacuum sublimation deposition on a Nafion membrane surface. The electrolytes were aqueous solutions of sulfuric acid of the summary concentration 5 mol dm^?3 (electrolyte A). The electrolyte B contained an addition of dimethylsulfoxide (DMSO); the water/DMSO molar ratio was 2 : 1. Based on a proposed equation, which takes diffusion resistance into account, the obtained sensor signals were analyzed for the flow rate within a range of 0–100 cm³ min^?1. The sensor response time was also determined for the above flow rate range.     

Efficient electrocatalyst utilization: electrochemical deposition of Pt nanoparticles using nafion membrane as a template

We deposit Pt particles electrochemically on an electrode covered with a Nafion membrane. Platinum ions travel through the hydrophilic channels of the membrane, and platinum deposits are formed at the place where the channels make contact with the planar electrode. This procedure deposits the catalyst only at the end of the hydrophilic channels that cross the membrane; no catalyst is placed under the hydrophobic domains, where it would not be in contact with the electrolyte. By performing a series of cyclic voltammograms with this system, we show that deposition of the platinum through the membrane achieves better platinum utilization than deposition of platinum on the naked electrode followed by the placement of the membrane on top.     

Electropolymerization of 3-methylthiophene at liquid 3-methylthiophene | aqueous solution | graphite three-phase junction

Droplets of 3-methylthiophene are mechanically attached to the surface of paraffin-impregnated graphite electrode (PIGE) and immersed into aqueous solution of LiClO₄. It is demonstrated that the oxidative electropolymerization (observed in non-aqueous solutions) can be accomplished by potential cycling between −0.3 and 1.4 V vs. saturated calomel electrode (SCE). Since the droplets do not contain a dissolved electrolyte, the electrochemical reaction starts at the very edge of the three-phase junction organic droplet | graphite | aqueous electrolyte.     

Microwave activation of electrochemical processes: enhanced PbO2 electrodeposition, stripping and electrocatalysis

Microwave activation of electrochemical processes has recently been introduced as a new technique for the enhancement and control of processes at electrode|solution (electrolyte) interfaces. This methodology is extended to processes at glassy carbon and boron-doped diamond electrodes. Deposition of both Pb metal and PbO₂ from an aqueous solution of Pb²⁺ (0.1 M HNO₃) are affected by microwave radiation. The formation of PbO₂ on anodically pre-treated boron-doped diamond is demonstrated to change from kinetically sluggish and poorly defined at room temperature to nearly diffusion controlled and well defined in the presence of microwave activation. Calibration of the temperature at the electrode|solution (electrolyte) interface with the Fe^3+/2+ (0.1 M HNO₃) redox system allows the experimentally observed effects to be identified as predominantly thermal in nature and therefore consistent with a localized heating effect at the electrode|solution interface. The microwave-activated deposition of PbO₂ on boron-doped diamond remains facile in the presence of excess oxidizable organic compounds such as ethylene glycol. An increase of the current for the electrocatalytic oxidation of ethylene glycol at PbO₂/boron-doped diamond electrodes in the presence of microwave radiation is observed. Preliminary results suggest that the electrodissolution of solid microparticles of PbO₂ abrasively attached to the surface of a glassy carbon electrode is also enhanced in the presence of microwave radiation. Electronic Publication     

Ionic Diode Characteristics at a Polymer of Intrinsic Microporosity (PIM) | Nafion “Heterojunction” Deposit on a Microhole Poly(ethylene‐terephthalate) Substrate

Ionic diode phenomena occur at asymmetric ionomer | aqueous electrolyte microhole interfaces. Depending on the applied potential, either an “open” or a “closed” diode state is observed switching between a high ion flow rate and a low ion flow rate. Physically, the “open” state is associated mainly with conductivity towards the microhole within the ionomer layer and the “closed” state is dominated by restricted diffusion‐migration access to the microhole interface opposite to the ionomer. In this report we explore a “heterojunction” based on an asymmetric polymer of intrinsic microporosity (PIM) | Nafion ionomer microhole interface. Improved diode characteristics and current rectification are observed in aqueous NaCl. The effects of creating the PIM | Nafion micro‐interface are investigated and suggested to lead to novel sensor architectures.     

Ion-transfer- and photo-electrochemistry at liquid|liquid|solid electrode triple phase boundary junctions: perspectives

Ion transfer at liquid|liquid junctions is one of the most fundamental processes in nature. It occurs coupled to simultaneous electron transfer at the line junction (or triple phase boundary) formed by the two liquids in contact to an electrode surface. The triple phase boundary can be assembled from a redox active microdroplet deposit of a water-immiscible liquid on a suitable electrode surface immersed into aqueous electrolyte. Ion transfer voltammetry measurements at this type of electrode allow both thermodynamic and kinetic parameters for coupled ion and electron transfer processes to be obtained. This overview summarises some recent advances in understanding and application of triple phase boundary redox processes at organic liquid|aqueous electrolyte|working electrode junctions. The design of novel types of electrodes is considered based on (i) extended triple phase boundaries, (ii) porous membrane processes, (iii) hydrodynamic effects, and (iv) generator-collector triple phase boundary systems. Novel facilitated ion transfer processes and photo-electrochemical processes at triple phase boundary electrodes are proposed. Potential future applications of triple phase boundary redox systems in electrosynthesis, sensing, and light energy harvesting are indicated.     

[Pt]—Ni（Ⅱ）电极的研究

我们首次发现Pt浸于镍、钴或铁盐溶液中,只有镍可形成[Pt]-Ni(Ⅱ)电极。在NaOH电解液中,此电极有明显的氧化还原峰,表现出Ni电极的特征。本文研究[Pt]-Ni(Ⅱ)电极的电化学性能、电极制备的影响因素。 1 实验部分 研究电极:Pt为基底,用5~#金相砂纸磨光,在王水中浸渍,二次蒸馏水冲洗(也可再进     

Effect of the thickness of the Pt film coated on a counter electrode on the performance of a dye-sensitized solar cell

The effects of the thickness and morphology of a Pt film coated on a counter electrode on the performance of a dye-sensitized solar cell (DSC) were investigated. Deposition of a Pt film ranging in thickness from 2 to 415 nm gradually decreases the sheet resistance of the counter electrode. No significant difference in the charge-transfer resistance at the electrolyte|counter electrode interface was observed for a Pt film thickness ranging from 25 to 415 nm. A high energy conversion efficiency of approximately 5% can be obtained for DSCs based on a counter electrode with a very thin Pt film of 2 nm, as well as with a 415-nm thick Pt film. These results are important for reducing production costs by reducing the required amount of expensive platinum.     

Mechanism for degradation of Nafion in PEM fuel cells from quantum mechanics calculations

We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH(●), H(●)) only when in the presence of H(2), O(2), and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H(2) (or H(+)) and O(2) in the presence of the Pt catalyst. We find a barrier of 0.53 eV for OH radical formation from HOOH chemisorbed on Pt(111) and of 0.76 eV from chemisorbed OOH(ad), suggesting that OH might be present during the ORR, particularly when the fuel cell is turned on and off. Based on the QM, we propose two chemical mechanisms for OH radical attack on the Nafion polymer: (1) OH attack on the S-C bond to form H(2)SO(4) plus a carbon radical (barrier: 0.96 eV) followed by decomposition of the carbon radical to form an epoxide (barrier: 1.40 eV). (2) OH attack on H(2) crossover gas to form hydrogen radical (barrier: 0.04 eV), which subsequently attacks a C-F bond to form HF plus carbon radicals (barrier as low as 1.00 eV). This carbon radical can then decompose to form a ketone plus a carbon radical with a barrier of 0.86 eV. The products (HF, OCF(2), SCF(2)) of these proposed mechanisms have all been observed by F NMR in the fuel cell exit gases along with the decrease in pH expected from our mechanism.     

Temperature dependence of oxygen reduction activity at Nafion-coated bulk Pt and Pt/carbon black catalysts

Oxygen reduction reaction (ORR) activity and H(2)O(2) formation at Nafion-coated film electrodes of bulk-Pt and Pt nanoparticles dispersed on carbon black (Pt/CB) were investigated in 0.1 M HClO(4) solution at 30 to 110 degrees C by using a channel flow double electrode method. We have found that the apparent rate constants k(app) (per real Pt active surface area) for the ORR at bulk-Pt (with and without Nafion-coating) and Nafion-coated Pt/CB (19.3 and 46.7 wt % Pt, d(Pt) = 2.6 to 2.7 nm) thin-film electrodes were in beautiful agreement with each other in the operation conditions of polymer electrolyte fuel cells (PEFCs), i.e., 30-110 degrees C and ca. 0.7 to 0.8 V vs RHE. The H(2)O(2) yield was 0.6-1.0% at 0.7-0.8 V on all Nafion-coated Pt/CB and bulk-Pt and irrespective of Pt-loading level and temperature. Nafion coating was pointed out to be a major factor for the H(2)O(2) formation on Pt catalysts modifying the surface property, because H(2)O(2) production was not detected at the bulk-Pt electrode without Nafion coating.