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.     

The problem of Ru dissolution from Pt–Ru catalysts during fuel cell operation: analysis and solutions

Platinum–ruthenium catalysts are widely used as anode materials in polymer electrolyte fuel cells (PEMFCs) operating with reformate gas and in direct methanol fuel cells (DMFCs). Ruthenium dissolution from the Pt–Ru anode catalyst at potentials higher than 0.5?V vs. DHE, followed by migration and deposition to the Pt cathode can give rise to a decrease of the activity of both anode and cathode catalysts and to a worsening of cell performance. A major challenge for a suitable application of Pt–Ru catalysts in PEMFC and DMFC is to improve their stability against Ru dissolution. The purpose of this paper is to provide a better knowledge of the problem of Ru dissolution from Pt–Ru catalysts and its effect on fuel cell performance. The different ways to resolve this problem are discussed.     

碱性聚合物电解质膜的表面锥形阵列结构提升燃料电池性能

燃料电池作为一种清洁高效的能量转换装置,被认为是构建未来社会可再生能源结构的关键一环。不同于质子交换膜燃料电池(PEMFC),碱性聚合物电解质燃料电池(APEFC)的出现使非贵金属催化剂的使用成为可能,因而受到了日益广泛的关注和研究。APEFC的关键结构是膜电极,主要由聚合物电解质膜和阴阳极(含催化层、气体扩散层)组成,膜电极是电化学反应发生的场所,其优劣直接决定着电池性能的好坏。因此,基于现有的碱性聚合物电解质及催化剂体系,如何构筑更加优化的膜电极结构,使APEFC发挥出更高的电池性能是亟待开展的研究。本文首先通过模板法在碱性聚合物电解质膜的表面构建出有序的锥形阵列,再将具有阵列结构的一侧作为阴极来构筑膜电极,同时,作为对比,制备了由无阵列结构的聚合物电解质膜构筑而成的膜电极,最后对基于两种不同膜电极的APEFC的电化学性能进行了对比研究。实验结果表明,锥形阵列结构可以将APEFC的峰值功率密度由1.04 W·cm-2显著提高到1.48 W·cm-2,这主要归因于在APEFC的阴极侧具有锥形阵列结构的聚合物电解质膜的亲水性的提升和催化剂电化学活性面积的增加。本工作为碱性聚合物电解质燃...     

Interfacial constraints on water and proton transport across nafion membranes

Water and proton transport across a Nafion membrane are measured as functions of water activity and applied electric potential with a polymer electrolyte hydrogen pump. Water and proton transport across the membrane must match water and proton transport entering and leaving the electrode/membrane/vapor three phase interfaces at the anode and cathode. At low applied electric potential proton and water fluxes are correlated. At moderate to high applied electric potential the proton current is constant, independent of applied electric potential, while the water transport increases with increasing electric potential. At high applied electric potential water and proton transport become uncoupled at the membrane interfaces; water is transported across the membrane/vapor interface and protons are transported across the membrane/electrode interface. The applied electric potential drives electro‐osmosis to redistribute the water in the membrane. Water redistribution is limited by the interfacial transport of water across the membrane/vapor interface. © 2015 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2015 , 53, 1580–1589     

Development of sulfonated poly (ether ether ketone) electrolyte membrane for applications in hydrogen sensor

The future economy is projected as hydrogen economy and fuel cells are set to become the energy source either replacing or augmenting the present oil based technology. A sulfonated poly ether ether ketone (SPEEK) membrane as the electrolyte for hydrogen sensor that operates at room temperature was developed in our lab. The electrolyte used was SPEEK, which is a proton conducting solid polymer membrane. The membranes were characterized using various available techniques like TGA, XRD, SEM, etc. The durability was studied using the Fenton’s reagent. The proton conducting ability was analyzed using impedance spectroscopy. The catalysts considered were platinum for the cathode and three different catalysts (Pt, Pt/Pd and Pd) for the anode. The MEAs were evaluated for their performance in hydrogen sensor and the one with platinum catalyst at the anode gave the best response among the three indicating its suitability for the SPEEK membrane for hydrogen sensor.     

A membrane electrode assembly for the electrochemical synthesis of hydrocarbons from CO2(g) and H2O(g)

We report the electrochemical reduction of CO₂ into hydrocarbons using a new electrochemical membrane reactor holding a yet unreported membrane electrode assembly comprising a copper mesh cathode and a Ti felt coated with mixed metal oxide (MMO) catalyst anode separated by a proton conductive membrane. CO_2(g) was supplied to the cathodic reduction compartment, whilst humidified N₂ was supplied to the anodic oxidation compartment. The MMO anode produces protons transported across the proton exchange membrane and electrons transported via the external circuit to the copper cathode to reduce CO_2(g). Production rates of methane, propane, propene, iso-butane and n-butane were determined as a function of cell potential at temperatures between 30 and 70 °C and relative humidity between ca. 25% and 75%. Maximum methane concentration and the current efficiency for production of hydrocarbons were 3.29 ppm and 0.12%, respectively. Whilst the observed product spectrum is desirable, such low current efficiencies require systematic optimization of the catalytic membrane system, in particular an improved cathode with an optimum contact between proton conducting membrane, electrode and catalyst is desired.     

A novel single electrode supported direct methanol fuel cell

In this paper a single electrode supported direct methanol fuel cell (DMFC) is fabricated and tested. The novel architecture combines the elimination of the polymer electrolyte membrane (PEM) and the integration of the anode and cathode into one component. The thin film fabrication involves a sequential deposition of an anode catalyst layer, a cellulose acetate electronic insulating layer and a cathode catalyst layer onto a single carbon fibre paper substrate. The single electrode supported DMFC has a total thickness of 3.88 × 10^?2 cm and showed a 104% improvement in volumetric specific power density over a two electrode DMFC configuration under passive conditions at ambient temperature and pressure (1 atm, 25 °C).     

Asymmetric double-layer composite electrolyte with enhanced ionic conductivity and interface stability for all-solid-state lithium metal batteries

All-solid-state Li metal battery has been regarded as a promising battery technology due to its high energy density based on the high capacity of lithium metal anode and high safety based on the all solid state electrolyte without inflammable solvent.However,challenges still exist mainly in the poor contact and unstable interface between electrolyte and electrodes.Herein,we demonstrate an asymmetric design of the composite polymer electrolyte with two different layers to overcome the interface issues at both the cathode and the anode side simultaneously.At the cathode side,the polypropylene carbonate layer has enough viscosity and flexibility to reduce the inter-facial resistance,while at the Li anode side,the polyethylene oxide layer modified with hexagonal boron nitride has high mechanical strength to suppress the Li dendrite growth.Owing to the synergetic effect between different components,the asprepared double layer composite polymer electrolyte demonstrates a large electrochemical window of5.17 V,a high ionic conductivity of 6.1×10~(-4) S/cm,and a transfe rence number of 0.56,featuring excellent ion transport kinetics and good chemical stability.All-solid-state Li metal battery assembled with LiFePO_4 cathode and Li anode delivers a high capacity of 150.9 mAh/g at 25℃ and 0.1 C-rate,showing great potential for practical applications.     

电解制备二氧化锰强酸性电解液中气体扩散电极的稳定性与失效行为

采用气体扩散电极(GDE)代替传统析氢阴极电解制备二氧化锰(EMD),重点研究了气体扩散电极在强酸性MnSO4-H2SO4电解液中的稳定性、寿命及失效行为.结果表明:气体扩散电极在MnSO4-H2SO4电解液中重现性好、具有一定的稳定性,寿命可达400 h;平行实验表明,阳极沉积一定厚度的EMD是槽电压第一次升高的主要原因;电流密度为100 A m-2时,气体扩散电极失效前阴极过程的速度由氧的离子化反应和氧的扩散混合控制,失效后阴极过程由氧去极化和氢去极化共同组成,主要发生析氢反应;催化层聚四氟乙烯(PTFE)网络结构的破坏和镍网层的溶解是电极失效的原因之一;Pt的团聚降低了电极的电催化活性,是电极失效的主要原因;阴极失效是槽电压再次升高的主要原因.     

An improved polymer electrolyte-based amperometric hydrogen sensor

An improved polymer electrolyte membrane (PEM) fuel cell-based amperometric hydrogen sensor that operates at room temperature has been developed. The electrolyte used in the sensor is a PVA/H₃PO₄ blend, which is a proton-conducting solid polymer electrolyte. A thin film of palladium is used as the anode and platinum supported on carbon as the cathode. The sensor functions as a fuel cell, H₂/Pd//PVA-H₃PO₄//Pt/O₂, and the short-circuit current is found to be linearly related to the hydrogen concentration. The basic principle, details of assembly, response behaviour of the sensor and its application are discussed.     

A new catalyst layer based on in situ pore generation of sulfonated poly(ether ether ketone) for PEMFC

A new concept of in situ pore generation to reduce water flooding in cathode catalyst layer (CCL) of polymer electrolyte membrane fuel cell (PEMFC) is proposed with the introduction of water soluble poly(ethylene glycol) (PEG) as a porogen to CCL based on sulfonated poly(ether ether ketone) (sPEEK). In this new type of CCL, PEG is directly removed by water produced during the cathode reaction. The new CCL exhibited much higher cell performance especially in mass transport limitation region compared to the pristine sPEEK-CCL. In addition, the presence of PEG in the new CCL lowered the glass transition temperature of the sPEEK binder, and it could improve the transference of catalyst layer onto the polymer electrolyte membrane.     

Stabilizing the Electrochemistry of Lithium-Selenium Battery via In situ Gelated Polymer Electrolyte: A Look from Anode

Li metal possesses a high theoretical specific capacity,high electronic conductivity,and a low electrochemical potential,making it a promising anode material for building next-generation rechargeable metal batteries.In case conventional liquid electrolytes were used,and the anode using Li metal has been hindered by unstable(electro)chemistry at Li/electrolyte interface and the accompanied dendrite issue.Specifically,for the Li-Se batteries,the dissolution and shuttle of polyselenide intermediates lead to the deposition of poorly-conductive species on the anode,which further aggravates the chemical environment at the anode.In this work,we proposed to stabilize the Li-Se electrochemistry by constructing a gel polymer electrolyte via in situ gelations of conventional ether-based electrolytes at room temperature.The results demonstrate that the in situ gelated electrolyte helps to build electrochemically stable electrode/electrolyte interfaces and promote the efficient transfer of charge carriers across the interface.Compared with the liquid electrolytes,the gelated electrolyte shows improved chemical compatibility with the Li metal anode,which effectively alleviates the unfavorable side reactions and dendrite formation at the anode/electrolyte interface,and the polyselenide shuttle from the cathode to the anode.As a result,the Li-Se battery shows a higher Coulombic efficiency and improved cycling performance.     

TEMPO-substituted polyacrylamide for an aqueous electrolyte-typed and organic-based rechargeable device

A hydrophilic radical polymer, poly(2,2,6,6-teteramethylpiperidinyloxyl-4-yl acrylamide) (PTAm), was synthesized via oxidation of the corresponding precursor polymer, poly(2,2,6,6-teteramethylpiperidine-4-yl acrylamide). Electrochemical properties of the PTAm layer were characterized in three aqueous electrolytes of sodium chloride (NaCl), sodium tetrafluoroborate (NaBF4), and sodium hexafluorophosphate (NaPF6) to optimize its activity as an organic cathode. The counter anion species significantly affected the capacity and the cycle performance of the PTAm layer. The PTAm layer in the presence of BF4? displayed quantitative redox capacity beyond 1 μm layer thickness and maintained the discharging capacity of 110 mAh g-1 (97% vs. the calculated capacity) even after 1000 cycle charging/discharging, which could be ascribed to its appropriate affinity to the aqueous electrolyte without any dissolution into the electrolyte. A totally organic-based rechargeable cell was fabricated using PTAm and poly(N-4,4’-bipyridinium-N-decamethylene dibromide) as the cathode and the anode, respectively, and the aqueous electrolyte of NaBF4. The cell gave a plateau voltage at 1.2 V both on charging and discharging and an excellent charging/discharging cyclability of >2000 with high coulombic efficiency of >95%.     

Distribution profile of hydrogen and oxygen permeating in polymer electrolyte membrane measured by mixed potential

We have succeeded to measure distribution profiles of hydrogen and oxygen permeating in polymer electrolyte membrane (PEM), the information of which contribute to clarify the Pt deposition mechanism inside the PEM during fuel cell operation. Seven platinum probes were inserted into the PEM to monitor the mixed potential determined by the ratio of O₂ to H₂ diffused from the cathode and the anode, respectively. It was found that an equivalent location L_A(eq) of a large potential jump from ca. 0 V to 0.8 V (vs. RHE) shifted to the cathode side with decreasing oxygen partial pressure in the oxidant gas. The values of L_A(eq) accord well with those calculated from the permeabilities of H₂ and O₂ in the PEM. It was suggested that Pt ions dissolved and diffused from the cathode catalysts were dominantly reduced by H₂ at L_A(eq), forming so-called “Pt band”.     

Catalytic layers in a reversible system comprising an electrolyzing cell and a fuel cell based on solid polymer electrolyte

Electrocatalytic layers of a fuel cell-electrolyzing cell reversible system with solid polymer electrolyte are studied. The system may be used as both a dc generator and a water electrolyzing cell. It is shown that the way the polytetrafluoroethylene (PTFE) additive is introduced into the cathode’s catalytic layer affects the cathode performance. The PTFE introduction in the form of suspension in an alcohol solution of MF-4SK polymer enhanced performance. Characteristics of platinum, iridium, and platinum-iridium anode catalysts are compared. The best characteristics are obtained using a composition based on platinum black and iridium black, applied layer-by-layer, with an iridium-black layer facing the surface of a solid-polymer membrane.     

Microfluidic hydrogen fuel cell with a liquid electrolyte

We report the design and characterization of a microfluidic hydrogen fuel cell with a flowing sulfuric acid solution instead of a Nafion membrane as the electrolyte. We studied the effect of cell resistance, hydrogen and oxygen flow rates, and electrolyte flow rate on fuel cell performance to obtain a maximum power density of 191 mW/cm2. This flowing electrolyte design avoids water management issues, including cathode flooding and anode dry out. Placing a reference electrode in the outlet stream allows for independent analysis of the polarization losses on the anode and the cathode, thereby creating an elegant catalyst characterization and optimization tool.     

P(VdF-HFP)-基离子液体复合聚合物电解质的阴极稳定性及热稳定性

以聚偏氟乙烯-六氟丙烯P(VdF-HFP)聚合物为基体, 制备了含离子液体1-甲基-3-乙基咪唑六氟磷酸盐(EMIPF6)、用于锂离子电池的离子液体复合聚合物电解质[P(VdF-HFP)/LiPF₆/EMIPF₆/EC(碳酸乙烯酯)-PC(碳酸丙烯酯)]. 采用热重分析法以及燃烧实验测试了复合聚合物电解质的热稳定性. 离子电导率测试表明, 离子液体的存在显著改善了复合聚合物电解质的离子传输; 循环伏安测试表明, 添加剂EC和PC的加入提高了复合电解质的阴极稳定性, 制得的离子液体复合聚合物电解质在0.3-4.3 V 电压范围内稳定存在. Li₄Ti₅O₁₂ 和LiCoO₂为电极材料、P(VdF-HFP)/LiPF₆/EMIPF₆/EC-PC 为电解质的半电池表现出优良的循环性能, 0.1C充放电倍率下, Li/LiCoO₂和Li/Li₄Ti₅O₁₂半电池的可逆容量分别为130和144 mAh·g^-1. 但EC、PC在一定程度上降低了离子液体复合聚合物电解质的热稳定性.     

Methanol Crossover through Modified Nafion Proton Exchange Membrane

The proton exchange membrane direct methanol fuel cells (PEMDMFC) show considerably lower performance than the hydrogen fuel cell because of inefficient methanol oxidation and the crossover of methanol through the membrane that separates the anode from the cathode. This paper describes electrochemical measurements made on a Nafion membrane modified by electrochemical deposition of poly(1-methyl pyrrole) on its side.     

Asymmetric polymer electrolyte membranes for water management of fuel cells

Water management is one of the critical issues of polymer electrolyte membrane fuel cells because dehydration of a membrane increases membrane-resistance whereas excessive water flooding at the cathode impedes the gaseous diffusion of oxygen to reaction sites at the wetted catalyst surface. In this study, we have developed an asymmetric polymer electrolyte membrane that facilitates water management. The structural modification of the membrane strongly affected water management, due primarily to the fact that water must move through the membrane during fuel cell operation. The asymmetric membrane improved transport of water from the cathode to the anode when the hydrophilic side of the membrane located to the cathode, thereby enhancing overall fuel cell performance under both fully humidified and non-humidified conditions.     

Impact of Membrane Types and Catalyst Layers Composition on Performance of Polymer Electrolyte Membrane Fuel Cells

Performance of a low temperature polymer electrolyte membrane fuel cell (PEMFC) is highly dependent on the kind of catalysts, catalyst supports, ionomer amount on the catalyst layers (CL), membrane types and operating conditions. In this work, we investigated the influence of membrane types and CL compositions on MEA performance. MEA performance increases under all practically relevant load conditions with reduction of the membrane thickness from 50 to 15 μm, however further decrease in membrane thickness from 15 to 10 μm leads to reduction in cell voltage at high current loads. A thick anode CL is found to be beneficial under wet operating conditions assuming more pore space is provided to accommodate liquid water, whereas under dry operating conditions, an intermediate thickness of the anode CL is beneficial. When studying the impact of catalyst layer thickness, too thin a catalyst layer again shows reduced performance due to increased ohmic resistance ruled out the performance of the MEAs which have identical Pt crystallite sizes on the cathode CLs i. e. the thinnest the cathode CL, the highest the voltage were achieved at a defined current load. Adaptation of the operating conditions is highly anticipated to achieve the highest MEA performance.