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 1.0 M 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 5 wt.% 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 20 wt.% 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 1 M NaOH at constant current density of 20 mA cm−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.

Electrocatalytic hydrogenation of acetophenone using a Polymer Electrolyte Membrane Electrochemical Reactor

The use of a solid polymeric electrolyte, spe, is not commonly found in organic electrosynthesis despite its inherent advantages such as the possible elimination of the electrolyte entailing simpler purification processes, a smaller sized reactor and lower energetic costs. In order to test if it were possible to use a spe in industrial organic electrosynthesis, we studied the synthesis of 1-phenylethanol through the electrochemical hydrogenation of acetophenone using Pd/C 30 wt% with different loadings as cathode and a hydrogen gas diffusion anode. A Polymer Electrolyte Membrane Electrochemical Reactor, PEMER, with a fuel cell structure was chosen to carry out electrochemical reduction with a view to simplifying an industrial scale-up of the electrochemical process. We studied the influence of current density and cathode catalyst loading on this electroorganic synthesis. Selectivity for 1-phenylethanol was around 90% with only ethylbenzene and hydrogen detected as by-products.

Electrochemical synthesis at pre-pilot scale of 1-phenylethanol by cathodic reduction of acetophenone using a solid polymer electrolyte

The pre-pilot scale synthesis of 1-phenylethanol was carried out by the cathodic hydrogenation of acetophenone in a 100 cm2 (geometric area) Polymer Electrolyte Membrane Electrochemical Reactor. The cathode was a Pd/C electrode. Hydrogen oxidation on a gas diffusion electrode was chosen as anodic reaction in order to take advantage of the hydrogen evolved during the reduction. This hydrogen oxidation provides the protons needed for the synthesis. The synthesis performed with only a solid polymer electrolyte, spe, has lower fractional conversion although a higher selectivity than that carried out using a support–electrolyte–solvent together with a spe. However, the difference between these two cases is rather small and since the work-up and purification of the final product are much easier when only a spe is used, this last process was chosen for the pre-pilot electrochemical synthesis of 1-phenylethanol.

Electrochemical oxidation of H 2, CO gas mixtures in polymer-electrolyte-membrane fuel cells

Magdeburg, Univ., Fak. für Verfahrens- und Systemtechnik, Diss., 2014

Hydrogen chloride electrolysis in a polymer-electrolyte-membrane reactor with oxygen-depolarized cathode

Magdeburg, Univ., Fak. für Verfahrens- und Systemtechnik, Diss., 2015

The effects of hydrogen sulfide on the polymer electrolyte membrane fuel cell anode catalyst: H(2)S-Pt/C interaction products

The performance of a polymer electrolyte membrane fuel cell (PEMFC) operating on a simulated hydrocarbon reformate is described. The anode feed stream consisted of 80% H(2),similar to 20% N(2), and 8 ppm hydrogen sulfide (H(2)S). Cell performance losses are calculated by evaluating cell potential reduction due to H(2)S contamination through lifetime tests. It is found that potential, or power, loss under this condition is a result of platinum surface contamination with elemental sulfur. Electrochemical mass spectroscopy (EMS) and electrochemical techniques are employed, in order to show that elemental sulfur is adsorbed onto platinum, and that sulfur dioxide is one of the oxidation products. Moreover, it is demonstrated that a possible approach for mitigating H(2)S poisoning on the PEMFC anode catalyst is to inject low levels of air into the H(2)S-contaminated anode feeding stream. (C) 2011 Elsevier B.V. All rights reserved.

Operation of polymer electrolyte membrane fuel cells with dry feeds: Design and operating strategies

The operation of polymer electrolyte membrane fuel cells (PEMFCs) with dry feeds has been examined with different fuel cell flow channel designs as functions of pressure, temperature and flow rate. Auto-humidified (or self-humidifying) PEMFC operation is improved at higher pressures and low gas velocities where axial dispersion enhances back-mixing of the product water with the dry feed. We demonstrate auto-humidified operation of the channel-less, self-draining fuel cell, based on a stirred tank reactor; data is presented showing auto-humidified operation from 25 to 115 degrees C at 1 and 3 atm. Design and operating requirements are derived for the auto-humidified operation of the channel-less, self-draining fuel cell. The auto-humidified self-draining fuel cell outperforms a fully humidified serpentine flow channel fuel cell at high current densities. The new design offers substantial benefits for simplicity of operation and control including: the ability to self-drain reducing flooding, the ability to uniformly disperse water removing current gradients and the ability to operate on dry feeds eliminating the need for humidifiers. Additionally, the design lends itself well to a modular design concept. (c) 2005 Elsevier B.V. All rights reserved.

A novel electrocatalyst support with proton conductive properties for polymer electrolyte membrane fuel cell applications

The objective of this study is to graft the Surface of carbon black, by chemically introducing polymeric chains (Nafion (R) like) with proton-conducting properties. This procedure aims for a better interaction of the proton-conducting phase with the metallic catalyst particles, as well as hinders posterior support particle agglomeration. Also loss of active surface call be prevented. The proton conduction between the active electrocatalyst site and the Nafion (R) ionomer membrane should be enhanced, thus diminishing the ohmic drop ill the polymer electrolyte membrane fuel cell (PEMFC). PtRu nanoparticles were supported on different carbon materials by the impregnation method and direct reduction with ethylene glycol and characterized using amongst others FTIR, XRD and TEM. The screen printing technique was used to produce membrane electrode assemblies (MEA) for single cell tests in H(2)/air(PEMFC) and methanol operation (DMFC). In the PEMFC experiments, PtRu supported on grafted carbon shows 550 mW cm(-2) gmetal(-1) power density, which represents at least 78% improvement in performance, compared to the power density of commercial PtRu/C ETEK. The DMFC results of the grafted electrocatalyst achieve around 100% improvement. The polarization Curves results clearly show that the main Cause of the observed effect is the reduction in ohmic drop, caused by the grafted polymer. (C) 2009 Elsevier B.V. All rights reserved.

Nonlinear frequency response analysis for the diagnosis of polymer electrolyte membrane fuel cells

Magdeburg, Univ., Fak. für Verfahrens- und Systemtechnik, Diss., 2012

Performance of a poly(2,5-benzimidazole)-based polymer electrolyte membrane fuel cell

The performance of an ABPBI-based High Temperature H-2/O-2 PEMFC system was studied under different experimental conditions. Increasing the temperature from 130 to 170 degrees C improved the cell performance, even though further increase was not beneficial for the system. Humidification of the H-2 stream ameliorated this behaviour, even though operating above 170 degrees C is not advisable in terms of cell performance. A significant electrolyte dehydration seems to negatively affect the fuel cell performance, especially in the case of the anode. In the presence of 2% vol. CO in the H-2 stream, the temperature exerted a positive effect on the cell performance, reducing the strong adsorption of this poison on the platinum sites. Moreover, humidification of the H-2 + CO stream increased the maximum power densities of the cell, further alleviating the CO poisoning effects. Actual CO-O-2 fuel cell results confirmed the significant beneficial effect of the relative humidity on the kinetics of the CO oxidation process. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Electrolito sólido polimérico: desde las pilas de combustible hasta la electrosíntesis orgánica

En este trabajo, en primer lugar, se presenta una nueva técnica desarrollada en nuestro laboratorio para el estudio electroquímico de las capas catalíticas de las pilas de combustible en células de tres electrodos, centrándonos en el proceso de electroxidación de ácido fórmico como reacción de test. Gracias a esta técnica se han estudiado parámetros de construcción como % en peso del metal, relación Nafion / sólidos totales y recubrimiento catalítico comprobando como la adsorción irreversible de adátomos de Bi sobre Pt soportado sobre Vulcan XC-72 favorece este proceso y como puede caracterizarse la capa catalítica de una pila de combustible de ácido fórmico (DFAFC) de forma integral utilizando estudios de sistemas nanoparticulados de Pt-Pd soportados sobre Vulcan XC-72 en el seno de ésta. En segundo lugar se ha introducido el concepto de PEMER (Polymer Electrolyte Membrane Electrochemical Reactor). De esta forma, una configuración electródica propia de las pilas de combustible se utiliza en electrosíntesis orgánica. Como reacciones test se han testeado la formación de 1-feniletanol como producto mayoritario por hidrogenación electrocatalítica de la acetofenona sobre nanopartículas de Pd soportadas sobre Vulcan XC-72 como electrocatalizador y, utilizando Pb (catalizador no noble) soportado sobre Vulcan XC-72, se ha estudiado la ruptura del puente disulfuro de L-cistina y N,N-diacetil-L-cistina (NNDAC) para obtener L-cisteína y N-acetil- L-cisteína (NAC). En ambas reacciones, hidrogenación y ruptura del puente disulfuro, se han analizado tanto parámetros constructivos de la capa catalítica como parámetros de proceso tanto a escala laboratorio con el uso de un reactor comercial de 25 cm² como a escala pre-piloto con la construcción de un reactor de 100 cm².

Experimental study on n-butane partial oxidation to maleic anhydride in a solid electrolyte membrane reactor

n-Butane, Partial oxidation, Maleic anhydride, electrochemical oxygen pumping, solid electrolyte membrane reactor

Local degradation of structural, mechanical, electrical and chemical properties of membrane electrode assembly in polymer electrolyte fuel cell

Polymer electrolyte fuel cell (PEMFC) is promising source of clean power in many applications ranging from portable electronics to automotive and land-based power generation. However, widespread commercialization of PEMFC is primarily challenged by degradation. The mechanisms of fuel cell degradation are not well understood. Even though the numbers of installed units around the world continue to increase and dominate the pre-markets, the present lifetime requirements for fuel cells cannot be guarantee, creating the need for a more comprehensive knowledge of material’s ageing mechanism. The objective of this project is to conduct experiments on membrane electrode assembly (MEA) components of PEMFC to study structural, mechanical, electrical and chemical changes during ageing and understanding failure/degradation mechanism. The first part of this project was devoted to surface roughness analysis on catalyst layer (CL) and gas diffusion layer (GDL) using surface mapping microscopy. This study was motivated by the need to have a quantitative understanding of the GDL and CL surface morphology at the submicron level to predict interfacial contact resistance. Nanoindentation studies using atomic force microscope (AFM) were introduced to investigate the effect of degradation on mechanical properties of CL. The elastic modulus was decreased by 45 % in end of life (EOL) CL as compare to beginning of life (BOL) CL. In another set of experiment, conductive AFM (cAFM) was used to probe the local electric current in CL. The conductivity drops by 62 % in EOL CL. The future task will include characterization of MEA degradation using Raman and Fourier transform infrared (FTIR) spectroscopy. Raman spectroscopy will help to detect degree of structural disorder in CL during degradation. FTIR will help to study the effect of CO in CL. XRD will be used to determine Pt particle size and its crystallinity. In-situ conductive AFM studies using electrochemical cell on CL to correlate its structure with oxygen reduction reaction (ORR) reactivity

Photo luminescent polymer electrolyte based on agar and containing europium picrate for electrochemical devices

Dispersion of photoluminescent rare earth metal complexes in polymer matrices is of great interest due to the possibility of avoiding the saturation of the photoluminescent signal. The possibility of using a natural ionic conducting polymer matrix was investigated in this study. Samples of agar-based electrolytes containing europium picrate were prepared and characterized by physical and chemical analyses. The FTIR spectra indicated strong interaction of agar O-H and 3.6-anhydro-galactose C-O groups with glycerol and europium picrate. The DSC analyses revealed no glass transition temperature of the samples in the -60 to 250 degrees C range. From the thermogravimetry (TG), a thermal stability of the samples of up to 180 degrees C was stated. The membranes were subjected to ionic conductivity measurement, which provided the values of 2.6 x 10(-6) S/cm for the samples with acetic acid and 1.6 x 10(-5) S/cm for the samples without acetic acid. Moreover, the temperature-dependent ionic conductivity measurements revealed both Arrhenius and VTF models of the conductivity depending on the sample. Surface visualization through scanning electron microscopy (SEM) demonstrated good uniformity. The samples were also applied in small electrochromic devices and showed good electrochemical stability. The present work confirmed that these materials may perform as satisfactory multifunctional component layers in the field of electrochemical devices. (C) 2012 Elsevier B.V. All rights reserved.

Study of the Electrochemical, Physical and Morphological Characteristics of Anode Catalysts for Perfluorosulfonic Acid (PFSA) Membrane Water Electrolysers

A number of supported and un-supported Oxygen Evolution Reaction (OER) iridium based electrocatalysts for Polymer Electrolyte Membrane Water Electrolysis (PEMWE) were synthesized using a polyol method. The electrocatalysts and the supports were characterized using a wide range of physical and electrochemical characterization methods. The effect of morphological characteristics of the OER electrocatalyst and the support on the OER activity was studied. The results of this thesis contribute to the existing research to reduce the cost of PEMWE by enhancing the utilization of precious metal for OER electrocatalysis. Iridium electrocatalysts supported on antimony tin oxide (Ir/ATO) were synthesized using the polyol method with two different heating techniques: conventional and microwave-irradiation. It was shown that the physical morphology and electrochemical properties of Ir/ATO synthesized with the two heating methods were comparable. However, the microwave irradiation method was extremely faster than the conventional heating method. Additionally, the effect of heat treatment (calcination temperature) on the morphology and OER activity of Ir/ATO synthesized electrocatalyst with the conventional polyol method. It was found that the iridium electrocatalyst synthesized with the polyol method, consisted of 1-5 nm particles, possessed an amorphous structure, and contained iridium with an average oxidation state of less than +4. Calcining the catalyst at temperatures more than 400 ºC and less than 700ºC: 1) increased the size of the iridium particles to 30 nm, 2) changed the structure of iridium particles from amorphous to crystalline, 3) increased the iridium oxidation state to +4 (IrO2), 4) reduced the electrochemically active surface area by approximately 50%, and 5) reduced the OER activity by approximately 25%; however, it had no significant effect on the physical and chemical morphology of the ATO support. Moreover, potential support metal carbides and oxides including: Tantalum Carbide (TaC), Niobium Oxide (Nb2O5), Niobium Carbide (NbC), Titanium Carbide (TiC), Tungsten Carbide (WC) and Antimony-doped Tin Oxide (ATO, Sb2O5-SnO2), were characterized, and used as support for the iridium OER electrocatalysts. TaC was found to be a promising support, and increasing its surface area by 4% improved the OER performance of the final supported catalyst by approximately 50%.