Preparation and voltammetric characterization of electrodes coated with Langmuir-Schaefer ultrathin films of Nafion®

Abstract

Filmes ultrafinos do polímero perfluorado Nafion ® foram depositados em eletrodos de óxido índio-titânio (ITO) usando a técnica de Langmuir-Scaefer (LS), depois da otimização das condições de composição da subfase. As características morfológicas das camadas foram obtidas por Microscopia de Força Atômica (AFM). Filmes de Nafion ® LS mostraram boa uniformidade e cobertura completa da superfície do eletrodo. No entanto, diferentes graus de organização das camadas poliméricas ficaram evidentes com respeito a filmes finos depositados por revestimento rotacional. Eletrodos ITO modificados com camadas de Nafion ® LS, pré-concentrados por cátions eletroativos de troca iônica, como o Ru[(NH 3 ) 6 ] 3+ , dissolveram-se em soluções diluídas. A espécie eletroativa foi retida pelo ITO com camada de Nafion ® LS, mesmo depois da mudança do eletrodo modificado para eletrodo de suporte purificado. Isto possibilitou o uso do complexo de rutênio como padrão voltamétrico para o teste do fenômeno de difusão nos filmes de Nafion ® LS. Os coeficientes de difusão aparentes (D app ) do Ru[(NH 3 ) 6 ] 3+ incorporado no filme de Nafion ® LS foram obtidos por medidas voltamétricas. Os valores de D app diminuíram levemente com o aumento da quantidade de complexo de rutênio incorporado no filme ultrafino e foram significativamente mais baixos do que os valores para filmes de Nafion ® recapados, em acordo com a natureza altamente condensada dos filmes de Nafion ® LS.Ultrathin films of Nafion ® perfluorinated polymer were deposited on indium-tin oxide electrodes (ITO) by using Langmuir-Schaefer (LS) technique, after optimization of the subphase composition conditions. Morphological characteristics of these coatings were obtained by Atomic Force Microscopy (AFM). Nafion ® LS films showed a good uniformity and complete coverage of the electrode surface, however a different organization degree of the polymer layer was evidenced with respect to thin films deposited by spin-coating. ITO electrodes modified with Nafion ® LS coatings preconcentrate by ion-exchange electroactive cations, such as Ru[(NH 3 ) 6 ] 3+ , dissolved in diluted solutions. The electroactive species is retained by the Nafion ® LS coated ITO also after transfer of the modified electrode into pure supporting electrolyte. This allowed the use of the ruthenium complex as voltammetric probe to test diffusion phenomena within the Nafion ® LS films. Apparent diffusion coefficients (D app ) of Ru[(NH 3 ) 6 ] 3+ incorporated in Nafion ® LS films were obtained by voltammetric measurements. D app values decrease slightly by increasing the amount of ruthenium complex incorporated in the ultrathin film. They are significantly lower than values typical for recasted Nafion ® films, in agreement with the highly condensed nature of the Nafion ® LS fims.Keywords: Langmuir-Schaefer films, Nafion ® , modified electrodes, Ru[(NH 3 ) 6 ] 3+ , diffusion coefficients IntroductionNafion ® , a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether, is one of the most interesting solid polyme...

Langmuir–Blodgett films of different ionomeric polymers deposited on electrode surfaces

“…6, indicate a thin layer behavior for v = 50 mV s −1 and planar diffusion control at higher scan rate. Such a transition between different transport regimes at polymer coated electrodes is observed at the scan rate at which the thickness of the diffusion layer (which decreases with increasing v) becomes comparable with the thickness of the coating [11,21]. These data agrees with a rather small thickness of the Nafion ® LB coating [15,21], which can be estimated around 100-150 nm for the 30 layers film, as measured by AFM for Nafion ® LS coatings [15].…”

“…Electrochemical applications cation (methylviologen and Ru(NH 3 ) 6 3+ ) incorporated by ion-exchange in Nafion ® LS-films are lower than values measured in recasted films [21], so indicating a higher condensation degree for the former coatings.…”

Intrinsic electrochemical activity of single walled carbon nanotube–Nafion assemblies

“…2,31,32 The accumulation of cations combined with barrier properties have been utilised for the detection of the neurotransmitter dopamine in the presence of ascorbic acid. [33][34][35][36][37][38][39][40][41] Nafion films have been employed on electrodes as drop-cast films, 42,43 and by layer-by-layer deposition methodologies including the Langmuir-Blodgett 44,45 and Langmuir-Schaefer 25,[46][47][48] techniques. These techniques have facilitated the co-deposition of Nafion, with a redox mediator pre-loaded within the film 29,30 or with nano-materials immobilized within the film.…”

Incorporation of Functionalized Palladium Nanoparticles within Ultrathin Nafion Films: A Nanostructured Composite for Electrolytic and Redox‐Mediated Hydrogen Evolution

“…[1] Among polymer membranes, Nafion, a perfluorinated ion-exchange polymer containing tetrafluoroethylene and perfluorovinyl ether units, terminated with a -SO 3 H group, is probably the most common polymer electrolyte used in PEFCs and DMFCs because of its good thermal and chemical stability, together with high proton conductivity. [2][3][4][5][6] These properties are further expanded through the ability of Nafion to preconcentrate cationic species, making it possible to host a wide range of entities such as redox mediators [7][8][9][10][11][12][13][14] and nanoparticles [15][16][17][18][19][20] for different types of catalytic applications. [21,22] An important factor limiting the practical development of DMFCs is methanol crossover from the anode to the cathode through the polymer membrane; this causes significant loss of fuel and concomitant poisoning of the catalyst at the cathode side.…”