AFM studies and electrochemical characterization of boron-doped diamond surfaces modified with metal oxides by the Sol-Gel method

Abstract

Com o objetivo de aprofundar investigações anteriores, foram realizadas modificações superficiais diretas em eletrodos de diamante dopados com boro (DDB), com óxidos metálicos (PtO x , RuO 2 , IrO 2 e PbO 2 ) e com alguns compósitos mistos, utilizando a técnica Sol-Gel. Estes materiais foram estudados por microscopia de força atômica (MFA) e os resultados indicaram a formação de sítios de deposição heterogênea. Técnicas eletroquímicas foram utilizadas para estabelecer a atividade catalítica para a reação de desprendimento de oxigênio (RDO) e para reação de oxidação de etanol em meio ácido utilizando os compósitos de PtO x e PtO x -RuO 2 . Testou-se ainda a estabilidade de um depósito de PtO x , recoberto por um filme de Nafion ® , por meio de operação contínua de longa duração. Estudos de voltametria cíclica comparativa mostraram que a área superficial ativa dos novos materiais mudou consideravelmente com o método de modificação proposto. O eletrodo de IrO 2 /BDD mostrou o melhor desempenho para a RDO, iniciando o processo de oxidação em ~ 1.4 V vs. HESS, valor este 200 mV menor do que o observado sobre um eletrodo de PtO x /BDD. Foi observada uma pequena perda da atividade do eletrodo de PtO x /BDD (6%) depois de realizada eletrólise de 4 horas, enquanto que 1000 ciclos voltamétricos deixaram a superfície praticamente inalterada. Os estudos realizados mostram que as atividades satisfatórias dos eletrodos preparados pelo método Sol-Gel podem constituir ferramentas interessantes de pesquisa, visando principalmente a utilização destes materiais em aplicações práticas.Continuing previous investigations, direct surface modifications of boron-doped diamond (BDD) electrodes with metal oxides (PtO x , RuO 2 , IrO 2 and PbO 2 ) and with some mixed composites were carried out by the Sol-Gel technique. The materials were studied by atomic force microscopy (AFM) to determine their surface topologies and by electrochemical techniques to establish the catalytic activity towards the oxygen evolution reaction (OER) and also, for the PtO x and PtO xRuO 2 composites, the ethanol oxidation reactions in acid media. The stability of PtO x coating covered by a Nafion ® film was also tested by long-term operation. The AFM results indicated sites of heterogeneous deposition and the electrochemical studies demonstrated that the active surface area changed considerably with the proposed method of modification. The IrO 2 /BDD electrode showed the best performance to the OER with the onset of the oxidation current at ~1.4 V, a value 200 mV lower than for the PtO x /BDD electrode. The enhanced stability of PtO x /BDD electrodes achieved by the application of a Nafion ® film and already reported in acid media was further proved using the ethanol oxidation reaction. Only a small loss of activity (6%) was observed after 4-hours electrolysis while one-thousand voltammetric cycles left the surface practically unchanged. In addition, preliminary studies for the same reaction on PtO x /BDD and PtO x -RuO 2 / BDD electrodes demonstrated the excell...

The Use of Diamond for Energy Conversion System Applications: A Review

“…The surface modification of BDD with IrO 2 and PbO 2 was studied by AFM technique and the results indicated the existence of sites with heterogeneous deposition; both catalysts showed good electrocatalytic activity; however, IrO 2 /BDD electrode exhibits better performance for the OER with respect to diamond (unmodified) and PbO 2 /BDD electrodes, as demonstrated by Suffredini et al [49].…”

“…In another study carried out by Suffredini et al [49] that used a similar electrode configuration (Pt/BBD + Nafion film), showed that 1000 voltammetric cycles for the ethanol oxidation reaction also left the surface practically unchanged.…”

“…Surface modifications of BDD electrodes have been carried out with several metal oxides and some mixed composites using the sol-gel method [49,50]. It is well known that sol-gel technique is a suitable process for coating substrates for energy storage materials and electrochemical devices; in either case, there are many interfaces between components and many components that have to perform reliably and safely.…”

“…The main factors that are important in development of thin films are the uniformity and thickness of film, its adhesion to the substrate, and resistance to cracking. In this context, some research groups are working on the BDD surface modification by sol-gel technique for different catalytic coatings such as metallic oxides (MO 2 , M = Pb, Ru, and Ir) [49] or metal catalyst like platinum.…”

“…The modification of the BDD electrode with other Ptmetal oxide catalysts prepared by sol-gel has been investigated with the aim to improve its electrocatalytic response to be used as a fuel cell anode. In this context, BDD electrodes with IrO 2 , PbO 2 , SnO 2 , Ta 2 O 5 and some mixed composites prepared by sol-gel have been investigated by electrochemical techniques to establish their catalytic activity towards methanol and/or ethanol oxidation reactions [49][50][51][52][53][54][55][56][57][58][59][60][61]. In Table 2 are presented different coating catalysts synthesized by sol-gel technique on BDD support electrode, indicating the precursors used in the synthesis, and the electro-oxidation reaction that was studied.…”