Este trabalho descreve o estudo voltamétrico de três aldeídos alifáticos: formaldeído, acetaldeído e propionaldeído sobre ânodos do tipo Dimensionalmente Estáveis (ADE ). Eletrodos com composição Ti/Ru 0.3 M 0.7 O 2 (onde M = Ti ou Sn) foram utilizados em solução de 0.5 mol dm -3 H 2 SO 4 usando uma célula do tipo filtro-prensa. Ambos os eletrodos apresentam um comportamento típico dos ADE frente a oxidação de formaldeído. Porém, para acetaldeído e propionaldeído, um desvio do padrão é observado na forma de uma diminuição da carga anódica faradaica normalizada (q fn ) e da densidade da corrente associada com a reação de desprendimento de oxigênio (RDO). Um possível mecanismo considerando a oxidação direta dos aldeídos é sugerido.This work describes the cyclic voltammetry study of three aliphatic aldehydes: formaldehyde, acetaldehyde and propionaldehyde at dimensionally stable anodes (DSA ). Electrodes of nominal composition Ti/Ru 0.3 M 0.7 O 2 (where M = Ti ou Sn) were used in 0.5 mol dm -3 H 2 SO 4 in a filter-press cell. Both electrodes exhibit behaviour typical of such materials in the presence of formaldehyde. However, with acetaldehyde and propionaldehyde non-typical behaviour is observed. This is characterised by a fall in the normalised faradaic anodic charge (q nf ) and also a decrease in the current density associated with the oxygen evolution reaction (OER). A possible reaction mechanism, considering the direct oxidation of the aldehyde at the electrode surface, is suggested.Keywords: formaldehyde, acetaldehyde, propionaldehyde, electrooxidation, DSA
IntroductionThe presently accepted model for organic oxidation at DSA electrodes is that proposed by Comninellis and De Battisti, 1 which considers that oxidation takes place under conditions of simultaneous oxygen evolution. The nature of the electrode material is known to affect the mechanism of oxidation, 1 where so called "active" electrodes mediate the oxidation of an organic species via the formation of higher oxides of the metal, (MO x+1 ), if a higher oxidation state is available (e.g. RuO 2 or IrO 2 ). This leads to selective oxidation. "Non-active" electrodes present no higher oxidation state available and the organic species is directly oxidised by an adsorbed hydroxyl radical -giving complete combustion (e.g. SnO 2 or PbO 2 ). Essentially, both processes require, as the initial step, the formation of ( • OH) ads .Apart from the nature of the electrode material, other factors, such as organic concentration 2 and the type of organic species present 3 are known to play an important role in the oxidation process. However, few studies deal with the effect of concentration or, in fact, deal with high organic concentration.Cyclic voltammograms of DSA electrodes in acidic media generally display broad peaks between the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), which correspond to oxidation state transitions (e.g. Ru(IV) to Ru(VI)). In cyclic voltammetry the oxidation of an organic species at DSA electrodes...