Formaldehyde Oxidation on a DSA-Type Electrode Modified by Pt or PbO[sub 2] Electrodeposition

Abstract

This work presents the preparation and characterization of dimensionally stable anodes ͑DSA͒ of nominal composition Ti/Ru 0.3 Ti 0.7 O 2 , modified by electrodeposition of small amounts of Pt or PbO 2 . Partial coverage of the anode surface with the modulator metals allowed us to change the coating properties in a significant way. The purpose of this preparation was to modulate the anode characteristics to enhance its electrocatalytic activity and obtain the maximum advantage from the mechanical resistance of DSA-type anodes. This new composite was applied to formaldehyde electro-oxidation. Bulk electrolysis experiments were carried out in acid medium. Electrode efficiency with respect to the formation of the more oxidized compound ͑CO 2 ͒ was shown to be related with the amount and distribution of electrodeposited platinum over the DSA surface. The DSA modified with PbO 2 ͑100 g cm −2 ͒ was more efficient than bare DSA. However, the amount of CO 2 obtained with the former electrode was still lower than that obtained with the platinum-modified ones. Bulk electrolysis results showed that DSA is not an inert substrate once it is clear that the same amount of electrodeposited catalyst on the RuO 2 -TiO 2 substrate increases CO 2 formation.Dimensionally stable anodes ͑DSA͒ consist of a metallic substrate containing a ceramic coating based on a mixture of RuO 2 and TiO 2 . Soon after its discovery, this material started being produced in large scale in the chlor-alcali industry. Many interesting properties have been attributed to it since then, including high surface area, excellent mechanical stability, and electrocatalytic activity. 1-3 Theoretically speaking, one can modulate the electrode surface properties by introducing different materials that may increase the electrode catalytic activity, thus allowing its application in electrosynthesis, 4-7 waste water treatment, 8,9 and oxygen evolution. 2 In all cases, the anodic material must have high performance concerning the conversion or combustion of a certain desired material. Considering the oxidation of small organic molecules over DSA-like compounds, we have observed that the oxidation of organic compounds occurs simultaneously with the oxygen evolution reaction ͑OER͒, 10 which is the main drawback of the use of Ti/RuO 2 -TiO 2 electrodes because of their short service life under high anodic polarization conditions.There are two ways of facing this problem. The first one is to attack the causes of electrode deactivation, so special attention has been paid to increasing the service life by improving the preparation technique 11 and to producing a stronger material by introducing stabilizing agents to promote protection against electrode wearing-out. 12 Even when these problems can be overcome, there still are limitations related to the low activation of these materials, which make them displace the desired reaction far from the OER. Thus, the introduction of new components capable of activating DSA-materials is a promising approach. Platinum is frequently used a...

Kinetics of the oxidation of formaldehyde in a flow electrochemical reactor with TiO2/RuO2 anode

“…Previous works on FA electrooxidation were either on a laboratory scale [1,2] or with analytical purposes [3,4]. The present work, in contrast, reports a pilot scale experimental unit for the electrochemical treatment of aqueous effluents containing formaldehyde.…”

“…Electrochemical technology has been considered as a tool for controlling formaldehyde (FA) concentration in aqueous media [1][2][3][4]. The performance of DSA type oxide anodes has been tested for the electrooxidation of organic pollutants in aqueous media, markedly in the potential region in which oxygen evolution occurs as a simultaneous process [5,6].…”

“…The performance of DSA type oxide anodes has been tested for the electrooxidation of organic pollutants in aqueous media, markedly in the potential region in which oxygen evolution occurs as a simultaneous process [5,6]. TiO 2 based RuO 2 or IrO 2 electrodes have been used for the electrooxidation of FA and a (TiO 2 ) 0.7 (RuO 2 ) 0.3 anode composition has exhibited higher FA and formic acid oxidation rates when compared to an IrO 2 containing electrode [1,2]. Low electrochemical activity of IrO 2 electrodes for FA oxidation has also been observed during cyclic voltammetry and electrochemical impedance spectroscopy experiments [3].…”

“…SnO 2 supported on Ti has been used as electrode for the oxidation of FA with a significant electro-catalytic activity [4]. By adding PbO 2 to TiO 2 /RuO 2 oxide anodes, combustion reaction of organics is favored [1]. Combustion reaction of organics is more likely to occur on SnO 2 and PbO 2 , while on RuO 2 or IrO 2 based anodes a selective oxidation process takes place [5,6].…”

“…Formaldehyde was chosen for this work because this organic molecule has been used as a model compound for the electrochemical oxidation of small organic molecules [1][2][3][4]. FA enters waterways via waste streams from hospitals and mortuaries.…”