Electrochimica Acta 94 (2013) 259–268 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Modeling analysis of electrode fouling during electrolysis of phenolic compounds Xiaoyun Yang, Jeffrey Kirsch, Jeffrey Fergus, Aleksandr Simonian ∗ Materials Research and Education Center, Mechanical Engineering Department, Auburn University, Auburn, AL, USA a r t i c l e i n f o Article history: Received 6 December 2012 Received in revised form 30 December 2012 Accepted 3 January 2013 Available online 10 January 2013 Keywords: Electrode fouling Phenolic compounds Potential drop Modeling analysis Potential–current relationship a b s t r a c t During the electrochemical analysis or disposal of most of phenolic compounds, insulated polymeric substrates are created and cover the electrode surface. This can cause the signal current to decay over time, which is called electrode fouling or electrode passivation. This paper describes a model based on the potential drop across the fouling layer that is helpful for deeper understanding of the mechanism of electrode fouling/passivation. Copper deposition and a controlled fouling process were used to verify this model and quantitatively determine the potential drop. This model successfully fitted the experimental data and describes how fouling can occur. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Phenolic compounds, such as phenol and cresol, have great importance in industry and are chemical pollutants widely present in the atmosphere, water systems, and many food products [1–5]. These compounds appear and can be introduced into the envi- ronment through wastewaters or other missions, include coal conversion, petroleum refining, pharmaceuticals, production of dyes, pesticides, surfactants, resins, and plastics [6–9]. Phenolic compounds are also found in the smoke of cigarettes [9,10]. They can be easily absorbed by animals and humans through the skin and mucous membranes, affect many organs, such as primarily lungs, liver, kidneys, and genitourinary system [11,12], and are also toxic to plants [11]. Many of them are known for persistence in environment, reacting with chlorine during water treatment, and biomagnifications [6,13–16]. For example, chlorinated phenols (CPs), nitro-phenols (NPs) and amino-phenols (APs) present widely in the atmosphere wastewater, rivers, ground water, and pesticide treated soil [17–20]. They are highly toxic and belong to prior- ity pollutants classified by the Environmental Protection Agency (EPA) [21]. The limit of p-nitrophenol set by European Commis- sion is 0.1 ppb in drinking water [22,23]. The accumulation in fish and other organisms increase their hazardous characteristics [17]. Cresol is another environmental pollutant. Moreover, its deriva- tive tricresyl phosphate (TCP) is used widely in jet engine oils and ∗ Corresponding author. Tel.: +1 334 844 4485; fax: +1 334 844 3400. E-mail addresses: simonal@auburn.edu, als@eng.auburn.edu (A. Simonian). has high potential to contaminate the aircraft cabin. TCP has been detected with electrochemical sensors incorporated with hydroly- sis to cresol [24–28]. Therefore, the reliable and effective determination and disposal of phenolic compounds are very important and has long been of interest [1,2]. Many technologies have been used for determination of phenolic compounds, such as gas and liquid chromatography [29–32], mass spectrometry [22,33], and calorimetry [34]. How- ever, they suffer from long sampling time, low sensitivity, need of preconcentration, need of skilled operator, or high cost [9]. Electro- chemical sensing provides an alternative technique for analysis or disposal since most phenolic compounds can be easily oxidized in an electrochemical cell [2], but, electrode fouling (electrode passiv- ation) can degrade the sensor signal. Similar phenomena occur in other electrochemical applications, such as batteries, where pheno- lic compounds are electrochemically oxidized [35–42], especially with high concentrations [2] and for the usage of solid electrodes, such as Pt, Au, Ag, Cu, Zn, Fe, Ni, Cr, Ti, and glassy carbon electrodes [36,37,43–46]. Electrode fouling in an amperometric chemical sensor leads to the decay of current during repetitive scans, continuous flow, or injections of samples, and is often caused by the formation of a passivating polymeric film on the electrode surface due to the elec- tropolymerization of phenolic compounds [35,36,47,48]. In some cases, this polymeric film can act as a protective coating, such as preventing metals from corroding [35,36,39,49–53]. However, the fouling is often a problem in electrochemical measurements and delays important electrode processes [35,36]. For example, it leads to a slow reaction rates during the treatment of wastewater [54,55] 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.01.019