# Studies on the Electrochemical Behavior of Sulfite on Incoloy 800 in a Neutral Environment
## 1 Introduction  
Sulfur dioxide is produced as waste in a variety of industrial processes, with most of it resulting from the burning of fossil fuels, particularly solid fuels, for which no desulfurization technique is used [1, 2]. Moreover, the metallurgical industry is a significantsource of sulfur dioxide pollution [3,4]. It is generally understood that sulfur dioxide emissions into the atmosphere endanger forest ecosystems, agricultural crops, and human health [5, 6, 7]. The consequences of acid rain are also well known, owing to the presence of sulfur dioxide in the environment [8, 9, 10]. These barriers enforced strict controls on sulfur dioxide. emissions, particularly in nations where coal burning accounts for a large portion of energy production: China, the United States, and Australia [11, 12, 13]. At the same time, methods for extracting sulfur dioxide from flue gases and converting it to sulfites [14, 15, 16] have been developed. Unfortunately, sulfites are powerful reducing chemicals that cannot be eliminated from the environment due to their harmful impacts on flora and wildlife [17]. This necessitates the oxidation of sulfites to sulfates, which may then be removed into the environment within the limitations set by regulation [18]. Given the abundance of leftover sulfites, research has focused on using them to produce various types of energy. The Latimer diagrams [19] and Frost diagrams [20] show that anodic oxidation of sulfites, which are generated as waste in numerous industrial processes, is one of the easiest techniques of converting them to sulfates [21]. As a result, sulfites can be utilized both as anodic depolarizers in water electrolysis to produce hydrogen and as reducers in sulfite/oxygen fuel cells [22, 23, 24]. According to the sulfur dioxide/hydrogen sulfite/sulfite balance diagram, the species present in aqueous solutions at neutral pH are hydrogen sulfite (HSO\({}_{3}\)\({}^{-}\)) and sulfite (SO\({}_{3}\)\({}^{2-}\)), in a molar ratio of roughly 1:1 [25]. As the pH of the solution rises, so does the concentration of sulfite ions, until at a pH of 9 or higher, the solution contains almost exclusively sulfite species. The proposed mechanisms for the anodic oxidation processes of the SO\({}_{2}\)/HSO\({}_{3}\)\({}^{-}\)/SO\({}_{3}\)\({}^{2-}\) chemical species are divided into two types: direct oxidation on the electrode surface via electron transfer from the chemical substrate to the electronic conductor, and indirect oxidation via an intermediate generated at the electrode. An anodic electron transfer from the chemical species SO\({}_{2}\)/HSO\({}_{3}\)\({}^{-}\)/SO\({}_{3}\)\({}^{2-}\) straight to the pure metal is uncommon because during anodic polarization in aqueous electrolyte solutions, the metals' surfaces are often coated with oxide or adsorbed oxygen [26]. As a result, the first investigations of anodic oxidation of the chemical species SO\({}_{2}\)/HSO\({}_{3}\)\({}^{-}\)/SO\({}_{3}\)\({}^{2-}\) were conducted on platinum, where the oxide layer generated during anodic polarization is very thin and is absorbed with a monomolecular layer of adsorbed atomic oxygen [27]. The findings lead to the proposal of two potential mechanisms [4]. The first process includes the oxidation of sulfite. to sulfate via two sequential electron transfer stages (1) and (2). \[\text{SO}_{3}\text{${}^{2-}$}\rightarrow\text{${}^{\bullet}$SO}_{3}\text{${} ^{-}$}+\text{e}\text{${}^{-}$} \tag{1}\]  
\[\text{${}^{\bullet}$SO}_{3}\text{${}^{-}$}+2\text{OH${}^{-}$}\rightarrow \text{SO}_{4}\text{${}^{2-}$}+\text{H}_{2}\text{O}+\text{e${}^{-}$} \tag{2}\]  
The second interpretation of the process acknowledges that the sulfite radicals created in the transfer reaction (1) dimerize with the creation of dithionate (3), which then disproportionate to sulfate and sulfite (4).