Carbonate-Mediated Fe(II) Oxidation in the Air-Cathode Fuel Cell: A Kinetic Model in Terms of Fe(II) Speciation

Abstract

Due to the high redox activity of Fe(II) and its abundance in natural waters, the electro-oxidation of Fe(II) can be found in many air-cathode fuel cell systems, such as acid mine drainage fuel cells and sediment microbial fuel cells. To deeply understand these iron-related systems, it is essential to elucidate the kinetics and mechanisms involved in the electro-oxidation of Fe(II). This work aims to develop a kinetic model that adequately describes the electro-oxidation process of Fe(II) in air-cathode fuel cells. The speciation of Fe(II) is incorporated into the model, and contributions of individual Fe(II) species to the overall Fe(II) oxidation rate are quantitatively evaluated. The results show that the kinetic model can accurately predict the electro-oxidation rate of Fe(II) in air-cathode fuel cells. FeCO3, Fe(OH)2, and Fe(CO3)2(2-) are the most important species determining the electro-oxidation kinetics of Fe(II). The Fe(II) oxidation rate is primarily controlled by the oxidation of FeCO3 species at low pH, whereas at high pH Fe(OH)2 and Fe(CO3)2(2-) are the dominant species. Solution pH, carbonate concentration, and solution salinity are able to influence the electro-oxidation kinetics of Fe(II) through changing both distribution and kinetic activity of Fe(II) species.

Electricity generation and recovery of iron hydroxides using a single chamber fuel cell with iron anode and air-cathode for electrocoagulation

“…In these cells, the ferrous ions are oxidized to iron hydroxide at the anode surface, while oxygen is reduced at the cathode. Based on this study by Logan's research group [30], a few other studies on air cathode fuel cells for treating ferrous iron have recently been conducted [31][32][33][34].…”

Understanding the Catalyst Regeneration Kinetics in the Chelated Iron Dehydrosulfurization Process: A Model in Terms of Fe(II) Speciation

“…The oxidation of Fe(II) is composed of several parallel reactions in which the individual Fe(II) species is oxidized at different rates. As shown in Figure 10,13,15,18,19 The Fe(OH) 2 0 and Fe(OH) + species are also neglected from eq 4 owing to their low concentrations. As a result, eq 4 is reduced to eqs 9 and 10 for the Fe(II)-EDTA and Fe(II)-NTA systems, respectively.…”

In Situ Fabrication of Electro-Fenton Catalyst from Fe2+ in Acid Mine Drainage: Influence of Coexisting Metal Cations

“…The NaCl was used as the electrolyte to ensure solution conductivity, and the NaHCO 3 was amended as a pH buffer to accelerate the electro-oxidation of Fe 2+ . 7,15 The CoCl 2 , MnCl 2 , NiCl 2 , CuCl 2 , AlCl 3 , and ZnCl 2 were, individually or in combination, added as coexisting metal cations. The concentration of coexisting metal cations in synthetic AMDs was 0.7 or 7.0 mM according to their relative concentrations to Fe 2+ in real AMDs.…”

“…The basic composition of synthetic AMDs consisted of 200 mM NaCl, 50 mM NaHCO 3 , and 7.0 mM FeCl 2 . The NaCl was used as the electrolyte to ensure solution conductivity, and the NaHCO 3 was amended as a pH buffer to accelerate the electro-oxidation of Fe 2+ . , The CoCl 2 , MnCl 2 , NiCl 2 , CuCl 2 , AlCl 3 , and ZnCl 2 were, individually or in combination, added as coexisting metal cations. The concentration of coexisting metal cations in synthetic AMDs was 0.7 or 7.0 mM according to their relative concentrations to Fe 2+ in real AMDs. − To prepare the synthetic AMD, the anodic chamber of AC-FC was first filled with 150 mL of NaCl and purged with a mixture of nitrogen and carbon dioxide to remove dissolved O 2 .…”