TY - JOUR
T1 - Factors affecting the Faradaic efficiency of Fe(0) electrocoagulation
AU - van Genuchten, C.M.
AU - Dalby, K.N.
AU - Ceccato, M.
AU - Stipp, S.L.S.
AU - Dideriksen, K.
N1 - Funding Information:
We gratefully acknowledge funding provided by a NWO Veni Grant (Project No. 14400) awarded to CMvG for the planning and execution of experiments, data analysis, and preparation of the article. We thank Henrik Jensen (Department of Pharmacy, University of Copenhagen) for providing access to electrochemical equipment and for useful discussions along the various stages of this work.
Publisher Copyright:
© 2017 The Authors.
PY - 2017/10
Y1 - 2017/10
N2 - Electrocoagulation (EC) using Fe(0) electrodes is a low cost water treatment technology that relies on efficient production of Fe(II) from the electrolytic dissolution of Fe(0) electrodes (i.e. a high Faradaic efficiency). However, the (electro)chemical factors that favor Fe(0) oxidation rather than O2 evolution during Fe(0) EC have not been identified. In this study, we combined electrochemical methods, electron microscopy and Fe measurements to systematically examine the interdependent effects of current density (i), anodic interface potential (EA) and solution chemistry on the Faradaic efficiency. We found that Fe(0) oxidation was favored (Faradaic efficiency >0.85) in chloride and bromide solutions at all i, whereas carbonate, phosphate, citrate, and nitrate solutions lead to Faradaic efficiencies <0.1. The anodic reaction (i.e. Fe(0) oxidation or O2 evolution) only depended on i in the sulfate and formate solutions. Experiments in binary-anion solutions revealed that molar ratios of [HCO3-]/[Cl-] near 100 and [NO3-]/[Cl-] near 20 separated the electrochemical domains of Fe(0) oxidation and O2 evolution in the EC system. These molar ratios were supported by experiments in synthetic groundwater solutions. We also found that the EA vs i curves for solutions with poor Faradaic efficiency overlapped but were situated 2-4 V vs Ag/AgCl higher than those of solutions with high Faradaic efficiency. Therefore, the position of the EA vs i curve, rather than the EA alone, can be used to determine unambiguously the reaction occurring on the Fe(0) anode during EC treatment.Graphical abstract
AB - Electrocoagulation (EC) using Fe(0) electrodes is a low cost water treatment technology that relies on efficient production of Fe(II) from the electrolytic dissolution of Fe(0) electrodes (i.e. a high Faradaic efficiency). However, the (electro)chemical factors that favor Fe(0) oxidation rather than O2 evolution during Fe(0) EC have not been identified. In this study, we combined electrochemical methods, electron microscopy and Fe measurements to systematically examine the interdependent effects of current density (i), anodic interface potential (EA) and solution chemistry on the Faradaic efficiency. We found that Fe(0) oxidation was favored (Faradaic efficiency >0.85) in chloride and bromide solutions at all i, whereas carbonate, phosphate, citrate, and nitrate solutions lead to Faradaic efficiencies <0.1. The anodic reaction (i.e. Fe(0) oxidation or O2 evolution) only depended on i in the sulfate and formate solutions. Experiments in binary-anion solutions revealed that molar ratios of [HCO3-]/[Cl-] near 100 and [NO3-]/[Cl-] near 20 separated the electrochemical domains of Fe(0) oxidation and O2 evolution in the EC system. These molar ratios were supported by experiments in synthetic groundwater solutions. We also found that the EA vs i curves for solutions with poor Faradaic efficiency overlapped but were situated 2-4 V vs Ag/AgCl higher than those of solutions with high Faradaic efficiency. Therefore, the position of the EA vs i curve, rather than the EA alone, can be used to determine unambiguously the reaction occurring on the Fe(0) anode during EC treatment.Graphical abstract
KW - Abbreviations Fe(0) EC Fe(0)electrocoagulation
KW - E anodic interface potential
KW - Fe experimental Fe concentration
KW - Fe theoretical Fe concentration
KW - i current density
KW - NO-GW nitrate contaminated groundwater
KW - SBGW synthetic Bangladesh groundwater
UR - http://www.scopus.com/inward/record.url?scp=85029673057&partnerID=8YFLogxK
U2 - 10.1016/j.jece.2017.09.008
DO - 10.1016/j.jece.2017.09.008
M3 - Article
AN - SCOPUS:85029673057
SN - 2213-3437
VL - 5
SP - 4958
EP - 4968
JO - Journal of Environmental Chemical Engineering
JF - Journal of Environmental Chemical Engineering
IS - 5
ER -