Electronic Control of Traditional Iron–Carbon Electrodes to Regulate the Oxygen Reduction Route to Scale Up Water Purification

Abstract

Shifting four-electron (4e–) oxygen reduction in fuel cell technology to a two-electron (2e–) pathway with traditional iron–carbon electrodes is a critical step for hydroxyl radical (HO•) generation. Here, we fabricated iron–carbon aerogels with desired dimensions (e.g., 40 cm × 40 cm) as working electrodes containing atomic Fe sites and Fe3C subnanoclusters. Electron-donating Fe3C provides electrons to FeN4 through long-range activation for achieving the ideal electronic configuration, thereby optimizing the binding energy of the *OOH intermediate. With an iron–carbon aerogel benefiting from finely tuned electronic density, the selectivity of 2e– oxygen reduction increased from 10 to 90%. The resultant electrode exhibited unexpectedly efficient HO• production and fast elimination of organics. Notably, the kinetic constant k M for sulfamethoxazole (SMX) removal is 60 times higher than that in a traditional iron–carbon electrode. A flow-through pilot device with the iron–carbon aerogel (SA-Fe0.4NCA) was built to scale up micropolluted water decontamination. The initial total organic carbon (TOC) value of micropolluted water was 4.02 mg L–1, and it declined and maintained at 2.14 mg L–1, meeting the standards for drinking water quality in China. Meanwhile, the generation of emerging aromatic nitrogenous disinfection byproducts (chlorophenylacetonitriles) declined by 99.2%, satisfying the public safety of domestic water. This work provides guidance for developing electrochemical technologies to satisfy the flexible and economic demand for water purification, especially in water-scarce areas.

Controllable Generation of Sulfate and Hydroxyl Radicals to Efficiently Degrade Perfluorooctanoic Acid in Cathode-Dominated Electrochemical Process

“…Previous work has indicated that the introduction of iron would favor the competitive 4e − oxygen reduction to H 2 O. 31 According to the experimental results of RRDE measurements (Figure 2b), the increased Fe content in the cathode reduced the H 2 O 2 selectivity. Although the presence of Fe can act as Fenton catalyst to decompose the generated H 2 O 2 into HO • , it is very hard to quantify relationship between HO • and the content of Fe.…”

“…The iron−nickel codoped carbon aerogel (denoted FeNiC) was synthesized through sol−gel formation, solvent exchange, and pyrolysis according to a modified method that was already reported in our previous work. 31 First, resorcinol, formaldehyde, sodium carbonate, and deionized water were mixed in a certain mole ratio to form a homogeneous solution. Then quantitative iron and nickel precursors (C 15 H 21 FeO 6 and C 10 H 14 NiO 4 ) were added into the solution, which was then poured into a transparent cuboid glass with a spacing of 5 mm, followed by reaction at 30 °C, 50 °C for 1 day, and 90 °C for 3 days.…”

“…The mobile phase was methanol/water (60:40, v/v, 0.8 mL min −1 ) with a wavelength of 355 nm at 25 °C. 31 ■ RESULTS AND DISCUSSION Efficient Degradation of PFOA with Controllable HO • and SO 4…”

“…Carbonaceous electrodes have the advantages of low preparation cost, a large specific surface area, and high conductivity, which make them a promising candidate material for electrochemical activation of peroxymonosulfate (PMS) and oxygen. , SO 4 •– could be favorably cathodic, generated from PMS activation by a one-electron transfer pathway . The electron density of active transition metals existing in the cathode (i.e., iron and nickel) assists the cleavage of an intramolecular peroxide bond in PMS to produce radicals (eqs and ). − Besides, the cathodic activation of O 2 via a two-electron transfer pathway can promote the electrochemical generation of H 2 O 2 and then be catalyzed into abundant HO • by a Fenton/Fenton-like reaction (eqs and ): , M n + + H S O 5 − → M false( n + 1 false) + + S O 4 · − + O H − M n + H S O 5 − → M false( n + 1 false) + + S O 4 2 − + O H · O 2 + 2 <...…”

“…32 The electron density of active transition metals existing in the cathode (i.e., iron and nickel) assists the cleavage of an intramolecular peroxide bond in PMS to produce radicals (eqs 1 and 2). 33−38 Besides, the cathodic activation of O 2 via a two-electron transfer pathway can promote the electrochemical generation of H 2 O 2 and then be catalyzed into abundant HO • by a Fenton/Fenton-like reaction (eqs 3 and 4): 31,39…”