Indirect Electrooxidation of Organic Substrates by Hydrogen Peroxide Generated in an Oxygen Gas-Diffusion Electrode

Electro-Fenton Process and Related Electrochemical Technologies Based on Fenton’s Reaction Chemistry

“…More recently, the same group explored the possibility of electrogenerating H 2 O 2 in seawater for disinfection using the membrane cell of Figure 7a with the O 2 -diffusion cathode. 139 Other authors 108,[140][141][142][143][144][145] have also reported the excellent performance of GDEs for H 2 O 2 electrogeneration in different three-and two-electrode systems. For example, Agladze et al 108 obtained current efficiencies up to 98-100% by recirculating 5 L of 0.05 M Na 2 SO 4 at pH 3.0-13.0 and 25-60 °C as the catholyte through a flow plant with a twoelectrode filter-press cell containing a heterogeneous MK-40 type proton-exchange membrane, a 100 cm 2 DSA anode, and a 100 cm 2 carbon-PTFE cathode fed with an O 2 or air flow rate of 30 g h -1 operating at 3 A and a liquid flow rate of 360 L h -1 for 60 min (see Table 2).…”

Electrochemical wastewater treatment with carbon nanotube filters coupled with in situ generated H2O2

“…The titanium cathode had a total surface area less than 15 cm 2 (current density of 0.05-0.50 mA cm −2 ), while the CNT cathode had a surface area around 5000 cm 2 (current density of 0.001-0.010 mA cm −2 ). 35,36 The initial increase of H 2 O 2 flux between −0.1 V and −0.4 V (vs. Ag/AgCl) was due to the enhanced kinetics, as indicated by the Butler-Volmer equation 37 for the reduction of oxygen to produce H 2 O 2 (eqn (1)). The increased surface area of the CNT cathode increased the fraction of potential going towards the cathodes for O 2 reduction, 33 and greatly reduced resistance to electron transfer, resulting in increased current efficiency, H 2 O 2 flux, and phenol removal kinetics.…”

“…34 The results also demonstrated that H 2 O 2 flux was related to the cathode potential, and the maximum H 2 O 2 flux was observed at −0.4 V (vs. Ag/AgCl), which was consistent with previous results in a batch system. 35,36 The initial increase of H 2 O 2 flux between −0.1 V and −0.4 V (vs. Ag/AgCl) was due to the enhanced kinetics, as indicated by the Butler-Volmer equation 37 for the reduction of oxygen to produce H 2 O 2 (eqn (1)). When the cathode potential was below −0.4 V (vs. Ag/ AgCl), H 2 O 2 flux gradually dropped because of side reactions, e.g., H 2 O 2 was decomposed to O 2 (eqn ( 2), E = +0.49 V vs. Ag/ AgCl at pH 6.46), O 2 was reduced to water (eqn ( 3), E = +0.62 V vs. Ag/AgCl at pH 6.46) and H 2 O 2 was directly reduced to H 2 O (eqn ( 4), E = +1.15 V vs. Ag/AgCl at pH 6.46).…”

Study on superoxide and hydroxyl radicals generated in indirect electrochemical oxidation by chemiluminescence and UV-Visible spectra

“…Superoxide anion and the hydroperoxide ion (HO 2 − ), the conjugated base of hydrogen peroxide (pKa = 11.62 at 25°C), may reach the anode and undergo a reverse reaction of 6, 8, and 9 on the cathode in an undivided cell, which consumes a lot of energy and greatly decreases the electrolysis efficiency, as the superoxide anion and hydroperoxide ion also compete with the organics for anodic reactions (Brillas et al, 2003;Kornienko et al, 2004). To avoid this disadvantage, many types of diaphragms, such as, glass frit (Do and Yeh, 1996;Harrington and Pletcher, 1999) and cationic exchange member (Kornienko et al, 2004), were used to separate two-chamber electrolysis reactors, which could reduce the degradation time and increase the total current efficiency.…”

“…To avoid this disadvantage, many types of diaphragms, such as, glass frit (Do and Yeh, 1996;Harrington and Pletcher, 1999) and cationic exchange member (Kornienko et al, 2004), were used to separate two-chamber electrolysis reactors, which could reduce the degradation time and increase the total current efficiency.…”