Effects of hydrodynamic conditions on OH radical production at Ti/Pt anodes during electrochemical treatment

Characterization of electrodes modified with sludge-derived biochar and its performance of electrocatalytic oxidation of azo dyes

Pyrolysis of waste sludge in sewage treatment can achieve a substantial reduction in solid waste and obtain sludge-based biochars with multiple functions. However, the electrochemical properties of sludge-derived biochar as electrode modification material and the electrocatalytic ability of biochar-modified electrodes are still unclear. In this study, sludge-based biochars were prepared at various pyrolysis temperatures (400 °C, 500 °C, 600 °C, 700 °C, and 800 °C) and then were cast on glassy carbon electrodes to fabricate composite biochar-electrodes (GC400, GC500, GC600, GC700, and GC800). The results of elemental analysis and Raman spectra showed that sludge-based biochar prepared at higher temperatures exhibited higher aromaticity and degree of defect structures. And the results of cyclic voltammetry and electrochemical impedance spectra confirmed that biochar-modified electrodes prepared at higher temperatures (>600 °C) possessed better electrocatalytic activity and electrochemical stability, and their higher oxygen evolution potential than control test could improve the electrocatalytic efficiency. In the electrocatalytic oxidation of methyl orange, the removal rate with GC800 was the highest, reaching 94.49% within 240 min, and the removal rates with other composite electrodes were 90.61% (GC700) > 86.96% (GC600) > 80.32% (GC). The free radical quenching experiment revealed that the electrocatalytic degradation of methyl orange mainly depended on the indirect oxidation of hydroxyl radicals generated by electrocatalysis, accounting for 81.3% of the removal rate. The biochar-modified electrode not only greatly improved the electrocatalytic ability of the electrode for the degradation of azo dyes, but also achieved the recycling application of products after pyrolysis of sludge waste.

Romo AI, Pudar S, Putnam ST, Bustos E, Rodríguez-López J. Real-Time Detection of Hydroxyl Radical Generated at Operating Electrodes via Redox-Active Adduct Formation Using Scanning Electrochemical Microscopy

The hydroxyl radical (•OH) is one of the most attractive reactive oxygen species due to its high oxidation power and its clean (photo)(electro)generation from water, leaving no residues and creating new prospects for efficient wastewater treatment and electrosynthesis. Unfortunately, in situ detection of •OH is challenging due to its short lifetime (few ns). Using lifetime-extending spin traps, such as 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to generate the [DMPO-OH]• adduct in combination with electron spin resonance (ESR), allows unambiguous determination of its presence in solution. However, this method is cumbersome and lacks the necessary sensitivity and versatility to explore and quantify •OH generation dynamics at electrode surfaces in real time. Here, we identify that [DMPO-OH]• is redox-active with E0 = 0.85 V vs Ag|AgCl and can be conveniently detected on Au and C ultramicroelectrodes. Using scanning electrochemical microscopy (SECM), a four-electrode technique capable of collecting the freshly generated [DMPO-OH]• from near the electrode surface, we detected its generation in real time from operating electrodes. We also generated images of [DMPO-OH]• production and estimated and compared its generation efficiency at various electrodes (boron-doped diamond, tin oxide, titanium foil, glassy carbon, platinum, and lead oxide). Density functional calculations, ESR measurements, and bulk calibration using the Fenton reaction helped us unambiguously identify [DMPO-OH]• as the source of redox activity. We hope these findings will encourage the rapid, inexpensive, and quantitative detection of •OH for conducting informed explorations of its role in mediated oxidation processes at electrode surfaces for energy, environmental, and synthetic applications.

Efficacy of an electrochemical flow cell introduced into the electrochemical Fenton-type process using a Cu(I)/HOCl system

An electrochemical flow cell was introduced into the electrochemical Fenton-type process using a Cu(I)/HOCl system. The effects of the current density and the initial cupric ion (Cu²⁺) concentration on the process performance were discussed. The current efficiency of the process improved from 6.1% for an electrolytic tank system to 33% for the electrochemical flow cell system at a current density of 5.0 mA/cm² and an initial Cu²⁺ concentration of 1.0 mM. The current efficiency increased to 58% for Cu²⁺ concentrations of 2.0 mM and beyond. The cathodic reduction of Cu²⁺ to the cuprous ion (Cu⁺) emerged as the rate-determining step in comparison to the anodic production of free chlorine. The introduction of the electrochemical flow cell enhanced the cathodic production of Cu⁺ by reinforcing the mass transfer of the Cu²⁺ to the cathode, and the detachment of micro bubbles generated electrochemically at the cathode surface. A decrease in the current density and an increase in the initial Cu²⁺ concentration also improved the current efficiency by promoting the cathodic production of Cu⁺. This involved the prevention of the cathodic reduction of protons to hydrogen gas and the elevation of the electrode potential of the cathodic reaction from Cu²⁺ to Cu⁺.

Development of an electrochemical antifouling system for seawater cooling pipelines of power plants using titanium

Biofouling is the undesirable adhesion and development of microorganisms and macroorganisms in a water environment. An electrochemical antifouling system based on management of primary adhesion of microorganisms was developed employing titanium electrode for antifouling of seawater cooling pipes and marine infrastructures. The system consists of an electrochemical reaction-monitoring unit, a power control unit, and a potential/current remote monitoring and a control unit. Titanium plates and iron plates were used as the working and counter electrode, respectively. Field experiment was conducted in the seawater cooling pipeline system of a thermal power station. Four titanium electrodes with 1.0 m length and 3.0 m width were set in the seawater intake pit and current density was controlled at 50-100 mA/m(2). The electrode surface maintained clean conditions for 2 years. The average wet weight of fouling organisms on the titanium electrode surface was below 100 g/m(2) whereas the corresponding wet weight was above 10 kg/m(2) on the control surface. Using titanium as the electrode material, chlorine and hypochlorite are not generated. The developed electrochemical antifouling system provided an effective, environmentally friendly, and feasible techniques for remote operations.