Thi Xuan Huong Le

A highly active based graphene cathode for the electro-fenton reaction

Reduced Graphene Oxide (rGO) was coated on Carbon Felt (CF) in order to design a novel cathode applied in the Electro-Fenton (EF) reaction for decontamination of wastewater polluted with Persistent Organic Pollutants (POPs). The new cathode was fabricated by an electrophoretic deposition of Graphene Oxide (GO) followed by its electrochemical reduction at a current density of −1.5 mA cm−2 for 10 min. The modified electrode and GO were characterized by SEM, AFM, XRD and XPS, showing the presence of rGO after optimization of the electrochemical conditions of synthesis. Electrode modification has improved the CF electrochemical properties as proved by the decrease of the charge-transfer resistance (Rct) determined by electrochemical impedance spectroscopy (EIS) and the increase of the CV response (2.5 times) of the FeIII/FeII couple used as a redox probe. Degradation of Acid Orange 7 (AO7), a model pollutant molecule, was monitored by UV-Vis spectrophotometry at the selected single wavelength λ = 485 nm. The results show that the degradation kinetics were 2 times higher on the graphene modified cathode compared to raw carbon felt proving the efficiency of this modification process.

A hierarchical CoFe-layered double hydroxide modified carbon-felt cathode for heterogeneous electro-Fenton process

Hierarchical CoFe-layered double hydroxide (CoFe–LDH) was grown on carbon felt (CF) as a heterogeneous catalyst by in situ solvothermal growth. The CoFe–LDH/CF serves as a cathode as well as a Fe2+ (catalyst) source in the electro-Fenton (EF) process. A combined structural and electrochemical characterization revealed highly ordered and well crystallized CoFe–LDH anisotropically grown on a CF substrate with highly dense urchin-like structures that were highly stable at circumneutral pH. EF experiments with the CoFe–LDH/CF cathode showed excellent mineralization of Acid Orange II (AO7) over a wide pH range (2–7.1). The mineralization of AO7 with CoFe–LDH/CF was by both homogeneous and surface-catalyzed processes at low acidic pH, whereas only the surface-catalyzed process occurs at circumneutral pH due to the stability of the LDH as well as precipitation of the catalyst. Higher mineralization was achieved with CoFe–LDH/CF compared to homogeneous EF with raw CF using the Fe2+/Co2+ catalyst at all pH values studied and the TOC removal with the CoFe–LDH/CF cathode was at least 1.7 and 3.5 times higher than that with the homogeneous system with Fe2+/Co2+ at pH 5.83 and 7.1, respectively. The enhanced performance observed with CoFe–LDH/CF was ascribed to (i) the surface-catalyzed reaction occurring at the surface of the cathode which can expand the working pH window, avoiding the precipitation of iron sludge as pH increases, (ii) enhanced generation of H2O2 due to the improved electroactive surface area of the cathode and (iii) the co-catalyst effect of the Co2+ in the LDH that can promote regeneration and additional production of Fe2+ and the hydroxyl radical, respectively. The CoFe–LDH/CF cathode exhibited relatively good reusability as the TOC removal after 2 h was still above 60% after 7 cycles of degradation, indicating that the prepared CoFe–LDH/CF is a promising cathode for the removal of organic pollutants by EF technology.

Design of a novel fuel cell-Fenton system: a smart approach to zero energy depollution

A model azo dye pollutant, Acid Orange 7 (AO7), was removed efficiently from an aqueous medium by a smart eco-friendly Fuel Cell-Fenton (FC-Fenton) system without any external power supply. In this approach, AO7 was degraded by an electro-Fenton process at a designed cathode (Carbon Felt (CF)/porous Carbon (pC)) supplied by direct clean electrical energy from abiotic glucose oxidation at a CF/gold anode (CF@Au). The highly active cathode was fabricated by an attractive route combining Atomic Layer Deposition (ALD) of ZnO on commercial carbon felts (CFs) followed by subsequent solvothermal conversion of the metal oxide to a metal organic framework (here ZIF-8). The as-prepared composite material was further calcined at high temperature under a controlled atmosphere. A pC-based support with high specific surface area and nitrogen as a dopant was thus obtained, enhancing both conductivity and electrocatalytic properties toward H2O2 production from oxygen reduction. Degradation kinetics of AO7 (0.1 mM initial concentration) at the CF@pC cathode was monitored by UV-vis spectrophotometry and High-Performance Liquid Chromatography (HPLC) to prove the efficiency of the composite material for the degradation of such a bio-refractory model molecule. Benefitting from the H2O2 production rate (9.2 mg L−1 h−1) by the pC layer, AO7 (35.0 mg L−1) was degraded by the electro-Fenton process in acidic medium (pH = 3) with removal efficiency reaching 90% in 10 h. The durability of the system was extended for more than 2 months with an average power output of 170 mW m−2, confirming this abiotic FC-Fenton system as a promising, green, future technology for both environmental and energy-related areas, including membrane-coupled reactor systems.

Surfactant- and Binder-Free Hierarchical Platinum Nanoarrays Directly Grown onto a Carbon Felt Electrode for Efficient Electrocatalysis

The future of fuel cells that convert chemical energy to electricity relies mostly on the efficiency of oxygen reduction reaction (ORR) due to its sluggish kinetics. By effectively bypassing the use of organic surfactants, the postsynthesis steps for immobilization onto electrodes, catalytic ink preparation using binders, and the common problem of nanoparticles (NPs) detachment from the supports involved in traditional methodologies, we demonstrate a versatile electrodeposition method for growing anisotropic microstructures directly onto a three-dimensional (3D) carbon felt electrode, using platinum NPs as the elementary building blocks. The as-synthesized materials were extensively characterized by integrating methods of physical (thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, inductively coupled plasma, and X-ray photoelectron spectroscopy) and electroanalytical (voltammetry, electrochemical impedance spectrometry) chemistry to examine the intricate relationship of material-to-performance and select the best-performing electrocatalyst to be applied in the model reaction of ORR for its practical integration into a microbial fuel cell (MFC). A tightly optimized procedure enables decorating an electrochemically activated carbon felt electrode by 40-60 nm ultrathin 3D-interconnected platinum nanoarrays leading to a hierarchical framework of ca. 500 nm. Half-cell reactions reveal that the highly rough metallic surface exhibits improved activity and stability toward ORR (Eonset ∼ 1.1 V vs reversible hydrogen electrode, p(HO2-) < 0.1%) and the hydrogen evolution reaction (-10 mA cm-2 for only 75 mV overpotential). Owing to its unique features, the developed material showed distinguished performance as an air-breathing cathode in a garden compost MFC, exhibiting better current and faster power generation than those of its equivalent classical double chamber. The enhanced performance of the material obtained herein is explained by the absence of any organic surfactants on the surface of the nanoarrays, the good metal-support interaction, particular morphology of the nanoarrays, and the reduced aggregation/detachment of particles. It promises a radical improvement in current surface reactions and paves a new way toward electrodes with regulated surface roughness, allowing for their successful application in heterogeneous catalysis.

Advances in Carbon Felt Material for Electro-Fenton Process

In electro-Fenton process, carbon-based materials, particularly 3D carbon felt, are the best choices for the cathodic electrodes because of several advantages such as low cost, excellent electrolytic efficiency, high surface area, and porosity. In this chapter, various aspects of this material are discussed in detail. This chapter is divided into three main sections, including (1) characterization of carbon felt (CF), (2) modification of CF, and (3) application of CF in electro-Fenton (EF) process to remove biorefractory pollutants. First of all, the typical characteristics of CF such as morphology, porosity, and conductivity are discussed. Next, in the modification section, we introduce different methods to improve the performance of CF. We especially focus on the surface area and electrochemical activity toward electrodes applications. Finally, both modified and non-modified CF is used as cathode materials for EF systems like homogeneous, heterogeneous, hybrid, or pilot-scale types.