The oxygen reduction reaction (ORR) is an important electrode reaction for energy storage and conversion devices based on oxygen electrocatalysis. This paper introduces the thermodynamics, reaction kinetics, reaction mechanisms, and reaction pathways of ORR in aqueous alkaline media. Recent advances of the catalysts for ORR were extensively reviewed, including precious metals, nonmetal-doped carbon, carbon–transition metal hybrids, transition metal oxides with spinel and perovskite structures, and so forth. The applications of those ORR catalysts to zinc–air batteries and alkaline fuel cells were briefly introduced. A concluding remark summarizes the current status of the reaction pathways, advanced catalysts, and the future challenges of the research and development of ORR.

Oxygen Reduction in Alkaline Media: From Mechanisms to Recent Advances of Catalysts

Waste biorefinery models towards sustainable circular bioeconomy: Critical review and future perspectives

This exhaustive review focuses on the fundamental principles and applications of heterogeneous electrochemical wastewater treatment based on Fenton’s chemistry reaction. The elementary equations involved in formation of hydroxyl radical in homogeneous electro-Fenton (EF) and photo electro-Fenton (PEF) processes was presented and the advantages of using insoluble solids as heterogeneous catalyst rather than soluble iron salts (heterogeneous electro-Fenton process) (Hetero-EF) was enumerated. Some of the required features of good heterogeneous catalysts were discussed, followed by the mechanisms of catalytic activation of H2O2 to reactive oxygen species (ROS) especially hydroxyl radical ( OH) by heterogeneous catalyst in Hetero-EF system. Extensive discussion on the two configuration of Hetero-EF system vis-a-vis added solid catalysts and functionalized cathodic materials were provided along with summaries of some relevant studies that are available in literature. The solid catalysts and the functionalized cathodic materials that have been utilized in Hetero-EF wastewater treatment were grouped into different classes and brief discussion on their synthesis route were given. Besides, the use of solid catalysts and iron-functionalized cathodic materials in bioelectrochemical system (BES) especially bioelectro-Fenton technology (BEF) using microbial fuel cells (MFCs) with concurrent electricity generation for Hetero-EF treatment of biorefractory organic pollutants was discussed. In the final part, emphasis was made on the challenges and future prospects of the Hetero-EF for wastewater treatment.

Heterogeneous electro-Fenton and photoelectro-Fenton processes: A critical review of fundamental principles and application for water/wastewater treatment

Recent advances in the use of different substrates in microbial fuel cells toward wastewater treatment and simultaneous energy recovery

Several industries are using dyes as coloring agents. The effluents from these industries are increasingly becoming an environmental problem. The removal of dyes from aqueous solution has a great potential in the field of environmental engineering. This paper reviews the classification, characteristics, and problems of dyes in detail. Advantages and disadvantages of different methods used for dye removal are also analyzed. Among these methods, Fenton process-based advanced oxidation processes are an emerging prospect in the field of dye removal. Fenton processes have been classified and represented as “Fenton circle”. This paper analyzes the recent studies on Fenton processes. The studies include analyzing different configurations of reactors used for dye removal, its efficiency, and the effects of various operating parameters such as pH, catalyst concentration, H2O2 concentration, initial dye concentration, and temperature of Fenton processes. From the present study, it can be conclude that Fenton processes are very effective and environmentally friendly methods for dye removal.

Degradation of dyes from aqueous solution by Fenton processes: a review

Microbial electrochemical technologies (MET) have significant potential to negate the impending energy, and renewable feedstock crisis. METs have evolved into a sustainable and eco-friendly solutions owing to their diverse applications like microbial fuel cell (MFC), for power generation, bioelectrochemical treatment (BET) for wastewater remeduiation, microbial desalination cell (MDC) for salt removal and resource recovery, microbial electrolysis cell (MEC) for the production of Hydrogen by applying external potential and bioelectrochemical syntheis (BES) for value-added products production and other applications such as plant microbial fuel cells (P-MFC) and artificially constructed wetlands fuel cells (CW-MFC) utilize the root exudates for power generation, biosensor applications, etc. This chapter draws light upon the multifaceted application of MET and their specific operational mechanism along with their futuristic integrations and developmental models.

Microbial Electrochemical Platform: Biofactory with Diverse Applications

Sequestering of CO2 to Value-Added Products through Various Biological Processes

Carbon credit reduction: A techno-economic analysis of "drop-in" fuel production.

Impact of thirteen run-of-river hydroelectric projects on land use land cover and ecosystem services in Nepal

Eutrophication in water bodies is a pervasive water quality issue that should be remediated to restore and recover natural resources. The systematic arrangement of aquatic macrophytes in the water bodies through ecological engineering principles will treat wastewater and rejuvenate the ecosystem. In this context, a novel semi-pilot scale Hybrid Eco-Electrogenic Engineered System (HEEES) was operated using aquatic macrophytes and a bioelectrogenic system to treat domestic wastewater and generate bioenergy. Three similar tanks were used with different functionally diverse biota, viz., floating macrophytes (water hyacinth) in tank A, submerged plants (water thymes) in tank B, and emergent plants (water lettuce) in tank C. Four different experimental setups (ES) were performed by placing specific parameters such as electrodes, aerators, and activated carbon viz., ES1 (plants), ES2 (Plants + Activated Carbon), ES3 (Plants + Activated Carbon + Aerators), and ES4 (Plants + Activated Carbon + Aerators + Electrodes). The results infer that tank A with water hyacinth showed maximum COD removal efficiency of 76.90 % (ES1), 77.24 % (ES2), 80.01 % (ES3), and 81.67 % (ES4), respectively. Maximum power and current density of 24.104 mW/m2 and 23.844 mA/m2 were attained, inferring that the ES4 condition showed the maximum pollutant removal efficiency and bioenergy generation. It is attained due to specific parameters in the system that increases the electrogenic activity by electrodes, adsorbing the property of activated carbon and increasing the oxygen concentration by aeration, enhancing effective treatment and bioenergy generation in the single-chambered hybrid system. The semi-pilot scale HEEES is a self-sustained system that mimics the natural cleansing function of aquatic bio-networks. 

G. Velvizhi

Papers

Microbial Electrochemical Platform: Biofactory with Diverse Applications

Sequestering of CO2 to Value-Added Products through Various Biological Processes

Carbon credit reduction: A techno-economic analysis of "drop-in" fuel production.

Impact of thirteen run-of-river hydroelectric projects on land use land cover and ecosystem services in Nepal

Self-sustained semi-pilot scale Hybrid Eco-Electrogenic Engineered System for the wastewater treatment and bioenergy generation