Raghuram Chetty

The present study reports an energy efficient electrochemical strategy to remediate hexavalent chromium Cr(VI) to less toxic Cr(III). The novelty in this system is the use of titania nanotubes (TNT) synthesized by anodization as cathode for the reduction of Cr(VI) with alkaline urea as an anolyte additive. The electrochemical reduction of Cr(VI) was evaluated using bare Ti and porous TNT/Ti cathodes, both with and without urea as an anolyte additive. The experimental results showed that the dual combination of alkaline urea oxidation at anode and acidic Cr(VI) reduction on TNT cathode showed the best performance, with enhanced degradation efficiency up to 97% at 5 V within 15 min for an initial concentration of 100 mg L−1 Cr. The optimized urea-TNT combination was evaluated for the effect of catholyte pH, temperature, initial metal ion concentration and the effect of other anions, such as Cl−, NO3−, PO42− and CO32−, which are commonly present in wastewater discharged from tannery or electroplating industries. Furthermore, the performance when evaluated with cow urine as an anolyte additive confirmed that the dual combination could be a promising in-situ treatment technique for simultaneous urine oxidation and Cr(VI) reduction.

The product distribution of electrochemical reduction of CO2 can be altered by modifying the surface of pure copper by deposition. In this study, chronoamperometric deposition of Cu on Cu (Cu/Cu) was carried out at two different CuSO4 bath concentrations, 0.25 M (high) and 0.025 M (low), termed as Cu/Cu-H and Cu/Cu-L respectively. These deposits were characterized by X-ray diffraction and they vary in their crystal orientation. Pure Cu and Cu/Cu were aligned towards (1 1 1) and (2 2 0) plane with a texture coefficient of 1.2 and 1.7, respectively. Electrodeposited electrodes were tested for the electrochemical reduction of CO2 in KCl electrolyte and the results were compared with that of pure Cu electrode. Electrochemical reduction of CO2 showed methane and ethane, with hydrogen as the byproduct. The product distribution varied with the crystal orientation of Cu electrodes. The maximum Faradaic efficiency of methane was 26% obtained on pure Cu electrode with (1 1 1) and (2 0 0) orientation, whereas Cu/Cu-L with dominating (2 2 0) orientation showed a maximum formation of ethane with Faradaic efficiency of 43%. A possible mechanism of product formation on Cu towards C1 and Cu/Cu towards C2 is also discussed.

In this chapter, preliminary discussion on the need for mitigation of greenhouse gas emissions in today’s scenario is emphasized, followed by the foundation to the conversion of CO2 into useful chemicals. Various techniques employed for CO2 sequestration are introduced, and in the midst of these approaches, electrochemical reduction of CO2 is emphasized, owing to its advantages in product selectivity, operation at ambient conditions without supplementary chemical requirements, environmental compatibility, relatively simple modularity and quick scalability. Different types of catalysts reported in the literature for activating and reducing CO2 are critically analysed. To start with, metallic electrodes in aqueous solutions and nanoporous materials are discussed. The reaction mechanism and effect of supporting electrolytes, pressure, and temperature are summarized. Combination of various techniques such as bio-electrochemical reduction and photocatalytic technologies have been accentuated. Furthermore, limitations and outlook of electrochemical reduction of CO2 are presented, in which development of modules similar to that of commercially available H2O electrolysers could pave the way for commercialization of electrocatalytic reduction of CO2.