Boron-doped diamond (BDD) has attracted considerable attention as an electrode material used for electrochemical disinfection of wastewater, due to its high oxygen evolution over-potential.[1], [2] This property enables the formation of highly reactive oxygen species (ROS) such as hydroxyl radicals, ozone, and hydrogen peroxide.[3]–[6] Despite the promise of BDD as a liquid disinfection electrode, there is little information in literature that details the optimal conditions for ROS generation. Effects of potential switching for inhibiting fouling of the electrode surface, evolving surface chemistry, and resultant energy efficiency in sanitizing wastewater are not widely reported. Knowledge of these conditions and their liquid disinfection properties would allow production of ROS with higher efficiency and therefore lower cost in real-world applications.

The present work investigates the generation of ROS and subsequent liquid disinfection of wastewater using as-grown boron-doped ultrananocrystalline diamond (BD-UNCD) electrodes. Static and potential switching methods of generating ROS are compared to determine their effects on liquid disinfection, chlorine generation, energy expenditure, electrode fouling, and electrode surface chemistry. These results build on an evolving understanding of the electrochemical generation of ROS from BDD electrodes.

Our results show that liquid disinfection of diluted wastewater can occur with negligible chlorination and efficient energy expenditure using potential switching methods. Comparison of potential switching to static potential methods show differences in energy expenditure, chlorination, and electrode scaling; as well as time needed for disinfection of liquid waste. It is proposed that the electrogeneration of functional groups at oxidative potentials of BD-UNCD allows for an increased current density during the successive electrolysis at reductive potentials, and that this electrogeneration correlates to an enhanced production of H₂O₂. Through potential switching, these functional groups can be stabilized and used continuously to more efficiently produce H₂O₂, and potentially other ROS, when compared to static potential methods at these same potentials by optimizing the applied potentials and duty cycle. Moreover, potential switching has been previously used to inhibit electrode fouling,[7]–[10] which is commonplace in liquid waste sanitation, and therefore offers a practical method for electrochemical disinfection of wastewater in large scale applications.

References 

[1] D. A. T. Fujishima, Akira, Y. Einaga, T. Narasinga Rao, Diamond electrochemistry. Elsevier Science, 2005.

[2] J. V. Macpherson, “A practical guide to using boron doped diamond in electrochemical research,” Phys. Chem. Chem. Phys., vol. 17, no. 5, pp. 2935–2949, 2015.

[3] J. Jeong, J. Y. Kim, and J. Yoon, “The Role of Reactive Oxygen Species in the Electrochemical Inactivation of Microorganisms,” Environ. Sci. Technol., vol. 40, no. 19, pp. 6117–6122, Oct. 2006.

[4] P. Michaud, E. Mahé, W. Haenni, and A. Perret, “Preparation of Peroxodisulfuric Acid Using Boron‐Doped Diamond Thin Film Electrodes,” Solid-State …, 2000.

[5] S. Palmas, A. Polcaro, A. Vacca, and M. Mascia, “Influence of the operating conditions on the electrochemical disinfection process of natural waters at BDD electrodes,” J. Appl., 2007.

[6] A. Fujishima, Diamond electrochemistry. 2005.

[7] M. Hupert, A. Muck, J. Wang, J. Stotter, Z. Cvackova, S. Haymond, Y. Show, and G. M. Swain, “Conductive diamond thin-films in electrochemistry,” Diam. Relat. Mater., vol. 12, no. 10–11, pp. 1940–1949, Oct. 2003.

[8] D. Shin, D. A. Tryk, A. Fujishima, A. Merkoçi, and J. Wang, “Resistance to Surfactant and Protein Fouling Effects at Conducting Diamond Electrodes,” Electroanalysis, vol. 17, no. 4, pp. 305–311, Mar. 2005.

[9] T. N. Rao and A. Fujishima, “Recent advances in electrochemistry of diamond,” Diam. Relat. Mater., vol. 9, no. 3, pp. 384–389, 2000.

[10] R. Trouillon and D. O’Hare, “Comparison of glassy carbon and boron doped diamond electrodes: Resistance to biofouling,” Electrochim. Acta, vol. 55, no. 22, pp. 6586–6595, 2010.