Pd Shape-Controlled Nanoparticles Decorated with Metals for Electrochemical Nitrate and Nitrite Reduction

Abstract

Nitrate (NO3 -) pollution of groundwater occurs due to anthropogenic activities such as the overuse of nitrogen-rich agriculture fertilizers. Furthermore, nitrite (NO2 -) causes adverse effects on human health such as methemoglobinemia (“blue baby syndrome”) and cancer. Currently, physicochemical technologies such as reverse osmosis or ion exchange are used for nitrate removal, but these approaches are not sustainable as waste disposal of the brines remains a critical challenge (requiring the use of expensive post-treatment processes). Electrochemical NO3 - remediation; however, offers several advantages when compared to physiochemical approaches for nitrate removal as NO3 - is directly converted to harmless dinitrogen (N2) gas resulting in no waste production. The main challenge with electrochemical NO3 - reduction is the low activity and selectivity of the NO3 - to N2. The activity is limited by the rate-determining step (NO3(ads) - to NO2(ads) -), and selectivity is determined by the reduction of NO2(ads) -to N2 and/or ammonium (NH4 +).To achieve an efficient activity and selectivity for the electrochemical denitrification, we develop Pd shape-controlled nanoparticles and introduce secondary metals on the surface of Pd electrocatalysts by chemical reduction methods. The decorated metals promote the reduction of NO3 - to NO2 - (rate determining step) and the Pd facets enhances the selectivity of NO2 - to N2. Rotating ring disk electrode (RRDE) tests enabled the measurement of improved activity and selectivity of NO3 - to N2 using shape-controlled Pd that contain surface modifications (metal atoms). This study demonstrates that electrochemical nitrate reduction is an important approach to reduce environmental impacts associated with removing NO3 - from water.