(Invited) Pd Shape-Controlled Nanoparticles Decorated with Promoter Metals for Electrochemical Nitrate Reduction

Abstract

Nitrate (NO3 -) is the world’s most widespread surface and ground water contaminant that causes adverse effects on human health such as methemoglobinemia (“blue baby syndrome”) and cancer. While most nitrate removal strategies occur through the use of ion exchange resins, these approaches are not sustainable as waste disposal of the brines remains a critical challenge. Electrocatalytic NO3 - remediation; however, is one emerging approach for nitrate removal which does not produce waste as NO3 - is converted directly to inert dinitrogen (N2) gas. The main challenge with electrocatalytic NO3 - reduction is the low activity and selectivity of the NO3 - to N2 because this conversion is a rate-determining step and results in undesirable products such as nitrite (NO2 -) and ammonium (NH4 +). To achieve an efficient activity and selectivity for the denitrification, we develop Pd shape-controlled nanoparticles and introduce secondary metals by using the underpotential deposition (UPD) method. The electrochemically deposited metals mainly promote the reduction of NO3 - to NO2 - and Pd facets catalyze the reduction of NO2 - to N2. Under the metal desorption area, we can control the surface coverage of metals by sweeping stopped at selected potentials. Conducting 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 work demonstrates that electrocatalytic nitrate reduction is an important approach to reduce environmental impacts associated with removing NO3 - from water.