Engineering Palladium-Copper Bimetals for Enhanced Electrochemical Nitrate Reduction to Nitrogen and Ammonia

Nitrate (NO−3 ) 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 NO−3 remediation; however, is one emerging approach for nitrate removal which does not produce waste as NO−3 is converted directly to inert dinitrogen (N2) gas. The main challenge with electrocatalytic NO−3 reduction is the low activity and selectivity of the NO−3 to N2. The production of equally harmful contaminant intermediate species such as nitrite (NO−2 ) and ammonium (NH+4 ), has limited the applicability of electrochemical routes for nitrate remediation. Here, we propose to investigate the electrocatalytic properties of palladium (Pd) which contains structured surfaces. The primary aim is to identify which facets are highly active and selective for nitrate and nitrite reduction. We first develop Pd shape-controlled nanoparticles (e.g. nanocubes, cuboctahedrons, octahedrons, concave nanocubes) and demonstrate the electrocatalytic activity of each shape-controlled nanoparticle for nitrate and nitrite reduction in alkaline electrolyte through the use of rotating ring disk electrode (RRDE) experiments. To achieve higher activity and selectivity for the denitrification, we introduce a copper (Cu) metal as a secondary metal on the surface of Pd nanocube by using the underpotential deposition (UPD) and solvothermal methods. The electrochemically deposited and doped Cu atoms promote the reduction of NO−3 to NO−2 (rate determining step), and Pd (100) facet catalyzes the reduction of NO−2 to N2. We can control the surface coverage of Cu by sweeping to various different potentials located within the UPD desorption area. RRDE experiments demonstrate an improvement in nitrate reduction activity (Cu submonoloayer on Pd nanocube/C > Pd nanocube/C > Commercial Pd/C) using shape-controlled Pd that contain surface modifications. Electrocatalytic nitrate/nitrite reductions is an important avenue to mitigate environmental impacts associated with removing harmful NO−3 and NO−2 from water. However, before electrochemical technologies can emerge as a viable solutions, there is a need for fundamental studies which expose the active surfaces for both NO−3 and NO−2 reduction.

Date

2022-02-09

Resource Type

Text

Resource Subtype

Dissertation

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