(490b) PtRu Alloys for the Electrocatalytic Reduction of Nitrate

High nitrate (NO₃^−) levels in water are toxic to humans and promote harmful algal blooms and dead zone formation. Electrocatalytic nitrate reduction (NO₃RR) is a promising approach to convert nitrate into value-added ammonium (NH₄⁺) or benign nitrogen (N₂) products using renewable electricity sources. However, NO₃RR requires improved electrocatalysts that are sufficiently stable, active, selective, and inexpensive to be industrially viable.

One of our recent studies using first-principles microkinetic modeling predicted that a Pt₃Ru alloy could be an active and selective NO₃RR catalyst. In this talk, we will discuss our results of synthesizing different compositions of Pt_xRu_y/C (x = 48–100%) and characterizing their activity and selectivity for nitrate reduction. By tuning the amount of Ru in the alloy, we show there is an optimum in nitrate and hydrogen binding energies that maximizes the electrocatalytic activity. Additionally, we demonstrate that these catalysts are selective towards ammonium (NH₄⁺) at 0.1 V vs. RHE.

To accomplish this work, a series of Pt_xRu_y/C alloys were synthesized with varying Ru compositions ranging from 0 to 52 at% of the total metal loading. Bulk structural characterization was performed by using X-ray diffraction, extended X-ray absorption fine structure, X-ray absorption near edge structure, and transmission electron microscopy. To ensure that intrinsic catalyst activities were normalized properly, we used hydrogen and copper underpotential deposition to measure the electrochemical active sites and compared these values to surface compositions determined by X-ray photoelectron spectroscopy. The intrinsic activities and ammonium selectivity of the synthesized catalysts were measured at different operating potentials. Density functional theory calculations predict increasing Pt_xRu_y activity as Ru content increases to 25 at%, followed by a decrease in activity at higher Ru content, consistent with intrinsic activity measurements. Ultimately, this works provides insights for characterizing and designing different compositions of alloys for optimal nitrate reduction and ammonium production.