pH Analysis of Pt_xRu_y/C Alloys for the Nitrate Reduction Reaction

Evan Ortiz

Pronouns: He/Him/His

UROP Fellowship: University of Michigan Energy Institute

Research Mentor(s): Zixuan Wang, PhD Candidate, Nirala Singh, PhD
Department of Chemical Engineering

Presentation Date: Wednesday, July 29, 2020 | Session 2 | Presenter: 5

Authors: Evan Ortiz, Zixuan Wang, Nirala Singh

Abstract

Nitrate is a pollutant primarily generated from agriculture and septic waste. High concentrations in water sources can cause algae blooms, and subsequently dead zones. Consumption of water with high levels of nitrate contaminants have been linked to blue baby syndrome and cancer. One method of remediation is to electrochemically reduce nitrate to other benign or commodity products. However, there does not exist an active, stable, selective, and inexpensive material to catalyze such a reaction. Current research has explored alloys as potential electrocatalysts. Specifically, computational predictions and experimental results have identified Pt_xRu_y to be active and selective for nitrate reduction reaction. However, these experiments were conducted under very acidic conditions, but typical waste streams tend to operate under more basic conditions. The specific goals of this research is to (1) understand the effect of pH on Pt_xRu_y/C catalyst performance, (2) find a model for the effect of proton concentration has on the rate of reaction, and (3) apply the model to existing waste streams with different conditions. Hydrogen underpotential deposition and chronoamperometry were used to determine the electrochemically active surface area and current at four different applied potentials (0.05, 0.075, 0.1, 0.15 V vs. RHE), respectively. This technique allows us to obtain the intrinsic activity of each catalyst for accurate comparison. Previous results have shown nitrate converts to ammonium under our reaction conditions. Thus, we can assume the reduction to ammonium as the only reaction taking place for the kinetic model. The reaction rate can be determined for each catalyst from the measured current densities and pH using Faraday’s Law. The measured reaction rates were fitted against the Langmuir-Hinshelwood models for unimolecular and bimolecular surface reactions. At low pH values, the bimolecular model demonstrated the most consistency with the experimental data. This suggests that the elementary rate determining step at low pH involves both adsorbed nitrate and adsorbed protons.

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Research Disciplines

Engineering