Novel electrode fabrication and reactor design for electrocatalytic nitrate and nitrite reduction in drinking water treatment

Nitrate (NO₃⁻) is the most ubiquitous groundwater contaminant in the U.S. and the world. Anthropologic nitrogen fixation for fertilizer production has greatly increased NO₃⁻ concentrations in ground and surface water, polluting drinking water sources and posing health risks to humans. Current go-to technologies like ion exchange (IX) and reverse osmosis (RO) produce concentrated NO₃⁻ brines that require further treatment and/or disposal, and alternatives like catalytic reduction suffer from gas-liquid mass transfer limitations that inhibit treatment performance in realistic continuous flow reactors. Electrocatalytic NO₃⁻ reduction has emerged as a promising option to overcome these shortcomings. A number of research groups have advanced mechanistic understanding of the reactions that drive this technology, but advancements in reactor engineering are needed to advance technology adoption. This dissertation covers three related projects that explore the design of a scalable flow reactor for electrocatalytic NO₃⁻ reduction and the evaluation of novel electrode materials to improve NO₃⁻ reduction activity, Faradaic efficiency, and selectivity for N₂ or NH₄⁺ end products. The first project explores the design of a scalable parallel-plate thin-layer (as known as filterpress) flow reactor with potential control, and the reactor performance for electrocatalytic nitrite (NO₂⁻) reduction using a carbon cloth electrode deposited with Pd–In bimetallic catalysts. The reactor was designed to be capable of stacking multiple electrodes for scale-up purposes. The performance results demonstrate high activity, Faradaic efficiency, and dinitrogen (N₂) selectivity, and identify the optimal operating potential and flow rate for efficient NO₂⁻ reduction. Also, a convection-diffusion-reaction-recirculation model was developed, and simulations indicate the reactor is not mass transfer limited. A sensitivity analysis allowed the determination of how cathode dimensions, flow channel thickness, intrinsic catalyst activity, and flow rate affect reactor scale-up. The second project explores the evaluation of five potentially active metals deposited on carbon cloth electrodes for NO₃⁻ reduction activity, Faradaic efficiency, and selectivity for N₂ or NH₄⁺. The best-performing metals are Cu and In, and further efforts were made to improve their performance by adding small amounts of Pd to form bimetallic electrodes. Results show that bimetallic Cu amended with an ultra-low amount of Pd provides the best activity, Faradaic efficiency, NH₄⁺ selectivity, and the capability of regeneration. The costs of electrocatalytic NO₃⁻ reduction with the Cu–Pd electrode was estimated and were less than those for NO₃⁻ removal using IX or catalytic treatment in most cases. The third project focuses on the fabrication, characterization, and performance of a novel type of TiO₂-doped electrospun carbon nanofiber electrodes decorated with Cu and heated under H₂ flow prior to use. These electrodes show the highest NO₃⁻ reduction activity and Faradaic efficiency among all electrodes evaluated in this thesis. Results from X-ray photoelectron spectroscopy suggest the improved performance likely originates from the synergistic effect between the deposited Cu and oxygen vacancies created in TiO₂ by heat treatment under H₂ flow.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Grantor

The University of Texas at Austin

Year dc:date.issued

2023

Author dc:creator

• Yan, Chenxu

Advisor dc:contributor.advisor

• Werth, Charles J.

Committee members dc:contributor.committeemember

• Mubeen, Syed
• Saleh, Navid B
• Cwiertny, David M
• Kumar, Manish

• Nitrate
• NO₃⁻
• Filterpress reactor
• Electrocatalytic reduction
• Reactor design
• Carbon nanofiber
• Faradaic efficiency
• TiO₂
• Electrospun
• Cu-Pd
• Bimetallic catalyst
• Copper
• Indium
• Energy consumption

Language dc:language.iso

en

Identifier URI

https://doi.org/10.26153/tsw/59168

OAI identifier oai:identifier

oai:repositories.lib.utexas.edu:2152/131824