Advancing carbon-based nanofiber electrode materials for (photo)electrochemical drinking water treatment
Creators: name: Butzlaff, Ashley Hesterberg
Publisher: name: University of Iowa
Year: 2025
Subjects: drinking water treatment
electrochemical
electrode
materials design
photoelectrochemical

description: Modern challenges facing drinking water treatment (e.g., emerging pollutant classes) and the increasing demand for renewable energy provide an opportunity to implement electrochemical (EC) drinking water treatment. EC treatment offers the promise of broadspectrum efficiency toward a wide range of contaminants with sustainable operation (e.g., powered by renewable energy, low energy and carbon demand) and little to no waste by using electrons (instead of chemical reagents). However, EC technologies cannot be implemented at full-scale, while maintaining sustainability and affordability, without improving material performance. The electrode material effects the stability, selectivity, activity, and affordability of EC drinking water treatment. Further, the reaction rate and process efficiency are defined by inherent electrode properties (i.e., potential, current density). The ideal electrode material for EC water treatment must possess high electroactive surface area, electrical conductivity, electrochemical and chemical stability, porosity, and water permeability while avoiding harmful by-product formation.
description: The overarching goal of this work was to systematically design and optimize the properties of electrospun, carbon-based electrodes for EC applications in water treatment via the oxidation of recalcitrant organic and inorganic contaminants. Electrospinning provided a flexible, highly tunable platform to produce nanoenabled materials with diverse physical, chemical, and electrical properties. Following electrospinning, polymer nanofibers were converted to carbon nanofibers (CNFs) via a two-step heat treatment process optimized for increasing the electrical conductivity and maintaining the mechanical strength of the resulting CNF electrode materials. All CNF electrode materials were then characterized for their physical, chemical, and electrical properties before testing their oxidation/reduction performance in environmentally relevant EC systems for water treatment.
description: As a whole, this work demonstrates the EC performance (i.e., selectivity, activity, product yield) and photoelectrochemical (PEC) activity of electrospun CNF materials with diverse compositions and properties. Optimal composites containing TiO2 (CNF/TiO2) provided EC and PEC activity with a high surface area and an electrical areal resistance comparable to commercial carbon-based electrode materials (e.g., Kynol Activated Carbon Cloth). For oxidation of a model recalcitrant organic contaminant (i.e., carbamazepine, CBZ), transformation experiments with CNF/TiO2 suggested the electrodes can function dually as sorbents, first binding CBZ prior to oxidation at positive applied potentials. Compared to EC systems (applied potential), PEC (applied potential + light) systems exhibiter higher currents and improved transformation rates. CNF/TiO2 electrodes also exhibited stability across repeated use, yielding consistent current densities over several experimental cycles. For the reduction of a recalcitrant inorganic pollutant (i.e., nitrate, NO3 - ), CNF/TiO2 deposited with a sustainable catalyst (i.e., copper, Cu) demonstrated the highest performance for NO3 - reduction compared to carbon only (CNF) and carbon-carbon nanotube composite (CNF/CNT) electrodes with the same Cu mass loading. Cu-deposited CNF/TiO2 also provided the highest ammonium (NH4 + ) selectivity, yield, and production, which is the most desired and favored NO3 - reduction product due to its potential for resource recovery. Electrochemical and spectroscopic (i.e., in situ Raman) methods supported the unique contributions of TiO2 in NO3 - reduction and highlight novel support/metal interaction with the addition of Cu. To further advance and probe the CNF/TiO2 electrode for NO3 - reduction, CNF/TiO2 electrodes were produced with various pristine TiO2 nanopowders with various crystal structures (anatase, rutile) and particle diameters. The crystal structure composition influenced the CNF/TiO2 reduction performance to a much greater extent than the particle diameter. For example, for CNF/TiO2 electrodes containing the rutile (more conductive) TiO2 phase only, NH4 + selectivity increased 2-fold compared to the previous CNF/TiO2 electrode. Ultimately, the results of this work will help guide electrode (or catalyst support) design for EC systems to increase their use in advanced drinking water treatment, particularly for otherwise recalcitrant pollutants or for treatment of waste streams from which valuable resources can be recovered.