Fundamental and Practical Studies of Capacitive Deionization Using Asymmetric Nanoporous Oxide Electrodes

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

0852780 Anderson Capacitive deionization (CDI) is a process that operates by sequestering ions in the electrical double layer near charged surfaces. Essentially, a solution of ions flows through a highly porous conducting pair of electrodes and anions or other negatively charged species are removed at the positive electrode while cations or positively charged species are separated from solution at the negative electrode. During the removal process, energy is being stored in a capacitive fashion and is readily available to lower the cost of energy consumption. In a recharge cycle, a reverse bias is applied forcing the electrochemically-sequestered ions to be released as brine, much as in both RO and evaporative distillation processes. Brine production is generally considered to be less for CDI than in RO operations. This proposal includes fundamental as well as practical studies of the CDI process using a novel asymmetric set of electrodes coated with nanoporous oxides. This research will utilize electrochemical impedance measurements and models tied to real-world pore size and pore size distributions to interpret our results. In addition, an insitu electrochemical FTIR system is to be developed to study molecular behavior inside these nanoporous oxide electrodes. From a practical perspective, many pairs of CDI electrodes must work in tandem, controlled electronically, and matched to water composition and flux for optimal ion removal. In this part of the proposed studies, a stack of electrodes will be assembled into a module and benchmarked with respect to ion removal versus time, electrode surface area, and energy cost per gallon of water processed. This portion of the proposed work will be completed in four parts: 1. Choosing an optimal supporting material for our electrodes 2. Coating this support with our best nanoporous oxide films. 3. Testing electrodes in four pair stacks and finally 4. Building a CDI prototype. Potentially, CDI can compete favorably as a desalination process. The CDI system proposed could be used by municipal facilities or in third-world communities providing potable water to people in severe need. This project will result in the training of one PhD and several undergraduate research students. It will contribute to renewed laboratory instrumentation to be employed in both research and teaching. In addition, this project will be used in a modified fashion as a device template for an undergraduate introductory course in engineering taught at the University of Wisconsin each fall semester. In this class, 16 students, forming an engineering team will cooperate with Engineers Without Borders (EWB), to develop a solar-powered CDI system that EWB will field-test in Kenya.