Suspension Electrodes for Flow-Assisted Electrochemical Systems

This chapter focuses on describing a new family of flowable electrochemical systems based on suspension electrodes to address key critical infrastructure needs: grid energy storage and water desalination. The research described herein combines classical aspects of electrochemistry, colloidal science, material science, and rheology to explain and characterize ion and charge percolation processes in suspension electrodes. Comprised of an active material suspended in electrolytic medium, their use enables, for the first time, scalability of electrical energy storage devices (supercapacitors and batteries). Moreover, it expands the principle of supercapacitors beyond small-scale energy storage to new and emerging applications such as deionization of water and energy generation. This chapter provides an overview of the inventory of solid materials and soluble ionic species that can be used in capacitive suspension electrodes. We demonstrate the use of both carbon-based and other inorganic (manganese oxide) materials in a suspension electrode and describe how compositional loading and material properties (conductivity, porosity, texture) affect electrochemical and rheological properties in a suspension electrode. With an ultimate goal of achieving high energy density, we explore opportunities for pseudocapacitive suspension electrodes via the addition of soluble organic molecules and metal ions for additional charge storage (faradic processes). This chapter discusses the role of carbon surface heteroatoms on the combined rheological, electrochemical, and deionizing properties of capacitive suspension electrodes for water desalination. Finally, the chapter concludes with a description of test methods and procedures used in acquiring key properties such as capacitance, conductivity, and rheological characteristics.