Nanostructured Electrodes for Hydrogen Fuel Cells and Nanostructured Electrolytes for Lithium Metal Batteries: Impact of Nanostructure on Performance

Abstract

Commercially viable low-cost, long-range, and safe electric vehicles (EVs) require advancements in batteries and fuel cells. Proton exchange membrane fuel cells (PEMFCs) require a sufficient amount of expensive platinum (Pt) catalyst to achieve high power density. Reducing Pt loadings in PEMFCs without sacrificing performance is a primary challenge. The limitations of lithium-ion batteries (LIBs), include low energy density and safety issues (e.g., fire and explosion) resulting from the use of organic liquid electrolytes. Development of high energy density lithium metal batteries (LMBs) with advanced solid polymer electrolytes (SPEs) that are safe and long-lasting is a primary challenge. In this study, an alternative electrode fabrication technique was investigated to reduce overall cost of PEMFCs. SPEs based on poly(ionic liquid) (PIL) multiblock polymers and crosslinked PIL multiblock polymers were developed and explored for safe, long-lasting LMBs.

A new simultaneous foam electrospinning and electrospraying (FE/E) technique was developed to produce nanofiber/nanoparticle electrodes at ultra-low Pt loadings for PEMFCs. The FE/E technique produced nanofiber/nanoparticle electrodes at high production rates with precision-controlled nanofiber contents, which allows for the exclusive study of the role of nanofiber on fuel cell performance. The results showed that fuel cell performance is strongly dependent on ionomer nanofiber content. The highest fuel cell power density was achieved at 0.04 mg cm−2 nanofiber content due to enhanced proton and gas transport stemming from the nanofiber network.

For safe LMBs, liquid electrolytes were replaced with SPEs based on PIL multiblock polymers that can combine the favorable properties of both ionic liquids (ILs) and multiblock polymers. The effects of chain architecture (ABC versus ABCBA) and crosslinking degree in PIL multiblock polymers were explored with regards to the morphology, ionic conductivity, mechanical properties, electrochemical stability, and battery cycling durability of ternary SPEs containing corresponding lithium salt and ionic liquid. The results show that the ABCBA pentablock SPE has higher mechanical properties than ABC triblock due to unique chain conformation, yielding stable battery cycling performance over 50 cycles at room temperature. The crosslinked PIL multiblock SPEs display orthogonal properties (i.e., high ionic conductivity and high mechanical strength), exhibiting high energy density and long-lasting battery performance.