Patterning Polymer Electrolyte Membranes for Fuel Cell and Electrolysis Applications

Abstract

Electrochemical processes have experienced a renaissance in recent years for the synthesis of commodity chemicals because their potential to integrate with electrified renewable energy sources and prospect to produce chemicals with a lower energy footprint under milder operating conditions. The heart of many electrochemical processes for electrolysis and energy storage and conversion, is the membrane electrode assembly (MEA) that intersects ions, electrons, and the products/reactants-percolating electrolyte. Optimizing the electrode-electrolyte interface in MEAs is vital for maximizing the thermodynamic efficiency of electrochemical processes. For example, the interface must foster facile mass transfer and charge-transfer to cater reaction kinetics. Patterning polymer electrolyte membranes’ (PEMs) surfaces is an attractive methodology capable of enlarging the electrode-electrolyte interfacial area, where reactants, catalysts, and PEMs coexist in MEAs. To date, there have been only a handful of micropatterned PEM demonstrations using 3D printing(1), plasma etching(2), mechanical abrasion(3), thermal imprint lithography(4, 5), multiplex lithography(6), photolithography(7), hot embossing(8), pulsed laser micromachining(9), or their combinations. It is more important to note that there exist even fewer demonstrations for their use in electrochemical technologies that provide electrical energy (e.g, fuel cells) and no demonstrations for electrolysis applications. This presentation reports our work on patterning PEM surfaces through photolithography and block copolymer lithography. Conventional photolithography methods enable micropatterning with feature sizes limited to above ~ 1 mm, whereas block copolymer lithography(10-12) allows nanopatterned features from sub-10nm to 100 nm over large areas without the need to directly write features (i.e., it is a low cost and scalable patterning technique). In this work, technical demonstrations of micro- and nano-patterned PEMs are given for alkaline anion-exchange membrane fuel cells, carbon dioxide electrolysis, and water electrolysis. Single-cell current-voltage relationships in addition to impedance spectra of the patterned PEMs used in MEAs for the aforementioned applications are provided. Connections between patterned feature sizes and MEA performance with individual resistance components will be discussed. Figure 1 below depicts a micropatterned PEM and self-assembled, nanostructured block copolymer templates.