The 2-Propanol Fuel Cell: Direct CO2-Free Electrification with a Liquid Hydrogen Carrier

Abstract

Molecular hydrogen is a gas at ambient conditions and requires compression or cryogenic liquefaction for storage and transport, leading to significant losses in efficiency. Therefore, liquid hydrogen carriers are desirable as they are storable without losses. One such fuel that has shown promise recently is 2-propanol (isopropanol), which is converted with high selectivity to acetone in a fuel cell.[1],[2],[3] Power densities over 200 mW/cm2 have been reported for direct isopropanol fuel cells (DIFCs), which rivals the best direct methanol fuel cells (DMFCs), and unlike methanol, isopropanol is non-toxic and it is not fully oxidized to CO2. [4] The literature has demonstrated many advantages of DIFCs, yet significant challenges remain.[5] Continuous operation at high current densities can be limited due to anodic catalyst layer network effects: slow removal of acetone from active sites and out of the catalyst layer. Additionally, perfluorinated sulfonic acid (PFSA) ionomers are not fully chemically compatible with 2-propanol and acetone. Operation at higher temperatures with a vaporized 2-propanol feed partially mitigates both of these disadvantages, yet the high energy cost of vaporization reduces the overall efficiency of the system. Future research should focus on stable, high-power operation with a liquid 2-propanol feed.This contribution chronicles the progress that has been made and discusses the current state-of-the-art and outlook of direct electrification with DIFCs. Recent advances in liquid-fed DIFCs are presented, including design of membrane-electrode-assemblies and operation strategies in full cells. Finally, the concept of using the 2-propanol/acetone couple as an electrochemical liquid organic hydrogen carrier is briefly introduced: a reversible hydrogenation and dehydrogenation cycle for storing and releasing molecular hydrogen on demand.