Covalent Organic Frameworks for Fuel Cell Applications

Abstract

Fuel Cells are electrochemical devices that convert the energy of the reaction between fuels, like hydrogen and oxygen into electricity. They are composed of an anode where the oxidation of the fuel takes place, i.e., the hydrogen oxidation reaction (HOR), a cathode, where the oxygen reduction reaction (ORR) occurs, and an electrolyte, where ions migrate to compensate the charges generated or consumed on the electrodes. In this chapter, the use of covalent-organic frameworks (COFs) in proton exchange membrane fuel cells (PEM-FCs) and alkaline anion exchange membrane fuel cells (AAEM-FCs) are discussed. These fuel cells operate at relatively low temperatures (<100°C), being a central component of the ion exchange membrane with high conductivity. In this direction, significant advances have been reached, developing COF membranes with high proton or ion conductivities. However, noble metal catalysts, like Pt, are usually employed on the electrodes. Many efforts have been done trying to replace these expensive metals for noble-metal free catalysts, particularly for the ORR, using Fe and Co-based catalysts. Going a step further, completely metal-free catalysts for the ORR have been investigated and developed. In this way, COFs, their derived carbonaceous materials, and single-atom modified COFs are current strategies to obtain catalysts for the ORR. Metals like Pt or Ni are necessary to catalyze the HOR. Hence, COFs are excellent precursors to bind metallic centers which can act as active sites for this reaction.