Enhanced proton conductivity of Nafion composite membrane by incorporating phosphoric acid-loaded covalent organic framework

Abstract

Abstract Design and fabrication of efficient proton transport channels within solid electrolytes is crucial and challenging to new energy-relevant devices such as proton exchange membrane fuel cells (PEMFCs). In this study, the phosphoric acid (H 3 PO 4 ) molecules are impregnated into SNW-1-type covalent organic frameworks (COFs) via vacuum assisted method. High loading of H 3 PO 4 in SNW-1 and low guest leaching rate are achieved due to the similar diameter between H 3 PO 4 and micropores in SNW-1. Then the COF-based composite membranes are fabricated for the first time with impregnated COFs (H 3 PO 4 @SNW-1) and Nafion matrix. For the composite membranes, the acid-base pairs formed between H 3 PO 4 @SNW-1 networks and Nafion optimize the interfacial interactions and hydrophilic domains. The acidic –PO 3 H 2 groups in pores of H 3 PO 4 @SNW-1 provide abundant proton transfer sites. As a result, the continuous proton transfer channels with low energy barrier are created. At the filler content of 15 wt%, the composite membrane exhibits a superior proton conductivity of 0.0604 S cm −1 at 51% relative humidity and 80 °C. At the same time, the maximum power density of single fuel cell is 60.3% higher than that of the recast Nafion membrane.