A fluorinated ionic liquid as a high-performance fuel cell electrolyte

This is the first report of a fuel cell with a proton-conducting ionic liquid (pIL) electrolyte that outperforms one with aqueous concentrated (85%) phosphoric acid over all current densities. The new pIL, 2-fluoropyridinium triflate (2-FPTf), is a fluorinated pIL that was made by mixing equimolar amounts of 2-fluoropyridine and triflic acid. A Pt-catalyzed fuel cell fed dry hydrogen and oxygen gases was stable at 80°C with neat 2-FPTf as the electrolyte. The polarization curve showed more than 15% improvement in performance (> 0.1 V cell voltage gain) compared to an identical fuel cell except with aqueous 85% phosphoric acid as the electrolyte. The stability of the fuel cell with 2-FPTf is attributed to it being a fluorinated electrolyte that does not wet Teflon. The improved fuel cell performance is attributed to low water-activity of the electrolyte leading to suppression of oxide formation on Pt and improved cathode performance. This was supported by the voltammetry of Pt in 2-FPTf electrolyte equilibrated with oxygen, which showed oxygen reduction begins near the thermodynamic limit of 1.2 V versus RHE at 80°C.