Progress in the use of ionic liquids as electrolyte membranes in fuel cells

Abstract

This work provides a critical review of the progress in the use of Room Temperature Ionic Liquids (RTILs) as Proton Exchange Membrane (PEM) electrolytes in Fuel Cells (FCs). It is well-known that for an efficient early commercialisation of this technology it is necessary to develop a proton exchange membrane with high proton conductivity without water dependency capable of working at temperatures above 100 ºC. The use of ionic liquids as electrolytes in electrochemical devices is an emerging field due to their high conductivity, as well as their thermal, chemical and electrochemical stability under anhydrous conditions. This paper attempts to give a general overview of the state-of-the-art, identifies the key factors for future research and summarises the recent progress in the use of ionic liquids as an innovative type of PEMs.

Nanotechnology for environmentally sustainable electromobility

“…Carbon nanotubes and graphene also exhibit more environmentally intensive 50,51 profiles and, like other carbon 7 nanostructures, their handling requires more precaution 56 than graphite 57 . The current carbon nanotube synthesis routes are energy intensive [58][59][60] . Even when potential economies of scale are taken into account, energy requirements for the synthesis of carbon nanotubes through chemical vapour deposition, arc discharge, or laser-assisted methods all remain significant 61 , which in turn result in high greenhouse gas emissions 62 .…”

“…These membranes have generally fallen short of the technical goals for PEMFCs for transport applications; they have lower device efficiency due to their lower ionic conductivity, or are unstable and lack the robustness required for an adequate device lifetime relative to Nafion membranes 50,55 . However, as discussed above, their lack of fluorine atoms generally makes these materials less environmentally intensive than fluorinated membranes and modifications such as covalent attachment of proton-conductive compounds, crosslinking and nanostructure are being explored as methods to overcome weaknesses 49,[56][57][58][59][60] . An exception to the technical performance of this category of membranes are phosphoric acid-doped polybenzimidazole-based membranes.…”

“…These membranes perform well in high temperatures with low humidity levels and are robust against fuel impurities. However, they also have reduced device lifetime due to lower mechanical strength and due to damage caused by phosphoric acid leachate formed under normal operating conditions; acid leaching also decreases the energy efficiency of the membrane via losses in proton conductivity 58,61 . Beyond the attributes considered here, phosphoric acid-PBI membranes may have issues with cold start due to poor device efficiency performance at lower temperatures.…”

Recent Progress on the Key Materials and Components for Proton Exchange Membrane Fuel Cells in Vehicle Applications

“…Room temperature ionic liquids (RTILs) electrolytes have attracted considerable attention in electrochemical applications [45] and can be a good candidate for high-temperature PEMFCs [46][47][48] application due to its more thermally stable at a wide temperature range [49,50] and non-volatile dopant than other acid doping composite membranes. Based on cationic structures, the RTILs can be classified into one of seven families [51] and it is possible to design desired physicochemical properties of RTILs by the choice of the ionic constituents.…”

“…Conductive oxides, carbides, and nitrides, such as TiO 2 [47], TiC [81][82][83], SiC [84][85][86] and WC [87], have also shown promising effects on the catalytic activity and durability of PEM fuel cell catalysts. Pt supported on carbon-doped TiO 2 /CNTs (Pt/C-TiO 2 /CNTs) showed a better oxygen reduction activity than a commercial Pt/C catalyst.…”