Abstract
Hydrogen-air proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are excellent fuel cells with high limits of energy density. However, the low carbon monoxide (CO) tolerance of the Pt electrode catalyst in hydrogen-air PEMFCs and methanol permanent in DMFCs greatly hindered their extensive use. Applying polybenzimidazole (PBI) membranes can avoid these problems. The high thermal stability allows PBI membranes to work at elevated temperatures when the CO tolerance can be significantly improved; the excellent methanol resistance also makes it suitable for DMFCs. However, the poor proton conductivity of pristine PBI makes it hard to be directly applied in fuel cells. In the past decades, researchers have made great efforts to promote the proton conductivity of PBI membranes, and various effective modification methods have been proposed. To provide engineers and researchers with a basis to further promote the properties of fuel cells with PBI membranes, this paper reviews critical researches on the modification of PBI membranes in both hydrogen-air PEMFCs and DMFCs aiming at promoting the proton conductivity. The modification methods have been classified and the obtained properties have been included. A guide for designing modifications on PBI membranes for high-performance fuel cells is provided.
Highlights
Fossil energy which is non-renewable still plays the dominant role in various energy applications [1,2]
For PBI polymer electrolyte membranes (PEMs) used for direct methanol fuel cells (DMFCs), doping inorganic nanofillers can add to the ion exchange sites through a variety of mechanisms, either promoting the acid retaining capacity or improving the proton transport through the hopping mechanism
The main advantage of PBI PEMs exists in two aspects: First, the high mechanical and chemical stability allow it to work at high temperatures that Pt-based electrode catalysts can bear higher carbon monoxide (CO) concentration
Summary
Fossil energy which is non-renewable still plays the dominant role in various energy applications [1,2]. Fuel cells, as an energy conversion technology, have received lots of attention for their considerable energy conversion efficiency and for being environmentally friendly They have great potential in performing as dominant power sources in various applications [4,5]. Though the final goal of all these methods is promoting the proton conductivity of PBI-based membranes, the mechanisms are different. For DMFCs, the excellent methanol resistance is the most valuable for PBI-based membranes, it should not be ignored in the process of modifying These issues make the promoting of the proton conductivity of PBI-based membranes more difficult, and researches have not been terminated till now. In this review, recently reported methods to promote the proton conductivity of PBI-based membranes in both hydrogen-air PEMFCs and DMFCs are classified and summarized. PBI has poor proton conductivity, in what way can give promotion on this? The available modification mechanisms are addressed in this part
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