Recent developments in bifunctional air electrodes for unitized regenerative proton exchange membrane fuel cells - A review

Unitized regenerative proton exchange membrane fuel cell (UR-PEMFC) technology has progressed in the recent past and has started appearing towards few applications. However, the UR-PEMFC viability is limited by its lower round-trip efficiency mainly due to several reasons such as sluggish air electrode reactions, lower performance/stability, higher materials cost etc. In this context, many approaches are being implemented for efficiency enhancement including design and development of effective bifunctional air electrodes (oxygen reduction and evolution reactions) materials both for fuel cell and electrolyzer modes as well as for optimization of operating condition for performance stability in real life applications. This review focusses on the recent developments of air electrode active materials design/development for performance improvement in UR-PEMFC. Among all developed electrode materials, the catalysts with Pt- and Ir-based metals still provided the maximum round-trip efficiency of about 50% at 500 mA cm(-2) in the unit cell. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.