Oxygen reduction electrochemistry at F doped carbons: A review on the effect of highly polarized C-F bonding in catalysis and stability of fuel cell catalysts.

[Display omitted] • Comprehensive understanding on the effect of C-F bonding on ORR kinetics and mechanism is described. • Special focus on the superiority of F-C vs. N-C carbons towards stability of carbon support is detailed. • Excellent and highly stable catalysts have been noticed with F and F, N co-doped catalysts. • Possible directions of future research & developments on the F-doped catalysts are suggested. Doped carbon materials, particularly N-doped carbon catalysts, have drawn considerable attention in recent years as metal-free catalysts for oxygen reduction reactions (ORR) and as a carbon corrosive resistance support for Pt and non-Pt nanoparticles. While nitrogen-doped carbons (N-doped carbons) were once the standard, F-doped carbons (F-doped carbons) have recently overtaken their popularity. This is because F doping gives carbon materials unique properties that not only differ from the N-doped carbons but also significantly improves the ORR activity and especially the durability. Being the highest electronegative element of the periodic table, F-doping can efficiently modify the electronic band structure of the carbon materials favoring for ORR. The edge F doping to the carbon is found to improve carbon corrosion resistance more than any other heteroatom doped catalyst discovered previously, including N doped carbons, both in highly acidic, alkaline pH conditions and high oxidative potentials that exists in the fuel cell including start-up and shut-down conditions. In this review, the fundamental understanding of effect of F-doping/F co-doping on the electrocatalytic reduction of O 2 into H 2 O and OH− in acidic and alkaline pH conditions, effect of F doping on stability and durability of fuel cell catalysts, careful considerations/guidelines one needs to know before working with F doped carbons (F doping advantages vs. poisoning effect on Pt or M/F-C (M = transition metal) catalysts, are being reviewed systematically. Finally, several strategies for future research directions on F-doped carbons were proposed to bridge the gap between laboratory-scale assessment to commercial aspects. [ABSTRACT FROM AUTHOR]