Mechanisms of oxygen reduction reaction on B doped FeN4G and FeN4CNT catalysts for proton‐exchange membrane fuel cells.

Summary: Density functional theory (DFT) was used to calculate the stability, oxygen reduction reaction (ORR) mechanism and activity of B‐doped FeN4CNT (carbon nano‐tube [CNT]) and FeN4G (G, graphene). The B‐doped catalysts are more stable and active than that of the un‐doped, especially for FeN4B2G and FeN4B2CNT. Based on the Mulliken charge and electrostatic potential surface of these catalysts, Fe atom is found to be the most active site for the adsorption of O‐contained species. It is shown that their adsorption energies decrease in the range: O > OH > Co‐ad OH > OOH > O2 > H2O > H2O2 on these catalysts. H2O2 will be directly dissociated into two co‐adsorbed OH* or O* + H2O* instead of H2O2 on the graphene series catalysts, and the process of reaction (H2O2 + * → 2OH*) on the active sites of the CNT series catalysts is strongly exothermic. Hence, desorption of H2O2* into the solution is difficult to proceed during the oxygen reduction process. All the catalysts are expected to promote a single site four electron process through the reaction path of I (O2 → O2* → OOH* → O* → OH* → H2O) except for the catalyst of FeN4CNT. The rate‐determining step (RDS) for ORR process on FeN4B2G is the first reduction step (O2* → OOH*), while the RDS is the fourth reduction step (OH* → H2O) for the other catalysts. FeN4B2G exhibits the largest on‐set potentials of 0.53 V, which is larger than the on‐set potential of un‐doped B FeN4G catalyst (0.39 V). In addition, the B‐doped FeN4CNT catalyst shows the better activity compared to the un‐doped ones. [ABSTRACT FROM AUTHOR]