Se-doping strategy regulating mass transfer and electronic structure of Fe-N-C electrocatalysts for proton exchange membrane fuel cells

The limited activity of atomically-dispersed M-N-C electrocatalysts severely restricts their applicability in the oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFC). Herein, we design and synthesize Se-doped Fe-N-C hierarchical porous electrocatalyst (FeN 4 /SeC 2 ) by optimizing carbon structure and FeN 4 coordination environment. The FeN 4 /SeC 2 electrocatalyst exhibits outstanding ORR activity in 0.1 mol L –1 HClO 4 , and the resulting PEMFC presents a peak power density of 1.20 W cm –2 in H 2 -O 2 condition at a back pressure of 200 kPa, ranking in the top levels among most reported non-precious metal catalyst-based fuel cells. The lower O 2 transfer resistance of FeN 4 /SeC 2 -based membrane electrode assembly than FeN 4 -based one means faster O 2 transport in triple-phase boundary (TPB), and Density functional theory calculation further reveals that the synergistic catalysis between porous SeC 2 and FeN 4 -OH species can efficiently lower the energy barriers for the rate-determining step of the ORR. In short, the outstanding performance of FeN 4 /SeC 2 in PEMFC is ascribed to the Se-doping, which introduces more defects and larger mesoporosity and therefore facilitates ionomer infiltration and O 2 transfer and charge transfer in TPB. The effective strategy of enhancing mass and charge transfers in TPB is anticipated to be applicable in the construction of highly efficient ORR electrocatalysts.