Nano-geometric deformation and synergistic Co nanoparticles-Co-N-4 composite sites for proton exchange membrane fuel cells

Co single-atom (Co-SA) catalysts of the CoN4 moiety usually show an unsatisfactory oxygen reduction reaction (ORR) activity due to poor O-2 activation. Herein, we open up a novel strategy to improve the ORR activity of the Co-SA-N-C catalyst. Its structure was first built to involve the deformed CoN4 site and enhance mesoporosity. Secondly, Co nanoparticle and CoN4 (Co-NP-CoN4) composite sites were created in the catalyst and the total CoN4 density was effectively replenished. Finally, the concave nanocube-like catalyst showed an excellent ORR performance in the RDE test (E-1/2 = 0.83 V vs. RHE, 12 mV loss after 50K cycles) in acidic media. Furthermore, the catalyst showed a high power density in the fuel cell test (P-max-H-2-O(2)ca. 1.207 W cm(-2)). Theoretical studies agree with experimental findings that both Co-NP-CoN4 composite sites and deformed CoN4 can enhance O-2 activation. In addition, the inhibited H2O2 formation and the enhanced adsorption of radical oxygen species due to Co-NP-CoN4 composite sites can greatly reduce carbon layer erosion, resulting in improved performance in both activity and durability. Our finding not only provides a novel strategy to develop ORR catalyst but also brings new insights into ORR fundamentals.