Nano-geometric deformation and synergistic Co nanoparticles—Co-N4 composite sites for proton exchange membrane fuel cells

Abstract

Co single-atom (Co_SA) catalysts of the CoN₄ moiety usually show an unsatisfactory oxygen reduction reaction (ORR) activity due to poor O₂ 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-H₂–O₂ca. 1.207 W cm⁻²). Theoretical studies agree with experimental findings that both Co_NP–CoN₄ composite sites and deformed CoN₄ can enhance O₂ 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.