(513ba) Noble-Metal Free Oxygen Reduction Electrocatalysts Based on Graphitic Carbon Nitride

The cathodic oxygen reduction reaction (ORR) is considered as the performance-determining step in fuel cells. Platinum based catalysts are currently standard bearer due to its high activity. However, there are still a number of issues such as high cost, corrosion of carbon support, susceptibility to CO poisoning and crossover methanol interference. Therefore, it is significant to design precious metal free materials for ORR. The two-dimensional (2D) graphitic carbon nitride (g-C₃N₄), rich in pyridinic nitrogen, possesses the potential to address most of the existing challenges simultaneously. Therefore, in this work, we focused on both the intrinsic physical properties (e.g., the electrical conductivity) and the potential reactivity of g-C₃N₄ pertinent to ORR. Based on Density Functional Theory (DFT) calculations, we found that both the electrical conductivity and ORR activity (rate-limiting step) can be manipulated and tuned, especially when paired with other 2D materials such as graphene and hexagonal boron nitride. Specifically, g-C₃N₄ is intrinsically active toward ORR, however, its large energy band gap hinders charge transfer. DFT calculations revealed that such large band gap can be narrowed by paring g-C₃N₄ with GN, and becomes suitable for electrochemical applications. The energy band gap can be completely eliminated in the Fe-doped g-C₃N₄ and g-C₃N₄/GN bilayer, and thus, charge transfer for ORR is further improved. With DFT, the bindings of ORR intermediates are found to be tunable as well, which influence the thermodynamics of each elementary reaction step to tune the ORR activity.