Enhancing the Electrocatalytic Activity of Graphitic Carbon Nitride Towards Oxygen Reduction Reaction Via Heteroatom Doping: A DFT Approach

Abstract

With the continued depletion of conventional fuel sources, the search for alternative fuel becomes increasingly important. Low temperature fuel cells such as PEMFCs and AFCs have attracted significant attention as a power generation technology. However, the cost of noble metals—which are important in speeding up the sluggish oxygen reduction reaction—remains an impediment in the commercialization of this technology. Metal-free catalysts are now being seen as possible alternatives to these noble metals. Among these metal-free catalysts is the graphitic carbon nitride. Graphitic carbon nitride, g-C3N4, is a polymeric material consisting of C, N, and some impurity H, connected via tris-triazine-based patterns. Due to its unique electronic structure, g-C3N4 and other graphene analogs have garnered interest in the material science community. While previous studies have been able to show experimentally the activity of g-C3N4 towards ORR, ab initio studies to explain and generalize the findings of the experiments remain scarce. Here we explain from the standpoint of density functional theory (DFT) calculations the effect of heteroatom doping (e.g., phosphorus, boron, sulfur) in further altering the material’s electronic structure in an effort to render g-C3N4 more active towards oxygen reduction reaction. The trends exhibited by graphitic carbon nitrides in our DFT computations indicate that this emerging class of material can pave the way for the rational design of fuel cell catalysts.