DFT Investigation for Better Efficiency of Fuel Cells in Presence of Nitrogen Containing Graphene sheets as Catalysts

Fuel cells can directly convert chemical energy into electric energy with high conversion efficiency and no pollution. Among many factors affecting the chemical-electrical energy conversion, oxygen reduction reaction (ORR) on cathode is the pivot in fuel cell. This reaction is a kinetically slow process, which dominates the overall performance of a fuel cell. The ORR can proceed through two ways. One is a direct four-electron pathway, in which O2 is reduced directly to water without involvement of hydrogen peroxide. The other is a less efficient two-step two-electron pathway in which hydrogen peroxide is formed as an intermediate. To achieve a high efficiency fuel cell, the four-electron pathway is expected to occur. Because the ORR process is very slow in nature, catalysts must be used to facilitate the four-electron pathway to boost the efficiency of fuel cells. Traditionally, such electro catalysts are platinum and its alloys, but they are expensive and susceptible to time-dependent drift and CO poisoning, which limits large-scale application of the fuel cell. There have been intensive research efforts to reduce or replace Pt and Pt based alloys electrodes in fuel cell. In this work using calculated NMR and NQR parameters in some nitrogen-containing graphene sheets (with one or two nitrogen), the effect of nitrogen atom on charge density of carbon atoms was studied. The results showed that in the presence of nitrogen, charge density of some carbon atoms decreased and these atoms are better candidate as catalyst active site than pure graphene.