Metal and nitrogen co-doped carbons (M-N/Cs) have emerged as promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR). Here, density functional theory calculations are used to investigate the adsorption of anions and impurities from the electrolyte on the active site, modelled as an M-N4 motif embedded in a planar carbon sheet (M= Cr , Mn, Fe , Co). The two-dimensional catalyst structure implies that each metal atom has two potential active sites, one on each side of the sheet. Adsorption of anions or impurities on both sites results in poisoning, but adsorption on one of the sites leads to a modified ORR activity on the remaining site. The calculated adsorption energies show that a number of species adsorb on one of the two sites only under realistic experimental conditions. A few of these adsorbates furthermore modify the adsorption energies of the ORR intermediates on the remaining site in such a way that the limiting potential is improved.
- Density functional calculations
- Fuell cells
- Heterogeneous catalysts
- Transition metals