Activating Transition Metal Dichalcogenides by Substitutional Nitrogen-Doping for Potential ORR Electrocatalysts

Abstract

One of the challenging goals in the large-scale realization of hydrogen-based fuel cells is to replace or minimize the use of expensive Pt-based electrocatalysts to reduce molecular oxygen at the cathode. Recently, non-metal doped nanosheets of transition metal dichalcogenides (TMDs) have emerged as a promising Pt-free electrocatalyst for hydrogen evolution reaction. Herein, we investigate the potential of nitrogen- and phosphorus- (N- and P-) doped TMDs (MoS2, MoSe2, WS2, and WSe2) as high-performing electrocatalysts for ORR using first principle calculations, motivated by recent experimental advances to incorporate single S/Se vacancies on the surface of TMD monolayers using electrochemical methods. We observed a strong hybridization of p-orbitals of N/P atom with the p- and d-orbitals of neighbouring S/Se and Mo/W atoms, respectively, activating pristine TMDs by increasing density of states near Fermi-level. Based on the free energy profiles of the four-electron reduction process, we expect that N-TMDs to be efficient in catalyzing ORR, whereas, too strong binding of reaction intermediates prevents ORR on P-TMDs. Among the candidates considered, N-WS2, is found to be a promising TMD as ORR catalyst with the overpotential as low as 0.31 V, stimulating further experimental studies.