Search

Developing highly efficient and stable electrocatalysts for oxygen reduction reaction (ORR) is a challenging task in energy conversion technologies. In this work, diverse axial ligands have been used to modify the ORR activity of transition metal and nitrogen codoped graphene (MN4-Gra). The weakening of the ORR intermediates by the axial ligand would activate these intermediates efficiently and improve the catalytic activity. Our study indicated that among the axial ligands adopted, nitrobenzene and benzene have good performance in improving the ORR activity. Several promising ORR catalysts are predicted. Among them, FeN4-Gra modified by nitrobenzene, i.e., FeN4-Gra/ben/NO2 has the best catalytic activity with a small overpotential of 0.21 V and energy barrier of 0.24 eV in the rate determining step, followed by RuN4-Gra/ben/NO2 and FeN4-Gra/benzene. These catalysts are also demonstrated to be stable by the calculated formation energies and dissolution potentials. The scaling relationships suggested that the adsorption energy of *OH and d band center would be good descriptors for predicting the highly efficient ORR catalysts. Therefore, axial ligand engineering would be a useful strategy to enhance the efficiency of ORR catalysts. [ABSTRACT FROM AUTHOR]

Developing high efficient and cheap electrocatalysts for carbon dioxide reduction reaction (CO 2 RR) is the key to achieve CO 2 transformation into clean energy. Herein, a series of transition metal dimer and nitrogen codoped graphene (M 2 N 6 -Gra, M = Cr–Cu) acting as electrocatalysts for CO 2 RR are investigated based on the density functional method. For M 2 N 6 -Gra (M = Cr, Mn), the selectivity is poor and CO poisoning is serious. Fe 2 N 6 -Gra is the best CO 2 RR catalyst due to the good selectivity and catalytic activity. The calculated overpotential is very small, i.e., 0.03 V for COOH channel, 0.05 V for HCOO channel. Hydrogen evolution reaction is also refrained on the Fe 2 N 6 -Gra surface, which further supports its high catalytic performance. For M 2 N 6 -Gra (M = Co, Ni, Cu), the catalytic activity is poor due to large overpotentials. These results indicate that if designed carefully, the transition metal dimer and nitrogen codoped graphene would be good candidate for the high efficient and selective CO 2 RR catalyst. Image 1 • The mechanism of CO 2 RR on M 2 N 6 -Gra (M = Cr–Cu), has been studied by using the DFT. • The studied M 2 N 6 -Gra (M = Cr–Cu) is stable thermodynamically. • Fe 2 N 6 -Gra exhibits high selectivity and catalytic activity for CO 2 RR. [ABSTRACT FROM AUTHOR]