Single Pd atoms supported by graphitic carbon nitride, a potential oxygen reduction reaction catalyst from theoretical perspective

Designing the low cost, long durability and high efficient substitutes for platinum (Pt) electrocatalyst to facilitate ORR is significant for the large-scale commercial application of fuel cells. In this work, single Pd atoms supported on graphitic carbon nitride (i.e., Pd/g-C3N4) with different Pd coverages acting as electrocatalyst for ORR is investigated by using the density functional theory calculations. Our study shows that the doping of Pd atoms can effectively decompose H2O2, leading to a four-electron mechanism via the sequential hydrogenation of *O2 giving *O+*H2O on Pdx/g-C3N4 (x = 1–4). With the increase of Pd coverages, the energy barriers increase in the rate determining step, which are 0.39 eV, 0.63 eV, 0.68 eV and 2.61 eV for Pdx/g-C3N4 (x = 1–4), respectively. This implies that Pdx/g-C3N4 (x = 1–3) have lower energy barrier than Pt (calculated value 0.80 eV), showing high ORR activity compared with Pt. The oxidized Pd2/g-C3N4 (i.e., Pd2/g-C3N4−O) shows similar ORR activity to Pd2/g-C3N4, but with different rate determining step. The working potentials are also discussed for the studied catalysts. Especially, the working potential for Pd2/g-C3N4 is up to 0.60 V, comparable to calculated value 0.73 V for Pt/Cu(100).