Impact of the dopant-induced ensemble structure of hetero-double atom catalysts in electrochemical NH production

Using spin-polarized density functional theory (DFT) calculations, we examined electrochemical N 2 reduction (N 2 RR) toward NH 3 production on hetero-RuM (M = 3d transition metals) double atom catalysts supported on defective graphene by means of analysis on the geometric ensemble structure, the N 2 RR mechanism, the decoupling of strain, dopant and configurational effects and the d-orbital resolved density of states (ORDOS) (d z 2 , d xz , d yz , d xy , and d x 2 - y 2 ) on the hetero-double atoms. In addition, we computationally screened novel catalysts by exploring 4d, 5d and p block metals as the hetero-M metals in the RuM system. First, we found the significantly enhanced N 2 RR activity of inclined pentagon M (Fe, Mn, and Sc) double atom catalysts (RuFe has the highest activity) compared to the homo-Ru 2 double atom catalyst. Our DFT calculations on the interplay of strain, dopant and configurational effects in the inclined pentagon M (Fe, Mn, and Sc) double atom catalysts predicted that (1) the dopant effect was the promoter to improve the N 2 RR activity of RuSc and RuMn, (2) the tensile strain (RuSc) tended to reduce the NH 3 productivity via the N 2 RR, while the effect of compressive strain (RuFe and RuMn) was insignificant, and (3) the dopant-support interaction induced a unique inclined pentagon M double atom ensemble structure, which leads to the large reduction of the N 2 RR activity of the hetero-RuSc double atom but the activity increases for the hetero-RuFe and RuMn cases. Finally, our DFT calculation on the analysis of the p-d (d z 2 , d xz , d yz , d xy , and d x 2 - y 2 ) orbital overlap identified the key d orbitals in determining the descriptor (NH 2 adsorption energy) for representing the N 2 RR. That is, the orbitals (d z 2 , d xz , and d yz ) having an orientation toward the z direction in the horizontal Ru 2 double atom played an important role in determining the NH 2 adsorption process, while for the inclined pentagon M double atoms (RuFe, RuSc, and RuMn), the d xz and d xy orbitals were found to be essential for the modification of NH 2 adsorption energy. Finally, a descriptor based DFT search additionally discovered promising hetero-RuOs and RuIr double atom catalysts. This study highlights that the dopant engineering of hetero-double atom catalysts supported on defective graphene can significantly modify the electrochemical reactivity, particularly by the dopant type and geometric ensemble structure. Compared to Ru single at