Coordination environments tune the activity of oxygen catalysis on single atom catalysts: A computational study

Abstract

Designing highly efficient bifunctional electrocatalysts for oxygen reduction and evolution reaction (ORR/OER) is extremely important for developing regenerative fuel cells and metal-air batteries. Single-atom catalysts (SACs) have gained considerable attention in recent years because of their maximum atom utilization efficiency and tunable coordination environments. Herein, through density functional theory (DFT) calculations, we systematically explored the ORR/OER performances of nitrogencoordinated transition metal carbon materials (TM-N x -C (TM = Mn, Fe, Co, Ni, Cu, Pd, and Pt; x = 3, 4)) through tailoring the coordination environment. Our results demonstrate that compared to conventional tetra-coordinated (TM-N 4 -C) catalysts, the asymmetric tri-coordinated (TM-N 3 -C) catalysts exhibit stronger adsorption capacity of catalytic intermediates. Among them, Ni-N 3 -C possesses optimal adsorption energy and the lowest overpotential of 0.29 and 0.28 V for ORR and OER, respectively, making it a highly efficient bifunctional catalyst for oxygen catalysis. Furthermore, we find this enhanced effect stems from the additional orbital interaction between newly uncoordinated d-orbitals and p-orbitals of oxygenated species, which is evidently testified via the change of d-band center and integral crystal orbital Hamilton population (ICOHP). This work not only provides a potential bifunctional oxygen catalyst, but also enriches the knowledge of coordination engineering for tailoring the activity of SACs, which may pave the way to design and discover more promising bifunctional electrocatalysts for oxygen catalysis.

Theoretical insights into dual-atom catalysts for the oxygen reduction reaction: the crucial role of orbital polarization

“…It is noteworthy that the adsorption strength of oxygen species on FeFeNC-4 becomes stronger after considering the solvent environment, which is consistent with previous studies. 7,51 Due to the enhanced binding strength, the overpotential of FeFeNC-4 in water solvent (0.34 V) is increased compared to that in a vacuum (0.15 V).O 2 + * + H + + e − → *OOHO 2 + * + H + + e − → *O + *OH*OOH + H + + e − → *O + H 2 O*O + *OH + H + + e − → *O + H 2 O*O + *OH + H + + e − → *OH + *OH*O + H + + e − → *OH*OH + H + + e − → H 2 O + *…”

“…† It is noteworthy that the adsorption strength of oxygen species on FeFeNC-4 becomes stronger aer considering the solvent environment, which is consistent with previous studies. 7,51 Due to the enhanced binding strength, the overpotential of FeFeNC-4 in water solvent (0.34 V) is increased compared to that in a vacuum (0.15 V).…”

“…Among them, nitrogen-coordinated transition atoms on the carbon matrix (TM-NC) are one of the most promising representatives in this community. 5–7 Up till now, a variety of TM-NC catalysts ( e.g. , Fe-NC, 8–10 Co-NC, 10,11 Ni-NC, 10 Cu-NC, 12 Zn-NC, 13 Mn-NC, 9 Cr-NC, 14 Mo-NC, 15 W-NC, 16 Ce-NC, 17 and Y-NC 18 ) were experimentally and theoretically investigated and were proved to exhibit attractive activity for catalyzing the ORR.…”

“…Among them, nitrogen-coordinated transition atoms on the carbon matrix (TM-NC) are one of the most promising representatives in this community. [5][6][7] Up till now, a variety of TM-NC catalysts (e.g., Fe-NC, [8][9][10] Co-NC, 10,11 Ni-NC, 10 Cu-NC, 12 Zn-NC, 13 Mn-NC, 9 Cr-NC, 14 Mo-NC, 15 W-NC, 16 Ce-NC, 17 and Y-NC 18 ) were experimentally and theoretically investigated and were proved to exhibit attractive activity for catalyzing the ORR. The activity of SACs is highly related to the transition metal and coordination environment of the center MN x species, which has a signicant effect on the reactivity through electronic transfer due to strong metalsupport interactions (SMSIs).…”

Identification of a Robust and Durable FeN4Cx Catalyst for ORR in PEM Fuel Cells and the Role of the Fifth Ligand

“…However, because of the low-coordination environment of the isolated Fe atom, it is possible that it adsorbs electrolyte ions or molecules from the electrocatalytic solution system. Effects of the coordination environment on ORR , and the presence of a functional ligand on one side of the FeN 4 /C catalyst along with the effects of different functional ligands on ORR activity have been discussed in recent theoretical and experimental studies. − For instance, Jia et al demonstrated that the pyridinic FeN 4 structures remain ORR active, especially the FeN 4 C 8 catalyst. They suggested that the presence of a fifth ligand (i.e., an NH 2 – ) may cause a significant increase in ORR activity.…”