Atomic Mechanism of Electrocatalytically Active Co–N Complexes in Graphene Basal Plane for Oxygen Reduction Reaction

Abstract

Superior catalytic activity and high chemical stability of inexpensive electrocatalysts for the oxygen reduction reaction (ORR) are crucial to the large-scale practical application of fuel cells. The nonprecious metal/N modified graphene electrocatalysts are regarded as one of potential candidates, and the further enhancement of their catalytic activity depends on improving active reaction sites at not only graphene edges but also its basal plane. Herein, the ORR mechanism and reaction pathways of Co-N co-doping onto the graphene basal plane have been studied by using first-principles calculations and ab initio molecular dynamics simulations. Compared to singly N-doped and Co-doped graphenes, the Co-N co-doped graphene surface exhibits superior ORR activity and the selectivity toward a four-electron reduction pathway. The result originates from catalytic sites of the graphene surface being modified by the hybridization between Co 3d states and N 2p states, resulting in the catalyst with a moderate binding ability to oxygenated intermediates. Hence, introducing the Co-N4 complex onto the graphene basal plane facilitates the activation of O2 dissociation and the desorption of H2O during the ORR, which is responsible for the electrocatalyst with a smaller ORR overpotential (∼1.0 eV) that is lower than that of Co-doped graphene by 0.93 eV. Our results suggest that the Co-N co-doped graphene is able to compete against platinum-based electrocatalysts, and the greater efficient electrocatalysts can be realized by carefully optimizing the coupling between transition metal and nonmetallic dopants in the graphene basal plane.

Exploring an effective oxygen reduction reaction catalyst via 4e− process based on waved-graphene

“…ΔG U = −neU, where n is the number of transferred electrons, e is the elementary charge, and U is the electrode potential referenced to SHE. As indicated by the computational hydrogen electrode (CHE) model, the free energy change ∆G is a function of the applied electrical potential (U) [14,36]. The free energy of (H + + e − ) in solution at standard conditions was assumed as the energy of 1/2 H 2 according to a computational hydrogen electrode model suggested by Nørskov et al [35] Taking the reaction HO*+ H + + e − → * + H 2 O as an example, at …”

“…A lot of efforts have been done to tune their electronic structures to enhance their ORR activity by doping a heteroatom [5][6][7][8][9], such as nitrogen (N), phosphorus (P), boron (B), sulfur (S), selenium (Se), antimony (Sb) or their mixtures [10][11][12][13]. Another way is to introduce active nonprecious transition metal (e.g., Fe, Co, and Ni) atoms or nanoparticles into heteroatom-doped graphene [14][15][16]. For example, Fe-N modified carbon electro-catalysts [17] have been reported by Zhu et al [18], Kong et al [19] and Zitolo et al [20] with high ORR activity and good durability in both alkaline and acidic media.…”

“…This is because the four-electron reduction pathway requires relatively active catalytic sites to activate O 2 molecules, resulting in the O−O bond breaking and the formation of O−H bond [14]. Because the formation of the graphene basal plane is thermodynamically favorable, it would limit the number of active sites in the graphenebased catalysts.…”

“…Considering its abundant active sites and high chemical reactivity, the WG could be a suitable ORR catalyst. It is well-known that a fuel cell working in an acidic medium is of practical significance due to the high CO tolerance during the ORR at the cathode [14,28]. Thus, in this work, we investigate the ORR performance of the WG in the acid medium based on the first-principles calculations.…”

Edge structures and properties of triangular antidots in single-layer MoS2

“…The bright areas are likely to serve as active sites due to high charge density, which facilitates charge transfer to the reactant molecules. 43 The inner bright triangle corresponds to the O atoms, with more intensity at the corners (O p z contributions) than along the edges (O p x /p y contributions), and the outer triangle on the S atoms, displaying p x /p y features. The intensity decreases gradually from the edges to the corners due to a structural effect: The protrusion of the edge Mo atoms weakens their bonding to the edge S atoms.…”