Gold-doped graphene: A highly stable and active electrocatalysts for the oxygen reduction reaction

Abstract

In addressing the growing need of renewable and sustainable energy resources, hydrogen-fuel-cells stand as one of the most promising routes to transform the current energy paradigm into one that integrally fulfills environmental sustainability. Nevertheless, accomplishing this technology at a large scale demands to surpass the efficiency and enhance the cost-effectiveness of platinum-based cathodes, which catalyze the oxygen reduction reaction (ORR). In this work, our first-principles calculations show that Au atoms incorporated into graphene di-vacancies form a highly stable and cost-effective electrocatalyst that is, at the same time, as or more (dependently of the dopant concentration) active toward ORR than the best-known Pt-based electrocatalysts. We reveal that partial passivation of defected-graphene by gold atoms reduces the reactivity of C dangling bonds and increases that of Au, thus optimizing them for catalyzing the ORR and yielding a system of high thermodynamic and electrochemical stabilities. We also demonstrate that the linear relation among the binding energies of the reaction intermediates assumed in computational high-throughput material screening does not hold, at least for this non-purely transition-metal material. We expect Au-doped graphene to finally overcome the cathode-related challenge hindering the realization of hydrogen-fuel cells as the leading means of powering transportation and portable devices.

On the Elusive Link between Adsorbate's Binding Energy and Bond Strength: An Illustration from CO Adsorption on Metal-Doped Graphene

“…In this work, we study metal‐doped graphene (M−Gr) systems in which a metal atom (M=Ru, Ir, Pd, Pt, Ag, Au) is incorporated into a 5‐8‐5 di‐vacancy of a graphene (Figure ). The reasons for this choice are: (a) This vacancy type is quite stable and known to trap transition metal atoms ,. (b) The selected M‐elements represent transition metals with varying number of d ‐electrons, and different magnitude of relativistic effects on d‐ bands, which is important for understanding the relationship between the electronic structure, E pert , and E rx .…”

“…Currently, since Density Functional Theory (DFT) total-energy calculations render binding energies relatively fast and inexpensively, some research groups try to find efficient catalysts by computational testing hundreds of materials (the high-1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 throughput screening). In contrast, we lean toward rational tuning of E B , [1,4] which is based on an educated pre-selection of several candidates for efficient catalysts followed by a computational "testing". This approach necessarily requires understanding the mechanisms underlying the binding of an adsorbate to a substrate.…”

“…One reason for this choice is that a number of graphene-based materials, especially doped defected graphene, demonstrate promising catalytic properties. [1,[16][17][18][19][20][21][22][23][24][25][26][27] Indeed, pristine graphene is too inert to facilitate catalytic reactions, whereas dangling carbon bonds around vacancies make defected graphene too reactive for many reactions. Nonetheless, it has been shown [1,21,24] that anchoring a metal atom to a graphene vacancy may create adsorption sites of favorable catalytic reactivity.…”

“…[1,[16][17][18][19][20][21][22][23][24][25][26][27] Indeed, pristine graphene is too inert to facilitate catalytic reactions, whereas dangling carbon bonds around vacancies make defected graphene too reactive for many reactions. Nonetheless, it has been shown [1,21,24] that anchoring a metal atom to a graphene vacancy may create adsorption sites of favorable catalytic reactivity. Next, since the electronic structure of doped graphene differs significantly from that of widely studied metal surface catalysts, [1,24] then one may expect new insight into the causes and effects of the perturbation on the binding of adsorbates.…”

“…The reasons for this choice are: (a) This vacancy type is quite stable and known to trap transition metal atoms. [1,[29][30][31] (b) The selected M-elements represent transition metals with varying number of d-electrons, and different magnitude of relativistic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 effects on d-bands, which is important for understanding the relationship between the electronic structure, E pert , and E rx .…”