Evaluating the Catalytic Efficiency of Paired, Single-Atom Catalysts for the Oxygen Reduction Reaction

Abstract

Paired, single-atom catalysts have been shown to demonstrate synergistic effects computationally and experimentally which enable them to outperform the benchmark catalyst, Pt/C, for electrochemical reactions. We explore the limit of these catalysts by screening different transition metal atoms (M = Co, Pt, Fe, Ni) in nitrogen-doped graphene for their ability to catalyze the oxygen reduction reaction (ORR). We employ density functional theory methods to explore the electronic factors affecting catalytic activity in an effort to rationalize trends in the performance of materials which are promising candidates for the next generation of electrocatalysts. It is found that CoPt@N8V4, composed of paired Co and Pt in a nitrogen-doped four-atom vacancy in graphene (N8V4), performs ideally for the ORR with an overpotential (η) of 0.30 V, followed closely by Co and Ni (η = 0.35 V) and paired Co (η = 0.37 V). The origin of activity is suggested to be the changing reduction potential of the active Co atom via the local distortion of the pore by the spectating metal partner. We utilize the ORR scaling relations and plot catalytic activity on a volcano plot, which we correlate with the degree of antibonding interactions with the O atom in the OH intermediate of the ORR. We establish that the local tuning of paired catalysts allows for the reactivity of metal atoms to be specifically modified for desirable reactivity.

Microenvironment modulation of single-atom catalysts and their roles in electrochemical energy conversion

“…The construction of dual-metal sites in SACs has been shown with synergistic effects in improving the ORR performance. Recently, DFT studies performed by Hunter et al (95) demonstrate that the spectating metal have been proposed as the best-performing system for ORR (Fig. 3H).…”

Improving the Catalytic Activity of Carbon‐Supported Single Atom Catalysts by Polynary Metal or Heteroatom Doping

“…[ 66,67 ] The catalytic activity is optimized by a balance between adsorption energies of reactive intermediates and reactive sites. [ 68 ] For example, based on the “volcano‐type” plot obtained by density functional theory methods, Pt–Co is considered to be the optimal metal pair for ORR activity, [ 69,70 ] and then different synthesis methods were explored to prepare a large‐scale Pt–Co SACs for experimental research and commercial application.…”

“…[ 78 ] Based on DFT simulation, the couple of Pt–Co shows the optimal catalytic activity for ORR among the different metal diatomic pairs with unary or polynary metals (M = Co, Pt, Fe, Ni). [ 69 ]…”

Accurate prediction of binding energies for two‐dimensional catalytic materials using machine learning

“…All of the original optimisation calculations are performed using the same density functional and computational hyperparameters (such as super-cell volume, mass of carbon, and number of k-points), as described in previous publications. [8][9][10] Details to the calculations are in the Supporting Information.…”

“…[9] Potentially, with the appropriate N-doped GR defects and two metal atoms, an even more efficient catalyst for different reactions could be created. [10] The strength of interaction between the metal atoms and the reactants and intermediates is critical to their performance, and is known to be correlated to the local environment of the metal centre. [11,12] This includes the geometric coordination of the surface to the metal as well as the electronic environment.…”