Design of molecular M-N-C dual-atom catalysts for nitrogen reduction starting from surface state analysis

Under electrocatalytic conditions, the state of a catalyst surface (e.g., adsorbate coverage) can be very dif-ferent from a pristine form due to the existing conversion equilibrium between water and H-and O-containing adsorbates. Dismissing the analysis of the catalyst surface state under operating conditions-may lead to misleading guidelines for experiments. Given that confirming the actual active site of the cat-alyst under operating conditions is indispensable to providing practical guidance for experiments, herein, we analyzed the relations between the Gibbs free energy and the potential of a new type of molecular metal-nitrogen-carbon (M-N-C) dual-atom catalysts (DACs) with a unique 5 N-coordination environ-ment, by spin-polarized density functional theory (DFT) and surface Pourbaix diagram calculations. Analyzing the derived surface Pourbaix diagrams, we screened out three catalysts, N3-Ni-Ni-N2, N3-Co-Ni-N2, and N3-Ni-Co-N2, to further study the activity of nitrogen reduction reaction (NRR). The results dis-play that N3-Co-Ni-N2 is a promising NRR catalyst with a relatively low DG of 0.49 eV and slow kinetics of the competing hydrogen evolution. This work proposes a new strategy to guide DAC experiments more precisely: the analysis of the surface occupancy state of the catalysts under electrochemical conditions should be performed before activity analysis. (c) 2023 Elsevier Inc. All rights reserved.

Automated summary

Under electrocatalytic conditions, the state of the catalyst surface can differ significantly from its original form, which may lead to misleading experimental guidelines if not properly analyzed. In this study, we analyzed the relationship between Gibbs free energy and potential of a new type of dual-atom catalysts and screened out three promising catalysts for nitrogen reduction reaction (NRR). Our results suggest that N3-Co-Ni-N2 has a relatively low DG and slower kinetics of competing reactions, making it a promising NRR catalyst. This work highlights the importance of analyzing the surface occupancy state of catalysts under electrochemical conditions before activity analysis.