Changing charge transfer mode with cobalt-molybdenum bimetallic atomic pairs for enhanced nitrogen fixation

The single-atom catalyst is currently regarded as a promising electrocatalyst for the electrochemical reduction of N₂ to NH₃ but its development is impeded by the sluggish kinetics of the proton-coupled electron transfer on the unitary single-atom site. To address this issue, we developed a novel type of electrocatalyst with atomically dispersed Co-Mo pairs anchored on N-doped carbon frameworks (Co-Mo-SA/NC). Remarkably, the theoretical calculations reveal that the formation of Co-Mo asymmetric bimetallic active sites not only changes the “acceptance-donation” charge transfer mode on a single active site to “donation-donation” mode but also modifies the d-band center of the corresponding single atom, leading to enhanced polarization of the N≡N triple bond and inhibition of the hydrogen evolution reaction. As a result, the Co-Mo-SA/NC catalyst achieves a high ammonia yield rate of 37.73 μg h⁻¹ mg_cat⁻¹ and a desirable faradaic efficiency of 23.18% at −0.1 V versus the reversible hydrogen electrode, which are twofold higher than those of the isolated single-atom Co (Co-SA/NC) or Mo (Mo-SA/NC) catalyst. This study provides a promising new strategic design of an electrocatalyst using atomically dispersed metal-pairs to enhance electrochemical nitrogen fixation.