Figure 1 . (a) Schematic diagram of the atomic diversity and atomic diversity free homonuclear DAC transformation. (b) The selected asymmetric structure of defective C3N monolayer and the transitional metal candidates for homonuclear dual atoms doping, the gray, plum, and blue ball representative of the C, N, and TM atom. (c) The formation energy of homonuclear dual TM atoms anchoring on defective C3N substrate. (c) Dissolution potential of the TM2@sitex (x = 1, 2, 3, 4).
After ensuring the stability of the TM-doped defective C3N systems, we next focus on evaluating the configuration-induced intrinsic properties’ variety of the atomic property-constant homonuclear DAC. We first investigated the structural properties of the doped TM’s configuration environment, for which the changes of coordinate environment can effectively tune the intrinsic properties for the homonuclear system, as confirmed by various electrocatalytic reactions for single atom catalyst55, 56. Quantitively, bond length values of each adjacent decorated atom could directly reflect the bonding nature between the TM atom and the coordinate C and N atom, which indirectly affects the intrinsic properties’ variety of the doped homonuclear TM atoms. As shown inFigure S2 and Table S2-S5 , we list the bond length values of each TM-C and TM-N in the inline filled diagram for site1, site2, site3, and site4. The bond length between dual TM atoms varies, demonstrating the differentiation of each TM atom, especially for the bond difference in site3 and site4, which can significantly impact the intrinsic properties of the active sites.
Next, to prove the coordination-induced intrinsic properties’ variety, the charge transfer between TM atoms and the substrate is quantitively investigated initially since the charge transfer plays an essential role in the electrocatalytic field, as confirmed in recent research for eNRR49, 57, 58. Nearly all the doped homonuclear TM atoms lost electrons since the average negative charges transfer (see inFigure 2 (a), (b)), which is suitable for charges transferred from the N2 molecule during the capture process. Differentially, it was proved that the quantity of charge transfer for each TM atom shows observable variety for nearly whole systems in TM2@sitex (x = 1, 2, 3, 4), especially for Fe, Cu, W, Re, Os, Ir in site1, Ni, Cu, Re, Ir, Pt, Au in site2, Cr, Co, Pd, W, Os, Pt in site3 and Co, Ni, Cu, Os, Pt in site4. However, the negligible charge transfer differentiation of Mo, Ru, Pt in site1, Pd, W, Os in site2, Ni, Ag in site3 and Fe, Ru in site4 suggested the inefficient modulation of the homonuclear DAC heteronuclear, and other factors should be considered for further investigation. The spin moment of the doped TM atoms could be an excellent descriptor to explain the catalytic behavior in electrocatalytic fields, which has been systematically studied by some scholars 59, 60, 61, 62, 63, 64, 65, 66, 67. So, we then compared the spin moment differences of the doped systems. It was worth noting that nearly half of the selected candidates show zero spin moment, so those systems are excluded for spin moment differentiating in this part. The rest systems, including Cr, Mn, Fe, Co, Mo, Ru, Re, Os in site1, Fe, Co, Ru, Os in site2, Fe, Co, Mo, Pd, W, Re, Pt in site3, V, Cr, Mn, Fe, Co, Ru, W, Re, Os, Ir, Au in site4, are investigated for further studying. As depicted in Figure S3 , among them, Cr2@site1, Fe2@site1, Fe2@site2, Fe2@site3, and Mn2@site4 show huge different spin moments of 6.10μB (TM1: -3.11μB; TM2: 3.00μB), 1.86μB, 1.90μB, 1.38μB, 3.08μB, revealing the fully heteronuclear of them, for the negligible charge difference of Mo, Ru, Pt in site1, Pd, W, Os in site2, Ni, Ag in site3 and Fe, Ru in site4. Parts of them show observable spin moment differences, such as Mo2@site1 (0.52μB), Ru2@site1 (0.15μB), Fe2@site4 (0.29μB) and Ru2@site4 (0.40μB). Those results proved that the intrinsic properties’ varieties of atomic property-constant homonuclear dual TM atoms are further differentiating.
Nevertheless, the d-band center of the TM atoms is also investigated further since the d-band center is highly related to the adsorption energy of the reactant molecule and their corresponding intermediates47, 68, as depicted in Figure S3(b) and (c), the d-band center difference varies from 0.01 to 1.70, indicating the complete differentiation of them. Among them, the indistinctive-liked charge transfer difference and zero spin moment of Pt2@site1, Pd2@site2, W2@site2, Os2@site2, Ni2@site3, Ag2@site3 exhibit d-band center difference of 0.07eV, 0.28 eV, 0.30 eV, 0.09 eV, 1.24 eV, 0.25 eV, respectively, suggest the observable intrinsic properties’ variety of the homonuclear dual TM atoms. Therefore, the doped homonuclear dual TM atoms would exhibit different properties from the geometric variety to electronic property difference since the mirror broke off the coordinate environment, which realizes heteronuclear-like homonuclear DAC on the fundament of atomic properties keeps constant.