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.