The electrocatalytic activity of transition-metal-based compounds is strongly related to the spin states. However, the underlying relationship connecting spin to catalytic activity remains unclear. ...Herein, we carried out density functional theory calculations on oxygen reduction reaction (ORR) catalyzed by Fe single-atom supported on C2N (C2N–Fe) to shed light on this relationship. It is found that the change of electronic spin moments of Fe and O2 due to molecular-catalyst adsorption scales with the amount of electron transfer from Fe to O2, which promotes the catalytic activity of C2N–Fe for driving ORR. The nearly linear relationship between the catalytic activity and spin moment variation suggests electronic spin moment as a promising catalytic descriptor for Fe single-atom based catalysts. Following the revealed relationship, the ORR barrier on C2N–Fe was tuned to be as low as 0.10 eV through judicious manipulation of spin states. These findings thus provide important insights into the relationship between catalytic activity and spin, leading to new strategies for designing transition metal single-atom catalysts.
Isolated single atomic site catalysts have attracted great interest due to their remarkable catalytic properties. Because of their high surface energy, single atoms are highly mobile and tend to form ...aggregate during synthetic and catalytic processes. Therefore, it is a significant challenge to fabricate isolated single atomic site catalysts with good stability. Herein, a gentle method to stabilize single atomic site metal by constructing defects on the surface of supports is presented. As a proof of concept, single atomic site Au supported on defective TiO2 nanosheets is prepared and it is discovered that (1) the surface defects on TiO2 nanosheets can effectively stabilize Au single atomic sites through forming the Ti–Au–Ti structure; and (2) the Ti–Au–Ti structure can also promote the catalytic properties through reducing the energy barrier and relieving the competitive adsorption on isolated Au atomic sites. It is believed that this work paves a way to design stable and active single atomic site catalysts on oxide supports.
Single atomic sites of Au are supported on defective TiO2 nanosheets and it is discovered that the surface defects on TiO2 nanosheets can effectively stabilize Au single atomic sites through forming a Ti–Au–Ti structure, and this Ti–Au–Ti structure can also promote the catalytic properties through reducing the energy barrier and relieving the competitive adsorption on isolated Au atomic sites.
Composite structures have been widely utilized to improve material performance. Here we report a semiconductor-metal hybrid structure (CuO/Ag) for CO oxidation that possesses very promising activity. ...Our first-principles calculations demonstrate that the significant improvement in this system's catalytic performance mainly comes from the polarized charge injection that results from the Schottky barrier formed at the CuO/Ag interface due to the work function differential there. Moreover, we propose a synergistic mechanism underlying the recovery process of this catalyst, which could significantly promote the recovery of oxygen vacancy created via the M-vK mechanism. These findings provide a new strategy for designing high performance heterogeneous catalysts.
We performed density functional theory (DFT) calculations to investigate the synergized O2 activation and CO oxidation by Ag8 cluster on TiO2(101) support. The excellent catalytic activity of the ...interfacial Ag atoms in O2 dissociation is ascribed to the positive polarized charges, upshift of Ag d-band center, and assistance of surface Ti5c atoms. CO oxidation then takes place via a two-step mechanism coupled with O2 dissociation: (i) CO + O2 → CO2 + O and (ii) CO + O → CO2. The synergistic effect of CO and O2 activations reduces the oxidation energy barrier (E a) of reaction (i), especially for the up-layered Ag atoms not in contact with support. It is found that the coadsorbed CO and O2 on the up-layered Ag atoms form a metal-stable four-center O–O–CO structure motif substantially promoting CO oxidation. On the oxygen defective Ag8/TiO2(101) surface, because of the decreased positive charges and the down-shift of d-band centers in Ag, the metal cluster exhibits low O2 adsorption and activation abilities. Although the dissociation of O2 is facilitated by the TiO2(101) defect sites, the dissociated O atoms would cover the defects so strongly that further CO oxidation would be prohibited unless much extra energy is introduced to recreate oxygen defects.
Developing efficient and economical electrocatalysts for acidic oxygen evolution reaction (OER) is essential for proton exchange membrane water electrolyzers (PEMWE). Cobalt oxides are considered ...promising non-precious OER catalysts due to their high activities. However, the severe dissolution of Co atoms in acid media leads to the collapse of crystal structure, which impedes their application in PEMWE. Here, we report that introducing acid-resistant Ir single atoms into the lattice of spinel cobalt oxides can significantly suppress the Co dissolution and keep them highly stable during the acidic OER process. Combining theoretical and experimental studies, we reveal that the stabilizing effect induced by Ir heteroatoms exhibits a strong dependence on the distance of adjacent Ir single atoms, where the OER stability of cobalt oxides continuously improves with decreasing the distance. When the distance reduces to about 0.6 nm, the spinel cobalt oxides present no obvious degradation over a 60-h stability test for acidic OER, suggesting potential for practical applications.
Inspired by the typical two-dimensional (2D) black-phosphorene-type structure with
mm2
point-group symmetry, the structural stability, electronic structure, and intrinsic piezoelectricity of 2D ...ternary GaXY (X = Se and Te; Y = Cl, Br, and I) monolayers are systematically studied by the first-principles density functional theory. Our calculations show that these ternary monolayer compounds exhibit desirable dynamical and thermal stabilities and a large variety of bandgaps. The calculated piezoelectric coefficients
d
11
is as large as 15.57 pm/V for GaTeF, and the largest
d
12
reaches to 3.78 pm/V for GaSeI. It is worth noting that the
e
ij
and
d
ij
coefficients of GaXY monolayers display anisotropic periodic trends with respect to the constituent elements, which could be interpreted by a linear correlation between the piezoelectric coefficients and the differences in anionic polarizabilities
α
X
or
α
Y
. It is found that
d
11
of GaXY monolayers is directly proportional to
(
α
X
-
α
Y
)
, while
d
12
is inversely proportional to
(
α
X
-
α
Y
)
. Such anisotropic correlation could be applicable to elucidate the origin of the piezoelectricity in other 2D ternary compounds.
Graphical abstract
The versatile properties of bimetallic nanoparticles greatly expand the range of catalyzed chemical reactions. We demonstrate that surface chemistry can be understood and predicted using a simple ...adsorbate–surface interaction descriptor that relates charge polarization to chemical reactivity. Our density functional theory studies of O2 activation and CO oxidation catalyzed by Au7–Cu1 bimetallic nanoparticles supported on the TiO2(101) surface demonstrate that the generated oxidized Cu atom (CuO x ) can efficiently inhibit the aggregation of the active Cu sites. Moreover, because of the strong dipole–dipole interaction between the surface and the adsorbate on the oxidized Cu site, the adsorption of CO + O2/CO + O can be significantly enhanced, which can decrease the CO oxidation barriers and further improve catalytic performance. The product of the two electric dipole moments provides a parameter that allows us to predict the key catalytic properties for different adsorption sites and reaction pathways. The reported findings provide important insights into the mechanism of chemical reactivity of metallic clusters and generate a valuable principle for catalyst design.
Water adsorption and decomposition on stoichiometrically perfect and oxygen vacancy containing ZnGa2O4 (100), (110), and (111) surfaces were investigated through periodic density functional theory ...(DFT) calculations. The results demonstrated that water adsorption and decomposition are surface-structure-sensitive processes. On a stoichiometrically perfect surface, the most stable molecular adsorption that could take place involved the generation of hydrogen bonds. For dissociative adsorption, the adsorption energy of the (111) surface was more than 4 times the energies of the other two surfaces, indicating it to be the best surface for water decomposition. A detailed comparison of these three surfaces showed that the primary reason for this observation was the special electronic state of the (111) surface. When water dissociated on the (111) surface, the special Ga3c-4s and 4p hybridization states at the Fermi level had an obvious downshift to the lower energies. This large energy gain greatly promoted the dissociation of water. Because the generation of O3c vacancy defects on the (100) and (110) surfaces could increase the stability of the dissociative adsorption states with few changes to the energy barrier, this type of defect would make the decomposition of water molecules more favorable. However, for the (111) surface, the generation of vacancy defects could decrease the stability of the dissociative adsorption states and significantly increase their energy barriers. Therefore, the decomposition of water molecules on the oxygen vacancy defective (111) surface would be less favorable than the perfect (111) surface. These findings on the decomposition of H2O on the ZnGa2O4 surfaces can be used toward the synthesis of water-splitting catalysts.
Dual-metal-site catalysts (DMSCs) have emerged as a frontier in heterogeneous catalysis, while the underlying relationships connecting their dual-site synergistic effects on catalytic performance ...remain unclear. Here we present a comprehensive first-principles study of O2 activation and CO oxidation on a series of N-coordinated DMSCs. We discovered that the N3-coordinated-adjacent dual-metal model has stronger synergistic and dynamic effects, leading to much higher catalytic activity than others investigated. Based on this model, detailed comparisons of various metal combinations (M = Fe, Co, Ni, Cu, and Pt) show that Fe-containing combinations are generally more active than others. In particular, the Fe–Ni combination, owing to its preferential coadsorption of CO+O2 and highest activity is identified as the most promising candidate for CO oxidation. To explore some universal descriptors for catalytic performance of different combinations, various relationships (50 in total) were systemically studied. It is found that the designed electronic/spectral descriptors of charge transfer, average charge on metals, average d-orbital center on metals, and stretching vibrational frequency of reactants may reflect the binding ability/stability of O2 as lone reactant. However, for multiple reactants (CO+O2), the binding stability/reactivity of the key-species (O2) descriptor has better performance. The transferability of such descriptors to multimolecular catalysis was confirmed by applying them to NO oxidation. These novel descriptors highlight the importance of structure–activity relationships under reaction conditions, thus providing potential design strategies for high-efficiency DMSCs.
Polynary single-atom structures can provide synergistic functions based on multiple active sites and reactants, which significantly improve their catalytic performance. However, the ...structure–activity relationships of these special structures remain elusive. Here, we report atomically dispersed Fe–Ni dual-metal catalysts anchored on N-doped graphene as an efficient catalyst for CO oxidation. The density functional theory (DFT) calculation results show that Ni serves as a catalytic nucleophilic center for CO adsorption, whereas Fe serves as an electrophilic center for O2 adsorption, making full use of the dual-metal active sites. Thus, a heteronuclear Fe1Ni1@NGr catalyst with the synergistic effect of combining dissimilar metal atoms has better catalytic activity and lower propensity for CO poisoning than its homonuclear counterparts. Comparing the Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) mechanisms for CO oxidation on Fe1Ni1@NGr, Ni2@NGr, and Fe2@NGr, we find that the LH mechanism with coadsorbed CO and O2 is dynamically more favorable. In addition, residual oxygen atoms attached to the Fe–Ni active sites can easily react with additional CO molecules, indicating the achievement of a high recycling rate. These findings reveal a synergistic catalytic mechanism of graphene-supported atomically dispersed transition dual-metal catalysts, providing important guidance for the rational design of atomically dispersed catalysts.
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