In-Situ Anchoring of Co Single-Atom Synergistically with Cd Vacancy of Cadmium Sulfide for Boosting Asymmetric Charge Distribution and Photocatalytic Hydrogen Evolution

In the context of reshaping the energy pattern, designing and synthesizing high-performance noble metal-free photocatalysts with ultra-high atomic utilization for hydrogen evolution reaction (HER) still remains a challenge. In a streamlined synthesis process, in-situ single atom anchoring is performed in parallel with HER by irradiating a precursory defect-state CdS/Co suspension (Co-DCdS-Ss) system under simulated sunlight and the in-situ synthesizing single-atom Co photocatalyst (Co5:DCdS) exhibits further improved catalytic performance (60.10 mmol g-1 h-1) compared with Co-DCdS-Ss (18.09 mmol g-1 h-1), reaching an apparent quantum yield of 57.6% at 500 nm and a solar-chemical energy conversion efficiency (SCC) of 6.26% at AM 1.5G. In-depth characterization tests and density functional theory (DFT) calculations prove that the anchoring of Co single atom deepens the asymmetric charge distribution of the two-coordination S atom adjacent to the cadmium vacancy (VCd). The synergy between electron delocalization VCd and Co single atom on the catalyst surface is constructed, which bifunctional sites responsible for boosting water adsorption-dissociation and hydrogen evolution. This study advances the understanding of the underlying mechanisms of synergy between surface defects and metal single atoms and opens a new horizon for the development of advanced materials in the field of photocatalysis.

Electronic Structure of Rh and Ir Single Atom Catalysts Supported on Defective and Doped ZnO: Assessment of Their Activity Towards CO Oxidation

This study investigated the electronic structure of single-atom Rhodium (Rh) and Iridium (Ir) adsorbed on defective and impurity-doped ZnO(0001) surfaces, and assessed their activity towards the CO oxidation reaction. Our findings reveal that surface impurities significantly influence the binding energies and electronic properties of the metal atoms, with Al and Cr serving as particularly effective promoters. While Rh and Ir acquire a positive charge upon incorporation on the unpromoted Zn(0001) surface, adsorption directly on the promoter results in a net negative charge, thus facilitating the activation of both CO and O2 species. These results highlight the potential of impurity-promoted ZnO surfaces in modulating and tailoring the electronic properties of SACs, which can be used for a rational design of active single-atom catalysts.

Discovery of highly efficient dual-atom catalysts for propane dehydrogenation assisted by machine learning

Propane dehydrogenation (PDH) is a highly efficient approach for industrial production of propylene, and the dual-atom catalysts (DACs) provide new pathways in advancing atomic catalysis for PDH with dual active sites. In this work, we have developed an efficient strategy to identify promising DACs for PDH reaction by combining high-throughput density functional theory (DFT) calculations and the machine-learning (ML) technique. By choosing the γ-Al2O3(100) surface as the substrate to anchor dual metal atoms, 435 kinds of DACs have been considered to evaluate their PDH catalytic activity. Four ML algorithms are employed to predict the PDH activity and determine the relationship between the intrinsic characteristics of DACs and the catalytic activity. The promising catalysts of CuFe, CuCo and CoZn DACs are finally screened out, which are further validated by the whole kinetic reaction calculations, and the highly efficient performance of DACs is attributed to the synergistic effects and interactions between the paired active sites.

Leveraging Interlayer Interaction in M-N-C Catalysts for Enhanced Activity in Oxygen Reduction Reactions

Atomically dispersed metal-nitrogen-carbon (M-N-C) materials are deemed promising catalysts for the oxygen reduction reaction (ORR) in fuel cells. Yet the multilayer nature of M-N-C has been largely neglected in computational analysis. To bridge the gap, we conducted a first-principles investigation using bilayer M-N-C models (TMNx/G-TMNy/G, TM = Mn, Fe, Co, Ni, Cu, G = graphene, x, y = 3 or 4), where the TMs on the top serves as the active center. While in-plane TMN4 at the bottom has a minimal impact on the ORR, out-of-plane TMN3 substantially influences the adsorption free energy of OH through a strong interlayer bonding interaction. By leveraging interlayer interactions, we appreciably lowered the overpotential of selected TMN4 (TM = Co, Ni, Cu) and achieved a minimum of 0.40 V on CoN4/G-CuN3/G. Constant potential calculations revealed weak dependence of OH binding energy on external voltage and obtained results comparable to constant charge calculation. This study provided new physical insight into modulating naturally occurring multilayer M-N-C catalysts.

Nb-doped NiO nanoflowers for nitrite electroreduction to ammonia

Electrocatalytic reduction of nitrite to ammonia (NO2RR) is considered as an appealing route to simultaneously achieve sustainable ammonia production and abate hazardous nitrite pollution. Herein, atomically Nb-doped NiO nanoflowers are designed as a high-performance NO2RR catalyst, which exhibits the highest NH3-Faradaic efficiency of 92.4% with an NH3 yield rate of 200.5 μmol h-1 cm-2 at -0.6 V RHE. Theoretical calculations unravel that Nb dopants can act as Lewis acid sites to render effective NO2- activation, decreased protonation energy barriers, and restricted hydrogen evolution, ultimately leading to a high NO2RR selectivity and activity.

Comprehensive Study of Oxygen Vacancies on the Catalytic Performance of ZnO for CO/H2 Activation Using Machine Learning-Accelerated First-Principles Simulations

Oxygen vacancies (OVs) play important roles on any oxide catalysts. In this work, using an investigation of the OV effects on ZnO(101̅0) for CO and H₂ activation as an example, we demonstrate, via machine learning potentials (MLPs), genetic algorithm (GA)-based global optimization, and density functional theory (DFT) validations, that the ZnO(101̅0) surface with 0.33 ML OVs is the most likely surface configuration under experimental conditions (673 K and 2.5 MPa syngas (H₂:CO = 1.5)). It is found that a surface reconstruction from the wurtzite structure to a body-centered-tetragonal one would occur in the presence of OVs. We show that the OVs create a Zn₃ cluster site, allowing H₂ homolysis and C-O bond cleavage to occur. Furthermore, the activity of intrinsic sites (Zn_3c and O_3c sites) is almost invariable, while the activity of the generated OV sites is strongly dependent on the concentration of the OVs. It is also found that OV distributions on the surface can considerably affect the reactions; the barrier of C-O bond dissociation is significantly reduced when the OVs are aligned along the [12̅10] direction. These findings may be general in the systems with metal oxides in heterogeneous catalysis and may have significant impacts on the field of catalyst design by regulating the concentration and distribution of the OVs.

Relationship between Acidity and Activity on Propane Conversion over Metal-Modified HZSM-5 Catalysts

A systematic study of the comparative performances of different metal-impregnated HZSM-5 catalysts (Zn, Ga, Mo, Co, and Zr) for propane conversion is presented. The physicochemical properties of catalysts were characterized by means of XRD, BET, SEM, TEM, FTIR, XPS, 27Al MAS NMR, NH3-TPD and Py-FTIR. It was found that the acidities of the catalysts were significantly influenced by loading metal. More specifically, Mo-, Co- or Zr-modified catalysts showed a large metal size and low acidic density, resulting high olefin selectivity, while Zn- or Ga-modified catalysts maintained their small metal size and acidic density, and mainly reduced B/L due to the Lewis acid sites created by Zn or Ga species, resulting in high aromatics selectivity. Experimental results also showed that there is a balance between metals size and medium and strong acidity on propane conversion. Moreover, based on the different acidity of metal-modified HZSM-5 catalysts, the mechanism of propane conversion was also discussed.