The electrochemical CO reduction reaction (CORR) typically uses transition metals as the catalysts. To improve the efficiency, tremendous efforts have been dedicated to tuning the morphology, size, and structure of metal catalysts and employing electrolytes that enhance the adsorption of CO. We report here a strategy to enhance CORR by constructing the metal-oxide interface. We demonstrate that Au-CeO shows much higher activity and Faradaic efficiency than Au or CeO alone for CORR. In situ scanning tunneling microscopy and synchrotron-radiation photoemission spectroscopy show that the Au-CeO interface is dominant in enhancing CO adsorption and activation, which can be further promoted by the presence of hydroxyl groups. Density functional theory calculations indicate that the Au-CeO interface is the active site for CO activation and the reduction to CO, where the synergy between Au and CeO promotes the stability of key carboxyl intermediate (*COOH) and thus facilitates CORR. Similar interface-enhanced CORR is further observed on Ag-CeO, demonstrating the generality of the strategy for enhancing CORR.

A major challenge limiting the practical applications of nanomaterials is that the activities of nanostructures (NSs) increase with reduced size, often sacrificing their stability in the chemical environment. Under oxidative conditions, NSs with smaller sizes and higher defect densities are commonly expected to oxidize more easily, since high-concentration defects can facilitate oxidation by enhancing the reactivity with O2 and providing a fast channel for oxygen incorporation. Here, using FeO NSs as an example, we show to the contrary, that reducing the size of active NSs can drastically increase their oxidation resistance. A maximum oxidation resistance is found for FeO NSs with dimensions below 3.2 nm. Rather than being determined by the structure or electronic properties of active sites, the enhanced oxidation resistance originates from the size-dependent structural dynamics of FeO NSs in O2. We find this dynamic size effect to govern the chemical properties of active NSs.

Graphene-like ZnO (g-ZnO) nanostructures (NSs) and thin films were prepared on Au(111), and their reactivities toward CO and H 2 were compared with that of wurtzite ZnO (w-ZnO) (0001) single crystals. The interaction and reaction between CO/H 2 and the different types of ZnO surfaces were studied using near-ambient-pressure scanning tunneling microscopy (NAP-STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The reactivity of the w-ZnO(0001) surface toward CO and H 2 was found to be more prominent than those on the surfaces of g-ZnO/Au(111). CO oxidation took place primarily at the edge sites of w-ZnO(0001) and the interface between g-ZnO NSs and Au(111), while g-ZnO thin films on Au(111) appeared to be inert below 600 K. Similarly, the w-ZnO(0001) surface could dissociate H 2 at 300 K, accompanied by a substantial surface reconstruction, while g-ZnO on Au(111) appeared inert for H 2 activation at 300 K. DFT calculations showed that the reactivities of ZnO surfaces toward CO could be related to the formation energy of oxygen vacancy (E Ovf ), which could be related to the charge transfer to lattice oxygen atoms or surface polarity.

Despite tremendous importance in catalysis, the design of oxide-metal interface has been hampered by the limited understanding of the nature of interfacial sites and the oxide-metal interaction (OMI). Through construction of well-defined Cu 2 O/Pt, Cu 2 O/Ag and Cu 2 O/Au interfaces, we find that Cu 2 O nanostructures (NSs) on Pt exhibit much lower thermal stability than on Ag and Au, although they show the same structure. The activities of these interfaces are compared for CO oxidation and follow the order of Cu 2 O/Pt > Cu 2 O/Au > Cu 2 O/Ag. OMI is found to determine the activity and stability of supported Cu 2 O NSs, which could be described by the formation energy of interfacial oxygen vacancy. Further, electronic interaction between Cu + and metal substrates is found center to OMI, where the d band center could be used as a key descriptor. Our study provides insight for OMI and for the development of Cu-based catalysts for low temperature oxidation reactions.

Rational synthesis of sub-nanocatalysts with controllable electronic and atomic structures remains a challenge to break the limits of traditional catalysts for superior performance. Here we report the atomiclevel precise synthesis of Pt/graphene sub-nanocatalysts (from single atom, dimer, and to cluster) by atomic layer deposition, achieved by a novel high temperature pulsed ozone strategy to controllably precreate abundant in-plane epoxy groups on graphene as anchoring sites. The speci c in-plane epoxy structure endows the deposited Pt species with outstanding uniformity, controllability and stability. Their size-depended electronic and geometric effects have been observed for ammonia borane hydrolysis, revealing a volcano-type dependence of intrinsic activity on their sizes. Their active site structures have been identi ed based on extensive characterizations, dynamic compensation effect, kinetic isotope experiments and density function theory simulation. The Pt dimers show the highest catalytic activity and good durability than Pt single atoms and nanoparticles, ascribed to the unique C-Pt-Pt-O (C5Pt2O, metalmetal bond dimer) active site structure. Our work provides new insights into the precise tailoring and catalytic mechanism in sub-nanometer level.

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The rational design and controlled construction of active centers remain grand challenges in heterogeneous catalysis, in particular for oxide catalysts with complex surface and interface structures. This work describes a facile way in the design of highly active Ni−O Lewis pairs for water activation where Ni and O sites act as Lewis acid and base, respectively. Surface science experiments indicate that dissociative adsorption of water occurs at edges of NiO x nanoislands grown on Au(111) and NiO x − Ni interfaces formed by further depositing metallic Ni layers along the edges of NiO x nanoislands. Enhanced activity of Ni−O Lewis pairs at the NiO x −Ni interface has been demonstrated by theoretical calculations, which are attributed to the higher Lewis acidity of metallic Ni sites and synergy of the metal and oxide components. Moreover, proton can migrate away from the NiO x −Ni interface and refresh the O base sites, leading to further hydroxylation of the neighboring Ni acid sites.

The interfacial sites of metal-support interface have been considered to be limited to the atomic region of metal/support perimeter, despite their high importance in catalysis. By using single-crystal surface and nanocrystal as model catalysts, we now demonstrate that the overgrowth of atomic-thick Cu2O on metal readily creates a two-dimensional (2D) microporous interface with Pd to enhance the hydrogenation catalysis. With the hydrogenation confined within the 2D Cu2O/Pd interface, the catalyst exhibits outstanding activity and selectivity in the semi-hydrogenation of alkynes. Alloying Cu(0) with Pd under the overlayer is the major contributor to the enhanced activity due to the electronic modulation to weaken the H adsorption. Moreover, the boundary or defective sites on the Cu2O overlayer can be passivated by terminal alkynes, reinforcing the chemical stability of Cu2O and thus the catalytic stability toward hydrogenation. The deep understanding allows us to extend the interfacial sites far beyond the metal/support perimeter and provide new vectors for catalyst optimization through 2D interface interaction.