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The interfacial sites of supported metal catalysts are often critical in determining their performance. Single-atom catalysts (SACs), with every atom contacted to the support, can maximize the number of interfacial sites. However, it is still an open question whether the single-atom sites possess similar catalytic properties to those of the interfacial sites of nanocatalysts. Herein, we report an active-site dependent catalytic performance on supported gold single atoms and nanoparticles (NPs), where CO oxidation on the single-atom sites is dramatically promoted by the presence of H 2 O whereas on NPs’ interfacial sites the promoting effect is much weaker. The remarkable H 2 O promoting effect makes the Au SAC two orders of magnitude more active than the commercial three-way catalyst. Theoretical studies reveal that the dramatic promoting effect of water on SACs originates from their unique local atomic structure and electronic properties that facilitate an efficient reaction channel of CO + OH.

Catalysis by supported single metal atoms has demonstrated tremendous potential for practical applications due to their unique catalytic properties. Unless they are strongly anchored to the support surfaces, supported single atoms, however, are thermodynamically unstable, which poses a major obstacle for broad applications of single-atom catalysts (SACs). In order to develop strategies to improve the stability of SACs, we need to understand the intrinsic nature of the sintering processes of supported single metal atoms, especially under various gas environments that are relevant to important catalytic reactions. We report on the synthesis of high number density Pt/FeO SACs using a facial strong adsorption method and the study of the mobility of these supported Pt single atoms at 250 °C under various gas environments that are relevant to CO oxidation, water-gas shift, and hydrogenation reactions. Under the oxidative gas environment, FeO supported Pt single atoms are stable even at high temperatures. The presence of either CO or H molecules in the gas environment, however, facilitates the movement of the Pt atoms. The strong interaction between CO and Pt weakens the binding between the Pt atoms and the support, facilitating the movement of the Pt single atoms. The dissociation of H molecules on the Pt atoms and their subsequent interaction with the oxygen species of the support surfaces dislodge the surface oxygen anchored Pt atoms, resulting in the formation of Pt clusters. The addition of HO molecules to the CO or H significantly accelerates the sintering of the FeO supported Pt single atoms. An anchoring-site determined sintering mechanism is further proposed, which is related to the metal-support interaction.

A synthetic route to achieve core/shell nanostructures consisting of noble metal cores and single crystal semiconductor shells with different crystal systems is proposed, which involves a simple phosphorization process from corresponding bimetallic heterostructures. The triphenylphosphine is designed to serve as both a capping agent and a phosphorous source during the formation of Au/Ni 12 P 5 core/shell nanoparticles (NPs) from Au-Ni bimetallic heterodimers. The semiconductor shells of the obtained Au/Ni 12 P 5 nanostructures are controlled to form single crystals with a thickness of B5 nm. The structure-dependent supercapacitor properties of Au-modified Ni 12 P 5 nanostructures were further investigated. The synergistic effect of the metal/semiconductor nanostructure is observed to be superior to its oligomer-like counterpart when serving as a supercapacitor electrode. The specific capacitance of an electrode fabricated from core/shell NPs is 806.1 F g À1 with a retention of 91.1% after 500 charge-discharge cycles.

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