Gas-generating catalysis is important to many energy-related research fields, such as photocatalytic water splitting, water electrolysis, etc. The technique of single-nanoparticle catalysis is an effective way to search for highly active nanocatalysts and elucidate the reaction mechanism. However, gas-generating catalysis remains difficult to investigate at the single-nanoparticle level because product gases, such as H and O, are difficult to detect on an individual nanoparticle. Here, we successfully find that nanobubbles can be used to study the gas-generating catalysis, i.e., H generation from formic acid dehydrogenation on a single Pd-Ag nanoplate, with a high time resolution (50 ms) via dark-field microscopy. The research reveals that the nanobubble evolution process includes nucleation time and lifetime. The nucleation rate of nanobubbles is proportional to the catalytic activity of a single nanocatalyst. The relationship between the catalytic activity and the nucleation rate is quantitatively described by a mathematical model, which shows that an onset reaction rate (r) exists for the generation of nanobubbles on a single Pd-Ag nanoplate. The research also reveals that a Pd-Ag nanoplate with larger size usually has a higher activity. However, some large-sized ones still have low activities, indicating the size of the Pd-Ag nanoplate is not the only key factor for the activity. Notablely, further research shows that Pd content is the key factor for the activity of single Pd-Ag nanoplates with similar size. The methodology and knowledge acquired from this research are also applicable to other important gas-generating catalysis reactions at the single-nanoparticle level.

Porous single-crystalline (P-SC) titanium dioxide in large size would significantly enhance their photoelectrochemical functionalities owing to the structural coherence and large surface area. Here we show the growth of P-SC anatase titanium dioxide on an 2 cm scale through a conceptually different lattice reconstruction strategy by direct removal of K/P from KTiOPO 4 lattice leaving the open Ti-O skeleton simultaneously recrystallizing into titanium dioxide. The (101) facet dominates the growth of titanium dioxide while the relative titanium densities on different parent crystal facets control the microstructures. Crystal growth in reducing atmospheres produces P-SC Ti n O 2n-1 ( n = 7~38) in magneli phases with enhanced visible-infrared light absorption and conductivity. The P-SC Ti n O 2n-1 shows enhanced exciton lifetime and charge mobility. The P-SC Ti n O 2n-1 boosts photoelectrochemical oxidation of benzene to phenol with P-SC Ti 9 O 17 showing 60.1% benzene conversion and 99.6% phenol selectivity at room temperature which is the highest so far to the best of our knowledge.

Previous studies show that the metalnitrogen moieties with unsaturated nitrogen coordination numbers possess higher catalytic activities and the reported smallest nitrogen coordination number is confirmed to be ≈2 for Co-N 2 and Fe-N 2 moieties using extended X-ray absorption fine structure spectra analysis. [4][5][6] These results indeed give an in-depth insight at the atomic level into structural dependence of catalytic activity of metal nitride nanoparticles by closely correlating the average structural information with catalytic performances. However, the active metalnitrogen moieties confined at the surface layer of materials that host catalysis reactions still remain unclear.Building metal-nitrogen moieties with unsaturated nitrogen coordination numbers to enhance material's catalytic activity remains a fundamental challenge. The state-of-the-art pyrolysis technique of specific precursors is commonly used to construct metal-nitrogen moieties. However, the simultaneous presence of multiple metal species in most composite catalysts makes it highly complex to understand the nature of metal-nitrogen moieties. [7][8][9][10] The short length scale of nanostructured catalysts makes it extremely challenging to quantify metal-nitrogen moiety structure and distributions and to correspondingly elucidate the electronic structure features and unusual activity. The metal-nitrogen moieties are indeed a kind of active clusters at atomic level, which are strictly confined at lattice in local structures in crystalline composites. The polycrystalline or amorphous states of composites make it highly uncertain to construct resolved metal-nitrogen moieties and to accordingly expose these active centers on material's surfaces to host catalysis reactions. Another consideration should be given to the resolved structural feature and chemical composition of moieties that tailor electronic structures to facilitate catalysis functionalities.Single crystals with porosity, combining the advantages of long-range structural coherence of bulk crystals and large surface areas of porous materials, could provide opportunities to host the metal-nitrogen moieties with unsaturated nitrogen coordination on surface. The long-range structural coherence in single crystals offers the possibility to stabilize the metalnitrogen moieties in lattice of local structures on crystalline surfaces especially on the condition that the surface moieties have similar chemical compositions to bulk crystals. Porous Altering a material's catalytic properties would require identifying structural features that deliver electrochemically active surfaces. Single-crystalline porous materials, combining the advantages of long-range ordering of bulk crystals and large surface areas of porous materials, would create sufficient active surfaces by stabilizing 2D active moieties confined in lattice and may provide an alternative way to create high-energy surfaces for electrocatalysis that are kinetically trapped. Here, a radical concept of building active metalnitrogen moieties ...