Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au-Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of ∼1.3 × 10(7) on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications.

Electroreduction of carbon dioxide (CO2) into high‐value and readily collectable liquid products is vital but remains a substantial challenge due to the lack of highly efficient and robust electrocatalysts. Herein, Bi‐based metal‐organic framework (CAU‐17) derived leafy bismuth nanosheets with a hybrid Bi/BiO interface (Bi NSs) is developed, which enables CO2 reduction to formic acid (HCOOH) with high activity, selectivity, and stability. Specially, the flow cell configuration is employed to eliminate the diffusion effect of CO2 molecules and simultaneously achieve considerable current density (200 mA cm−2) for industrial application. The faradaic efficiency for transforming CO2 to HCOOH can achieve over 85 or 90% in 1 m KHCO3 or KOH for at least 10 h despite a current density that exceeds 200 mA cm−2, outperforming most of the reported CO2 electroreduction catalysts. The hybrid Bi/BiO surface of leafy bismuth nanosheets boosts the adsorption of CO2 and protects the surface structure of the as‐prepared leafy bismuth nanosheets, which benefits its activity and stability for CO2 electroreduction. This work shows that modifying electrocatalysts by surface oxygen groups is a promising pathway to regulate the activity and stability for selective CO2 reduction to HCOOH.

Although aqueous synthesis of nanocrystals is advantageous in terms of the cost, convenience, environmental friendliness, and surface cleanness of the product, nanocrystals of Pt and non-noble metal alloys are difficult to obtain with controlled morphology and composition from this synthesis owing to a huge gap between the reduction potentials of respective metal salts. This huge gap could now be remedied by introducing a sulfite into the aqueous synthesis, which is believed to resemble an electroless plating mechanism, giving rise to a colloid of Pt-M (M=Ni, Co, Fe) alloy nanowires with an ultrasmall thickness (ca. 2.6 nm) in a high yield. The sulfite also leads to the formation of surface M-S bonds and thus atomic-level Pt/M-S(OH) interfaces for greatly boosted hydrogen evolution kinetics under alkaline conditions. An activity of 75.3 mA cm has been achieved with 3 μg of Pt in 1 m KOH at an overpotential of 70 mV, which is superior to previously reported catalysts.

The electroreduction of carbon dioxide is a promising strategy to synthesize value‐added feedstocks and realize carbon neutralization. Copper catalysts are well‐known to be active for selective electroreduction of CO2 to multicarbon products, although the role played by the surface architecture is not fully understood. Herein, mesoporous Cu nanoribbons are constructed via in‐situ electrochemical reduction of Cu based metal organic frameworks for the highly selective synthesis of C2+ chemicals. With the mesoporous structure, a high C2+ Faradaic efficiency of 82.3% with a partial current density of 347.9 mA cm−2 is achieved in a flow‐cell electrolyzer. Controlled electroreduction of CO2 with Cu nanoribbons exhibited clearly greater selectivity towards C2+ products than Cu nanoleaves and Cu nanorods without porous structures. Finite difference time domain results indicate that the mesoporous structure can enhance the electric field on the catalyst surface, which increases the concentration of K+ and OH−, thus allowing the authors to promote CO2 reduction pathways towards C2+ products.

Herein, a facile seed‐assisted strategy for preparing Cu nanoparticles (NPs) with polyvinyl pyrrolidone (PVP) capping is presented. Compared to the Cu NPs with deficient PVP protection, the Cu NPs capped with a sufficient amount of PVP remain almost completely as Cu0 species. In contrast, the Cu NPs that are considered PVP deficient form an oxide structure in which the inner layer is face‐centered cubic Cu and the outer layer is, at least in part, made up of Cu2O species. Furthermore, to eliminate CO2 molecule diffusion and simultaneously obtain significant current density (200 mA cm−2) for industrial applications, a flow cell configuration is used for carbon dioxide electro reduction reaction (CO2RR) testing in 0.5 m potassium hydroxide solution. The Cu NPs with zero valence deliver Faradaic efficiencies (FEs) for the CO2 reduction to CH4 of over 70%, with a current density exceeding 200 mA cm−2, outstripping the performances of the majority of the reported CO2 electrocatalysts. Interestingly, the distribution of products catalyzed by the Cu NPs with +1 valence includes multicarbon products (C2+) such as C2H4, C2H5OH, CH3COOH, and C3H7OH with combined FEs of >80%, with current densities of up to 300 mA cm−2. The above results unambiguously establish that surface oxidation of Cu species plays a crucial role in the CO2RR.

An interfacial self-assembly strategy was developed to synthesize sub-100 nm noble metal colloidosomes, showing intriguing collective optical and catalytic properties.

Ultra-small platinum nanoparticles loaded over titania is a promising catalyst for the low-temperature water− gas shift (WGS) reaction and shows the potential to work in a mobile hydrogen fuel cell system. Their precise size engineering (<3 nm) and reliable stabilization remain challenging. To address these issues, we report a reverse-micelle synthesis approach, which affords uniform ultra-small platinum nanoparticles (tunable in ∼1.0−2.6 nm) encapsulated in hollow titania nanospheres with a shell thickness of only ∼3−5 nm and an overall diameter of only ∼32 nm. The Pt@TiO 2 yolk/ shell nanostructured catalysts display extraordinary stability and monotonically increasing activity with the decreasing size of the Pt nanoparticles in the WGS. The size-dependent variation in the electronic property of the Pt nanoparticles and the reducible oxide encapsulation that prevents the Pt nanoparticles from sintering are ascribed as the main reasons for the excellent catalytic performance.

On one hand, the capping ligand adsorbs on the surface of noble metal nanocrystals, which minimizes their surface energy and provides interparticle repulsion forces to afford a stable colloid of the noble metal nanocrystals, rather than their aggregates. [9] On the other hand, conventionally, the control of the morphology of noble metal nanocrystals heavily relies on the selective adsorption of capping ligands on specific facets of the noble metal nanocrystals. [2c] Therefore, colloidal nanocrystals are synthesized exclusively as a hybrid with an inorganic core that is enclosed by a capping ligand.Although the capping ligands are essential in controlling the crystal growth of the noble metal nanocrystals and maintaining their colloidal property, they are usually detrimental to their activities in many applications, such as surfaceenhanced Raman scattering (SERS) and catalysis. [10] Au and Ag based noble metal nanocrystals show strong localized surface plasmon resonance (LSPR) in the visible range of the spectrum, which produces intense electromagnetic fields at their close vicinity and makes them outstanding substrates for SERS-based chemical and biosensing applications. [11] The SERS activity is highly dependent on the formation of "hotspots," where the electromagnetic field is extremely strong. These hotspots, however, are usually occupied by the capping ligands, which makes the hotspots inaccessible to the analytes, leading to weak Raman signals and thus low detecting sensitivity of the analytes. [10a,b] On the other hand, noble metal nanocrystals represent an emerging family of heterogeneous catalysts for many organic, electrocatalytic, and gas-phase reactions, with the metal surface or the metal/ support interface being the catalytically active site. [1c,12] The ligands strongly bound to the surface usually prevent the reactants from approaching the active sites, leading to partially or fully poisoning of the catalyst. [10b] Therefore, it is highly desirable to remove the capping ligands after the colloidal synthesis of the noble metal nanocrystals, which promises significantly enhanced optical and catalytic properties.Up to date, harsh physical and chemical processes are usually employed to remove the capping ligands from the noble metal nanocrystals. These processes include plasma cleaning, [13] UV-ozone cleaning, [14] cleaning by concentrated acetic acid, [12f ] and thermal annealing in air. [15] The capping Noble metal nanocrystals that are free of capping ligands promise significantly enhanced activities in surface-enhanced Raman scattering (SERS) and catalytic applications. Conventional physical and chemical processes to remove the capping ligands are usually too harsh to retain the morphology and surface structure of the noble metal nanocrystals. In this work, a mild, effective, and robust strategy is presented to remove the capping ligands from the surface of noble metal nanocrystals. Polyvinylpyrrolidone and oleylamine, which are generally known to adsorb strongly on the metal surface, have b...