17 Search Results

Efficient C–C bond cleavage and oxidation of alcohols to CO₂ is the key to developing highly efficient alcohol fuel cells for renewable energy applications. In this work, we report the synthesis of core/shell Au/Pt nanowires (NWs) with stepped Pt clusters deposited along the ultrathin (2.3 nm) stepped Au NWs as an active catalyst to effectively oxidize alcohols to CO₂. The catalytic oxidation reaction is dependent on the Au/Pt ratios, and the Au_1.0/Pt_0.2 NWs have the largest percentage (~75%) of stepped Au/Pt sites and show the highest activity for ethanol electro-oxidation, reaching an unprecedented 196.9 A/mg_Pt (32.5 A/mg_Pt+Au). This NW catalystmore » is also active in catalyzing the oxidation of other primary alcohols, such as methanol, n-propanol, and ethylene glycol. In situ X-ray absorption spectroscopy and infrared spectroscopy are used to characterize the catalyst structure and to identify key reaction intermediates, providing concrete evidence that the synergy between the low-coordinated Pt sites and the stepped Au NWs is essential to catalyze the alcohol oxidation reaction, which is further supported by DFT calculations that the C–C bond cleavage is indeed enhanced on the undercoordinated Pt–Au surface. Here, our study provides important evidence that a core/shell structure with stepped core/shell sites is essential to enhance electrochemical oxidation of alcohols and will also be central to understanding electro-oxidation reactions and to the future development of highly efficient direct alcohol fuel cells for renewable energy applications.« less

While nanoscale mimics of peroxidase have been extensively developed over the past decade or so, their catalytic efficiency as a key parameter has not been substantially improved in recent years. Herein, we report a class of highly efficient peroxidase mimic–nickel–platinum nanoparticles (Ni–Pt NPs) that consist of nickel-rich cores and platinum-rich shells. The Ni–Pt NPs exhibit a record high catalytic efficiency with a catalytic constant (K_cat) as high as 4.5 × 10⁷ s^–1, which is ~46- and 10⁴-fold greater than the K_cat values of conventional Pt nanoparticles and natural peroxidases, respectively. Density functional theory calculations reveal that the unique surface structuremore » of Ni–Pt NPs weakens the adsorption of key intermediates during catalysis, which boosts the catalytic efficiency. Furthermore, the Ni–Pt NPs were applied to an immunoassay of a carcinoembryonic antigen that achieved an ultralow detection limit of 1.1 pg/mL, hundreds of times lower than that of the conventional enzyme-based assay.« less

Abstract Permanent magnets are a class of critical materials for information storage, energy storage, and other magneto‐electronic applications. Compared with conventional bulk magnets, magnetic nanoparticles (MNPs) show unique size‐dependent magnetic properties, which make it possible to control and optimize their magnetic performance for specific applications. The synthesis of MNPs has been intensively explored in recent years. Among different methods developed thus far, chemical synthesis based on solution‐phase reactions has attracted much attention owing to its potential to achieve the desired size, morphology, structure, and magnetic controls. This Minireview focuses on the recent chemical syntheses of strongly ferromagnetic MNPs ( Hmore » _c >10 kOe) of rare‐earth metals and FePt intermetallic alloys. It further discusses the potential of enhancing the magnetic performance of MNP composites by assembly of hard and soft MNPs into exchange‐coupled nanocomposites. High‐performance nanocomposites are key to fabricating super‐strong permanent magnets for magnetic, electronic, and energy applications.« less

While various effects of physicochemical parameters (e.g., size, facet, composition, and internal structure) on the catalytic efficiency of nanozymes (i.e., nanoscale enzyme mimics) have been studied, the strain effect has never been reported and understood before. Herein, we demonstrate the strain effect in nanozymes by using Pd octahedra and icosahedra with peroxidase-like activities as a model system. Strained Pd icosahedra were found to display 2-fold higher peroxidase-like catalytic efficiency than unstrained Pd octahedra. Theoretical analysis suggests that tensile strain is more beneficial to OH radical (a key intermediate for the catalysis) generation than compressive strain. Pd icosahedra are more activemore » than Pd octahedra because icosahedra amplify the surface strain field. As a proof-of-concept demonstration, the strained Pd icosahedra were applied to immunoassay of biomarkers, outperforming both unstrained Pd octahedra and natural peroxidases. The findings in this research may serve as a strong foundation to guide the design of high-performance nanozymes.« less

Abstract Efficient electro‐oxidation of formic acid, methanol, and ethanol is challenging owing to the multiple chemical reaction steps required to accomplish full oxidation to CO ₂ . Herein, a ternary CoPtAu nanoparticle catalyst system is reported in which Co and Pt form an intermetallic L1 ₀ ‐structure and Au segregates on the surface to alloy with Pt. The L1 ₀ ‐structure stabilizes Co and significantly enhances the catalysis of the PtAu surface towards electro‐oxidation of ethanol, methanol, and formic acid, with mass activities of 1.55 A/mg _Pt , 1.49 A/mg _Pt , and 11.97 A/mg _Pt , respectively in 0.1  m HClO ₄more » . The L1 ₀ ‐CoPtAu catalyst is also stable, with negligible degradation in mass activities and no obvious Co/Pt/Au composition changes after 10 000 potential cycles. The in situ surface‐enhanced infrared absorption spectroscopy study indicates that the ternary catalyst activates the C−C bond more efficiently for ethanol oxidation.« less

Abstract Efficient electro‐oxidation of formic acid, methanol, and ethanol is challenging owing to the multiple chemical reaction steps required to accomplish full oxidation to CO ₂ . Herein, a ternary CoPtAu nanoparticle catalyst system is reported in which Co and Pt form an intermetallic L1 ₀ ‐structure and Au segregates on the surface to alloy with Pt. The L1 ₀ ‐structure stabilizes Co and significantly enhances the catalysis of the PtAu surface towards electro‐oxidation of ethanol, methanol, and formic acid, with mass activities of 1.55 A/mg _Pt , 1.49 A/mg _Pt , and 11.97 A/mg _Pt , respectively in 0.1  m HClO ₄more » . The L1 ₀ ‐CoPtAu catalyst is also stable, with negligible degradation in mass activities and no obvious Co/Pt/Au composition changes after 10 000 potential cycles. The in situ surface‐enhanced infrared absorption spectroscopy study indicates that the ternary catalyst activates the C−C bond more efficiently for ethanol oxidation.« less

Monodisperse nanoparticles are successful model systems for understanding structure–property relationships at the nanoscale and applications like catalysis and nanomedicine.

Abstract We report a general chemical approach to synthesize strongly ferromagnetic rare‐earth metal (REM) based SmCo and SmFeN nanoparticles (NPs) with ultra‐large coercivity. The synthesis started with the preparation of hexagonal CoO+Sm ₂ O ₃ (denoted as SmCo‐O) multipods via decomposition of Sm(acac) ₃ and Co(acac) ₃ in oleylamine. These multipods were further reduced with Ca at 850 °C to form SmCo ₅ NPs with sizes tunable from 50 to 200 nm. The 200 nm SmCo ₅ NPs were dispersed in ethanol, and magnetically aligned in polyethylene glycol (PEG) matrix, yielding a PEG‐SmCo ₅ NP composite with the room temperature coercivity ( Hmore » _c ) of 49.2 kOe, the largest H _c among all ferromagnetic NPs ever reported, and saturated magnetic moment ( M _s ) of 88.7 emu g ⁻¹ , the highest value reported for SmCo ₅ NPs. The method was extended to synthesize other ferromagnetic NPs of Sm ₂ Co ₁₇ , and, for the first time, of Sm ₂ Fe ₁₇ N ₃ NPs with H _c over 15 kOe and M _s reaching 127.9 emu g ⁻¹ . These REM based NPs are important magnetic building blocks for fabrication of high‐performance permanent magnets, flexible magnets, and printable magnetic inks for energy and sensing applications.« less

We report here a general chemical approach to synthesize strongly ferromagnetic rare-earth metal (REM) based SmCo and SmFeN nanoparticles (NPs) with ultra-large coercivity. The synthesis started with the preparation of hexagonal CoO+Sm₂O₃ (denoted as SmCo-O) multipods via decomposition of Sm(acac)₃ and Co(acac)₃ in oleylamine. These multipods were further reduced with Ca at 850 °C to form SmCo₅ NPs with sizes tunable from 50 to 200 nm. The 200 nm SmCo₅ NPs were dispersed in ethanol, and magnetically aligned in polyethylene glycol (PEG) matrix, yielding a PEG-SmCo₅ NP composite with the room temperature coercivity (H_c) of 49.2 kOe, the largest H_cmore » among all ferromagnetic NPs ever reported, and saturated magnetic moment (M_s) of 88.7 emu g^-1, the highest value reported for SmCo₅ NPs. The method was extended to synthesize other ferromagnetic NPs of Sm₂Co₁₇, and, for the first time, of Sm₂Fe₁₇N₃ NPs with H_c over 15 kOe and M_s reaching 127.9 emu g^-1. These REM based NPs are important magnetic building blocks for fabrication of high-performance permanent magnets, flexible magnets, and printable magnetic inks for energy and sensing applications.« less