Utilizing ballistic nanoparticle impact to reconfigure the metal support interaction in Pt–TiN electrocatalysts (original) (raw)
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Electrochimica Acta, 2017
A facile approach to enhance catalytic activity and durability of TiO 2-supported Pt nanocatalysts by tuning strong metal support interaction (SMSI) is investigated in this work. No need for a high temperature treatment, the strong metal-support interaction (SMSI) in TiO 2-supported Pt can be induced at 200 C by H 2 reduction. Moreover, electrochemical methods (methanol oxidation reaction and cyclic voltammetry) are first reported ever to be effective characterization tools for the coverage state caused by SMSI. In addition, the SMSI has also been confirmed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and Transmission Electron Microscopy. It is found that the encapsulation of TiO 2-x species on the surface Pt clusters was induced and modified by thermal reduction and fluoric acid treatment. The catalytic activity and durability of the TiO 2-supported Pt nanocatalysts are strongly dependent of the state of SMSI. The proposed SMSI-tunable approach to enhance the ORR activity and stability is also proved applicable to Pt/Ti 0.9 Nb 0.1 O 2 nanocatalysts. We believe that the reported approach paves the way for manipulating the activity and stability of other TiO 2-supported metal nanocatalysts. Furthermore, the suggested electrochemical methods offer facile and effective ways to verify the presence of coverage state before combining with other physical analysis.
The surface atomic structure and chemical state of Pt is consequential in a variety of surface-intensive devices. Herein we present the direct interrelationship between the growth scheme of Pt films, the resulting atomic and electronic structure of Pt species, and the consequent activity for methanol electro-oxidation in Pt/TiO2 nanotube hybrid electrodes. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements were performed to relate the observed electrocatalytic activity to the oxidation state and the atomic structure of the deposited Pt species. The atomic structure as well as the oxidation state of the deposited Pt was found to depend on the pretreatment of the TiO2 nanotube surfaces with electrodeposited Cu. Pt growth through Cu replacement increases Pt dispersion, and a separation of surface Pt atoms beyond a threshold distance from the TiO2 substrate renders them metallic, rather than cationic. The increased dispersion and the metallic character of Pt results in strongly enhanced electrocatalytic activity toward methanol oxidation. This study points to a general phenomenon whereby the growth scheme and the substrate-to-surface-Pt distance dictates the chemical state of the surface Pt atoms, and thereby, the performance of Pt-based surface-intensive devices.
Journal of the American Chemical Society, 2015
We have employed Identical Location Transmission Electron Microscopy (IL-TEM) to study changes in the shape and morphology of faceted Pt nanoparticles as a result of the electrochemical cycling; a procedure typically employed for activating platinum surfaces. We find that the shape and morphology of the as-prepared hexagonal nanoparticles are rapidly degraded as a result of potential cycling up to +1.3V. As few as 25 potential cycles are sufficient to cause significant degradation, and after about 500-1,000 cycles the particles are dramatically degraded. We also see clear evidence of particle migration during potential cycling. These finding suggest that great care must be exercised in the use and study of shaped Pt nanoparticles (and related systems) as electrocatlysts, especially for the oxygen reduction reaction (ORR) where high positive potentials are typically employed.
Journal of Catalysis, 2019
Intermetallic compounds are unique catalyst platforms for mechanistic studies and industrial applications, because of their ordered structures in comparison to random alloys. Despite the intrinsically defined stoichiometry of intermetallic compounds, compositional deviations can still occur in intermetallic catalysts. The location of the extra metal atoms could differ the catalytic properties of intermetallic compounds with non-stoichiometric composition if those metal atoms end up on/near the surface. In this study, we synthesized PtSn intermetallic compounds with accurate stoichiometry and slightly Pt-/Sn-rich compositions. We used furfural hydrogenation and acetylene semi-hydrogenation as probe reactions to investigate the surface structures of PtSn intermetallic catalysts after reduction at different temperatures. Even though the intermetallic PtSn is the major bulk phase among nonstoichiometric compositions, the intermetallic PtSn surface can only be observed under the hightemperature reduction in Sn-rich PtSn intermetallic nanoparticles (iNPs), while the Pt-rich PtSn iNPs show Pt-rich-surfaces regardless of reduction temperatures. Four structural models were constructed based on the comprehensive surface and bulk characterizations. This work extends the understanding of intermetallic catalysts with non-stoichiometric compositions to tailor the intermetallic surface structures for catalysis.
Electrochimica Acta, 2013
Highly dispersed Pt nanoparticles have been extensively studied for the electrocatalytic oxygen reduction reaction (ORR). Pt bulk and supported-nanoparticle electrodes have exhibited varying degrees of surface structure sensitivity toward the ORR for two main reasons: first, preferential adsorption of supporting electrolyte or water; and second, intrinsic variation of reaction kinetics on different Pt(h k l) surfaces or atomic scale imperfections on the Pt surface (e.g. steps, kinks, edges, and corners). The impact of surface atom coordination on ORR activity is seldom reported because there are few techniques that lend themselves to detailed, in situ assessment of catalyst surface site distribution. Surface active sites on ORR electrocatalysts have been inferred from application of bulk crystal structure data to specific nanoparticle geometries that account for electrocatalytically active surface area, ECA (cm 2 /g Pt). This approach fails to capture the wide variety of active sites present on electrocatalyst surfaces under operating conditions, particularly at nanoparticle sizes that span the atomic cluster to nanocrystal transition. In this paper, we apply the techniques developed by Feliu et al. to determine surface site distribution in situ and, for the first time in the field, correlate these observations with ORR mass activity, MA (A/g Pt), and surface activity, SA (A/cm 2 Pt) on Pt nanoparticle catalysts. This approach indicates that the predominant active site available for ORR on nanoparticles in the size range of 1.8-6.9 nm is (1 1 0) or (3 1 1). This observation is confirmed by using perchloric acid, sulfuric acid, and potassium hydroxide to demonstrate that the supporting electrolyte has little influence on ORR kinetics for these nanoparticles. Such behavior suggests that the Pt nanoparticle surfaces investigated consist of stepped adlayers on (1 1 1) or (1 0 0) facets that eliminate the (1 1 1) terraces historically associated with ORR activity. The predominance of such a stepped surface on Pt ORR electrocatalysts is unexpected and demonstrates the need for in situ characterization of active site distribution.
The Journal of Physical Chemistry C, 2011
P roperties of the nanoparticles have been studied extensively both in catalysis and electrocatalysis. 1 In the latter case, these studies have been carried out with two main objectives: (i) understanding of fundamental aspects of the surface electrochemical activity and (ii) the development of new materials for practical applications, for example, in fuel cells. Despite the high cost, Pt and its alloys are among the most promising candidates both for cathode and anode catalysts in the fuel cell applications.
2013
Platinum electrocatalysts (Pt-B/TON-N 2 , Pt-B/TON-air and Pt-H/TON-air) incorporated on annealed titanium oxide nanotubes (TONs) have been successfully synthesized by chemical deposition method using sodium borohydride and hydrazine, reducing agents. TONs were firstly prepared by anodization of pure Ti foil in HF solution followed by annealing in air and N 2 atmosphere. The morphology and structure of the electrocatalysts were characterized by scanning (SEM), transmission (TEM) electron microscopies, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and electrochemical techniques. SEM, TEM, XRD and EDX characterization indicate the presence of platinum nanoparticles with diameter less than 50 nm and uniformly incorporated into TON arrays. The electrocatalytic activities results show that the Pt-B/TON-N 2 catalyst has higher catalytic activity for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) compared with Pt-B/TON-air and electrodes prepared using hydrazine as reducing agent because the better conductivity. In addition, the Pt-B/TON-N 2 catalyst exhibits better poison tolerance and two times higher methanol oxidation current density than that reported for Pt/carbon catalyst. This suggests that the Pt-B/TON-N 2 catalyst supported on TON-N 2 has promising potential applications in electrocatalyst reactions.
Eliminating Dissolution of Pt-based Electrocatalysts at the Atomic Scale
2020
28 A remaining challenge for deployment of proton-exchange membrane fuel cells is the 29 limited durability of Pt-nanoscale materials that operate at high voltages during the 30 cathodic oxygen reduction reaction. In this work, atomic-scale insight into well-defined 31 single crystalline, thin-film, and nanoscale surfaces exposed Pt dissolution trends that 32 governed the design and synthesis of durable materials. A newly defined metric, intrinsic 33 dissolution, is essential to understanding the correlation between the measured Pt loss, 34 surface structure, size and ratio of Pt-nanoparticles in carbon support. It was found that 35 utilization of Au underlayer promotes ordering of Pt surface atoms towards (111)36 structure, while Au on the surface selectively protects low-coordinated Pt sites. This 37 mitigation strategy was applied towards 3 nm Pt3Au/C nanoparticles, resulting in 38 elimination of Pt dissolution in liquid electrolyte, including 30-fold durability improvement 39 vs...