Utilizing ballistic nanoparticle impact to reconfigure the metal support interaction in Pt–TiN electrocatalysts (original) (raw)
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...
International Journal of Hydrogen Energy, 2010
Platinum was deposited by pulsed laser deposition at different kinetic energy by varying the He background pressure in the deposition chamber. As a result, the porosity of the film varies from 5 to 86% as the He pressure is increased. This yields to an increase of the electrochemically active surface area and to an increased resistance to poisoning by CO, as evidenced by a 45 mV shift of the peak potential of the CO stripping peak towards less positive values. Similarly, the electrocatalytic activity of the films for the oxygen reduction reaction, as measured by the potential at half limiting diffusion current, is enhanced. However, a comparison between the intrinsic electrocatalytic activities of the films show that they have similar values (within a factor of 1.8) and do not significantly differ from that of a polycrystalline Pt disk, indicating that the increased activity for the ORR is mainly due to a geometric (electrochemically active surface area) effect.
Journal of Electroanalytical Chemistry
The electrokinetic properties of Pt nanoparticles supported on Carbon (Pt/C) and Boron Carbide-Graphite composite (Pt/BC) are compared over a wide potential range. The influence of the support on the electronic state of Pt was investigated via in-situ X-ray Absorption Spectroscopy. Pt d-band filling, determined from XANES white line analysis, was lower and nearly constant between 0.4 and 0.95 V vs. RHE for Pt/BC, indicating more positively charged particles in the double layer region and a delay in the onset of oxide formation by about 0.2 V compared to the Pt/C catalyst, which showed a marked increase in d-band vacancies above 0.8 V vs. RHE. Moreover, Δμ analysis of the XANES data indicated a lack of sub-surface oxygen for the Pt/BC catalyst compared to the Pt/C catalyst above 0.9 V vs. RHE. Additional anion adsorption on the Pt/BC in the double layer region, detected by CO displacement, was also confirmed by XANES analysis of the d-band occupancy. The H 2 oxidation activities of electrodes with low catalyst loadings were assessed under high mass transport conditions using the floating electrode methodology. The metal-support interaction between the Pt and BC support improved the maximum hydrogen oxidation current density by 1.4 times when compared to Pt/C.
Eliminating dissolution of platinum-based electrocatalysts at the atomic scale
Nature Materials, 2020
A remaining challenge for deployment of proton-exchange membrane fuel cells is the limited durability of Pt-nanoscale materials that operate at high voltages during the cathodic oxygen reduction reaction. In this work, atomic-scale insight into well-defined single crystalline, thin-film, and nanoscale surfaces exposed Pt dissolution trends that governed the design and synthesis of durable materials. A newly defined metric, intrinsic dissolution, is essential to understanding the correlation between the measured Pt loss, surface structure, size and ratio of Pt-nanoparticles in carbon support. It was found that utilization of Au underlayer promotes ordering of Pt surface atoms towards (111)structure, while Au on the surface selectively protects low-coordinated Pt sites. This mitigation strategy was applied towards 3 nm Pt 3 Au/C nanoparticles, resulting in elimination of Pt dissolution in liquid electrolyte, including 30-fold durability improvement vs. 3 nm Pt/C over extended potential range up to 1.2 V.
Chemical Deposition and Electrocatalytic Activity of Platinum
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.
Simulations of the Electrochemical Oxidation of Pt Nanoparticles of Various Shapes
arXiv (Cornell University), 2022
The activity and stability of a platinum nanoparticle (NP) is not only affected by its size but additionally depends on its shape. To this end, simulations can identify structure-property relationships to make a priori decisions on the most promising structures. While activity is routinely probed by electronic structure calculations on simplified surface models, modeling the stability of NP model systems in electrochemical reactions is challenging due to the long timescale of relevant processes such as oxidation beyond the point of reversibility. In this work, a routine for simulating electrocatalyst stability is presented. The procedure is referred to as GREG after its main ingredients -a grand-canonical simulation approach using reactive force fields to model electrochemical reactions as a function of the galvanic cell potential. The GREG routine is applied to study the oxidation of 3 nm octahedral, cubic, dodecahedral, cuboctahedral, spherical, and tetrahexahedral platinum NPs. The oxidation process is analyzed using adsorption isobars as well as interaction energy heat maps that provide the basis for constructing electrochemical phase diagrams. Onset potentials for surface oxidation increase in the sequence cube ≈ dodecahedron ≤ octahedron ≤ tetrahexahdron < sphere < cuboctahedron, establishing a relationship between oxidation behavior and surface facet structure. The electrochemical results are rationalized using structural and electronic analysis.