國立虎尾科技大學 |

The Electrocatalytic Behavior of Bismuth-Modified Platinum : = Platinum-Bismuth Alloy Versus Bismuth Adatoms.

紀錄類型:	書目-語言資料,手稿 : Monograph/item
正題名/作者:	The Electrocatalytic Behavior of Bismuth-Modified Platinum :/
其他題名:	Platinum-Bismuth Alloy Versus Bismuth Adatoms.
作者:	Tonnis, Kevin.
面頁冊數:	1 online resource (130 pages)
附註:	Source: Dissertations Abstracts International, Volume: 82-05, Section: B.
Contained By:	Dissertations Abstracts International82-05B.
標題:	Chemical engineering. -
電子資源:	click for full text (PQDT)
ISBN:	9798691218613

The Electrocatalytic Behavior of Bismuth-Modified Platinum : = Platinum-Bismuth Alloy Versus Bismuth Adatoms.
Tonnis, Kevin.

The Electrocatalytic Behavior of Bismuth-Modified Platinum :Platinum-Bismuth Alloy Versus Bismuth Adatoms. - 1 online resource (130 pages)

Source: Dissertations Abstracts International, Volume: 82-05, Section: B.

Thesis (Ph.D.)--University of Cincinnati, 2020.

Includes bibliographical references

In this dissertation, new electroanalytic measurements and electron microscopy observations are applied to obtain fundamental understanding of how the incorporation of bismuth (Bi) with platinum (Pt) either as an alloy or a surface adatom Pt enhances the dimethyl ether electrooxidation reaction (DMEOR). Previous works have shown that incorporating other metals into a Pt electrocatalyst, such as Ru, Cu, or Bi, enhances electrooxidation activity toward DME, formic acid, ethanol and other organic compounds. When incorporated in alloy form and then dealloyed, these metals can potentially benefit structure sensitive electro-oxidation reactions through both the electronic effect of alloying as well as by increasing the strain in the Pt lattice structure when dealloyed, altering the bond length. When surface adatoms or complexes are used, they can also prevent poisoning of the catalytic surface by promoting the oxidation of intermediate species such as COads through either bi-functional or ensemble effects. The role of atomic surface structure in Bi-modified catalysts on DMEOR activity has not been previously revealed. In addition, while previous research has demonstrated the improved durability of Bi-containing electrocatalyst during DMEOR, an explanation as regards how poison resistance correlated to surface reactivity was not provided.In this work, Bi is incorporated into Pt (NP) from PtCl4 and Bi2O3 solution using SnCl2 as both a stabilizing and reducing agent. Two methods have been investigated. In the first, the Pt and Bi are reacted simultaneously yielding spherical nanoparticles (PtBi SP) in which the Bi is not fully reduced to metal and is found as a complex on the Pt metal surface. In the second method, Bi is first reduced with SnCl2 to Bi metal which is then used as a precursor in forming Pt2Bi alloy nanoplatelets (Pt2Bi NPT). Electrochemical analyses were performed on each of these types of catalysts for the DMEOR in order to probe how differences in nanoparticle structure affect electrocatalytic behavior. The PtBi SP were also synthesized using a variety of synthesis conditions, with the Sn:Pt ratio ranging from 7.5:1 to 10:1 and the Pt:Bi ratio ranging from 1:1.5 to 1:2.5 in order to yield nanoparticles of several different shapes and sizes so the effects of shape and size on electrocatalytic activity could be determined. Similarly, Pt2Bi NPT were synthesized using precursors with Sn:Bi ranging from 3:1 to 9:1 and Sn:Pt ratios ranging from 7.5:1 to 10:1 to make and characterize nanoplatelets of various shapes and sizes. Chemical acceleration methods to remove excess Sn and Bi from the surface of the nanoparticles and their effects on electrocatalytic activity were also investigated.The electrocatalysts were characterized for the DMEOR using cyclic voltammetry (CV) and chronoamperometry. CV scans in nitrogen saturated electrolyte were used to measure the initial electrochemical surface area (ECSA) of the electrocatalysts and the loss of ECSA after exposure to DME. CV scans in DME saturated electrolyte were performed at several different potential sweep rates. Anodic peaks associated with COads electrooxidation on Pt(100) and Pt(111) sites were observed on all electrocatalysts investigated, as were anodic peaks associated with the electrooxidation of other DME intermediates. Comparison of the relative changes in peak potential and current were correlated to relative changes in rates of reaction on the associated active sites. Chronoamperometry was used to find the current that could be sustained when the electrode was held at a potential for an extended period of time. The peak current and potentials of COads oxidation peaks during CV were compared at various sweep rates to find the Tafel slopes and transfer coefficients and examine the facility of the electrocatalysts for DME electrooxidation. At room temperature, Pt2Bi NPT have lower COads oxidation potentials than the carbon-supported PtBi SP(PtBi-C SP) and the commercial Pt-C (COM). The peak currents for the Bi are higher than the COM and NPTs. The activities are difficult to directly compare at RT because the two oxidation peaks associated with Pt(111) and Pt(100) are difficult to deconvolute. At 50oC, the Pt2Bi alloy NPTs, PtBi-C SP, and Pt-C COM had Tafel slopes for the first COads oxidation peak of 60+/-4, 163+/-10, and 83+/-10 V/dec respectively at low sweep rates. The second peak had Tafel slopes of 11+/-4, 53+/-4, and 70+/-2 V/dec respectively for the NPTs, SP, and Pt-C COM. The anodic transfer coefficient is greater than 1 for both peaks with the NPTs and for the second peak with the SP, indicating an initial electron transfer step is not rate limiting, unlike the Pt-C COM. The Tafel slope was found to increase with sweep rate, suggesting that CO2 diffusion may increase the surface reaction rate relative to electron transfer. Because the Pt2Bi alloy NPT had an ECSA of about 40% of the other two electrocatalysts, it had the highest specific activity despite the lower mass activity. The CO oxidation peaks for the Pt-C COM and PtBi-C SP occur at nearly the same potential while the peaks for Pt2Bi alloy NPTs occur at lower potentials. COads oxidation on Pt(111) occurred at a lower overpotential with the alloy than Pt alone or a PtBi complex. CVs in DME saturated H2SO4 had 2 oxidation peaks while CVs in DME saturated HClO4 had only one. Such behavior suggests that, bisulfite from the H2SO4 electrolyte interacts with the electrode causing a second peak to appear.The chronoamperometry at .7 V vs RHE at room temperature had both the Bi containing electrocatalysts drop from about 7 A/gPt to about 1 A/gPt after 10 min and the Pt-C COM drop to 0 A in about 2 minutes at room temperature. At 50oC the current for the two Bi containing electrocatalysts dropped from about 25 A/gPt to about 5 A/gPt in 1 hour and the Pt-C COM reached 0 A in 1 hour. The Pt- C COM ECSA dropped by 22.0% and 35.8% at room temperature and 50oC respectively while the Pt2Bi alloy NPTs dropped by 6.1% and 12.2%, and the PtBi-C SP dropped by 9.5% and 19.6%. The small drop in ECSA for the Bi containing electrocatalysts and the high chronoamperometric current indicate that the Bi helps prevent poisoning and is most effective in the alloy. In terms of specific activity, overpotential, and resistance to poisoning, the alloy is best for the DMEOR. The low ECSA for the nanoplatelets limits the measured mass activity in electrochemical analysis. Pt2Bi alloy NPTs chemically accelerated in 2 M H2NO3 at 60oC for 1 hour were tested in a DDMEFC by Advent Technologies. At 450 mV vs RHE, a 50% increase in current density was observed compared with commercial PtRu.Changing the amount of Sn present in the Bi precursor or the reactor slurry for the Pt2Bi alloy NPTs had little effect on the ECSA of the resulting NPTs and on the CVs in DME saturated electrolyte. However, changing the Sn:other metal concentration in the reactor slurry for the PtBi-C SPs from 7.5:3 to 9:3 and 10:3 caused an increase in ECSA from 44.0 m2/gPt to 55.0 m2/gPt and 60.3 m2/gPt respectively. Smaller SPs with a higher surface area per unit mass were obtained by increasing the amount of Sn available to form stabilizing ligands.This work shows how varying the potentiometric sweep rate can reveal how alloying Pt with Bi can substantially enhance the structure-sensitive reaction rate for DMEOR intermediates. When combined with EXAFS to elucidate changes to surface structure, the approach also reveals the importance of electrolyte diffusion on preventing surface poisoning.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798691218613Subjects--Topical Terms:

555952
Chemical engineering.
Subjects--Index Terms:

Fuel cellsIndex Terms--Genre/Form:

554714
Electronic books.

The Electrocatalytic Behavior of Bismuth-Modified Platinum : = Platinum-Bismuth Alloy Versus Bismuth Adatoms.
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520 $a In this dissertation, new electroanalytic measurements and electron microscopy observations are applied to obtain fundamental understanding of how the incorporation of bismuth (Bi) with platinum (Pt) either as an alloy or a surface adatom Pt enhances the dimethyl ether electrooxidation reaction (DMEOR). Previous works have shown that incorporating other metals into a Pt electrocatalyst, such as Ru, Cu, or Bi, enhances electrooxidation activity toward DME, formic acid, ethanol and other organic compounds. When incorporated in alloy form and then dealloyed, these metals can potentially benefit structure sensitive electro-oxidation reactions through both the electronic effect of alloying as well as by increasing the strain in the Pt lattice structure when dealloyed, altering the bond length. When surface adatoms or complexes are used, they can also prevent poisoning of the catalytic surface by promoting the oxidation of intermediate species such as COads through either bi-functional or ensemble effects. The role of atomic surface structure in Bi-modified catalysts on DMEOR activity has not been previously revealed. In addition, while previous research has demonstrated the improved durability of Bi-containing electrocatalyst during DMEOR, an explanation as regards how poison resistance correlated to surface reactivity was not provided.In this work, Bi is incorporated into Pt (NP) from PtCl4 and Bi2O3 solution using SnCl2 as both a stabilizing and reducing agent. Two methods have been investigated. In the first, the Pt and Bi are reacted simultaneously yielding spherical nanoparticles (PtBi SP) in which the Bi is not fully reduced to metal and is found as a complex on the Pt metal surface. In the second method, Bi is first reduced with SnCl2 to Bi metal which is then used as a precursor in forming Pt2Bi alloy nanoplatelets (Pt2Bi NPT). Electrochemical analyses were performed on each of these types of catalysts for the DMEOR in order to probe how differences in nanoparticle structure affect electrocatalytic behavior. The PtBi SP were also synthesized using a variety of synthesis conditions, with the Sn:Pt ratio ranging from 7.5:1 to 10:1 and the Pt:Bi ratio ranging from 1:1.5 to 1:2.5 in order to yield nanoparticles of several different shapes and sizes so the effects of shape and size on electrocatalytic activity could be determined. Similarly, Pt2Bi NPT were synthesized using precursors with Sn:Bi ranging from 3:1 to 9:1 and Sn:Pt ratios ranging from 7.5:1 to 10:1 to make and characterize nanoplatelets of various shapes and sizes. Chemical acceleration methods to remove excess Sn and Bi from the surface of the nanoparticles and their effects on electrocatalytic activity were also investigated.The electrocatalysts were characterized for the DMEOR using cyclic voltammetry (CV) and chronoamperometry. CV scans in nitrogen saturated electrolyte were used to measure the initial electrochemical surface area (ECSA) of the electrocatalysts and the loss of ECSA after exposure to DME. CV scans in DME saturated electrolyte were performed at several different potential sweep rates. Anodic peaks associated with COads electrooxidation on Pt(100) and Pt(111) sites were observed on all electrocatalysts investigated, as were anodic peaks associated with the electrooxidation of other DME intermediates. Comparison of the relative changes in peak potential and current were correlated to relative changes in rates of reaction on the associated active sites. Chronoamperometry was used to find the current that could be sustained when the electrode was held at a potential for an extended period of time. The peak current and potentials of COads oxidation peaks during CV were compared at various sweep rates to find the Tafel slopes and transfer coefficients and examine the facility of the electrocatalysts for DME electrooxidation. At room temperature, Pt2Bi NPT have lower COads oxidation potentials than the carbon-supported PtBi SP(PtBi-C SP) and the commercial Pt-C (COM). The peak currents for the Bi are higher than the COM and NPTs. The activities are difficult to directly compare at RT because the two oxidation peaks associated with Pt(111) and Pt(100) are difficult to deconvolute. At 50oC, the Pt2Bi alloy NPTs, PtBi-C SP, and Pt-C COM had Tafel slopes for the first COads oxidation peak of 60+/-4, 163+/-10, and 83+/-10 V/dec respectively at low sweep rates. The second peak had Tafel slopes of 11+/-4, 53+/-4, and 70+/-2 V/dec respectively for the NPTs, SP, and Pt-C COM. The anodic transfer coefficient is greater than 1 for both peaks with the NPTs and for the second peak with the SP, indicating an initial electron transfer step is not rate limiting, unlike the Pt-C COM. The Tafel slope was found to increase with sweep rate, suggesting that CO2 diffusion may increase the surface reaction rate relative to electron transfer. Because the Pt2Bi alloy NPT had an ECSA of about 40% of the other two electrocatalysts, it had the highest specific activity despite the lower mass activity. The CO oxidation peaks for the Pt-C COM and PtBi-C SP occur at nearly the same potential while the peaks for Pt2Bi alloy NPTs occur at lower potentials. COads oxidation on Pt(111) occurred at a lower overpotential with the alloy than Pt alone or a PtBi complex. CVs in DME saturated H2SO4 had 2 oxidation peaks while CVs in DME saturated HClO4 had only one. Such behavior suggests that, bisulfite from the H2SO4 electrolyte interacts with the electrode causing a second peak to appear.The chronoamperometry at .7 V vs RHE at room temperature had both the Bi containing electrocatalysts drop from about 7 A/gPt to about 1 A/gPt after 10 min and the Pt-C COM drop to 0 A in about 2 minutes at room temperature. At 50oC the current for the two Bi containing electrocatalysts dropped from about 25 A/gPt to about 5 A/gPt in 1 hour and the Pt-C COM reached 0 A in 1 hour. The Pt- C COM ECSA dropped by 22.0% and 35.8% at room temperature and 50oC respectively while the Pt2Bi alloy NPTs dropped by 6.1% and 12.2%, and the PtBi-C SP dropped by 9.5% and 19.6%. The small drop in ECSA for the Bi containing electrocatalysts and the high chronoamperometric current indicate that the Bi helps prevent poisoning and is most effective in the alloy. In terms of specific activity, overpotential, and resistance to poisoning, the alloy is best for the DMEOR. The low ECSA for the nanoplatelets limits the measured mass activity in electrochemical analysis. Pt2Bi alloy NPTs chemically accelerated in 2 M H2NO3 at 60oC for 1 hour were tested in a DDMEFC by Advent Technologies. At 450 mV vs RHE, a 50% increase in current density was observed compared with commercial PtRu.Changing the amount of Sn present in the Bi precursor or the reactor slurry for the Pt2Bi alloy NPTs had little effect on the ECSA of the resulting NPTs and on the CVs in DME saturated electrolyte. However, changing the Sn:other metal concentration in the reactor slurry for the PtBi-C SPs from 7.5:3 to 9:3 and 10:3 caused an increase in ECSA from 44.0 m2/gPt to 55.0 m2/gPt and 60.3 m2/gPt respectively. Smaller SPs with a higher surface area per unit mass were obtained by increasing the amount of Sn available to form stabilizing ligands.This work shows how varying the potentiometric sweep rate can reveal how alloying Pt with Bi can substantially enhance the structure-sensitive reaction rate for DMEOR intermediates. When combined with EXAFS to elucidate changes to surface structure, the approach also reveals the importance of electrolyte diffusion on preventing surface poisoning.
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653 $a Fuel cells
653 $a Dimethyl ether
653 $a Platinum alloys
653 $a Bismuth
653 $a Electrocatalysts
653 $a Adatom
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