We report on synthesis–structure–activity–stability relationships of Pt3Co nanoparticle electroca... more We report on synthesis–structure–activity–stability relationships of Pt3Co nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). We have synthesized Pt3Co alloy electrocatalysts using liquid impregnation techniques followed by reductive annealing at high and low temperatures. We have performed detailed structural X-ray diffraction (XRD)-based structural characterization (symmetry, lattice parameters and composition) of individual Pt–Co alloy phases before and, importantly, after electrochemical rotating disk electrode (RDE) measurements. This enables us to directly evaluate the corrosion stability of various Pt–Co alloy phases under typical fuel cell cathode conditions.Pt3Co prepared at low annealing temperatures (600 °C) resulted in multiple phases including (i) a disordered face-centered cubic (fcc) Pt95Co5 phase and (ii) an ordered face-centered tetragonal (L10) Pt50Co50 phase; high temperature annealing (950 C) resulted in a single ordered primitive cubic (L12) Pt3Co phase. The ordered alloy phases in both catalysts were not stable under electrochemical treatment: The ordered face-centered tetragonal (fct) phase showed corrosion and dissolution, while the ordered primitive cubic (L12) Pt3Co phase transformed into a disordered structure. The ordered primitive cubic structure exhibited higher resistance to sintering.Low annealing temperatures resulted in higher Pt surface-area specific activities for ORR. Kinetic Tafel analysis confirmed a general shift in the formation potential of oxygenated surface species, such as Pt–OH, for both alloy catalysts. Reduced OH coverage alone proved insufficient to account for the observed activity trends of the two alloy catalysts.
Dealloyed Pt25Cu75 bimetallic nanoparticle electrocatalysts exhibit up to 6 times higher oxygen r... more Dealloyed Pt25Cu75 bimetallic nanoparticle electrocatalysts exhibit up to 6 times higher oxygen reduction reaction activities than Pt-C catalysts. The effects of annealing temperature and duration on the catalyst activity are studied, with annealing temperature varied from ...
Corrosion and ORR activity of Pt alloy electrocatalysts during voltammetric pretreatment. [ECS Tr... more Corrosion and ORR activity of Pt alloy electrocatalysts during voltammetric pretreatment. [ECS Transactions 3, 139 (2006)]. Peter Strasser, Nathan T. Hahn, Shirlaine Koh. Abstract. This paper addresses the impact of voltammetric ...
A method of producing de-alloyed nanoparticles. In an embodiment, the method comprises admixing m... more A method of producing de-alloyed nanoparticles. In an embodiment, the method comprises admixing metal precursors, freeze-drying, annealing, and de-alloying the nanoparticles in situ. Further, in an embodiment de-alloyed nanoparticle formed by the method, wherein the nanoparticle further comprises a core-shell arrangement. The nanoparticle is suitable for electrocatalytic processes and devices.
Voltammetric dealloying of bimetallic platinum-copper (Pt-Cu) alloys has been shown to be an effe... more Voltammetric dealloying of bimetallic platinum-copper (Pt-Cu) alloys has been shown to be an effective strategy to modify the surface electrocatalytic reactivity of Pt bimetallic nanoparticles (S. Koh and P. Strasser, J. Am. Chem. Soc., 2007, 129, 12624). Using cyclic voltammetry and structural XRD studies, we systematically characterize the Pt-Cu precursor compounds as well as the early stages of the selective Cu surface dissolution (dealloying) process for Pt(25)Cu(75), Pt(50)Cu(50), and Pt(75)Cu(25) alloy nanoparticles annealed at both low and high temperature. We also assess the impact of the synthesis conditions on the electrocatalytic reactivity for the oxygen reduction reaction (ORR). To gain atomistic insight into the observed voltammetric profiles, we compare our experimental results with periodic DFT calculations of trends in the thermodynamics of surface Cu dissolution potentials from highly stepped and kinked Pt(854) single crystal surfaces. The modeling suggests a dependence of the electrochemical Cu dissolution potentials on the detailed atomic environment (coordination number, nature of coordinating atoms) of the bimetallic Pt-Cu surfaces. The DFT-predicted shifts in electrochemical Cu dissolution potentials are shown to qualitatively account for the observed voltammetric profiles during Cu dealloying. Our study suggests that metal-specific energetics have to be taken into account to explain the detailed dealloying behavior of bimetallic surfaces.
We report a synthetic electrochemical strategy to deliberately modify the catalytic reactivity of... more We report a synthetic electrochemical strategy to deliberately modify the catalytic reactivity of Pt bimetallic surfaces. The strategy consists of voltammetric surface dealloying of the non-noble constituent from Pt-poor bimetallic precursor compounds. We exemplify this method by ...
... J.Erlebacher, MJAziz, A.Karma, N.Dimitrov, and K.Sieradzki, “Evolution of nanoporosity in dea... more ... J.Erlebacher, MJAziz, A.Karma, N.Dimitrov, and K.Sieradzki, “Evolution of nanoporosity in dealloying,” Nature (London), 410, 450 (2001). RCNewman and K.Sieradzki, Science, 263, 1708 (1994). HWPickering, Corros. Sci., 23, 1107 (1983). SGCorcoran, in Critical Factors in ...
We report on synthesis–structure–activity–stability relationships of Pt3Co nanoparticle electroca... more We report on synthesis–structure–activity–stability relationships of Pt3Co nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). We have synthesized Pt3Co alloy electrocatalysts using liquid impregnation techniques followed by reductive annealing at high and low temperatures. We have performed detailed structural X-ray diffraction (XRD)-based structural characterization (symmetry, lattice parameters and composition) of individual Pt–Co alloy phases before and, importantly, after electrochemical rotating disk electrode (RDE) measurements. This enables us to directly evaluate the corrosion stability of various Pt–Co alloy phases under typical fuel cell cathode conditions.Pt3Co prepared at low annealing temperatures (600 °C) resulted in multiple phases including (i) a disordered face-centered cubic (fcc) Pt95Co5 phase and (ii) an ordered face-centered tetragonal (L10) Pt50Co50 phase; high temperature annealing (950 C) resulted in a single ordered primitive cubic (L12) Pt3Co phase. The ordered alloy phases in both catalysts were not stable under electrochemical treatment: The ordered face-centered tetragonal (fct) phase showed corrosion and dissolution, while the ordered primitive cubic (L12) Pt3Co phase transformed into a disordered structure. The ordered primitive cubic structure exhibited higher resistance to sintering.Low annealing temperatures resulted in higher Pt surface-area specific activities for ORR. Kinetic Tafel analysis confirmed a general shift in the formation potential of oxygenated surface species, such as Pt–OH, for both alloy catalysts. Reduced OH coverage alone proved insufficient to account for the observed activity trends of the two alloy catalysts.
Dealloyed Pt25Cu75 bimetallic nanoparticle electrocatalysts exhibit up to 6 times higher oxygen r... more Dealloyed Pt25Cu75 bimetallic nanoparticle electrocatalysts exhibit up to 6 times higher oxygen reduction reaction activities than Pt-C catalysts. The effects of annealing temperature and duration on the catalyst activity are studied, with annealing temperature varied from ...
Corrosion and ORR activity of Pt alloy electrocatalysts during voltammetric pretreatment. [ECS Tr... more Corrosion and ORR activity of Pt alloy electrocatalysts during voltammetric pretreatment. [ECS Transactions 3, 139 (2006)]. Peter Strasser, Nathan T. Hahn, Shirlaine Koh. Abstract. This paper addresses the impact of voltammetric ...
A method of producing de-alloyed nanoparticles. In an embodiment, the method comprises admixing m... more A method of producing de-alloyed nanoparticles. In an embodiment, the method comprises admixing metal precursors, freeze-drying, annealing, and de-alloying the nanoparticles in situ. Further, in an embodiment de-alloyed nanoparticle formed by the method, wherein the nanoparticle further comprises a core-shell arrangement. The nanoparticle is suitable for electrocatalytic processes and devices.
Voltammetric dealloying of bimetallic platinum-copper (Pt-Cu) alloys has been shown to be an effe... more Voltammetric dealloying of bimetallic platinum-copper (Pt-Cu) alloys has been shown to be an effective strategy to modify the surface electrocatalytic reactivity of Pt bimetallic nanoparticles (S. Koh and P. Strasser, J. Am. Chem. Soc., 2007, 129, 12624). Using cyclic voltammetry and structural XRD studies, we systematically characterize the Pt-Cu precursor compounds as well as the early stages of the selective Cu surface dissolution (dealloying) process for Pt(25)Cu(75), Pt(50)Cu(50), and Pt(75)Cu(25) alloy nanoparticles annealed at both low and high temperature. We also assess the impact of the synthesis conditions on the electrocatalytic reactivity for the oxygen reduction reaction (ORR). To gain atomistic insight into the observed voltammetric profiles, we compare our experimental results with periodic DFT calculations of trends in the thermodynamics of surface Cu dissolution potentials from highly stepped and kinked Pt(854) single crystal surfaces. The modeling suggests a dependence of the electrochemical Cu dissolution potentials on the detailed atomic environment (coordination number, nature of coordinating atoms) of the bimetallic Pt-Cu surfaces. The DFT-predicted shifts in electrochemical Cu dissolution potentials are shown to qualitatively account for the observed voltammetric profiles during Cu dealloying. Our study suggests that metal-specific energetics have to be taken into account to explain the detailed dealloying behavior of bimetallic surfaces.
We report a synthetic electrochemical strategy to deliberately modify the catalytic reactivity of... more We report a synthetic electrochemical strategy to deliberately modify the catalytic reactivity of Pt bimetallic surfaces. The strategy consists of voltammetric surface dealloying of the non-noble constituent from Pt-poor bimetallic precursor compounds. We exemplify this method by ...
... J.Erlebacher, MJAziz, A.Karma, N.Dimitrov, and K.Sieradzki, “Evolution of nanoporosity in dea... more ... J.Erlebacher, MJAziz, A.Karma, N.Dimitrov, and K.Sieradzki, “Evolution of nanoporosity in dealloying,” Nature (London), 410, 450 (2001). RCNewman and K.Sieradzki, Science, 263, 1708 (1994). HWPickering, Corros. Sci., 23, 1107 (1983). SGCorcoran, in Critical Factors in ...
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