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Activity descriptor identification for oxygen reduction on platinum-based bimetallic nanoparticles: in situ observation of the linear composition-strain-activity relationship.

Jia Q, Liang W, Bates MK, Mani P, Lee W, Mukerjee S - ACS Nano (2015)

Bottom Line: Despite recent progress in developing active and durable oxygen reduction catalysts with reduced Pt content, lack of elegant bottom-up synthesis procedures with knowledge over the control of atomic arrangement and morphology of the Pt-alloy catalysts still hinders fuel cell commercialization.Despite their different atomic structure, the oxygen reduction reaction (ORR) activity of PtxCo/C and Pt/C NPs is linearly related to the bulk average Pt-Pt bond length (RPt-Pt).These linear correlations together demonstrate that (i) the improved ORR activity of PtxCo/C NPs over pure Pt NPs originates predominantly from the compressive strain and (ii) the RPt-Pt is a valid strain descriptor that bridges the activity and atomic composition of Pt-based bimetallic NPs.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Chemical Biology and ‡Department of Biology, Northeastern University , Boston, Massachusetts 02115, United States.

ABSTRACT
Despite recent progress in developing active and durable oxygen reduction catalysts with reduced Pt content, lack of elegant bottom-up synthesis procedures with knowledge over the control of atomic arrangement and morphology of the Pt-alloy catalysts still hinders fuel cell commercialization. To follow a less empirical synthesis path for improved Pt-based catalysts, it is essential to correlate catalytic performance to properties that can be easily controlled and measured experimentally. Herein, using Pt-Co alloy nanoparticles (NPs) with varying atomic composition as an example, we show that the atomic distribution of Pt-based bimetallic NPs under operating conditions is strongly dependent on the initial atomic ratio by employing microscopic and in situ spectroscopic techniques. The PtxCo/C NPs with high Co content possess a Co concentration gradient such that Co is concentrated in the core and gradually depletes in the near-surface region, whereas the PtxCo/C NPs with low Co content possess a relatively uniform distribution of Co with low Co population in the near-surface region. Despite their different atomic structure, the oxygen reduction reaction (ORR) activity of PtxCo/C and Pt/C NPs is linearly related to the bulk average Pt-Pt bond length (RPt-Pt). The RPt-Pt is further shown to contract linearly with the increase in Co/Pt composition. These linear correlations together demonstrate that (i) the improved ORR activity of PtxCo/C NPs over pure Pt NPs originates predominantly from the compressive strain and (ii) the RPt-Pt is a valid strain descriptor that bridges the activity and atomic composition of Pt-based bimetallic NPs.

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Co/Pt atomic ratio of the PtxCo/C catalysts obtained by ex situ element analysis (dots) and obtained using the experimentally determined coordination numbers (Table 3) (circles). The data of PtCo/C and PtCo3/C catalysts in refs (33) and (38) are included for comparison purposes.
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fig7: Co/Pt atomic ratio of the PtxCo/C catalysts obtained by ex situ element analysis (dots) and obtained using the experimentally determined coordination numbers (Table 3) (circles). The data of PtCo/C and PtCo3/C catalysts in refs (33) and (38) are included for comparison purposes.

Mentions: As the bulk RPt–Pt of the PtxCo/C NPs is linearly related to the ORR activity, it is of particular interest to identify what controls the bulk RPt–Pt. A monotonic correlation between the bulk RPt–Pt and the nominal atomic composition is not observed (Figure S8). This is likely caused by the different Co loss extent during the acid pretreatment for the PtxCo/C catalysts with different initial Co content as suggested by Δμ-XANES and/or the different atomic distribution revealed by EXAFS. To test the hypothesis, we present in Figure 7 the Co/Pt ratios of the as-synthesized PtxCo/C dry powders and the corresponding in situ electrodes under electrochemical control, in addition to the results of the dealloyed PtCo/C and PtCo3/C NPs reported by us previously.33,38 The in situ Co/Pt atomic ratio is derived from the experimentally measured coordination numbers (Table 3) following the equation564


Activity descriptor identification for oxygen reduction on platinum-based bimetallic nanoparticles: in situ observation of the linear composition-strain-activity relationship.

Jia Q, Liang W, Bates MK, Mani P, Lee W, Mukerjee S - ACS Nano (2015)

Co/Pt atomic ratio of the PtxCo/C catalysts obtained by ex situ element analysis (dots) and obtained using the experimentally determined coordination numbers (Table 3) (circles). The data of PtCo/C and PtCo3/C catalysts in refs (33) and (38) are included for comparison purposes.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492796&req=5

fig7: Co/Pt atomic ratio of the PtxCo/C catalysts obtained by ex situ element analysis (dots) and obtained using the experimentally determined coordination numbers (Table 3) (circles). The data of PtCo/C and PtCo3/C catalysts in refs (33) and (38) are included for comparison purposes.
Mentions: As the bulk RPt–Pt of the PtxCo/C NPs is linearly related to the ORR activity, it is of particular interest to identify what controls the bulk RPt–Pt. A monotonic correlation between the bulk RPt–Pt and the nominal atomic composition is not observed (Figure S8). This is likely caused by the different Co loss extent during the acid pretreatment for the PtxCo/C catalysts with different initial Co content as suggested by Δμ-XANES and/or the different atomic distribution revealed by EXAFS. To test the hypothesis, we present in Figure 7 the Co/Pt ratios of the as-synthesized PtxCo/C dry powders and the corresponding in situ electrodes under electrochemical control, in addition to the results of the dealloyed PtCo/C and PtCo3/C NPs reported by us previously.33,38 The in situ Co/Pt atomic ratio is derived from the experimentally measured coordination numbers (Table 3) following the equation564

Bottom Line: Despite recent progress in developing active and durable oxygen reduction catalysts with reduced Pt content, lack of elegant bottom-up synthesis procedures with knowledge over the control of atomic arrangement and morphology of the Pt-alloy catalysts still hinders fuel cell commercialization.Despite their different atomic structure, the oxygen reduction reaction (ORR) activity of PtxCo/C and Pt/C NPs is linearly related to the bulk average Pt-Pt bond length (RPt-Pt).These linear correlations together demonstrate that (i) the improved ORR activity of PtxCo/C NPs over pure Pt NPs originates predominantly from the compressive strain and (ii) the RPt-Pt is a valid strain descriptor that bridges the activity and atomic composition of Pt-based bimetallic NPs.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Chemical Biology and ‡Department of Biology, Northeastern University , Boston, Massachusetts 02115, United States.

ABSTRACT
Despite recent progress in developing active and durable oxygen reduction catalysts with reduced Pt content, lack of elegant bottom-up synthesis procedures with knowledge over the control of atomic arrangement and morphology of the Pt-alloy catalysts still hinders fuel cell commercialization. To follow a less empirical synthesis path for improved Pt-based catalysts, it is essential to correlate catalytic performance to properties that can be easily controlled and measured experimentally. Herein, using Pt-Co alloy nanoparticles (NPs) with varying atomic composition as an example, we show that the atomic distribution of Pt-based bimetallic NPs under operating conditions is strongly dependent on the initial atomic ratio by employing microscopic and in situ spectroscopic techniques. The PtxCo/C NPs with high Co content possess a Co concentration gradient such that Co is concentrated in the core and gradually depletes in the near-surface region, whereas the PtxCo/C NPs with low Co content possess a relatively uniform distribution of Co with low Co population in the near-surface region. Despite their different atomic structure, the oxygen reduction reaction (ORR) activity of PtxCo/C and Pt/C NPs is linearly related to the bulk average Pt-Pt bond length (RPt-Pt). The RPt-Pt is further shown to contract linearly with the increase in Co/Pt composition. These linear correlations together demonstrate that (i) the improved ORR activity of PtxCo/C NPs over pure Pt NPs originates predominantly from the compressive strain and (ii) the RPt-Pt is a valid strain descriptor that bridges the activity and atomic composition of Pt-based bimetallic NPs.

Show MeSH
Related in: MedlinePlus