In Situ Probing of the Active Site Geometry of Ultrathin Nanowires for the Oxygen Reduction Reaction

Abstract

To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (∼2 nm) core-shell Pt∼Pd9Au nanowires, which have been previously shown to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu∼Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Hence, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general.

In Situ Integration of Ultrathin PtCu Nanowires with Reduced Graphene Oxide Nanosheets for Efficient Electrocatalytic Oxygen Reduction

“…Figure 1b displays the corresponding Ramanspectra of the two samples, which are used to investigate the structure of rGO and the interaction between PtCu particles and rGO. [13] From the magnified TEM image of as ingle nanowires hown in Figure 2d,w ell-resolved lattice fringesc an be clearly observed with the lattice spacings of 0.230 nm, corresponding to the {111}p lane of face-centered cubic (fcc) PtCu. Generally,t he I D /I G ratio is related to the size of sp 2 domains.…”

“…Such 1D anisotropic PtCu nanowires with ultrathin sizea nd high aspect ratio would be conducive to the electrocatalysis owing to the path directing effect of the structural anisotropy and enormouss urface atoms. [13] From the magnified TEM image of as ingle nanowires hown in Figure 2d,w ell-resolved lattice fringesc an be clearly observed with the lattice spacings of 0.230 nm, corresponding to the {111}p lane of face-centered cubic (fcc) PtCu. It is noted that the lattice fringes are discontinuous,i mplying that the formation of PtCu nanowires may originate from the oriented attachment of primary nanoparticles.…”

Platinum Group Nanowires for Efficient Electrocatalysis

“…Researchers also designed the core–shell Pt nanowires to enhance the electrocatalytic performance, since it not only increases the utilization of Pt atoms, but also amplifies the specific activity via strain effect and electronic effect. A typical example is demonstrated by Pd/Pt core–shell nanowires, which show outstanding area and mass activities of 0.77 mA cm −2 and 1.83 A mg Pt −1 , respectively . The ORR activity was further improved after introducing Au into Pd core, since Au can reduce Pt dissolution and migration.…”

From Galvanic to Anti‐Galvanic Synthesis of Bimetallic Nanoparticles and Applications in Catalysis, Sensing, and Materials Science

“…[74] More recently, Crooks' group reported that Au@Pt NPs are better electrocatalysts than monometallic PtNPs and AuNPs for the cathodic reaction governing proton-exchangemembrane fuel cells (PEMFCs), namely the oxygen-reduction reaction (ORR). [77] Multi-metallic nanocatalysts have been designed by control of their components on the basis of the activity/selectivity in various reactions. [76] Very recently this research group has designed the synthesis, using GR, of polyamidoamine (PAMAM) dendrimer-encapsulated trimetallic Pd@Pt-Au nanowires, as efficient electrocatalysts for the ORR.…”