Bimetallic and postsynthetically alloyed PtCu nanostructures with tunable reactivity for the methanol oxidation reaction

Recent progress on the synthesis of metal alloy nanowires as electrocatalysts

Benefiting from both one-dimensional (1D) morphology and alloy composition, metal alloy nanowires have been exploited as advanced electrocatalysts in various electrochemical processes. In this review, the synthesis approaches for metal alloy nanowires are classified into two categories: direct syntheses and syntheses based on preformed 1D nanostructures. Ligand systems that are of critical importance to the formation of alloy nanowires are summarized and reviewed, together with the strategies imposed to achieve the co-reduction of different metals. Meanwhile, different scenarios that form alloy nanowires from pre-synthesized 1D nanostructures are compared and contrasted. In addition, the characterization and electrocatalytic applications of metal alloy nanowires are briefly discussed.

Engineering PtCu nanoparticles for a highly efficient methanol electro-oxidation reaction

Achieving a highly efficient and durable methanol electro-oxidation catalyst in acid media is critical for the practical utilization of direct methanol fuel cells (DMFCs) at the commercial scale. Herein, we report a facile and effective one-pot strategy for the synthesis of carbon-supported PtCu alloy nanoparticles (PtCu NPs) with a Pt-rich surface, small particle size and uniform dispersion. The as-prepared PtCu NPs with the optimal alloy composition (Pt₂Cu) exhibit a significantly improved electrochemical methanol oxidation reaction performance in terms of a high activity, superior CO tolerance and remarkable durability, in contrast to those of commercial Pt/C catalysts in acid media. Particularly, the Pt₂Cu/C catalyst exerts a 4.5 times enhancement in the mass activity and a larger I_f/I_b value compared to those of commercial Pt/C (Pt/C_comm). The enhanced catalytic activities can be ascribed to the high utilization of Pt and the high index facets of the surface. Also, the addition of Cu downshifts the d-band center of Pt and improves the CO tolerance during the methanol oxidation reaction process. This work provides an efficient strategy for designing desired Pt-based alloys for various catalytic reactions.

The catalytic activity of PtnCum (n = 1-3, m = 0-2) clusters for methanol dehydrogenation to CO

A large number of experiments show that PtCu catalyst has a good catalytic effect on methanol decomposition. Therefore, density functional theory (DFT) was used to further study the dehydrogenation of methanol catalyzed by Pt_nCu_m (n = 1-3, m = 0-2). The energy diagrams of O-adsorption path and H-adsorption path were drawn. By calculation, the Pt is the active site of the whole reaction process, and the barrier energy of the rate-determining step is 11.09 kcal mol^-1 by Pt₂Cu, which is lower than that of Pt₃ and PtCu₂. However, the complete dehydrogenation product of methanol, CO, is easier to dissociate from PtCu₂ clusters than from Pt₃ and Pt₂Cu clusters. Therefore, Cu doping can improve the catalytic activity and anti-CO toxicity of Pt to a certain extent.

Zinc-Coordination Polymer-Derived Porous Carbon-Supported Stable PtM Electrocatalysts for Methanol Oxidation Reaction

Porous carbon (PC) is obtained by carbonizing a zinc-coordination polymer (MOF-5) at 950 °C and PtM (M = Fe, Co, Ni, Cu, Zn) nanoparticles (NPs), which are deposited on PC using the polyol method. Structural and morphological characterizations of the synthesized materials are carried out by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), and the porosity was determined using a N2 adsorption/desorption technique. The results revealed that PtM NPs are alloyed in the fcc phase and are well dispersed on the surface of PC. The electrochemical results show that PtM/PC 950 catalysts have higher methanol oxidation reaction (MOR) performances than commercial Pt/C (20%) catalysts. After 3000 s of chronoamperometry (CA) test, the MOR performances decreased in the order of Pt1Cu1/PC 950 > Pt1Ni1/PC 950 > Pt1Fe1/PC 950 > Pt1Zn1/PC 950 > Pt1Co1/PC 950. The high MOR activities of the synthesized catalysts are attributed to the effect of M on methanol dissociative chemisorption and improved tolerance of Pt against CO poisoning. The high specific surface area and porosity of the carbon support have an additional effect in boosting the MOR activities. Screening of the first row transition metals (d 5+n , n = 1, 2, 3, 4, 5) alloyed with Pt binary catalysts for MOR shows that Pt with d 8 (Ni) and d 9 (Cu) transition metals, in equivalent atomic ratios, are good anode catalysts for alcohol fuel cells.

Dewetting of PtCu Nanoalloys on TiO2 Nanocavities Provides a Synergistic Photocatalytic Enhancement for Efficient H2 Evolution

We investigate the co-catalytic activity of PtCu alloy nanoparticles for photocatalytic H₂ evolution from methanol-water solutions. To produce the photocatalysts, a few-nanometer-thick Pt-Cu bilayers are deposited on anodic TiO₂ nanocavity arrays and converted by solid-state dewetting via a suitable thermal treatment into bimetallic PtCu nanoparticles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results prove the formation of PtCu nanoalloys that carry a shell of surface oxides. X-ray absorption near-edge structure (XANES) data support Pt and Cu alloying and indicate the presence of lattice disorder in the PtCu nanoparticles. The PtCu co-catalyst on TiO₂ shows a synergistic activity enhancement and a significantly higher activity toward photocatalytic H₂ evolution than Pt- or Cu-TiO₂. We propose the enhanced activity to be due to Pt-Cu electronic interactions, where Cu increases the electron density on Pt, favoring a more efficient electron transfer for H₂ evolution. In addition, Cu can further promote the photoactivity by providing additional surface catalytic sites for hydrogen recombination. Remarkably, when increasing the methanol concentration up to 50 vol % in the reaction phase, we observe for PtCu-TiO₂ a steeper activity increase compared to Pt-TiO₂. A further increase in methanol concentration (up to 80 vol %) causes for Pt-TiO₂ a clear activity decay, while PtCu-TiO₂ still maintains a high level of activity. This suggests improved robustness of PtCu nanoalloys against poisoning from methanol oxidation products such as CO.