PDA-assisted formation of ordered intermetallic CoPt3 catalysts with enhanced oxygen reduction activity and stability

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Facile synthesis of L10-PtFe/C intermetallic catalysts with superior catalytic durability for the oxygen reduction reaction

An o-PtFe/C intermetallic catalyst was prepared by a facile thermal reduction method with the average particle size of only 6.6 nm in the presence of urea. The loss of mass activity is only 25.9% after 50 000 cycles. This work provides guidance on the suppression of grain coarsening for high-temperature synthesis of Pt-based intermetallic catalysts.

Pt-Co Electrocatalysts: Syntheses, Morphologies, and Applications

Pt-Co electrocatalysts have attracted significant attention because of their excellent performance in many electrochemical reactions. This review focuses on Pt-Co electrocatalysts designed and prepared for electrocatalytic applications. First, the various synthetic methods and synthesis mechanisms are systematically summarized; typical examples and core synthesis parameters are discussed for regulating the morphology and structure. Then, starting with the design and structure-activity relationship of catalysts, the research progress of the morphologies and structures of Pt-Co electrocatalysts obtained based on various strategies, the structure-activity relationship between them, and their properties are summarized. In addition, the important electrocatalytic applications and mechanisms of Pt-Co catalysts, including electrocatalytic oxidation/reduction and bifunctional catalytic reactions, are described and summarized, and their high catalytic activities are discussed on the basis of their mechanism and active sites. Moreover, the advanced electrochemical in situ characterization techniques are summarized, and the challenges and direction concerning the development of high-performance Pt-Co catalysts in electrocatalysis are discussed.

Unusual Role of the Surfactant in the Self-Assembly of Pt Alloy in Ordered Mesoporous Carbon: Tuning the Nanocluster Size

In the one-step self-assembly synthesis of metallic nanocrystals in ordered mesoporous carbon (OMC), the surfactant functionalizes well as the structure directing agent and mesopore template. Interestingly, this work demonstrates another unusual role the surfactant plays: tuning the size of the nanocrystals. Our investigation shows that the decreasing molecular weight of the PS segment of PEO-b-PS leads to sequentially reduced PtRu particle sizes of 4.4, 3.9, and 2.9 nm, while F127 which has a distinctly smaller hydrophobic PO domain with a bending structure in the micelles successfully results in sub-2 nm PtM (M = Ru, Ir, Rh, Pd) nanoclusters in OMC. This well indicates that the nanocluster size is largely decided by the volume of the hydrophobic segment of the surfactant to which the metallic precursor is linked. The smaller the volume, the fewer the precursor molecules are adsorbed, and the smaller the alloy nanoclusters. In the electrocatalytic methanol oxidation reaction, the mass activity of PtRu-1.6/OMC with 1.6 nm PtRu clusters at 0.87 V reaches 1.07 A mg_Pt^-1, which is 2.9 times that of commercial PtRu/C with an average alloy size of 2.7 nm. In principle, a wide range of ultrafine metallic clusters embedded in OMC can be prepared via this route for various applications.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.

Crystal Orientation in Pt-Based Alloys Induced by W(CO)6: Driving Oxygen Electroreduction Catalysis

Integrating crystal orientation as well as structural and compositional advantages into one catalyst might be a promising strategy for high-performance Pt-based catalysts for proton-exchange membrane fuel cells. Herein, by introducing W(CO)₆ as a structure-oriented template, Pt-based alloys with a well-defined crystal orientation along the (111) facet were obtained. The oxygen reduction reaction mass and specific activities of the crystal-facet-tuned alloys reach a new level. Moreover, the outstanding durability stems from the combination of their exposed crystal facets and incorporated W. The density functional theory calculation results reveal that the formation of the preferred (111) alloys can be attributed to the lower free energy of (111) facets and the weaker adsorption of CO released by W(CO)₆. This proposed synthesis strategy of using transition-metal carbonyl compounds as additives to synthesize alloys with strong crystal orientation may open a door to the design of various alloy catalysts with ultrahigh activity.

Recent advances in Pt-based electrocatalysts for PEMFCs

In order to reduce the cost and improve the performance of proton exchange membrane fuel cells (PEMFCs), it is imperative to further enhance the activity and durability of Pt based electrocatalysts for the oxygen reduction reaction (ORR). This article analyzes the latest advances in Pt-based ORR electrocatalysts, including the Pt alloys, Pt–M core–shell structures, particle size effects, support effects, doping in Pt/PtM and post treatment. In addition, the performance of some of the developed novel electrocatalysts in membrane electrode assemblies (MEA) is also included for comparison, as they are rarely available and the superior activity and durability exhibited in RDE frequently doesn't translate into MEA.

In this paper, the latest progress in the design of Pt-based ORR electrocatalysts is reviewed, including the understanding of research progress in the synthesis of high activity and high stability catalysts.

Electrospinning Synthesis of Carbon-Supported Pt3Mn Intermetallic Nanocrystals and Electrocatalytic Performance towards Oxygen Reduction Reaction

To realize the large-scale application of fuel cells, it is still a great challenge to improve the performance and reduce the cost of cathode catalysts towards oxygen reduction reaction (ORR). In this work, carbon-supported ordered Pt₃Mn intermetallic catalysts were prepared by thermal annealing electrospun polyacrylonitrile nanofibers containing Platinum(II) acetylacetonate/ Manganese(III) acetylacetonate. Compared with its counterparts, the ordered Pt₃Mn intermetallic obtained at 950 °C exhibits a more positive half-potential and higher kinetic current density during the ORR process. Benefiting from their defined stoichiometry and crystal structure, the Mn atoms in Pt₃Mn intermetallic can modulate well the geometric and electronic structure of surface Pt atoms, endowing Pt₃Mn catalyst with an enhanced ORR catalytic activity. Moreover, it also has a better catalytic stability and methanol tolerance than commercial Pt/C catalyst. Our study provides a new strategy to fabricate a highly active and durable Pt₃Mn intermetallic electrocatalyst towards ORR.

Remarkable Improvement of the Catalytic Performance of PtFe Nanoparticles by Structural Ordering and Doping

To achieve fuel cell commercialization, the performance improvement and cost reduction of catalysts are still the main challenges. To enhance the catalytic activity and durability for oxygen reduction reaction (ORR), we prepare Au-PtFe particles entrapped in a porous carbon and then convert them to have a fine-grained and highly ordered intermetallic structure. The optimal Au-PtFe particles in catalyzing ORR exhibit initial specific and mass activities 9 times higher than the commercial catalyst of Pt/C. Such a large enhancement is much higher than most of the Pt-based ordered intermetallic catalysts reported in the literature. Accelerated durability testing induces little degradation of the catalytic activity to the ordered structure, particularly the Au-doped one, after potential cycling for many thousands of cycles under harsh electrochemical conditions involving an acidic medium and a high potential range of 0.66-1.3 V. This is in big contrast with the large degradation shown by most previous catalysts. The excellent activity and durability are attributed to synergistic effects of the fine-grained and ordered structure of the particles, the confining support of the porous carbon, and the homogeneous incorporation of a trace amount of Au. The new intermetallic catalyst of Au-PtFe/C represents a new strategy for performance enhancement and cost reduction and thus promotes practical applications of proton-exchange membrane fuel cells.

High temperature self-assembly one-step synthesis of a structurally ordered PtFe catalyst for the oxygen reduction reaction

Herein, we present a high-temperature self-assembly strategy that directly allows the transformation of adsorbed Pt(NH₃)₄²⁺ and Fe³⁺ sources into structurally ordered face-centered tetragonal (fct)-PtFe alloy NPs (2.6 ± 0.2 nm).