Ordered Intermetallic PtCu Catalysts Made from Pt@Cu Core/Shell Structures for Oxygen Reduction Reaction

Kinetics-Driven Crystal Facet Evolution Mechanism of Atomically Ordered Intermetallic PtFe Nanocubes toward Electrochemical Catalysis

Crystal structure engineering in nanoparticles has been regarded as a vital method in catalyst development and design. Herein, PtFe nanocubes, manufactured with ordered PtFe intermetallic structure and a desired facet of {202}, have been successfully prepared via the combination of selective deposition strategy and spatial barrier effect. In-situ X-ray photoelectron spectroscopy found that the growth of the high-index facet and formation of the nanocube for o-PtFe-202 materials arise from the surface Fe2+ modification stabilized effect and the selective deposition of Cl-, respectively. Moreover, density functional theory calculations and X-ray adsorption spectroscopies further proved that the improved oxygen reduction reaction activity and stability of o-PtFe-202 mainly originate from the synergistic effect of the desired high-index facet, ordered crystal structure, and resulting optimal d-band center of Pt. As expected, the o-PtFe-202 exhibits excellent mass activity (2.48 mA·ugPt-1) and specific activity (7.78 mA·cm-2), with only a 7.3% decrease in mass activity after 30 000 cycles.

Gas-Solid Reaction Synthesis and Electrocatalytic Oxygen Reduction of Pt-Skin L10-PtFe/C

Compared to Pt/C, the atomic ordered Pt-based intermetallic compounds can deliver higher efficiency and reliable stability, and they are considered one of the ideal cathode catalysts for the next generation of fuel cells. This work proposed a simple ferrocene atmosphere annealing method to improve commercial Pt/C and convert Pt to L10-PtFe. After further acid etching treatment, the obtained carbon-supported Pt-skin L10-PtFe (Pt-skin L10-PtFe/C) with superfine particle size (∼3.3 nm) not only was highly dispersed on the carbon but possesses a thin Pt skin, like the armor of L10-PtFe. As excepted, the ORR activity of Pt-skin L10-PtFe/C (0.375 A mg-1; 0.921 mA cm-2) is far better than that of commercial Pt/C (0.121 A mg-1; 0.260 mA cm-2), and its stability is also greatly improved. Our proposed gas-solid reaction is straightforward and has great potential in producing Pt-based intermetallic catalysts on a large scale.

Enhancing Surface Strain of Intermetallic Fuel Cell Catalysts by Composition-Induced Phase Transition

The lattice parameter of platinum-based intermetallic compounds (IMCs), which correlates with the intrinsic activity of the oxygen reduction reaction (ORR), can be modulated by crystal phase engineering. However, the controlled preparation of IMCs with unconventional crystal structures remains highly challenging. Here, we demonstrate the synthesis of carbon-supported PtCu-based IMC catalysts with an unconventional L10 structure by a composition-regulated strategy. Experiment and machine learning reveal that the thermodynamically favorable structure changes from L11 to L10 when slight Cu atoms are substituted with Co. Benefiting from crystal-phase-induced strain enhancement, the prepared L10-type PtCu0.8Co0.2 catalyst exhibits much-enhanced mass and specific activities of 1.82 A mgPt-1 and 3.27 mA cmPt-2, which are 1.91 and 1.73 times higher than those of the L11-type PtCu catalyst, respectively. Our work highlights the important role of crystal phase in determining the surface strain of IMCs, and opens a promising avenue for the rational preparation of IMCs with different crystal phases by doping.

Innovative Fabrication of Metal Alloy Structures via Laser-Induced Forward Transfer on Flexible Substrates

Laser-induced forward transfer is a contactless, nozzle free process which enables accurate, precise and fast development of 3D structures. However, a number of shortcomings such as shockwave generation, poor adhesion to receiver substrates and uniform depositions limit LIFT to be utilized. Therefore, this research tends to put forward easy and effective solutions for successful mitigation of the LIFT limitations. Receiver surface modifications and low-pressure conditions are introduced through laser surface texturing (LST) and a vacuum pump. A number of textures and orientations are investigated for determining the optimal copper (Cu) deposition. Furthermore, utilization of the same laser system for LST enables the manufacturing process cost and time effective. In addition to Cu depositions, additive layers of silver (Ag) and platinum (Pt) are deposited. Finally, Ag and Pt micropillars are fabricated on their respective additive layers leading to formation of Cu-Ag and Cu-Pt alloys structure. Subsequently, electrical and material characterizations are made to validate for potential applications. Experimental evidence shows greater adhesion with electrical properties for LST-based LIFT in low pressure conditions. Finally, an energy analysis is performed based on theoretical and finite element methods (FEM) to gain greater insights into mechanics of the LIFT process.

Separation of Nanoparticle Seed Pseudoisomers via Amplification of Their Crystallographic Differences

Seed-mediated syntheses rely on small nanoparticle (NP) precursors that act as templates for growth but are often inhomogeneous with respect to their internal twinning structures (e.g., single crystalline, multiply twinned), leading to nonuniform product morphologies. To address this, we developed a method for separating seed NPs of the same approximate size (∼ 10 nm) but with different interior twinning (i.e., NP "pseudoisomers") by exaggerating their crystallographic differences through heteroexpitaxial metal overgrowth. Specifically, single crystalline and pentatwinned Au seeds that are natively inseparable via traditional methods exhibit drastically different Ag shell morphologies that allow for their selective precipitation through colloidal depletion forces. Oxidation of the Ag shell from separated particles results in seeds that are both size uniform and crystallographically pure (>99%), allowing for the controlled synthesis of a library of Oh- and D5h-symmetric gold NPs bearing {111}, {110}, {730}, {310}, {720}, and {100} facets, several of which have no precedent in the literature. These results lay the foundation for precision nanosynthesis by establishing a new paradigm for the purification of NP precursors.

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.

Polyethylenimine-Ethylenediamine-Induced Pd Metallene toward Alkaline Oxygen Reduction

Designing two-dimensional (2D) materials functionalized with organic molecules is an effective tactic to enhance catalytic performances for the oxygen reduction reaction (ORR). Herein, we synthesize Pd metallene with in situ modification of polyethylenimine-ethylenediamine (Pd@PEI-EDA metallene), in which PEI-EDA serves as both the structure-directing agent and modifier. Pd@PEI-EDA metallene has ample active sites and tuneable electronic structures due to ultrathin nanosheets with abundant wrinkles and interfacial structure. In contrast with commercial Pd/C and Pt/C, Pd@PEI-EDA metallene displays preferable catalytic ORR performance under alkaline conditions. This work offers an in situ interface engineering tactic for the preparation of 2D polymer-metal electrocatalysts to boost the ORR performance.