All-metal layer-by-layer films: bimetallic alternate layers with accessible mesopores for enhanced electrocatalysis

The enhancement in the performance of ultra-small core-shell Au@AuPt nanoparticles toward HER and ORR by surface engineering

In this work, ultra-small core-shell (USCS) Au_38.4@Au_4.1Pt_57.5 nanoparticles (NPs) with an optimal Pt-to-Au ratio were successfully prepared by the optimal etching treatment of USCS Au@AuPt NPs by Fe(III) ions to remove some exposed Au atoms on their outermost surfaces. The as-prepared USCS Au_38.4@Au_4.1Pt_57.5 NPs with Fe(III)-etching treatment for 2 h loaded on carbon black as catalysts (USCS^2h Au_38.4@Au_4.1Pt_57.5-NP/C catalysts) exhibit superior electrocatalytic activity and durability for both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in acidic media. For instance, the overpotential of USCS^2h Au_38.4@Au_4.1Pt_57.5-NP/C catalysts toward the HER is 13 mV at a current density of -10 mA cm^-2 (η₁₀ = 13 mV), which is much better than that of commercial Pt/C catalysts (η₁₀ = 31 mV). Moreover, their mass activity (63.8 A mg_Pt^-1) is about 16.4 times larger than that of commercial Pt/C catalysts (3.9 A mg_Pt^-1). In addition, they also present better long-term stability. Furthermore, they also show an improved activity toward the ORR in terms of the half-wave potential (E_1/2) (0.89 V vs. RHE), which is more positive by about 38 mV than commercial Pt/C catalysts (0.852 V). In addition, they also show a higher kinetic current density (14.22 mA cm^-2 at 0.85 V) and better long-term durability. This etching-treatment strategy can be extended to further improve the catalytic performance of ultra-small Au-based bimetallic or multi-metallic NPs by surface engineering.

Facile Synthesis Of Composition-Controllable PtPdAuTe Nanowires As Superior Electrocatalysts For Direct Methanol Fuel Cells

Multicomponent Pt-based nanowires (NWs) have attracted widespread attention as eletrocatalysts toward direct alcohol fuel cells because of their unique one-dimensional structure and high reaction dynamics. Quaternary PtPdAuTe NWs are designed via a facile template method, and NWs with a different composition are obtained by adjusting the feed ratio of metal precursors. The direct displacement reaction of metal precursors with Te NWs and the partial oxidation of Te lead to the formation of quaternary NWs. The rough surface and abundant reactive sites deriving from the rearrangement of metal atoms on the Te NWs surface endow the PtPdAuTe NWs with a superior electrocatalytic property and durability for methanol oxidation. The Pt₂₀ Pd₂₀ Au₁₀ Te₅₀ NWs display the largest mass activity and best stability among all catalysts. The preparation of PtPdAuTe NWs could provide a viable strategy for the preparation of other multicomponent NWs.

Oxygen Reduction Reaction and Hydrogen Evolution Reaction Catalyzed by Pd–Ru Nanoparticles Encapsulated in Porous Carbon Nanosheets

Developing bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for enhancing the energy transfer efficiency of metal–air batteries and fuel cells, as well as producing hydrogen with a high purity. Herein, a series of Pd–Ru alloyed nanoparticles encapsulated in porous carbon nanosheets (CNs) were synthesized and employed as a bifunctional electrocatalyst for both ORR and HER. The TEM measurements showed that Pd–Ru nanoparticles, with a size of approximately 1–5 nm, were uniformly dispersed on the carbon nanosheets. The crystal and electronic structures of the PdxRu100−x/CNs series were revealed by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The as-prepared samples exhibited effective ORR activity in alkaline media and excellent HER activity in both alkaline and acid solutions. The Pd50Ru50/CNs sample displayed the best activity and stability among the series, which is comparable and superior to that of commercial 10% Pd/C. For ORR, the Pd50Ru50/CNs catalyst exhibited an onset potential of 0.903 V vs. RHE (Reversible Hydrogen Electrode) and 11.4% decrease of the current density after 30,000 s of continuous operation in stability test. For HER, the Pd50Ru50/CNs catalyst displayed an overpotential of 37.3 mV and 45.1 mV at 10 mA cm−2 in 0.1 M KOH and 0.5 M H2SO4, respectively. The strategy for encapsulating bimetallic alloys within porous carbon materials is promising for fabricating sustainable energy toward electrocatalysts with multiple electrocatalytic activities for energy related applications.

Facile synthesis of bimetallic gold-palladium nanocrystals as effective and durable advanced catalysts for improved electrocatalytic performances of ethylene glycol and glycerol oxidation

In this work, well-defined bimetallic AuPd alloyed nanocrystals (AuPd NCs) were facilely synthesized by a straightforward and controllable one-step wet-chemical strategy, using a biomolecule (L-hydroxyproline, L-Hyp) as the green stabilizer and the structure-directing agent. Their morphology, size, composition, crystal structures and growth mechanism were investigated by a series of techniques. The synthesized architectures exhibited enlarged electrochemically active surface area (ECSA), improved catalytic activity, enhanced durability and stability towards ethylene glycol oxidation reaction (EGOR) and glycerol oxidation reaction (GOR) in alkaline electrolytes in comparison with commercial Pd black catalyst.

MOF-Derived Flower-like MoS2@TiO2 Nanohybrids with Enhanced Activity for Hydrogen Evolution

A simple hydrothermal method is developed for synthesizing crystalline MoS₂@TiO₂ nanohybrids with metal-organic framework (MOF) as precursor. At an optimal ratio of 14.6 wt % MoS₂, the resultant material exhibits prominent catalytic activity for hydrogen evolution reaction (HER) with a high hydrogen production rate of 10 046 μmol h^-1 g^-1 under visible light illumination with fluorescein as photosensitizer. Furthermore, the synthesized catalyst also possesses an attractive electrocatalytic activity with an onset overpotential of -300 mV (vs RHE) and a Tafel slope of ∼81 mV dec^-1. The enhanced catalyst performances are mainly attributed to the in situ formed active sites, featuring a uniform dispersion and strong connection of MoS₂ and TiO₂, which can facilitate electron transfer. In addition, the MoS₂@TiO₂ nanohybrids are highly stable and completely recyclable over HER.

Pd-on-Au Supra-nanostructures Decorated Graphene Oxide: An Advanced Electrocatalyst for Fuel Cell Application

We report a very easy and effective approach for synthesizing unique palladium-on-gold supra-nanostructure (Au@Pd-SprNS)-decorated graphene oxide (GO) nanosheets. The SprNSs comprising Au nanorods as core and a unique close-packed assembly of tiny anisotropic Pd nanoparticles (NPs) as shell were homogeneously distributed on the GO surface via electrostatic self-assembly. Compared with the traditional one-pot method for synthesis of metal NPs on GO sheets, the size and shape of core-shell Au@Pd SprNSs can be finely controlled and uniformly distributed on the GO carrier. Interestingly, this Au@Pd-SprNSs/GO nanocomposite displayed high electrocatalytic activities toward the oxidation of methanol, ethanol, and formic acid, which can be attributed to the abundance of intrinsic active sites including high density of atomic steps, ledges and kinks, Au-Pd heterojunctions and cooperative action of the two metals of the SprNSs. Additionally, uniform dispersion of the SprNSs over the GO nanosheets prevent agglomeration between the SprNSs, which is of great significance to enhance the long-term stability of catalyst. This work will introduce a highly efficient Pd-based nanoelectrocatalyst to be used in fuel cell application.

Gaseous NH3 Confers Porous Pt Nanodendrites Assisted by Halides

Tailoring the morphology of Pt nanocrystals (NCs) is of great concern for their enhancement in catalytic activity and durability. In this article, a novel synthetic strategy is developed to selectively prepare porous dendritic Pt NCs with different structures for oxygen reduction reaction (ORR) assisted by NH₃ gas and halides (F⁻, Cl⁻, Br⁻). The NH₃ gas plays critical roles on tuning the morphology. Previously, H₂ and CO gas are reported to assist the shape control of metallic nanocrystals. This is the first demonstration that NH₃ gas assists the Pt anisotropic growth. The halides also play important role in the synthetic strategy to regulate the formation of Pt NCs. As-made porous dendritic Pt NCs, especially when NH₄F is used as a regulating reagent, show superior catalytic activity for ORR compared with commercial Pt/C catalyst and other previously reported Pt-based NCs.

Shape-controlled synthesis of porous AuPt nanoparticles and their superior electrocatalytic activity for oxygen reduction reaction

Control of structure and morphology of Pt-based nanomaterials is of great importance for electrochemical energy conversions. In this work, we report an efficient one-step synthesis of bimetallic porous AuPt nanoparticles (PAuPt NPs) in an aqueous solution. The proposed synthesis is performed by a simple stirring treatment of an aqueous reactive mixture including K₂PtCl₄, HAuCl₄, Pluronic F127 and ascorbic acid at a pH value of 1 without organic solvent or high temperature. Due to their porous structure and bimetallic composition, as-made PAuPt NPs exhibit excellent electrocatalytic activity for oxygen reduction reaction.

Facile and shape-controlled electrochemical synthesis of gold nanocrystals by changing water contents in deep eutectic solvents and their electrocatalytic activity

Au NCs with different morphologies were synthesized in DESs by changing water contents, and used as electrocatalysts for ethanol electrooxidation.

Silicon carbide-supported iron nanoparticles encapsulated in nitrogen-doped carbon for oxygen reduction reaction

Iron nanoparticles encapsulated in nitrogen-doped carbon (Fe@N–C) supported on a SiC core with a derived nitrogen-doped carbon shell (SiC@N–C) show much higher activity for oxygen reduction reaction than SiC, SiC@N–C and SiC-supported Fe₃Si in alkaline medium.