•Hollow PdAu NCs were synthesized successfully by a successive reduction method.•The morphology, alloy degree and composition of the PdAu NCs can be well controlled.•Hollow PdAu NCs showed an enlarged ECSA and improved performance for CH3OH oxidation.Pd-based nanocatalysts (NCs) are the potential substitutes for the Pt-based NCs used in the direct methanol fuel cells (DMFCs) because of their lower cost and comparable catalytic performance. The catalytic performance of Pd-based NCs is highly connected with the morphology, composition and surface structure of the catalysts. Here, solid bimetallic PdAu and hollow PdAu NCs were synthesized by a successive reduction and co-reduction method, respectively, using P123 both as reducing reagent and protectant. Compared with the solid PdAu NCs and commercial Pd black catalyst, the hollow PdAu NCs exhibited enlarged electrochemical surface areas (ECSA), and showed an enhanced electrocatalytic activity and stability for methanol oxidation reaction (MOR) in alkaline solution. The excellent electrocatalytic performance is contributed to the unique hollow structure and alloy effects of the PdAu NCs.

•Pt nanoparticles are synthesized by a facile one-pot hydrothermal synthesis for the first time.•The size of the Pt nanoparticles can be well controlled.•The Pt nanoparticles show a better electrochemical performance than commercial Pt/C catalyst.Pt nanoparticles are synthesized by a facile one-pot hydrothermal synthesis using one kind triblock Pluronic copolymers as reducer and stabilizer for the first time. The size of the Pt nanoparticles can be controlled through simply varying the reaction conditions. The morphology and structure of the Pt nanoparticles were well characterized by different techniques. The electrocatalytic test indicated that the obtained Pt nanoparticles exhibit a better electrocatalytic performance for methanol oxidation in acidic media compared to the commercial Pt/C catalyst. The results of this paper provide a promising approach to prepare Pt-based nanocatalysts for direct alcohols fuel cells (DAFCs).

High-dispersed Pd nanospheres were synthesized successfully by a facile and green method using polyoxypropylenepolyoxyethylene copolymer as reducer and stabilizer. The size and shape of the nanospheres can be well controlled through simply varying the reaction temperature. The morphology and structure of the nanospheres were characterized by Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray powder diffraction (XRD). The electrocatalytic test indicated that the obtained Pd nanospheres exhibit more negative onset oxidation potential and much higher current density for methanol oxidation in alkaline media compared to the bulk Pd electrode. The results of this paper provides a promising approach to prepare Pd-based nanocatalysts for alkaline fuel cells.Highlights► High dispersed Pd nanospheres were synthesized with a facile and green method. ► The size and shape of the Pd nanospheres can be well controlled by simply varying the reaction temperature. ► The Pd nanospheres provided high catalytic performance for CH3OH oxidation in alkaline medium. ► We provided a facile and green method to prepare Pd-based nanocatalyst for alkaline fuel cells.

Water-soluble polymeric tungsten citrate (Him)10n(NH4)2n[(WO2)2O(Hcit)2]3n·10nH2O (1) and octanuclear tungsten citrate (Him)8(NH4)13{[(WO2)2O(Hcit)(cit)H(cit)(Hcit)O(WO2)2][(WO2)2O(cit)2]2}·14H2O (2) (H4cit = citric acid, im = imidazole), were obtained from aqueous solution. They were characterized by elemental analyses, NMR and IR spectra, thermogravimetric (TG) analyses and X-ray structural analyses. The basic units of the two complexes contain a dimeric tungsten citrate in different protonated forms, where tungsten atom is six-coordinated in an approximately octahedral geometry. Each citrate ligand uses its α-alkoxy, α-carboxy and one β-carboxy group to act as a tridentate ligand, while the other β-carboxy or carboxylic acid group is uncoordinated. The presences of the protonated/deprotonated terminal carboxylates and their participation in hydrogen-bonding interactions play an important role in the overall structures. In complex 1, a hexanuclear tungsten citrate species [(WO2)2O(Hcit)2]312− is linked by strong H-bonding between β-carboxylic acid group and terminal oxygen [2.587(6) Å], which extends into one-dimensional polymeric chain. In complex 2, there exist two types of strong hydrogen bonds between β-carboxy and carboxylic acid groups [2.467(8), 2.516(6) Å], forming an octanuclear species {[(WO2)2O(Hcit)(cit)H(cit)(Hcit)O(WO2)2][(WO2)2O(cit)2]2}21−. This is supported by the absence of IR band around 1700 cm−1 for protonated carboxylic acid. 13C NMR spectra show the coordination of α-alkoxy and α-carboxy groups of citrate ligand in both complexes.Graphical abstractTwo polymeric tungsten citrate complexes have been synthesized and characterized. The structural analysis indicates that changing the pH value leads to the different structures. The uncoordinated β-carboxy groups of citrate ligand are of different degree of protonation and form intermolecular hydrogen bonds leading to a polymeric chain structure of the two complexes.Highlights► Two new tungsten citrate complexes were synthesized from aqueous solution. ► The reaction shows that the pH value plays a key role. ► H-bond formed by terminal carboxylates plays an important role in the structures. ► 13C NMR spectra show the coordination of citrate to W in both complexes.