It is conventionally assumed that the growth of monodisperse colloidal nanocrystals requires a temporally discrete nucleation followed by monomer attachment onto the existing nuclei. However, recent studies have reported violations of this classical growth model, and have suggested that inter-particle interactions are also involved during the growth. Mechanisms of nanocrystal growth still remain controversial. Using in situ transmission electron microscopy, we show that platinum nanocrystals can grow either by monomer attachment from solution onto the existing particles or by coalescence between the particles. Surprisingly, an initially broad size distribution of the nanocrystals can spontaneously narrow. We suggest that nanocrystals take different pathways of growth based on their size- and morphology-dependent internal energies. These observations are expected to be highly relevant for other nanocrystal systems.

Observation of Single Colloidal Platinum Nanocrystal Growth Trajectories

The synthesis of 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) is a highly attractive route to a renewable fuel. However, achieving high yields in this reaction is a substantial challenge. Here it is described how PtCo bimetallic nanoparticles with diameters of 3.6 ± 0.7 nm can solve this problem. Over PtCo catalysts the conversion of HMF was 100% within 10 min and the yield to DMF reached 98% after 2 h, which substantially exceeds the best results reported in the literature. Moreover, the synthetic method can be generalized to other bimetallic nanoparticles encapsulated in hollow carbon spheres.

Platinum-cobalt bimetallic nanoparticles in hollow carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfural

Applications of Phosphorene and Black Phosphorus in Energy Conversion and Storage Devices

In this report, NiCo2O4 nanostructures with different morphologies were directly grown on conductive substrates (stainless steel and ITO) by a facile electrodeposition method in addition to a post-annealing process. The morphology changes on different conductive substrates are discussed in detail. The NiCo2O4 on stainless steel (SS) had a high surface area (119 m2 g−1) and was successfully used in the electrocatalytic oxidation of methanol. The electrocatalytic performance was investigated by cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy (EIS) measurements. Impressively, the NiCo2O4 showed much higher electrocatalytic activity, lower overpotential and greater stability compared to that of only NiO or Co3O4 synthesized by the same method. The higher electrocatalytic activity is due to the high electron conductivity, large surface area of NiCo2O4 and the fast ion/electron transport in the electrode and at the electrolyte–electrode interface. This is important for further development of high performance non-platinum electrocatalysts for application in direct methanol fuel cells.

Direct growth of NiCo2O4 nanostructures on conductive substrates with enhanced electrocatalytic activity and stability for methanol oxidation

The rising interest in fuel cell vehicle technology (FCV) has engendered a growing need and realization to develop rational chemical strategies to create highly efficient, durable, and cost-effective fuel cells. Specifically, technical limitations associated with the major constituent components of the basic proton exchange membrane fuel cell (PEMFC), namely the cathode catalyst and the proton exchange membrane (PEM), have proven to be particularly demanding to overcome. Therefore, research trends within the community in recent years have focused on (i) accelerating the sluggish kinetics of the catalyst at the cathode and (ii) minimizing overall Pt content, while simultaneously (a) maximizing activity and durability as well as (b) increasing membrane proton conductivity without causing any concomitant loss in either stability or as a result of damage due to flooding. In this light, as an example, high temperature PEMFCs offer a promising avenue to improve the overall efficiency and marketability of fuel cell technology. In this Critical Review, recent advances in optimizing both cathode materials and PEMs as well as the future and peculiar challenges associated with each of these systems will be discussed.

A concise guide to sustainable PEMFCs: recent advances in improving both oxygen reduction catalysts and proton exchange membranes

Three-dimensional (3D) platinum–cobalt alloy networks nanostructures with a high alloying degree were synthesized through a room temperature wet-chemical synthetic method using the K2PtCl4/K3Co(CN)6 cyanogel as reaction precursor in the absence of surfactants and templates. The size, morphology and surface composition of platinum–cobalt alloy networks nanostructures were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrum (EDS), selected area electron diffraction (SAED), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The 3D backbone structure and double-metallic property of the K2PtCl4/K3Co(CN)6 cyanogel are responsible for the 3D structure and the high alloying degree of the as-prepared products, respectively. Compared to the pure Pt nanoparticles, 3D platinum–cobalt alloy networks nanostructures exhibit superior electrocatalytic activity and stability for the methanol oxidation reaction (MOR), which is ascribed to their unique 3D structure and alloy properties.

Platinum–Cobalt alloy networks for methanol oxidation electrocatalysis

Three-dimensional platinum nanochain network (Pt-3NCNW) nanostructures are synthesized through a thermal decomposition method using platinum(IV)-complexes as reaction precursors in the absence of surfactants and templates. The size, morphology and surface composition of Pt-3NCNWs are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). These spectral studies confirm the as-papered products are three-dimensionally interconnected network nanostructures with primary Pt nanochains as building blocks, and the Pt nanochains grow from the primary spheric Pt nanoparticles via oriented attachment. Compared to the commercial Pt black catalyst, the Pt-3NCNW nanostructures exhibit superior electrocatalytic activity and stability towards oxygen reduction reactions, which is ascribed to their unique properties such as the few surface defect sites and the low hydroxyl surface coverage on one-dimensional Pt nanochains, as well as fast O2 diffusion in three-dimensional structures.

One-pot synthesis of three-dimensional platinum nanochain networks as stable and active electrocatalysts for oxygen reduction reactions

Preparation of highly dispersed palladium–phosphorus nanoparticles and its electrocatalytic performance for formic acid electrooxidation

We design and synthesize a multiwalled carbon nanotubes (MWCNTs) supported platinum nanochains (Pt-NCs) catalyst (Pt-NCs/MWCNTs) through the electrostatic self-assembly between phosphonate functionalized Pt-NCs and polyallylamine (PAH) functionalized MWCNTs. The grown mechanism, morphology, structure, and composition of the Pt-NCs are investigated by ultraviolet–visible (UV–vis), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and zeta potential analysis. XPS and elemental maps measurements confirm the successful immobilization of PAH on the MWCNTs surface. The resultant Pt-NCs/MWCNTs catalyst exhibits better electrocatalytic activity for the oxygen reduction reaction (ORR) than the commercial Pt/C catalyst due to the unique structure and low hydroxyl surface coverage.

Jiangfeng Xu

Papers

Platinum–Cobalt alloy networks for methanol oxidation electrocatalysis

One-pot synthesis of three-dimensional platinum nanochain networks as stable and active electrocatalysts for oxygen reduction reactions

Preparation of highly dispersed palladium–phosphorus nanoparticles and its electrocatalytic performance for formic acid electrooxidation

Electrostatic self-assembly of platinum nanochains on carbon nanotubes: A highly active electrocatalyst for the oxygen reduction reaction

Fabrication of phosphonate functionalized platinum nanoclusters and their application in hydrogen peroxide sensing in the presence of oxygen