176 research outputs found
Large-scale preparation of porous ultrathin Ga-doped ZnO nanoneedles from 3D basic zinc carbonate superstructures
No full textA facile procedure for large-scale preparation of porous ZnO 1D nanomaterials with good electrical conductivity has been demonstrated for the first time. Porous ultrathin Ga-doped ZnO nanoneedles can be prepared by calcining the precursor of ultrathin Ga-doped basic zinc carbonate (BZC) nanoneedles obtained from BZC 3D superstructures, which are synthesized by a simple chemical co-precipitation method at room temperature, without using any catalyst, template or surfactant. There is evidence that the growth mechanisms of the BZC 3D superstructures and nanoneedles are correlated with the concentrations of ammonium ions and ethanol in the synthesis solution. The as-prepared porous Ga-doped ZnO nanoneedles have a thickness of only a couple of nanometers, consisting of many fine nanoparticles in a few nanometers. Electrical conductivity measurements indicate that porous ultrathin ZnO nanoneedles have a volume resistivity similar to that of the spherical Ga-doped ZnO nanoparticles. The porous nanostructures and good electrical conductivity make the porous ultrathin ZnO 1D nanoneedles promising candidates for applications in electrochemical fields
Summary and Perspective
No full textBased on the information covered by other chapters, this chapter summarizes the progress and challenges faced by one-dimensional catalysts, and perspective for the future research and development to meet the requirements of proton exchange membrane fuel cells.</p
Pt-based nanowires as electrocatalysts in proton exchange fuel cells
No full textPlatinum (Pt)-based nanowires can give excellent performance as electrochemical catalysts in low-temperature proton exchange fuel cells (PEFCs). Several preparation methods have been developed for this kind of application. In this paper, we review the development history of Pt-based nanowires for low-temperature fuel cells, focusing on the preparation method from the early template technique for the polycrystalline nanowires to the simple wet chemical approaches for preparing single crystal ones today. The limitations and future developments are also discussed
Proton Exchange Membrane Fuel Cell Electrodes From One-Dimensional Nanostructures
No full textThis chapter presents the PEMFC electrodes built and tested from one-dimensional (1D) nanostructures, including using the conventional electrode fabrication concept from catalyst ink by mixing 1D nanostructures and electrolyte ionomer, the nanostructured thin film catalyst electrode and the gas diffusion electrode from aligned 1D catalysts.</p
Introduction
No full textThis chapter discusses the requirements of proton exchange membrane fuel cells, status and challenges of catalysts and electrodes, and gives a brief introduction to one-dimensional nanostructures. It provides an overview of the book, its organization, and unique appeal.</p
Proton Exchange Membrane Fuel Cells (PEMFCs)
Get PDFThe proton exchange membrane fuel cell is an electrochemical energy conversion device, which transforms a fuel such as hydrogen and an oxidant such as oxygen in ambient air into electricity with heat and water byproducts. The device is more efficient than an internal combustion engine because reactants are directly converted into energy through a one-step electrochemical reaction. Fuel cells combined with water electrolyzers, which electrochemically split water into hydrogen and oxygen using renewable energy sources such as solar, mitigate global warming concerns with reduced carbon dioxide emissions. This collection of papers covers recent advancements in fuel cell technology aimed at reducing cost, improving performance, and extending durability, which are perceived as crucial for a successful commercialization. Almost all key materials, as well as their integration into a cell, are discussed: the bus plates that collect the electrical current, the gas diffusion medium that distributes the reactants over catalysts promoting faster reactions, and the membrane separating oxygen and hydrogen gases and closing the electrical circuit by transporting protons. Fuel cell operation below the freezing point of water and with impure reactant streams, which impacts durability, is also discussed
One-Dimensional Nanostructured Catalysts for Hydrocarbon Oxidation Reaction
No full textThe development of one-dimensional (1D) nanostructures for hydrocarbon oxidation reaction has attracted increasing efforts. The unique anisotropic morphology and special surface properties of 1D catalysts endow them with many advantages as compared with conventional 0D nanoparticles in proton exchange membrane fuel cells applications with liquid fuels. In this chapter, we discuss the recent progress in 1D Pt, Pt-based alloy, and non-Pt precious catalysts for this application, with a focus on the understanding of structure-catalytic property relationships in the electrooxidation of methanol, ethanol, and formic acid for potential fuel cell applications.</p
A new measure of molecular attractions between nanoparticles near kT adhesion energy
No full textThe weak molecular attractions of nanoparticles are important because they drive self-assembly mechanisms, allow processing in dispersions e. g. of pigments, catalysts or device structures, influence disease through the attraction of viruses to cells and also cause potential toxic effects through nanoparticle interference with biomolecules and organs. The problem is to understand these small forces which pull nanoparticles into intimate contact; forces which are comparable with 3kT/2z the thermal impact force experienced by an average Brownian particle hitting a linear repulsive potential of range z. Here we describe a new method for measuring the atomic attractions of nanoparticles based on the observation of aggregates produced by these small forces. The method is based on the tracking of individual monosize nanoparticles whose diameter can be calculated from the Stokes-Einstein analysis of the tracks in aqueous suspensions. Then the doublet aggregates are distinguished because they move slower and are also very much brighter than the dispersed nanoparticles. By finding the ratio of doublets to singlets, the adhesive energy between the particles can be calculated from known statistical thermodynamic theory using assumptions about the shape of the interaction potential. In this way, very small adhesion energies of 2kT have been measured, smaller than those seen previously by atomic force microscopy (AFM) and scanning tunneling microscopy (STM)
Annealing behaviour of Pt and PtNi nanowires for proton exchange membrane fuel cells
Get PDFPtNi alloy and hybrid structures have shown impressive catalytic activities toward the cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, such promise does not often translate into improved electrode performances in PEMFC devices. In this contribution, a Ni impregnation and subsequent annealing method, translatable to vertically aligned nanowire gas diffusion electrodes (GDEs), is shown in thin-film rotating disk electrode measurements (TFRDE) to enhance the ORR mass activity of Pt nanowires (NWs) supported on carbon (Pt NWs/C) by around 1.78 times. Physical characterisation results indicate that this improvement can be attributed to a combination of Ni alloying of the nanowires with retention of the morphology, while demonstrating that Ni can also help improve the thermal stability of Pt NWs. These catalysts are then tested in single PEMFCs. Lower power performances are achieved for PtNi NWs/C than Pt NWs/C. A further investigation confirms the different surface behaviour between Pt NWs and PtNi NWs when in contact with electrolyte ionomer in the electrodes in PEMFC operation. Indications are that this interaction exacerbates reactant mass transport limitations not seen with TFRDE measurements
Materials for PEMFC Electrodes
No full textAs part of a sustainable energy future, much attention has been drawn to the use of hydrogen fuel as it can be formed renewably through the electrolysis of water. As part of this proposed hydrogen economy, polymer electrolyte membrane fuel cells (PEMFCs) may play a key role as clean power generators in vehicles, buildings, and portable devices. However, before becoming commercially viable, high performance and durable devices need to be produced. This article discusses the material used for electrodes and how advanced development can help to address the challenge faced by PEMFCs
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