Jianbo Xu

Non-precious Co3O4 nano-rod electrocatalyst for oxygen reduction reaction in anion-exchange membrane fuel cells

We report preparation of carbon-supported Co3O4 electrocatalysts with nano-rods and spherical structures by the solvent-mediated morphological control method. The catalytic properties of the prepared catalysts for the oxygen reduction reaction (ORR) in alkaline media are investigated. We show that the ORR catalytic activity of the prepared catalysts is sensitive to the number and activity of surface-exposed Co3+ ions that can be tailored by the morphology of cobalt oxides. In particular, we demonstrate that the non-precious Co3O4 electrocatalyst with the nano-rod structure (∼12 nm in length and ∼5.1 nm in diameter) prepared in the mixed solvent of water to dimethylformamide ratio of 1 : 1 exhibits a higher current density than a much more expensive palladium-based catalyst does at the low potential region.

High performance of a carbon supported ternary PdIrNi catalyst for ethanol electro-oxidation in anion-exchange membrane direct ethanol fuel cells

In this paper, we report the synthesis of a carbon supported ternary PdIrNi catalyst for the ethanol oxidation reaction in anion-exchange membrane direct ethanol fuel cells (AEM DEFCs). We demonstrate that the use of the ternary PdIrNi catalyst at the anode of an AEM DEFC can increase the peak power density by more than 122% as compared with the use of the monometallic Pd catalyst, 69% as compared with the use of the bimetallic PdIr catalyst, and 44% as compared with the use of the bimetallic PdNi catalyst. Cyclic voltammetry and chronopotentiometry analyses prove that the ternary PdIrNi catalyst is catalytically much more active and more stable than the monometallic Pd catalyst and the bimetallic PdIr and PdNi catalysts.

Mesoporous carbon with uniquely combined electrochemical and mass transport characteristics for polymer electrolyte membrane fuel cells

The design of electrodes for polymer electrolyte membrane fuel cells (PEMFCs) is a delicate balance of electrochemical and mass transport issues. High performance fuel cell electrode materials require nanoarchitectures with established nanoscopic reaction zones and efficient molecular transport of gas- or liquid-phase reactants and products to and from the electrochemical reaction zones. Mesoporous carbon (MC), with uniquely combined electrochemical and mass transport characteristics is an ideal electrode material for polymer electrolyte membrane fuel cells as its mesoscopic structures not only enables electrocatlysts to be highly dispersed, but also offers ideal pore morphologies that facilitate mass transport. Recently, a wide variety of applications of MCs in PEMFCs have been exploited. This article provides a review of these past efforts with an attempt to gain a better understanding of the role of MCs in PEMFCs. The contribution of MCs in the gas diffusion layer is addressed first and their roles in the catalyst layer are then discussed. The advantages and disadvantages, the acting mechanism to promote electrochemical and mass transport characteristics, and the strategies to improve present electrode materials are discussed.

Ab initio prediction of a silicene and graphene heterostructure as an anode material for Li- and Na-ion batteries

Silicene has been predicted to be an extraordinary anode material for lithium-ion batteries with a large capacity and low lithium migration energy barriers, but the free-standing form of silicene is unstable, virtually requiring a substrate support. In this work, we propose to use graphene as a substrate and a protective layer of silicene, forming a van der Waals heterostructure of silicene and graphene (Si/G) to serve as a prospective anode material for lithium/sodium-ion batteries. Ab initio calculations show that the Si/G heterostructure not only preserves the silicenes large lithium/sodium capacity (487 mA h g−1) and low lithium/sodium migration energy barriers (<0.4 eV for lithium and <0.3 eV for sodium), but also provides much larger lithium/sodium binding energies via a synergistic effect, which can effectively inhibit the formation of dendrites. Density of states results show that the Si/G heterostructure is metallic before and after lithium/sodium intercalation, ensuring a good electronic conductivity. In addition, the mechanical stiffness of the Si/G heterostructure is found to be larger than that of pristine silicene or graphene, which helps preserve the structural integrity and enhance the cycle performance.

FUEL CELLS – DIRECT ALCOHOL FUEL CELLS | Overview

Direct alcohol fuel cells (DAFCs) are a type of electrochemical energy conversion device that directly convert the chemical energy stored in a liquid alcohol fuel, commonly methanol but also ethanol, ethylene glycol, or n-propanol, to electricity. Because of their simplicity, high energy density, instantaneous recharging, and presumably long life, DAFCs have been identified as the most promising candidate to replace batteries in micropower applications. This article presents an overview of DAFC technology, including its working principle, features, challenges, and application opportunities.

Lattice Boltzmann simulation of mass transfer coefficients for chemically reactive flows in porous media

We present lattice Boltzmann (LB) simulations for the mass transfer coefficient from bulk flows to pore surfaces in chemically reactive flows for both ordered and disordered porous structures. The ordered porous structure under consideration consists of cylinders in a staggered arrangement and in a line arrangement, while the disordered one is composed of randomly placed cylinders. Results show that the ordered porous structure of staggered cylinders exhibits a larger mass transfer coefficient than ordered porous structure of inline cylinders does. It is also found that in the disordered porous structures, the Sherwood number (Sh) increases linearly with Reynolds number (Re) at the creeping flow regime; the Sh and Re exhibit a one-half power law dependence at the inertial flow regime. Meanwhile, for Schmidt number (Sc) between 1 and 10, the Sh is proportional to Sc; for Sc between 10 and 100, the Sh is proportional to Sc. [DOI: 10.1115/1.4038555]