A Pd/C-CeO2 Anode Catalyst for High-Performance Platinum-Free Anion Exchange Membrane Fuel Cells.

One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM-FCs). The anion exchange membrane fuel cell (AEM-FC) has long been proposed as a solution as non-Pt metals may be employed. Despite this, few examples of Pt-free AEM-FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt-free AEM-FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt-free AEM-FC that employs a mixed carbon-CeO2 supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM-FC tests run on dry H2 and pure air show peak power densities of more than 500 mW cm(-2) .

Interactive effect of hysteresis and surface chemistry on gated silicon nanowire gas sensors.

Gated silicon nanowire gas sensors have emerged as promising devices for chemical and biological sensing applications. Nevertheless, the performance of these devices is usually accompanied by a "hysteresis" phenomenon that limits their performance under real-world conditions. In this paper, we use a series of systematically changed trichlorosilane-based organic monolayers to study the interactive effect of hysteresis and surface chemistry on gated silicon nanowire gas sensors. The results show that the density of the exposed or unpassivated Si-OH groups (trap states) on the silicon nanowire surface play by far a crucial effect on the hysteresis characteristics of the gated silicon nanowire sensors, relative to the effect of hydrophobicity or molecular density of the organic monolayer. Based on these findings, we provide a tentative model-based understanding of (i) the relation between the adsorbed organic molecules, the hysteresis, and the related fundamental parameters of gated silicon nanowire characteristics and of (ii) the relation between the hysteresis drift and possible screening effect on gated silicon nanowire gas sensors upon exposure to different analytes at real-world conditions. The findings reported in this paper could be considered as a launching pad for extending the use of the gated silicon nanowire gas sensors for discriminations between polar and nonpolar analytes in complex, real-world gas mixtures.

Molecular gating of silicon nanowire field-effect transistors with nonpolar analytes.

Silicon nanowire field-effect transistors (Si NW FETs) have been used as powerful sensors for chemical and biological species. The detection of polar species has been attributed to variations in the electric field at the conduction channel due to molecular gating with polar molecules. However, the detection of nonpolar analytes with Si NW FETs has not been well understood to date. In this paper, we experimentally study the detection of nonpolar species and model the detection process based on changes in the carrier mobility, voltage threshold, off-current, off-voltage, and subthreshold swing of the Si NW FET. We attribute the detection of the nonpolar species to molecular gating, due to two indirect effects: (i) a change in the dielectric medium close to the Si NW surface and (ii) a change in the charged surface states at the functionality of the Si NW surface. The contribution of these two effects to the overall measured sensing signal is determined and discussed. The results provide a launching pad for real-world sensing applications, such as environmental monitoring, homeland security, food quality control, and medicine.

Enhanced sensing of nonpolar volatile organic compounds by silicon nanowire field effect transistors.

Silicon nanowire field effect transistors (Si NW FETs) are emerging as powerful sensors for direct detection of biological and chemical species. However, the low sensitivity of the Si NW FET sensors toward nonpolar volatile organic compounds (VOCs) is problematic for many applications. In this study, we show that modifying Si NW FETs with a silane monolayer having a low fraction of Si-O-Si bonds between the adjacent molecules greatly enhances the sensitivity toward nonpolar VOCs. This can be explained in terms of an indirect sensor-VOC interaction, whereby the nonpolar VOC molecules induce conformational changes in the organic monolayer, affecting (i) the dielectric constant and/or effective dipole moment of the organic monolayer and/or (ii) the density of charged surface states at the SiO(2)/monolayer interface. In contrast, polar VOCs are sensed directly via VOC-induced changes in the Si NW charge carriers, most probably due to electrostatic interaction between the Si NW and polar VOCs. A semiempirical model for the VOC-induced conductivity changes in the Si NW FETs is presented and discussed.

Systematic cross-linking changes within a self-assembled monolayer in a nanogap junction: a tool for investigating the intermolecular electronic coupling.

Here, we show that a controllable cross-linking within a self-assembled monolayer can be used as a tool for investigating the (lateral) intermolecular coupling between adjacent organic molecules. We draw this conclusion based on macroscopic electrical experiments with self-assembled hexyltrichlorosilane (HTS) having different degrees of Si-O-Si intermolecular bonds in a planar nanogap junction.

Silicon nanowires terminated with methyl functionalities exhibit stronger Si-C bonds than equivalent 2D surfaces.

Silicon nanowires (Si NWs) terminated with methyl functionalities exhibit higher oxidation resistance under ambient conditions than equivalent 2D Si(100) and 2D Si(111) surfaces having similar or 10-20% higher initial coverage. The kinetics of methyl adsorption as well as complementary surface analysis by XPS and ToF SIMS attribute this difference to the formation of stronger Si-C bonds on Si NWs, as compared to 2D Si surfaces. This finding offers the possibility of functionalising Si NWs with minimum effect on the conductance of the near-gap channels leading towards more efficient Si NW electronic devices.