Grazing incidence X-Ray diffraction: identifying the dominant facet in copper foams that electrocatalyze the reduction of carbon dioxide to formate.

Copper foams have been shown to electrocatalyze the carbon dioxide reduction reaction (CO2RR) to formate (HCOO-) with significant faradaic efficiency (FE) at low overpotentials. Unlike the CO2RR electrocatalyzed at copper foils, the CO2RR electrocatalyzed at porous copper foams selects for HCOO- essentially to the exclusion of hydrocarbon products. Formate is an environmentally friendly organic acid with many applications such as food preservation, textile processing, de-icing, and fuel in fuel cells. Thus, HCOO- is an attractive product from the CO2RR if it is produced at an overpotential lower than that at other electrocatalysts. In this study, grazing incidence X-ray diffraction (GIXRD) was used to identify the dominant surface facet of porous copper foams that accounts for its selectivity for HCOO- during the CO2RR. Included are data from the CO2RR at different temperatures using copper foams as the electrocatalyst. Under optimal reaction conditions at 2 °C, the FE for converting CO2 to HCOO- at Cu foams approaches 50% while the FE for hydrogen gas (H2) falls below 40%, a significant departure from that obtained at polycrystalline Cu foils. Computational studies by others have proposed (200) and (111) facets of Cu foils thermodynamically favour methane and other hydrocarbons, CO, HCOO- from the CO2RR. Results from the GIXRD studies indicate Cu foams are dominated by the (111) facet, which accounts for the selectivity of Cu foams toward HCOO- regardless of temperature used for the CO2RR.

In Situ Measurement of Voltage-Induced Stress in Conducting Polymers with Redox-Active Dopants.

Minimization of stress-induced mechanical rupture and delamination of conducting polymer (CP) films is desirable to prevent failure of devices based on these materials. Thus, precise in situ measurement of voltage-induced stress within these films should provide insight into the cause of these failure mechanisms. The evolution of stress in films of polypyrrole (pPy), doped with indigo carmine (IC), was measured in different electrochemical environments using the multibeam optical stress sensor (MOSS) technique. The stress in these films gradually increases to a constant value during voltage cycling, revealing an initial break-in period for CP films. The nature of the ions involved in charge compensation of pPy[IC] during voltage cycling was determined from electrochemical quartz crystal microbalance (EQCM) data. The magnitude of the voltage-induced stress within pPy[IC] at neutral pH correlated with the radius of the hydrated mobile ion in the order Li(+) > Na(+) > K(+). At acidic pH, the IC dopant in pPy[IC] undergoes reversible oxidation and reduction within the range of potentials investigated, providing a secondary contribution to the observed voltage-induced stress. We report on the novel stress response of these polymers due to the presence of pH-dependent redox-active dopants and how it can affect material performance.

Surface Modification Approach to TiO2 Nanofluids with High Particle Concentration, Low Viscosity, and Electrochemical Activity.

This study presents a new approach to the formulation of functional nanofluids with high solid loading and low viscosity while retaining the surface activity of nanoparticles, in particular, their electrochemical response. The proposed methodology can be applied to a variety of functional nanomaterials and enables exploration of nanofluids as a medium for industrial applications beyond heat transfer fluids, taking advantage of both liquid behavior and functionality of dispersed nanoparticles. The highest particle concentration achievable with pristine 25 nm titania (TiO2) nanoparticles in aqueous electrolytes (pH 11) is 20 wt %, which is limited by particle aggregation and high viscosity. We have developed a scalable one-step surface modification procedure for functionalizing those TiO2 nanoparticles with a monolayer coverage of propyl sulfonate groups, which provides steric and charge-based separation of particles in suspension. Stable nanofluids with TiO2 loadings up to 50 wt % and low viscosity are successfully prepared from surface-modified TiO2 nanoparticles in the same electrolytes. Viscosity and thermal conductivity of the resulting nanofluids are evaluated and compared to nanofluids prepared from pristine nanoparticles. Furthermore, it is demonstrated that the surface-modified titania nanoparticles retain more than 78% of their electrochemical response as compared to that of the pristine material. Potential applications of the proposed nanofluids include, but are not limited to, electrochemical energy storage and catalysis, including photo- and electrocatalysis.

Viologens as charge carriers in a polymer-based battery anode.

Viologens, either as anions in solution or as pendant substituents to pyrrole, were incorporated as dopants to electrodeposited films of polypyrrole. The resulting polymer films exhibited redox activity at -0.5 V vs Ag/AgCl. The film consisting of polypyrrole with pendant viologens exhibited the best charge-discharge behavior with a maximum capacity of 55 mAh/g at a discharge current of 0.25 mA/cm(2). An anode consisting of polypyrrole (pPy) doped with viologen (V) was coupled to a cathode consisting of pPy doped with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to yield a polymer-based battery with a cell electromotive force (emf) of 1.0 V, maximum capacity of 16 mAh/g, and energy density of 15 Wh/kg.

Antioxidant deactivation on graphenic nanocarbon surfaces.

This article reports a direct chemical pathway for antioxidant deactivation on the surfaces of carbon nanomaterials. In the absence of cells, carbon nanotubes are shown to deplete the key physiological antioxidant glutathione (GSH) in a reaction involving dissolved dioxygen that yields the oxidized dimer, GSSG, as the primary product. In both chemical and electrochemical experiments, oxygen is only consumed at a significant steady-state rate in the presence of both nanotubes and GSH. GSH deactivation occurs for single- and multi-walled nanotubes, graphene oxide, nanohorns, and carbon black at varying rates that are characteristic of the material. The GSH depletion rates can be partially unified by surface area normalization, are accelerated by nitrogen doping, and suppressed by defect annealing or addition of proteins or surfactants. It is proposed that dioxygen reacts with active sites on graphenic carbon surfaces to produce surface-bound oxygen intermediates that react heterogeneously with glutathione to restore the carbon surface and complete a catalytic cycle. The direct catalytic reaction between nanomaterial surfaces and antioxidants may contribute to oxidative stress pathways in nanotoxicity, and the dependence on surface area and structural defects suggest strategies for safe material design.