Synthesis and evaluation of HfO2 as a prospective filler in inorganic-organic hybrid membranes based on Nafion for PEM fuel cells.

Hybrid inorganic-organic Nafion membranes modified with metal oxides (typically TiO2, ZrO2, WO3) are a good alternative for fuel cell applications. However, one of their main limitations is associated with their relative low proton conductivity at temperatures above 80 °C. In this work, we overcome this issue using HfO2 as a filler. HfO2 was prepared by a sol-gel method, and it was compared with a recast Nafion membrane (named as recast). Deconvolved XPS spectra confirmed the presence of hafnia, while EDS analysis was used to determine its weight content resulting in a 1.88 wt%. FT-IR ATR experiments indicated that the HfO2 hybrid membrane possess a higher capability to retain water than the recast. Thus, the water uptake, swelling degree, conductivity tests and fuel cell evaluations were performed. The water uptake analysis revealed that the hybrid membrane presented a higher retention percentage at 100 °C (61%) than recast (29%). This improvement enabled a higher ionic conductivity at 80 °C and 100 °C. The hybrid membrane displayed a higher conductivity at 100 °C than the recast membrane (112 versus 82 mS cm-1), increasing the cell performance to 0.36 W cm-2; being this performance almost two-fold higher to that obtained for the recast membrane. In summary, herein we demonstrated that HfO2 can be considered as an excellent substitute to conventional fillers.

Evaluation of single and stack membraneless enzymatic fuel cells based on ethanol in simulated body fluids.

The purpose of this work is to evaluate single and double-cell membraneless microfluidic fuel cells (MMFCs) that operate in the presence of simulated body fluids SBF, human serum and blood enriched with ethanol as fuels. The study was performed using the alcohol dehydrogenase enzyme immobilised by covalent binding through an array composed of carbon Toray paper as support and a layer of poly(methylene blue)/tetrabutylammonium bromide/Nafion and glutaraldehyde (3D bioanode electrode). The single MMFC was tested in a hybrid microfluidic fuel cell using Pt/C as the cathode. A cell voltage of 1.035V and power density of 3.154mWcm-2 were observed, which is the highest performance reported to date. The stability and durability were tested through chronoamperometry and polarisation/performance curves obtained at different days, which demonstrated a slow decrease in the power density on day 10 (14%) and day 20 (26%). Additionally, the cell was tested for ethanol oxidation in simulated body fluid (SBF) with ionic composition similar to human blood plasma. Those tests resulted in 0.93V of cell voltage and a power density close to 1.237mWcm-2. The double cell MMFC (Stack) was tested using serum and human blood enriched with ethanol. The stack operated with blood in a serial connection showed an excellent cell performance (0.716mWcm-2), demonstrating the feasibility of employing human blood as energy source.

Copper-palladium core-shell as an anode in a multi-fuel membraneless nanofluidic fuel cell: toward a new era of small energy conversion devices.

A membraneless nanofluidic fuel cell with flow-through electrodes that works with several fuels (individually or mixed): methanol, ethanol, glycerol and ethylene-glycol in alkaline media is presented. For this application, an efficient Cu@Pd electrocatalyst was synthesized and tested, resulting outstanding performance until now reported, opening the possibility of power nano-devices for multi-uses purposes, regardless of fuel re-charge employed.

A nanofluidic direct formic acid fuel cell with a combined flow-through and air-breathing electrode for high performance.

The use of three-dimensional flow-through nanoporous electrodes and the merging of a flow-through and air-breathing cathode were explored and successfully applied in a formic acid air-breathing nanofluidic fuel cell. The effects of fuel concentration, reaction stoichiometry and catalyst mass loading were investigated, resulting in power densities ranging from 28 to 100 mW cm(-2).

Hybrid microfluidic fuel cell based on Laccase/C and AuAg/C electrodes.

A hybrid glucose microfluidic fuel cell composed of an enzymatic cathode (Laccase/ABTS/C) and an inorganic anode (AuAg/C) was developed and tested. The enzymatic cathode was prepared by adsorption of 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and Laccase on Vulcan XC-72, which act as a redox mediator, enzymatic catalyst and support, respectively. The Laccase/ABTS/C composite was characterised by Fourier Transform Infrared (FTIR) Spectroscopy, streaming current measurements (Zeta potential) and cyclic voltammetry. The AuAg/C anode catalyst was characterised by Transmission electron microscopy (TEM) and cyclic voltammetry. The hybrid microfluidic fuel cell exhibited excellent performance with a maximum power density value (i.e., 0.45 mW cm(-2)) that is the highest reported to date. The cell also exhibited acceptable stability over the course of several days. In addition, a Mexican endemic Laccase was used as the biocathode electrode and evaluated in the hybrid microfluidic fuel cell generating 0.5 mW cm(-2) of maximum power density.

AuPd/polyaniline as the anode in an ethylene glycol microfluidic fuel cell operated at room temperature.

AuPd/polyaniline was used for the first time, for ethylene glycol (EG) electrooxidation in a novel microfluidic fuel cell (MFC) operated at room temperature. The device exhibits high electrocatalytic performance and stability for the conversion of cheap and fully available EG as fuel.

Role of muscarinic M2 receptors in regulating beta-adrenergic responsiveness in maturing rabbit airway smooth muscle.

Muscarinic M2 and M3 receptor subtypes have been pharmacologically distinguished in airway smooth muscle. Whereas M3 receptors have been associated with smooth muscle contraction, M2 receptors have been implicated in Gi protein-coupled inhibition of adenylyl cyclase. To determine whether the role of M2 receptors varies with age in tracheal smooth muscle (TSM), dose-dependent relaxation responses to isoproterenol were compared in TSM isolated from 3-day-old and adult rabbits precontracted with acetylcholine (ACh) in the absence (control) and presence of an M2 receptor antagonist (gallamine or methoctramine). From sustained half-maximal ACh contractions, adult TSM were 5.6-fold less sensitive than 3-day-old tissues to isoproterenol-induced relaxation. Furthermore, the magnitude of muscarinic functional antagonism of isoproterenol-mediated TSM relaxation, assessed by varying the initial degree of ACh-induced contraction, significantly increased with age. In gallamine- and methoctramine-treated tissues, the relaxation-response curves to isoproterenol were shifted to the left in both 3-day-old and adult TSM. In contrast, pretreatment with either M2 receptor antagonist had no significant effect on the magnitude of muscarinic functional antagonism at either age. Moreover, Western blot analysis of G alpha i common and specific subunit expression in TSM membranes demonstrated qualitatively similar levels in 3-day-old and adult TSM. Collectively, these findings provide new evidence that 1) there exist inherent age-dependent differences in both the airway relaxant responsiveness to beta-adrenoceptor stimulation and muscarinic functional antagonism of beta-adrenergic relaxation, and 2) the latter are attributed to mechanisms other than ontogenetic alteration in M2 receptor function or Gi protein expression in maturing rabbit TSM.