Electrochemical versus Photoelectrochemical Water Oxidation Kinetics on Bismuth Vanadate (Photo)anodes.

This study reports a comparison of the kinetics of electrochemical (EC) versus photoelectrochemical (PEC) water oxidation on bismuth vanadate (BiVO4) photoanodes. Plots of current density versus surface hole density, determined from operando optical absorption analyses under EC and PEC conditions, are found to be indistinguishable. We thus conclude that EC water oxidation is driven by the Zener effect tunneling electrons from the valence to conduction band under strong bias, with the kinetics of both EC and PEC water oxidation being determined by the density of accumulated surface valence band holes. We further demonstrate that our combined optical absorption/current density analyses enable an operando quantification of the BiVO4 photovoltage as a function of light intensity.

Cooperative Effects Drive Water Oxidation Catalysis in Cobalt Electrocatalysts through the Destabilization of Intermediates.

A barrier to understanding the factors driving catalysis in the oxygen evolution reaction (OER) is understanding multiple overlapping redox transitions in the OER catalysts. The complexity of these transitions obscure the relationship between the coverage of adsorbates and OER kinetics, leading to an experimental challenge in measuring activity descriptors, such as binding energies, as well as adsorbate interactions, which may destabilize intermediates and modulate their binding energies. Herein, we utilize a newly designed optical spectroelectrochemistry system to measure these phenomena in order to contrast the behavior of two electrocatalysts, cobalt oxyhydroxide (CoOOH) and cobalt-iron hexacyanoferrate (cobalt-iron Prussian blue, CoFe-PB). Three distinct optical spectra are observed in each catalyst, corresponding to three separate redox transitions, the last of which we show to be active for the OER using time-resolved spectroscopy and electrochemical mass spectroscopy. By combining predictions from density functional theory with parameters obtained from electroadsorption isotherms, we demonstrate that a destabilization of catalytic intermediates occurs with increasing coverage. In CoOOH, a strong (∼0.34 eV/monolayer) destabilization of a strongly bound catalytic intermediate is observed, leading to a potential offset between the accumulation of the intermediate and measurable O2 evolution. We contrast these data to CoFe-PB, where catalytic intermediate generation and O2 evolution onset coincide due to weaker binding and destabilization (∼0.19 eV/monolayer). By considering a correlation between activation energy and binding strength, we suggest that such adsorbate driven destabilization may account for a significant fraction of the observed OER catalytic activity in both materials. Finally, we disentangle the effects of adsorbate interactions on state coverages and kinetics to show how adsorbate interactions determine the observed Tafel slopes. Crucially, the case of CoFe-PB shows that, even where interactions are weaker, adsorption remains non-Nernstian, which strongly influences the observed Tafel slope.

Inspiratory flow rate through a dry powder inhaler (Clickhaler) in children with asthma.

Dry powder inhalers (DPIs) are increasingly being used to deliver drugs for the treatment of asthma. Both the aerosolization and delivery of the drug from a DPI to the lung are dependent on an adequate inspiratory effort from the patient, and it is well-known that the air flow achieved early in the inspiratory profile is important in determining particle size distribution from the inhaler. The present study assessed the peak inspiratory flow (PIF) generated through the Clickhaler DPI, and the early inspiratory flow at 150 mL of inspired volume (IF(150)), in asthmatic children. These measurements were made in a well-controlled setting, and two attempts were recorded to establish maximum achievement. Results were obtained from 57 children aged 6-17 years, showing a (mean +/- SD) best PIF of 60.5 +/- 18.7 L/min (range, 26.8-97.0). The mean PIF overall was 54.2 +/- 20.8 L/min (7.9-97.0). For children aged 6-8 years, the mean best PIF was 46.5 +/- 14.6 L/min (26.8-71.1); for those aged 9 years or more, it was >65 L/min (30.3-97.0). PIF values were unrelated to % predicted FEV(1) measurements. Best IF(150) (mean +/- SD) was 42.9 +/- 13.6 L/min (23.1-66.6) in children aged 6-8 years, and >55 L/min (28.0-86.4) for the older children, showing that high flow rates were achieved early in the inspiratory profile. These data indicate that children with stable asthma can generate adequate inspiratory flow rates to operate the Clickhaler effectively.