Effect of Electrode Configuration on Nitric Oxide Gas Sensor Behavior.

The influence of electrode configuration on the impedancemetric response of nitric oxide (NO) gas sensors was investigated for solid electrochemical cells [Au/yttria-stabilized zirconia (YSZ)/Au)]. Fabrication of the sensors was carried out at 1050 °C in order to establish a porous YSZ electrolyte that enabled gas diffusion. Two electrode configurations were studied where Au wire electrodes were either embedded within or wrapped around the YSZ electrolyte. The electrical response of the sensors was collected via impedance spectroscopy under various operating conditions where gas concentrations ranged from 0 to 100 ppm NO and 1%-18% O2 at temperatures varying from 600 to 700 °C. Gas diffusion appeared to be a rate-limiting mechanism in sensors where the electrode configuration resulted in longer diffusion pathways. The temperature dependence of the NO sensors studied was independent of the electrode configuration. Analysis of the impedance data, along with equivalent circuit modeling indicated the electrode configuration of the sensor effected gas and ionic transport pathways, capacitance behavior, and NO sensitivity.

Identifying Implementation Strategies to Enhance HIV Pre-Exposure Prophylaxis Uptake Among Black Cisgender Women in New Orleans, Louisiana.

There is an unmet need for HIV prevention among Black cisgender women. From January to November 2020, we conducted formative research to develop locally informed implementation strategies to enhance pre-exposure prophylaxis (PrEP) uptake among Black cisgender women in New Orleans, Louisiana. Following an iterative process, we conducted in-depth interviews (IDIs) with Black women who were not taking PrEP and used those findings to inform IDIs with Black women taking PrEP. We asked about PrEP awareness, social support, PrEP-related norms, medical mistrust, motivation to take PrEP, and potential implementation strategies. Data were analyzed using applied thematic analysis. We established the Black Women and PrEP (BWAP) Task Force-a diverse group of 25 Black female community representatives who reviewed the IDI findings and identified strategies to address these determinants of PrEP uptake. We interviewed 12 Black women who were not taking PrEP and 13 Black women who were taking PrEP. Two main PrEP uptake barriers were identified from the IDI findings and Task Force discussions. First, Black women do not know of other Black women taking PrEP. Women perceived PrEP as a drug for gay men. Most said that testimonials from Black women taking PrEP would make its use more relatable. Second, Black women are not frequently offered PrEP by their providers. Many preferred accessing PrEP through women's health providers. The Task Force identified two strategies to address these barriers: a social media campaign for women and an educational initiative to train providers to discuss and prescribe PrEP. These implementation strategies require further study.

Kinetics of nitric oxide and oxygen gases on porous Y-stabilized ZrO2-based sensors.

Using impedance spectroscopy the electrical response of sensors with various porous Y-stabilized ZrO2 (YSZ) microstructures was measured for gas concentrations containing 0-100 ppm NO with 10.5%O2 at temperatures ranging from 600-700 °C. The impedance response increased substantially as the sensor porosity increased from 46%-50%. Activation energies calculated based on data from the impedance measurements increased in magnitude (97.4-104.9 kJ/mol for 100 ppm NO) with respect to increasing YSZ porosity. Analysis of the oxygen partial pressure dependence of the sensors suggested that dissociative adsorption was the dominant rate limiting. The PWC/DNP theory level was used to investigate the gas-phase energy barrier of the 2NO+O2 → 2NO2 reaction on a 56-atom YSZ/Au model cluster using Density Functional Theory and Linear Synchronous Transit/Quadratic Synchronous Transit calculations. The reaction path shows oxygen surface reactions that begin with NO association with adsorbed O2 on a Zr surface site, followed by O2 dissociative adsorption, atomic oxygen diffusion, and further NO2 formation. The free energy barrier was calculated to be 181.7 kJ/mol at PWC/DNP. A qualitative comparison with the extrapolated data at 62% ± 2% porosity representing the YSZ model cluster indicates that the calculated barriers are in reasonable agreement with experiments, especially when the RPBE functional is used.

Investigation of an Impedimetric LaSrMnO3-Au/Y2O3-ZrO2-Al2O3 Composite NOx Sensor.

Composite NOx sensors were fabricated by combining partially and fully stabilized yttria-doped zirconia with alumina forming a composite electrolyte, Y2O3-ZrO2-Al2O3, and strontium-doped lanthanum manganese oxide mixed with gold to form the composite sensing electrode, La0.8 Sr0.2MnO3-Au. A surface chemistry analysis of the composite sensor was conducted to interpret defects and the structural phases present at the Y2O3-ZrO2-Al2O3 electrolyte, as well as the charge conduction mechanism at the LaSrMnO3-Au electrode surface. Based on the surface chemistry analysis, ionic and electronic transport properties, and microstructural features of sensor components, the working principle was described for NOx sensing at the composite sensor. The role of the composite materials on the NOx sensing response, cross-sensitivity to O2, H2O, CO, CO2, and CH4, and the response/recovery rates relative to sensor accuracy were characterized by operating the composite NOx sensors via the impedimetric method. The composite sensors were operated at temperatures ranging from 575 to 675 °C in dry and humidified gas environments with NO and NO2 concentrations varying from 0 to 100 ppm, where the balance gas was N2. It was found that the microstructure of the composite NOx sensor electrolyte and sensing electrode had a significant effect on interfacial reactions at the triple phase boundary, as well as the density of active sites for oxygen reactions. Overall, the composite NOx sensor microstructure enabled a high NOx sensing response, along with low cross-sensitivity to O2, CO, CO2, and CH4, and promoted NO detection down to 2 ppm.