Effect of Doping Concentration on Grain Boundary Conductivity of Samaria Doped Ceria Composites

This work aims to study the effect of Sm3+ doping concentration on the grain boundary ionic conductivity of ceria. The materials were prepared by a modified co-precipitation method, where molecular water associated with the precursor has been utilized to facilitate the hydroxylation process. The synthesized hydroxide / hydrated oxide materials were calcined and the green body (pellet) has been sintered at high temperature in order to achieve highly dense (~ 96 %) pellet. The structural analyses were done using XRD and Raman spectroscopy, which confirm the single phase cubic structure of samaria doped ceria (SDC) nanoparticles and the surface morphology of sintered samples was studied using FESEM. The ionic conductivity was measured by AC impedance spectroscopy of the sintered pellets in the temperature range of 400-700 °C, which shows superior grain boundary conductivity. The grain boundary ionic conductivity of around 0.111 S/cm has been obtained for 15SDC composition at 600 °C.

Boosting efficiency in light-driven water splitting by dynamic irradiation through synchronizing reaction and transport processes

This work elaborates the effect of dynamic irradiation on light-driven molecular water oxidation to counteract catalyst deactivation. It highlights the importance of overall reaction engineering to overcome limiting factors in artificial photosynthesis reactions. Systematic investigation of a homogenous three component ruthenium-based water oxidation system revealed significant potential to enhance the overall catalytic efficiency by synchronizing the timescales of photoreaction and mass transport in a capillary flow reactor. The overall activity could be improved by a factor of more than 10 with respect to the turnover number and a factor of 31 referring to the external energy efficiency by controlling the local availability of photons. Detailed insights into the mechanism of light driven water oxidation could be obtained using complementary methods of investigation like Raman, IR and UV-vis/emission spectroscopy, unraveling the importance of avoiding high concentrations of excited photosensitizers.

Boosting efficiency in light-driven water splitting by dynamic irradiation through synchronizing reaction and transport processes

This work elaborates the effect of dynamic irradiation on light-driven molecular water oxidation to counteract catalyst deactivation. It highlights the importance of overall reaction engineering to overcome limiting factors in artificial photosynthesis reactions. Systematic investigation of a homogenous three component ruthenium-based water oxidation system revealed significant potential to enhance the overall catalytic efficiency by synchronizing the timescales of photoreaction and mass transport in a capillary flow reactor. The overall activity could be improved by a factor of more than 10 with respect to the turnover number and a factor of 31 referring to the external energy efficiency by controlling the local availability of photons. Detailed insights into the mechanism of light driven water oxidation could be obtained using complementary methods of investigation like Raman, IR and UV-vis/emission spectroscopy, unraveling the importance of avoiding high concentrations of excited photosensitizers.

Two-transition-metal water oxidation catalysts. Faster rates via electronic structure tuning

Mixed 3d-metal oxides are some of the most promising water oxidation catalysts (WOCs), but it is very difficult to know the active site structures and thus structure-catalytic activity correlations at the molecular level in such insoluble materials. This study reports a molecular water oxidation catalyst, [Co2Ni2(PW9O34)2]10- (Co2Ni2P2), that constitutes a molecular model of the heterogeneous WOC, cobalt-nickel oxide. Both Co2Ni2P2 and its isostructural analogue, [Co4(PW9O34)2]10- (Co4P2), have the same CoO5(H2O) active sites but Co2Ni2P2 is an order of magnitude faster than Co4P2. Co2Ni2P2 is prepared by a new synthesis, and both the location and percent occupancy of Co and Ni in Co2Ni2P2 (Co outside and Ni inside the central belt are >97% for each) is confirmed by multiwavelength synchrotron X-radiation anomalous dispersion scattering (synchrotron XRAS), a technique applied for the first time to such complexes. Density functional theory (DFT) studies predicated and reveal that Co4P2 and Co2Ni2P2 have greatly altered frontier orbitals, while stopped-flow kinetic studies and DFT calculations indicate that water oxidation by both complexes follows analogous multi-step mechanisms, including Co-OOH formation, with the energetics of most steps being lower for Co2Ni2P2 than for Co4P2.

IMPACT DAMAGE DETECTION LIMITS OF MICROWAVE NDE TECHNIQUE FOR POLYMER COMPOSITES

Despite recent advances, the need for improved non-destructive evaluation (NDE) techniques to detect and quantify early-stage damage in polymer matrix composites remains critical. A recently developed microwave based NDE technique which capitalizes on the ubiquitous presence of moisture within a polymer matrix has yielded positive results. The chemical state of moisture directly affects dielectric properties of a polymer matrix composite. Thus, the preferential diffusion of ‘free’ water into microcracks and voids associated with physical damage allows for damage detection through spatial permittivity mapping using techniques that are sensitive to moisture content and molecular water state. While it has been demonstrated that the method can detect damage at low levels of moisture and impact damage, the specific parameters under which the technique will accurately and reliably capture damage within a composite are unknown. The three variables affecting the performance of the method to detect impact damage are moisture content, extent of damage, and resolution of the dielectric scanning technique. Here, we report on the impact of the latter as a function of the two environmental variables (moisture and damage extent). To understand limits and optimize execution of the technique, the interrelationships between each of the variables must be explored. This study investigates the relationship between moisture content and scan resolution. Two BMI/quartz laminates were impacted at 9 Joules to induce barely visible impact damage. The specimens were inspected at a variety of gravimetric moisture levels, and several variations of the spatial permittivity map were created for each moisture level. Detection standards for the technique were investigated based on moisture content and desired scan accuracy; findings showed at 0.05-0.4% moisture content (by wt.) the technique can detect damage location and size with a minimum of 88% accuracy. Pareto frontiers were generated at each moisture level to optimize scan speed and accuracy.