Different-sized CdSe quantum dots have been assembled on TiO2 films composed of particle and nanotube morphologies using a bifunctional linker molecule. Upon band-gap excitation, CdSe quantum dots inject electrons into TiO2 nanoparticles and nanotubes, thus enabling the generation of photocurrent in a photoelectrochemical solar cell. The results presented in this study highlight two major findings: (i) ability to tune the photoelectrochemical response and photoconversion efficiency via size control of CdSe quantum dots and (ii) improvement in the photoconversion efficiency by facilitating the charge transport through TiO2 nanotube architecture. The maximum IPCE (photon-to-charge carrier generation efficiency) obtained with 3 nm diameter CdSe nanoparticles was 35% for particulate TiO2 and 45% for tubular TiO2 morphology. The maximum IPCE observed at the excitonic band increases with decreasing particle size, whereas the shift in the conduction band to more negative potentials increases the driving force and favors fast electron injection. The maximum power-conversion efficiency

Substantial progress has been made in reducing proton-exchange membrane fuel cell (PEMFC) cathode platinum loadings from 0.4-0.8 mgPt/cm(2) to about 0.1 mgPt/cm(2). However, at this level of cathode Pt loading, large performance loss is observed at high-current density (>1 A/cm(2)), preventing a reduction in the overall stack cost. This next developmental step is being limited by the presence of a resistance term exhibited at these lower Pt loadings and apparently due to a phenomenon at or near the catalyst surface. This issue can be addressed through the design of catalysts with high and stable Pt dispersion as well as through development and implementation of ionomers designed to interact with Pt in a way that does not constrain oxygen reduction reaction rates. Extrapolating from progress made in past decades, we are optimistic that the concerted efforts of materials and electrode designers can resolve this issue, thus enabling a large step toward fuel cell vehicles that are affordable for the mass market.

Experimental section, discussion on high current density and heat rejection limit, and physical and electrochemical properties of different carbon supports (PDF)

Single wall carbon nanotube (SWCNT) architecture when employed as conducting scaffolds in a TiO2 semiconductor based photoelectrochemical cell can boost the photoconversion efficiency by a factor of 2. Titanium dioxide nanoparticles were dispersed on SWCNT films to improve photoinduced charge separation and transport of carriers to the collecting electrode surface. The shift of approximately 100 mV in apparent Fermi level of the SWCNT-TiO2 system as compared to the unsupported TiO2 system indicates the Fermi level equilibration between the two systems. The interplay between the TiO2 and SWCNT of attaining charge equilibration is an important factor for improving photoelectrochemical performance of nanostructured semiconductor based solar cells. The feasibility of employing a SWCNT-TiO2 composite to drive the water photoelectrolysis reaction has also been explored.

We demonstrate the unprecedented proton exchange membrane fuel cell (PEMFC) performance durability of a family of dealloyed Pt-Ni nanoparticle catalysts for the oxygen reduction reaction (ORR), exceeding scientific and technological state-of-art activity and stability targets. We provide atomic-scale insight into key factors controlling the stability of the cathode catalyst by studying the influence of particle size, the dealloying protocol and post-acid-treatment annealing on nanoporosity and passivation of the alloy nanoparticles. Scanning transmission electron microscopy coupled to energy dispersive spectroscopy data revealed the compositional variations of Ni in the particle surface and core, which were combined with an analysis of the particle morphology evolution during PEMFC voltage cycling; together, this enabled the elucidation of alloy structure and compositions conducive to long-term PEMFC device stability. We found that smaller size, less-oxidative acid treatment and annealing significantly reduced Ni leaching and nanoporosity formation while encouraged surface passivation, all resulting in improved stability and higher catalytic ORR activity. This study demonstrates a successful example of how a translation of basic catalysis research into a real-life device technology may be done.DFG, SPP 1613, Regenerativ erzeugte Brennstoffe durch lichtgetriebene Wasserspaltung: Aufklärung der Elementarprozesse und Umsetzungsperspektiven auf technologische Konzep