Search

Photocatalytic H2 evolution from ethanol dehydrogenation is a convenient strategy to store solar energy in a highly valuable fuel with potential zero net CO2 balance. Herein, we report on the synthesis of CoTiO3/TiO2 composite catalysts with controlled amounts of highly distributed CoTiO3 nanodomains for photocatalytic ethanol dehydrogenation. We demonstrate these materials to provide outstanding hydrogen evolution rates under UV and visible illumination. The origin of this enhanced activity is extensively analyzed. In contrast to previous assumptions, UV–vis absorption spectra and ultraviolet photoelectron spectroscopy (UPS) prove CoTiO3/TiO2 heterostructures to have a type II band alignment, with the conduction band minimum of CoTiO3 below the H2/H+ energy level. Additional steady-state photoluminescence (PL) spectra, time-resolved PL spectra (TRPLS), and electrochemical characterization prove such heterostructures to result in enlarged lifetimes of the photogenerated charge carriers. These experimental evidence point toward a direct Z-scheme as the mechanism enabling the high photocatalytic activity of CoTiO3/TiO2 composites toward ethanol dehydrogenation. In addition, we probe small changes of temperature to strongly modify the photocatalytic activity of the materials tested, which could be used to further promote performance in a solar thermophotocatalytic reactor., This work was supported by projects MICINN/FEDER RTI2018-093996-B-C31 and RTI2018-095498-J-I00. J.A., T.Z., and X.H. thank funding from GC 2017 SGR 327 and the MINECO project (ENE2017-85087-C3). ICN2 thanks the support from the Severo Ochoa program (MINECO, no. SEV-2013-0295) and the CERCA program/Generalitat de Catalunya. N.G. and Y.L. thank the Swiss National Science Foundation (SNF) for funding under the Ambizione Energy (no. PZENP2_166871). Y.Z., C.X., X.W., and T.Z. acknowledge the China Scholarship Council (CSC) for scholarship support. Part of the present work has been performed in the framework of the Universitat Autónoma de Barcelona Materials Science PhD program. J.L. is a Serra Hunter fellow and is grateful to GC 2017 SGR 128 and the ICREA Academia program.

The ultimate control over chain self assembly is key to unravel and optimize the relationship between film microstructure and charge carrier mobility in solution processable conjugated polymer semiconductors. Here we employ preparatory size exclusion chromatography to produce fractions of a poly(thieno)thiophene polymer coded PBTTT C12 with varying number average molecular weight Mn from 5.8 to 151 kDa and low polydispersity index of 1.1 1.4. Solution processing of these samples into bottom contact bottom gate field effect transistors reveals a strong dependence of transistor performance on the molecular weight. Further analysis of the films' microstructure and crystallinity show three distinct regions: fiber formation (ca. 5 20 kDa) terrace formation (20 50 kDa) and a rough morphology (50 150 kDa). The performance of low Mn films was found to increase rapidly with increasing chain length and while the best transistor performance was found with the terrace morphology films not exhibiting the terraced morphology (using 80 kDa polymer) were capable of similar performance. In addition by blending only 5 wt of a high molecular weight fraction into a low Mn film we demonstrate the ability to drastically increase the measured charge carrier mobility of the low Mn material without attaining a terraced morphology. This illustration suggests a viable route to easily increase the processability and transistor performance of low molecular weight conjugated polymeric or oligomeric semiconductors. In addition GIXRD and thermal analysis of select fractions further indicate that the films of higher molecular weight exhibit a reduced side chain crystallinity due to chain entanglement; the degree of backbone crystallinity remains more constant. © 2013 American Chemical Society.