CdS sensitized sol-gel derived thin films of self-patterned micro-blocks of closely-packed SnO2 nanoparticles as high-performance photoanodes in alkaline solution of methanol

Abstract

Materials with patterned micro-/nano-structures fabricated via self-organization for the conversion and utilization of solar energy are attractive. Thin films of self-patterned irregular micro-blocks of closely packed SnO2 nanoparticles have been achieved here as photoanodes in photoelectrochemical cells for the first time, which are accomplished facilely by annealing SnO2 gel coatings on conducting glass substrates at 500 °C. During the annealing, the gel coating evolves into closely packed SnO2 nanoparticles. They self-assemble into irregular micro-blocks (mostly about 10 μm in size), generating dense network micro-cracks (∼2 μm wide in average) around the micro-blocks and nano-cracks embedded in the micro-blocks due to the thermal contraction stress that the SnO2 nanocrystallization and self-assembly induce. Optimally, the self-patterned SnO2 film is well sensitized with nanolayers of CdS nanoparticles by successive ionic layer adsorption and reactions for six cycles. Under optimized conditions, the prepared SnO2/CdS film demonstrates an apparent anodic photocurrent density as high as 10 mA cm−2 while holding the potential at 0 V (vs. SMSE) in a photoelectrochemical cell with 2 M NaOH +1 M methanol under visible light illumination of 100 mW cm−2, which is among the highest record for SnO2/CdS photoanodes. We ascribe its high performance not only to the patterned micro/nano-structure and the type-II energy level alignments of the SnO2/CdS photoanode, but also to the photo-electro synergistic catalyses in methanol oxidation reaction.