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SUMMARY:Nanostructures for Energy Conversion:  From Metal Oxides to Electr
 oactive Covalent Organic Frameworks - Prof. Thomas Bein\,  Department of C
 hemistry and Center for NanoScience (CeNS)\, University of Munich (LMU)\, 
 Germany
DTSTART:20151210T143000Z
DTEND:20151210T153000Z
UID:TALK60362@talks.cam.ac.uk
CONTACT:Sharon Connor
DESCRIPTION:Light-driven water splitting on semiconducting metal oxides is
  an attractive technology for generating hydrogen fuel in a sustainable wa
 y. The efficiency of this process is\, however\, far below theoretical pre
 dictions due to different loss mechanisms in photoelectrode materials\, in
 cluding a high overpotential for the overall water splitting reaction. In 
 the first part\, we will describe recent strategies towards creating metal
  oxide nano-morphologies based on the assembly of ultrasmall mixed metal o
 xide building blocks\, biotemplating using nanocrystalline cellulose\, and
  hierarchical structures aimed at understanding and optimizing light harve
 sting\, charge transport and electrocatalysis in such systems. \n\nFor exa
 mple\, zinc ferrite (ZnFe2O4) was recently recognized as a promising photo
 anode material\, but understanding of its intrinsic semiconductor properti
 es and surface reaction kinetics has been lacking. Using well-defined thin
  films of zinc ferrite\, prepared for the first time by atomic layer depos
 ition (ALD)\, we find a considerably higher charge transfer efficiency of 
 ZnFe2O4 compared to benchmark hematite (Fe2O3).  This is the result of a s
 ignificantly lower rate of surface recombination and a similar rate of cha
 rge transfer compared to hematite. By integrating such films into porous\,
  transparent conductive scaffolds we obtain hierarchical electrodes combin
 ing the low onset potential of zinc ferrite thin films with a much higher 
 photocurrent. \n\nIn the second part\, we will explore the opportunities o
 ffered by spatially integrating photoactive molecular building blocks into
  a crystalline lattice based on the paradigm of covalent organic framework
 s (COFs)\, thus creating models for organic bulk heterojunctions. We will 
 address means of controlling the morphology and packing order of COFs thro
 ugh additives\, in thin films\, and with spatially locked-in building bloc
 ks. We will discuss different strategies aimed at creating electroactive n
 etworks capable of light-induced charge transfer. For example\, we have de
 veloped a COF containing stacked thienothiophene-based building blocks act
 ing as electron donors with a 3 nm open pore system\, which showed light-i
 nduced charge transfer to an intercalated fullerene acceptor phase. Contra
 sting this approach\, we have recently designed a COF integrated heterojun
 ction consisting of alternating columns of stacked donor and acceptor mole
 cules\, promoting the photo-induced generation of mobile charge carriers i
 nside the COF network. Due to the great structural diversity and the large
  degree of morphological precision that can be achieved with COFs\, these 
 materials are viewed as intriguing model systems for organic heterojunctio
 ns.\n
LOCATION:Pfizer Lecture Theatre\,  Department of Chemistry
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