COMPLEX MATERIALS THROUGH SOLUTION SYNTHESIS; FROM MOLECULES TO MATERIALS

摘要

Robust low cost synthesis routes to highly complex nano-materials are required for practical application in many areas of sustainable energy conversion and storage, catalysis and magneto-electric applications. Solution based processing routes allowing for designed multi-phase, multi-elemental nano-materials in one or few steps are probably the best suited for achieving this. Here synthesis routes to complex oxides, nano-composites and metals using homo- or hetero-metallic alkoxides or salt complexes yielding thin and ultra thin films and coatings will be described. Multi component oxides were prepared at very low temperatures in the forms of polycrystalline and epitaxial thin and ultra thin films on flat and nano-structured surfaces such as wires and porous nano-structures. Systems of varying complexities will be discussed such as doped and non-doped Fe_2O_3, TiO_2 and ZnO and CoFe_2O_4 and perovskites. The influence of the alkoxide precursor and thermal treatment will be discussed in relation to the structure, processing temperature and quality of the target oxides as well as the option to make thermodynamically unstable extended doping-levels when using reactive alkoxides in a controlled way. Further it will be described how tailored metal salt complexes can yield thin- or ultra-thin metal films and coatings on oxide nano-structures. These simple low cost routes allow for nano-crystalline materials to be prepared with crystallite sizes below 10 nm as well as ultra-thin coatings on nano-structured structured oxides including powders, wires and electrodes. Temperatures in the range 150-500℃ were used and no reducing gas was necessary. Similarly metal-in-ceramic composite films and thin or ultra-thin coatings on wires and porous oxide electrodes with a wide range of metals (Ni, Co, Cu, Ru, Pt...) and oxide matrixes, having particle sizes down a few nm and loadings up to ＞80% were prepared. The scalability of the processes have been shown by an industrial pilot 50 m roll-to-roll coating of robust, record efficiency spectrally selective solar thermal absorbers consisting of graded Ni-Al_2O_3 films and large scale production of superior hardness and toughness mining and excavation tools. The Ni-Al_2O_3 composites have also been proven for methane activation in the dry-reforming reaction of CO_2 + CH_4 to CO + 2H_2, which requires all sub 6-9 nm sized Ni particles to avoid carbon filament growth deactivating the catalyst.