Inkjet printing and electrocatalysis

The transition in energy matrix, from fossil to renewable energy sources, will require the utilization of grid levelling alternatives to cope with the intermittent characteristic of renewable energy. Advanced electrochemical energy conversion and storage devices, ranging from batteries to fuel cells, play a crucial role in that process. Many of these electrochemical devices are based on the oxidation and reduction reactions of oxygen, a compound that can conveniently be taken from air and released to the environment. However, sluggish kinetics of the oxygen reactions at current electrode materials require the synthesis and study of more efficient and stable electrocatalysts and catalyst layers made thereof. This thesis focuses on combined drop-on-demand inkjet printing coupled with pulsed light sintering for the fabrication of catalyst layers containing advanced electrocatalyst materials. Inkjet printing allowed the precise control of the material loading inside the catalyst layers and the pulsed light-induced post-processing enabled rapid drying and even material functionalization, such as changing the oxidation state of the metals for improved electrochemical performance. The electrocatalysts were in particular studied for their activity and stability towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). First, an ink with an advanced non-precious metal-based catalyst, nitrogen-doped re-duced graphene oxide supported cobalt oxide nanoparticles (i.e., Co3O4/N-rGO), was prepared and inkjet printed in form of a catalyst layer on large glassy carbon electrodes. The application of the flash lamp reduced in a rapid, non-equilibrium thermal process, the oxidation state of cobalt within a short high intensity light pulse and modified the catalytic properties for the ORR. The electrocatalyst proper-ties are discussed in detail in Chapter III and compared with catalyst layers that were prepared by us-ing equilibrium thermal processing in a furnace. In Chapter IV, the application of inkjet printing and flash light processing for the syn-thesis of nanoparticles from printed, dissolved metal precursors is presented. This concept was recently introduced as "Print-Light-Synthesis" and was herein applied to fabricate Pt nanostructures on glassy carbon substrates. The process is based on the light-induced thermal decomposition of the Pt precursor. It represents a promising, low material consumption and highly controllable alternative to standard wet chemical synthesis of nanoparticles in reactors. Based on the Print-Light-Synthesis, Chapter V describes the development of mixed NiFe nano-composites with well-defined material ratios and loadings in the corresponding inks. Catalyst layer of the composites were fabricated as OER electrocatalysts. A support layer of carbon-nanotubes was used as "light-to-heat-absorber" and alcohols in the ink as reducing agents for the efficient decomposition of the chloride-based Ni and Fe precursors. The last section of this thesis presents future perspectives of the current work. The possibilities in which this research can engender will be discussed. Focus will be drawn to possible industrial applications of the proposed and developed techniques presented in this thesis. Mainly it is demonstrated the possibility of having, through the combination of inkjet printing and flash light processing as two state-of-art techniques the possibility of fabricating in an easily-up scalable w