Abstract
Environmental friendly technologies for storage and reutilization energy are important for the future of humanity on earth. Scientific efforts cover not only the investigation of new technologies to close the carbon cycle, but also by advancing already existing applications such as batteries and fuel cells. Major challenges for these electrocatalytic reactions are the detailed understanding of their reaction mechanisms and increasing the performance and stability of the catalysts. In this thesis, I reveal new insights on the behavior of promising catalysts during the CO2 reduction reaction (CO2RR) and the Formic Acid Oxidation Reaction (FAOR). By systematically studying single crystals as well as shaped nanoparticle and bimetallic catalysts during potentiostatic and pulsed reaction conditions, correlations between the catalyst structure and the reaction performance are identified.
In the electrocatalytic CO2RR, the role of surface Cu atoms is still not well understood. Thus, one research focus has been set to study surface-selectivity relationships by investigating the surface structure of a stepped Cu(310) single crystal and its influence on the CO2RR. In particular, it was found that these catalysts provide mostly hydrogen and only small amounts of hydrocarbons or ethanol.
Furthermore, the presence and the role of oxide species during CO2RR remain an elusive scientific discussion. In order to understand how oxides tune the catalytic selectivity, the use of potential pulses with different time lengths to periodically regenerate the oxide species was established. In particular, under certain pulse-length conditions, a doubled ethanol production was obtained as compared to non-pulsed conditions has been observed. The nature of the Cu species and structures responsible for this selectivity was investigated using operando techniques.
The role of nanocubes (NCs) decorated with a co-catalyst was investigated both, for the CO2RR and the FAOR. Au-Cu2O NC catalysts displayed higher C2+ yields than bare Cu2O NCs. Furthermore, the type, amount and role of CuAu alloys on the CO2RR was elucidated. Moreover, for the FAOR, Pd NCs were decorated with a SnO2 shell, which exceeded the performance of pure Pd by reducing poisoning intermediates. By in situ and operando techniques, the structural and chemical alterations under these reaction conditions were investigated.
This thesis unveils the role of surface termination, oxides and bimetallic catalyst structures on the acivity and selectivity of CO2RR and FAOR electrocatalysts. The here presented insights contribute to a knowledge-driven design of electrocatalysts, that can be used in the future to steer the reactions towards highly-valuable products and high performances, emphasizing the importance of characterizing these catalysts under operating conditions and establishing useful structure-selectivity relationships.
