Metal Catalysts for the Electrochemical Reduction of CO2

The world by and large has adopted the The Paris Agreement, which commits any signing party to cut greenhouse emissions drastically and prevent global heating above 2 °C beyond pre-industrial levels. For this ambitious goal to be met, ratifying states need to undergo a rapid energy transition away from fossil fuels to renewables for which large scale energy storage is needed. Fuels such as acetaldehyde and ethanol offer a cost-effective measure to store low-energy-density renewable energy in the form of chemical bonds. One promising technology that achieves both CO2 emissions reduction and energy storage is the electrochemical CO2 reduction reaction (CO2RR). In here, CO2 is converted using electricity into value added chemicals. Although promising, several hurdles will need to be taken for this technology to become competitive: 1) catalysts with high product selectivity will need to be designed, 2) reactor design will need to be optimized for specific products, 3) reactors will need to run >10,000 of hours at high conversion.In this thesis, great attention was spent to the design, synthesis, characterization and CO2RR performance of electrocatalysts on the lab scale. Special focus was placed on Cu-based catalysts for their unique capabilities to make carbon-carbon bonds, required to produce energy-dense fuels. Design strategies to fashion selective metal catalysts were discussed in depth based on experimental data spanning three decades. Based on this discussion, two size regimes were selected that could yield promising potential catalysts, and lacked previous investigations. The first regime is that of the bulk, where in particular the role of the catalyst surface, i.e., the facet exposed and the electronic structure, affects the selectivity in CO2RR. These effects were investigated by synthesizing Cu-M with M = Ag and Ag-Pd nanoparticles >10 nm of specific shapes having, therefore, specific facets, i.e., (100) and (111), exposed at the surface and a specific electronic structure as based on their relative composition. To achieve this, a new wet-chemistry synthesis was developed that allowed to produce facet-controlled surface alloys independent of component miscibility. Further, a new characterization method based on inductively coupled plasma mass spectrometry was established to determine the composition distribution of said alloys with ensemble representative statistics. Based on the deconvolution of composition, i.e., electronic structure and facet, a clear trend in the selectivity for liquid fuels in CO2RR could be discerned.The second regime is that of clusters in which electrocatalyst performance is governed to a large degree by the total number of atoms in the cluster and composition and to a lesser degree by the cluster-support interaction. To probe the effect of cluster size, composition and support in CO2RR, Cu(-Ag) clusters 90%) was observed for the Cu clusters independent of support.Finally, we draw conclusions and offer perspectives on the further improvement of the technological readiness level of promising electrocatalysts beyond the lab scale. And propose avenues based on reactor design that are considered most promising in bringing CO2RR technologies to fruition.