title: Free standing Cu nanowire networks as catalyst for electrochemical CO₂ reduction
Creators: name: Ulrich, Nils
Publisher: name: UNSPECIFIED
Year: 2024

description: To tackle the threats of global warming, finding effective ways to decrease the CO₂ emissions caused by the human population must advance with outmost priority. Thus, efficient progress is necessary regarding decarbonization, carbon sequestration and carbon recycling. Among these approaches, carbon recycling is most promising as it offers a path towards a carbon-neutral circular economy. Through electrochemical CO₂ reduction reactions for carbon neutral electrosynthesis processes, CO₂ can be converted into valueadded chemicals.
This thesis focuses on the fabrication of three-dimensional, highly interconnected copper (Cu) nanowire networks and their application as catalysts for electrochemical CO₂ reduction reactions. The networks are
grown by electrodeposition of Cu in porous polycarbonate membranes which are produced by means of ion-track nanotechnology. The geometrical parameters of the networks are varied with respect to length,
diameter and number density of the nanowires. Compared to a 1 cm² planar sample area, the fabricated Cu nanowire networks surfaces reach up to 300 cm². The characterization of the nanowire networks involves
techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), both before and after the CO₂ reduction reaction.
The electrochemically active surface area of the nanowire networks is determined by evaluating the double layer capacitance via cyclic voltammetry. In all cases, the experimentally measured electrochemically
active surface surpasses the calculated values based on the geometrical wire surface, most probably due to surface roughness resulting from the chemical treatment in the pre-cleaning process.
A variety of Cu nanowire networks are tested as catalysts for electrochemical CO₂ reduction. The conversion efficiency and selectivity of CO₂ reduction towards liquid- and gas-phase products are studied
at different applied potentials. The networks exhibit structural stability and conversion efficiencies up to 30% for the reaction of CO₂ to its reduction products within a potential range between -0.5 V and -0.93 V
vs. RHE. At higher potentials, cathodic corrosion causes nanowire degradation. This directly leads to changes in surface structure and wire morphology due to material dissolution and redeposition processes.
To assess the long-term performance, the CO₂ reduction reaction at the nanowire networks is operated for 8 h at different potentials. No significant trends for the current density and gas-phase reaction products
are observed within this time frame. However, under operation, the Cu nanowire networks undergo gradual degradation as indicated by a loss in cell resistance and increased surface roughness.
Overall, this thesis offers valuable insights into the design, fabrication, and characterization of highly interconnected copper nanowire networks and their application and performance as catalysts for electrochemical CO₂ reduction. It also highlights the challenges associated with cell design, catalyst stability and product analysis during the CO₂ reduction reaction and proposes new approaches for future
experiments.