Our world has witnessed the devastating effects of fossil fuels extraction; the primary energy source for modern society. Transitioning to sustainable energy sources requires exploring alternative fuel production methods, focusing on utilizing captured anthropogenic CO2. Electrochemical reduction of CO2 (CO2RR) using renewable electricity presents an attractive option for storing energy in chemical bonds. While many electrocatalysts efficiently reduce CO2 to CO, only a few, such as copper, can produce high energy-dense molecules like ethanol or methanol with selectivities exceeding 60%. Molecular catalysts (MCs) hold promise as alternatives to metallic electrocatalysts, particularly when immobilized on the surface of gas diffusion electrodes (GDEs), where state-of-the-art CO2RR takes place. However, their efficiency and scalability must be addressed for industrial applications. Our work focuses on evaluating the impact of engineering the micro-environment at the interface where CO2RR occurs, for the purposes of optimizing the performance of MCs systems.

Specifically, the electrode active-site interaction for the CO2-to-ethanol pathway was investigated using a nickel iron-tetraphenylporphyrin (Ni-FeTPP) electrocatalyst. We explored the challenges of translating a molecular catalyst system from an unconventional 3D electrode design to a GDE-based electrolyzer. The difficulty lies in replicating the strong electronic coupling between Ni and FeTPP necessary for enabling the CO2-to-ethanol pathway; which led to two methods of coupling Ni to FeTPP: drop-casting and spray-coating. Although our system did not achieve CO2 reduction to ethanol, it provided significant insights into the impact of subtle micro-environment changes. These changes uncovered possible unintended interactions, suggesting the formation of nickel hydride species that could greatly influence the CO2-to-ethanol pathway catalyzed by Ni-FeTPP. Moreover, the competing behavior between CO2 and CO to enhance the CO2-to-methanol pathway was adressed by using cobalt phthalocyanine supported on multi-walled carbon nanotubes (CoPc/MWCNT). We engineered the local environment where molecular catalysts interact by introducing silver nanoparticles and PTFE particles to increase local CO availability near the active sites and promote further CO reduction. This approach resulted in a remarkable 4-fold and 17-fold increase in the Faradaic efficiency of methanol, from the addition of silver nanoparticles and PTFE particles, respectively. Our results demonstrate the CO2-to-methanol pathway is enhanced through the modification of the catalyst surface microenvironment of the GDE. Our research contributes to a deeper understanding of the prospect for improving the challenging electrochemical reduction of CO2 beyond CO.