(307b) Catalyst Synthesis for Fuel Cell Application and Fundamental Understanding of CO2 Reduction Mechanism

The electrochemical reduction of CO₂ is a promising way to produce fuels and chemicals. However, CO₂ electroreduction currently suffers from poor selectivity and stability and low energetic efficiency at practical reaction rates. To overcome some of the drawbacks and achieve a viable route for CO₂ reduction, the reaction should be split into a two-step process. Initially, CO₂ is reduced to CO, followed by a further reduction to the desired multi-carbons (e.g., C₂H₄, C₂H₅OH, etc.). Decoupling the process into two steps allows for CO electrolysis in highly alkaline conditions, enabling enhanced efficiency. Prior works have shown progress towards understanding the impact of electrolyte ions, pH, mass transport, temperature, and pressure on electrode activity and selectivity. A gas diffusion electrode (GDE) has been incorporated into a flow cell reactor to facilitate better transport and distribution of reactants and circumvent mass transport limitations. The development of an operando technique compatible with a flow cell reactor is highly desirable.

A promising technique that can provide insight reaction information in real-time is the flow electrolyzer mass spectrometry (FEMS). This analytical technique collects volatile products of the reaction in the immediate vicinity of the electrode. Using FEMS, we investigated the electrochemical carbon monoxide reduction reaction (eCORR) on polycrystalline copper and elucidated the acetaldehyde formation's oxygen incorporation mechanism. Combining FEMS and isotopic labeling, we showed that the oxygen in the as-formed acetaldehyde intermediate originates from the reactant CO, while ethanol and n-propanol contained mainly solvent oxygen.

As a part of my graduate studies, I have had the opportunity to conduct research on complex electrochemical processes. My doctoral dissertation focused on catalyst synthesis and electrochemical and physicochemical characterization. We identified the effect of catalyst support on the metal particle distribution and size, which has a broader impact on catalyst activity during electrochemical processes. Carbon black (CB), such as Vulcan XC-72, has been widely investigated and proposed as support for PEMFCs catalysts. Vulcan XC-72 exhibits an ideal high surface area and low production cost. However, organo-sulfuric impurities and the inaccessible metal particle sites inside the micropores may often lead to low catalytic activity values. These drawbacks turned the interest into alternative carbon-based supports such as carbon nanotubes (CNT), graphene (Gr), and Biochar (BC) which are all characterized by high specific surface area and high electronic conductivity. Comparing various carbon supports, we found that carbon structure and metal particle size play an important role in fuel cell electrocatalytic activity. Notably, carbon structures of high crystallinity (graphene and carbon nanotubes) and low pzc (point of zero charge) values facilitate the formation of smaller particles. These catalysts exhibit better performances in a PEM fuel cell under pure hydrogen and CO poisoning feeding conditions. On the other hand, Biochar and Carbon black exhibit amorphous phases and high values of pzc, resulting in catalysts with large metal particle size and low electrocatalytic activity.