(389a) In Situ Characterization of Interfacial Properties in (Photo)Electrochemical Systems

Electrification of the chemical manufacturing industry is a promising pathway to reduce the use of fossil fuels and decrease CO₂ emissions. Benefits of electrochemical conversion include the use of renewable electricity, low operating temperature and pressure, and modular reactor design. In this presentation I will discuss two areas where thermochemical processes can be supplemented with electrochemical systems: (1) carbon dioxide reduction (CO₂RR) to fuels and chemicals and (2) recovery of ammonia from wastewater through nitrate reduction (NO₃RR). Both reduction reactions are performed in aqueous electrolyte and face the key challenges of low selectivity, which results in prohibitively expensive product separation, and low efficiency, where the cost of the energy needed to drive the reaction may exceed the value of the product.

To address these challenges, we must gain a fundamental understanding of the reaction mechanisms that occur in the electric double layer (EDL), which forms at the electrode–electrolyte interface when a potential bias is applied. In my research I use in situ characterization techniques that can probe this local reaction environment. Attenuated total reflectance–surface-enhanced infrared adsorption spectroscopy (ATR–SEIRAS) can provide information about the adsorbed reactants, intermediates, and local pH within 5–10 nm of the cathode surface. To truly investigate on the molecular scale, I use X-ray reflectivity (XRR), which provides atomic-level resolution of the laterally averaged electron density profile along the surface normal. When coupled with resonant anomalous X-ray reflectivity (RAXR), we can reveal the structure of the EDL, such as the number of ordered molecular layers, the distance of each layer from the surface, the ion surface coverage, and the degree of hydration of ions in each layer. Results from this study could inform how changes to the bulk electrolyte composition can alter the EDL and enhance the selectivity and efficiency of the desired reaction.

These in situ characterization techniques require unique electrochemical cell designs, separate from the electrochemical cells used for precise, quantitative product analysis needed to measure reaction selectivity. Coupling bulk and surface techniques allows us to characterize electrode performance and understand molecular mechanisms. In this talk I will highlight the design considerations of the electrochemical cells that enabled the ATR–SEIRAS and XRR experiments. The combination of expertise in cell design with in situ characterization will lead to the development of more selective and efficient electrodes and electrolyte engineering strategies to address some of the most urgent needs of our time by converting putative wastes to sustainable fuels, chemicals, and fertilizer.