UC Berkeley

The electrochemical reduction of carbon dioxide (CO₂R) offers a promising route for converting renewable electricity into carbon-neutral fuels and chemical feedstocks. However, most CO₂ reduction reactions require large overpotentials, limiting energy efficiency and hindering integration with renewable energy systems. While significant efforts have focused on engineering catalyst surfaces to improve activity and selectivity at low overpotentials, increasing evidence suggests that the electrochemical microenvironment at the catalyst–electrolyte interface plays an equally critical role in governing reaction energetics and intermediate stabilization. Understanding how ions, solvent molecules, and adsorbates interact within this dynamic interfacial region is therefore essential for developing efficient electrocatalytic systems.This dissertation investigates how electrochemical microenvironments influence CO₂ reduction using a combination of in situ vibrational and electronic spectroscopy. Two representative catalytic systems are examined to elucidate distinct mechanisms through which microenvironmental effects regulate catalytic activity.The first part of this work focuses on nanoparticle-ordered ligand interlayer (NOLI) catalysts, which exhibit unusually low overpotentials for CO₂ reduction. Using in situ nano-FTIR spectroscopy, ligand dynamics during electrochemical operation are directly visualized with nanometer spatial resolution, revealing that ligand detachment and nanoparticle coarsening lead to the formation of a confined interfacial architecture. Within this ligand-defined pocket, in situ SEIRAS and total electron yield X-ray absorption spectroscopy show that electrolyte cations undergo partial desolvation and stabilize intermediates through partial covalent interaction. These observations support a mechanistic model in which ligand-modulated cation desolvation facilitates cation-coupled electron transfer, thereby lowering the activation barrier for CO₂ activation and enabling low-overpotential CO₂ reduction.The second part of this dissertation investigates the electrochemical microenvironment of copper catalysts, which uniquely produce multi-carbon products during CO₂ reduction. In situ nano-FTIR measurements reveal nanoscale heterogeneity in ion distributions and interfacial water structures near evolving Cu surfaces. Complementary SERS and SEIRAS measurements on Cu nanograin catalysts show that carbonate-derived species, oxygen-containing co-adsorbates, and CO intermediates coexist at the catalytic interface. The spectral evolution of CO adsorption further indicates that dipole–dipole interactions, adsorbate coverage, and local electric fields collectively influence the stability and vibrational signatures of intermediates. These findings demonstrate that CO₂ reduction on Cu occurs within a dynamically evolving interfacial environment shaped by electrolyte species, catalyst morphology, and adsorbate interactions.Together, these studies establish the electrochemical microenvironment as a key determinant of catalytic behavior in CO₂ reduction. By revealing how confined interfacial structures, ion solvation, and adsorbate interactions influence reaction energetics, this thesis provides new mechanistic insight into the role of electrolyte–surface interactions in electrocatalysis. More broadly, the concepts and experimental approaches developed here offer a framework for engineering interfacial microenvironments to enable low-overpotential electrochemical reactions, advancing the design of efficient catalysts for sustainable energy conversion.