Controlling Confinement: Covalent Organic Frameworks induced Confinement of Water probed via EC-SEIRAS

The study of confinement at the nanoscale in electrochemistry necessitates a well-understood bulk system, a way to induce reproducible confinement, and a method to probe the electrochemical/-catalytic behaviour at the interface. Herein, we utilize electrochemical surface enhanced infrared absorption spectroscopy (EC-SEIRAS) to characterize the potential-dependent behaviour of water confined in covalent organic framework (COF) films with varying nanopore sizes and chemical pore environments at a gold electrode. Combined with molecular dynamics (MD) simulations and solvation shell spectroscopy, we revealed an increased sensitivity of hydrogen-bonded water (H 2 O HB ) as a function of the pore size in an isorecticular COF series as well as a coordinative chemical effect upon confinement. We additionally revealed a decreased sensitivity of H 2 O HB to the applied potential in these confined systems with respect to unmodified electrodes, providing a hitherto missing molecular level insight into the manifold observed effects of COF based confinement on electrochemical reactions in recent literature. These fundamental insights are critical to pave the way toward a knowledge-based design of COFs with specific pore sizes and chemical functionalities to improve reaction pathways and product selectivity in electrocatalytic applications.