Directly‐Deposited Ultrathin Solid Polymer Electrolyte for Enhanced CO2 Electrolysis

Abstract The economic viability of carbon dioxide electroreduction (CO 2 R) relies on improved performance accompanied by scalable system design. Membranes are commonly used for the separation of reduction and oxidation products as well as to provide a suitable micro‐environment for CO 2 R. Commercial membranes often address only one of the key challenges in CO 2 R: either they offer a suitable micro‐environment for CO 2 R (e.g., anion exchange membrane) or suppress carbonate cross‐over (e.g., cation exchange membrane and bipolar membrane). This work presents a cation‐infused ultrathin (≈3 µm) solid polymer electrolyte (CISPE) that concomitantly addresses both challenges via a bidirectional ion transport mechanism and suppressed cathode flooding. This directly‐deposited CISPE (that substitutes the commonly used pre‐made membrane) enables record high full‐cell energy efficiency of 28% at 100 mA cm −2 for one‐step CO 2 electrolysis to ethylene (C 2 H 4 ) with ≈110 h of stable operation. This translates into a record low energy cost of 290 GJ per ton C 2 H 4 for the end‐to‐end process (i.e., CO 2 capture and electroreduction, carbonate regeneration, CO 2 separation from anode and cathode streams) in a membrane electrode assembly CO 2 R. The present work offers a versatile design paradigm for functional polymer electrolytes, opening the door to stable, and efficient electrolysis of high‐value feedstock chemicals and fuels using low‐cost catalysts.