Understanding How the Interfacial Properties of ALD‐Crafted In2S3 Thin Films Promote Enhanced Formate Electrosynthesis

Abstract The electrochemical reduction of carbon dioxide (eCO 2 R) to formate is a promising technology for CO 2 utilization and potential industrial application. Despite extensive research on catalyst layer design, interpreting performance is often hindered by the complexity of composite layers. In this study, plasma‐enhanced and thermal Atomic Layer Deposition (ALD) are employed to fabricate In 2 S 3 thin films on gas diffusion electrodes, creating model catalyst layers without ionomers or binders. The uniform ALD films enables fine‐tuning of hydrophobicity, underscoring its critical role at the triple‐phase boundary (TPB) and enhancing formate production via eCO 2 R at high current densities. For example, a thermal ALD‐deposited In 2 S 3 thin film (150 µg cm −2 ) achieved a formate Faradaic efficiency of 93% at 1 A cm −2 . The system exhibits high selectivity, with minimal hydrogen evolution and carbon monoxide as the sole by‐product, facilitating the determination of key electrokinetic parameters such as exchange and limiting current densities. Reaction kinetic modeling further clarified the influence of hydrophobicity on these parameters. This work provides valuable insights into the role of interfacial properties in electrocatalysis, advancing the development of efficient electrocatalysts and processes for industrial formate production.