Recent Advances in Photoelectrochemical Water Splitting Enabled by Covalent Organic Frameworks

Owing to its near‐zero greenhouse gas emissions and its emerging role as an energy source in a wide range of applications, hydrogen has gained significant relevance, particularly in the context of combating climate change. Thus, a key area of focus in fossil fuel‐free energy is solar‐driven water splitting for the H 2 evolution predominantly via photo‐ and photoelectrochemical catalytic processes (PC or PEC). Beyond a broad spectrum of well‐established photoactive inorganic catalysts, organic semiconductors are gaining increasing attention as versatile alternatives owing to their tunable chemical composition. In this context, the polymeric material class of 2D covalent organic frameworks (2D COFs) is emerging as an intriguing absorber layer and catalyst for the light‐driven PEC processes, accounting to its chemical durability and immense structural diversity combined with long‐range order. This review outlines the construction principles of 2D COFs, including building block design and linkage motif, and the use of 2D COFs in photo(electro)catalytic water splitting. A particular emphasis is given to COF film fabrication techniques and surface deposition methods addressing challenges associated with device fabrication for PEC catalysis.