2D metal-organic frameworks and their composites for water splitting: Catalytic insights, synthesis pathways, and structural engineering strategies

In response to the challenges of climate change and energy insecurity, electrochemical water splitting, which generates green hydrogen energy through the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), plays a pivotal role in achieving carbon neutrality by offering a sustainable energy pathway. Two-dimensional metal-organic frameworks (2D MOFs) have emerged as next-generation electrocatalysts due to their unique structural properties such as atomic-scale thickness, abundant active sites, high surface area, tunable porosity, and flexible structure modulations, which collectively enhance electrical conductivity, catalytic activity, and long-term stability. This review systematically summarizes recent progress in 2D MOF-based electrocatalysts for HER, OER, and overall water splitting, starting with an overview of the fundamental principles of water electrolysis. It focuses on advanced synthetic methodologies for 2D MOFs and their composites to boost catalytic performance, explores structural engineering approaches, including defect engineering, ligand engineering, and metal node engineering, to optimize their electronic structures and catalytic activity, and highlights the integration of 2D MOFs with conductive materials to improve conductivity, stability, and overall performance. This review not only presents the cutting-edge developments in 2D MOF-based electrocatalysts but also provides insights into future directions for designing high-performance 2D MOF materials in sustainable energy conversion technologies.