Water-stable MOFs and composites: a greener and sustainable approach for enhanced reactivity towards the electrochemical nitrate reduction reaction

The electrochemical nitrate reduction reaction (eNO₃⁻ RR) is a promising strategy to mitigate nitrate pollution, which has become a critical environmental concern due to its harmful effects on water resources and ecosystems. Metal-organic frameworks (MOFs), known for their highly tunable structures, large surface areas, and exceptional porosity, have emerged as an affordable technology and a cost-effective solution for catalyzing the eNO₃⁻ RR. However, the water stability of MOFs remains a major challenge in achieving efficient, durable NO₃⁻ RR under aqueous conditions. Recent advancements in water-stable MOF (WS-MOF) based materials offer promising solutions to this problem, enabling robust performance in electrochemical applications. This review explores the design, synthesis, and application of WS-MOFs for the eNO₃⁻ RR. Key strategies for enhancing water stability include the incorporation of hydrophobic ligands, post-synthetic modifications, and the development of MOF composites. The review examines the role of metal centers, such as transition metals (e.g., Fe, Cu, Co, and Ni), and their interaction with organic linkers in promoting selective eNO₃⁻ RR to environmentally benign products including nitrogen gas (N₂) and ammonia (NH₃). The integration of MOFs with conductive materials to improve electrical conductivity and catalytic performance is also discussed. In addition to reviewing recent progress in water-stable MOF catalysts for the eNO₃⁻ RR, this review highlights challenges such as reaction selectivity, competitive side reactions, and long-term stability in electrochemical cells. Prospective directions for future research are outlined, including the development of more efficient catalysts, understanding reaction mechanisms at the molecular level, and scaling up MOF based eNO₃⁻ RR systems for practical applications.