Proton-conducting copper-based MOFs for fuel cells

Metal-organic frameworks (MOFs) are emerging as promising alternatives for proton-conductive materials due to their high porosity, large surface area, stability, and relatively low cost. Among these, copper-based MOFs (Cu-MOFs) stand out with unique advantages, including open metal sites, variable valence states, and strongly electrophilic Cu centers. In this review, we discuss recent advances and developments in the use of Cu-MOFs as proton-conductive materials, with a particular focus on their application as proton exchange membranes (PEMs). We introduce the most common strategies employed to date and review the key features that have contributed to the construction of efficient proton transport pathways in Cu-MOFs. Additionally, we review PEMs fabricated via direct thin-film deposition or as mixed-matrix membranes (MMMs) incorporating Cu-MOF fillers. Finally, we address the challenges that must be overcome in the coming years to develop more robust Cu-MOFs and to create more efficient thin films and Cu-MOF-based MMMs.