Carboxyl‐Driven Water Networks on 2D Metal Organic Frameworks for Enhanced Proton Conduction in PEMFCs

Abstract Precisely constructing the well‐defined proton transport platform and studying its transport behavior are of great importance yet remain challenging. Here, a Zr‐BTB‐X nanosheet via post‐synthetic modifying Zr‐BTB with terephthalic acid (BDC) and trimesic acid (BTC) is developed, which coordinate to the unsaturated Zr₆ clusters. The increased –COOH groups endow Zr‐BTB‐BTC nanosheets significant improvement in proton conductivity, achieving 490.9 mS cm −1 at 80 °C and 100% RH, compared to 2.19 mS cm −1 for the original Zr‐BTB nanosheets. Density functional theory calculations and water adsorption studies reveal that the formation of enriched water networks induced by the –COOH groups facilitates efficient proton dissociation and reduces the proton transport barrier. The assembled Zr‐BTB‐BTC lamellar membrane, retaining high conductivity properties of nanosheet, reaches 242.4 mS cm −1 at 80 °C and 100% RH. It also delivers a superior performance in proton exchange membrane fuel cell (PEMFC), achieving ultrahigh peak power (0.91 W cm −2 ), maximum current density (3.59 A cm −2 ), and good durability (100 h of OCV test).