Air-Stable Cu(I) Metal–Organic Framework for Hydrogen Storage

Abstract

Metal-organic frameworks (MOFs) that contain open metal sites have the potential for storing hydrogen (H₂) at ambient temperatures. In particular, Cu(I)-based MOFs demonstrate very high isosteric heats of adsorption for hydrogen relative to other reported MOFs with open metal sites. However, most of these Cu(I)-based MOFs are not stable in ambient conditions since the Cu(I) species display sensitivity toward moisture and can rapidly oxidize in air. As a result, researchers have focused on the synthesis of new air-stable Cu(I)-based materials for H₂ storage. Here, we have developed a <i>de novo</i> synthetic strategy to generate a robust Cu(I)-based MOF, denoted as <b>NU-2100</b>, using a mixture of Cu/Zn precursors in which zinc acts as a catalyst to transform an intermediate MOF into <b>NU-2100</b> without getting incorporated into the final MOF structure. <b>NU-2100</b> is air-stable and displays one of the initial highest isosteric heats of adsorption (32 kJ/mol) with good hydrogen storage capability under ambient conditions (10.4 g/L, 233 K/100 bar to 296 K/5 bar). We further elucidated the H₂ storage performance of <b>NU-2100</b> using a combination of spectroscopic analysis and computational modeling studies. Overall, this new synthetic route may enable the design of additional stable Cu(I)-MOFs for next-generation hydrogen storage adsorbents at ambient temperatures.