Evidence of Nanoconfinement Effects in the Adsorption of Hydrogen on Coinage Metal Complexes Dispersed within Porous Carbon

Abstract

In this article, we report the results of careful, room-temperature, high-pressure adsorption studies, in which simple complexes of copper and silver reversibly adsorb hydrogen when dispersed within nanoporous carbon. Whereas these complexes alone did not adsorb hydrogen, when they were nanoconfined within carbon, they adsorbed 1–3 mol of H2 per metal center. As a figure of merit, nanoconfined cupric formate adsorbed ∼2.6 H2/Cu at 100 bar and 20 °C, much larger than any reported metal-containing adsorption medium. On carbon alone, the heat of hydrogen adsorption decreased with an increase in adsorption extent, limiting to insufficient levels of uptake. By contrast, when these metal salts were dispersed within the carbon, the heats of adsorption increased markedly in a linear manner, meaning that the thermodynamics has moved in the right direction and is not self-limiting. Such thermodynamic behavior is associated with side-on dihydrogen binding onto a metal center, the so-called Kubas binding. Such intera...