Hydrogen Storage at Ambient Temperature by the Spillover Mechanism

Yang , Ralph T.

University of Michigan, Ann Arbor, MI

关键词: Desorption;    Zeolites Hydrogen Storage;    Transition Elements;    Adsorption;    Hydrogen;   

DOI  :  10.2172/1004576
RP-ID  :  GO15078
RP-ID  :  FC36-05GO15078
RP-ID  :  1004576

美国|英语

来源: UNT Digital Library

【 摘 要 】

The goal of this project was to develop new nanostructured sorbent materials, using the hydrogen spillover mechanism that could meet the DOE 2010 system targets for on-board vehicle hydrogen storage. Hydrogen spillover may be broadly defined as the transport (i.e., via surface diffusion) of dissociated hydrogen adsorbed or formed on a first surface onto another surface. The first surface is typically a metal (that dissociates H2) and the second surface is typically the support on which the metal is doped. Hydrogen spillover is a well documented phenomenon in the catalysis literature, and has been known in the catalysis community for over four decades, although it is still not well understood.1, 2 Much evidence has been shown in the literature on its roles played in catalytic reactions. Very little has been studied on hydrogen storage by spillover at ambient temperature. However, it is also known to occur at such temperature, e.g., direct evidence has been shown for spillover on commercial fuel-cell, highly dispersed Pt/C, Ru/C and PtRu/C catalysts by inelastic neutron scattering.3 To exploit spillover for storage, among the key questions are whether spillover is reversible at ambient temperature and if the adsorption (refill) and desorption rates at ambient temperature are fast enough for automotive applications. In this project, we explored new sorbents by using a transition metal (e.g., Pt, Ru, Pd and Ni) as the H2 dissociation source and sorbents as the hydrogen receptor. The receptors included superactivated carbons (AX-21 and Maxsorb), metal organic frameworks (MOFs) and zeolites. Different metal doping methods have been used successfully to achieve high metal dispersion thereby allowing significant spillover enhancements, as well as a bridging technique used for bridging to MOFs. Among the metals tested, Pt is the hardest to achieve high metal dispersion (and consequently spillover) while Ru is the easiest to disperse. By properly dispersing Pt on superactivated carbons (by following detailed doping and activation conditions given in our publications, e.g., Ref. 12), the storage capacities are increased two-fold (doubled) while slightly more than doubled by Ru doping. The bridging technique remains highly empirical and sample-to-sample consistency is difficult to achieve; however, significant enhancements by spillover can be achieved if the synthesis and pretreatment are done properly. Pitfalls in sample syntheses for both metal doped and bridged sorbents are pointed out in the report; deviations from the synthesis and pretreatment conditions will lead to diminished or no spillover effects. Due to the high bulk densities of zeolites, metal doped zeolites are shown to be most promising for achieving high volumetric storage capacities by spillover. Kinetics of both spillover and reverse spillover (i.e., desorption) at ambient temperature are also studied. This report summarizes the progress made in the project.