Hydrogen storage in carbon materials can be increased by hydrogen spillover from a supported catalyst; a systematic investigation of various carbon supports was used to better understand how hydrogen spillover affects hydrogen storage on carbon materials. Secondary spillover experiments effectively eliminated experimental variables associated with primary spillover, evidenced by materials clustering around the carbon type for a variety of supported catalyst-carbon mixtures. Providing a supported catalyst to act as a hydrogen source enhances the overall hydrogen uptake of a carbon material; for example, simple mixing of carbon nanotubes with supported palladium increased the uptake of the carbons by a factor of three. However, the baseline adsorption of the carbon was the predominant factor in the magnitude of the overall hydrogen uptake, even when hydrogen spillover was active. Three observations illustrated that a dynamic steady-state model is needed for predictive capacity of hydrogen spillover.

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The synergistic role of increased oxygen functional groups and water on hydrogen adsorption via hydrogen spillover is explored. A potassium hydroxide (KOH) treatment is used to increase the surface density of oxygen groups on a high surface area-activated carbon (AC), which serves as a secondary receptor for hydrogen spillover after physical mixing with a common Pt-based spillover catalyst. Consistent with previous results, XPS shows that KOH treatment increases atomic concentration of oxygen and the fraction of carbonyl/quinone groups on the surface of the AC. Increased surface density of oxygen groups leads to a significant enhancement of hydrogen spillover at pressures <100 mbar. At 300 K, the hydrogen uptake is 1.1 wt % at 100 mbar and increases to 1.4 wt % at 20 bar. However, only 0.4 wt % of this is desorbable via a pressure reduction at room temperature, and appreciable spillover is observed only when trace water is present during pretreatment. The trace water is believed to affect the development of active surface sites based on characterization of the development of oxygen groups by XPS and FTIR. The synergistic role of oxygen groups and water and a plausible mechanism on the effect on hydrogen isotherms are discussed.

We provide evidence of low-temperature hydrogen evolution and possible hydrogen trapping in an anthracite coal derivative, formed via reactive ball milling with cyclohexene. No molecular hydrogen is added to the process. Raman-active molecular hydrogen vibrations are apparent in samples at atmospheric conditions (300 K, 1 bar) for samples prepared 1 year previously and stored in ambient air. Hydrogen evolves slowly at room temperature and is accelerated upon sample heating, with a first increase in hydrogen evolution occurring at approximately 60 degrees C. Subsequent chemical modification leads to the observation of crystalline carbons, including nanocrystalline diamond surrounded by graphene ribbons, other sp2-sp3 transition regions, purely graphitic regions, and a previously unidentified crystalline carbon form surrounded by amorphous carbon. The combined evidence for hydrogen trapping and carbon crystallization suggests hydrogen-induced crystallization of the amorphous carbon materials, as metastable hydrogenated carbons formed via the high-energy milling process rearrange into more thermodynamically stable carbon forms and molecular hydrogen.

Sorption and desorption equilibria of phenanthrene with respect to three different types of geosorbents were measured, as were the rates of desorption and biological mineralization of this representative hydrophobic organic contaminant. The chemical nature of the organic matter associated with each geosorbent was characterized using solid state 13C‐NMR spectrometry. The results of these studies reveal that both the desorption behavior and the microbial bioavailability of the sorbed contaminant are influenced by the physicochemical character of the organic matter. The more reduced and condensed the organic matter, the greater the extent of sorption‐desorption hysteresis, the slower the desorption rate, and the less readily bioavailable the sorbed contaminant. These observations are consistent with projections predicated on a dual reactive domain model introduced earlier to describe the sorptive reactivities of different types of soil/sediment organic matter with hydrophobic organic contaminants.