A robust volumetric apparatus and method for measuring high pressure hydrogen storage properties of nanostructured materials

Carbon dioxide separation and capture by adsorption: a review

Rising adverse impact of climate change caused by anthropogenic activities is calling for advanced methods to reduce carbon dioxide emissions. Here, we review adsorption technologies for carbon dioxide capture with focus on materials, techniques, and processes, additive manufacturing, direct air capture, machine learning, life cycle assessment, commercialization and scale-up.

A review of common practices in gravimetric and volumetric adsorption kinetic experiments

The availability of commercial gravimetric and volumetric systems for the measurement of adsorption equilibrium has seen also a growth of the use of these instruments to measure adsorption kinetics. A review of publications from the past 20 years has been used to assess common practice in 180 cases. There are worrying trends observed, such as lack of information on the actual conditions used in the experiment and the fact that the analysis of the data is often based on models that do not apply to the experimental systems used. To provide guidance to users of these techniques this contribution is divided into two parts: a discussion of the appropriate models to describe diffusion in porous materials is presented for different gravimetric and volumetric systems, followed by a structured discussion of the main trends in common practice uncovered reviewing a large number of recent publications. We conclude with recommendations for best practice to avoid incorrect interpretation of these experiments.

Methods for quantifying the influences of pressure and temperature variation on metal hydride reaction rates measured under isochoric conditions

Analysis techniques for determining gas-solid reaction rates from gas sorption measurements obtained under non-constant pressure and temperature conditions often neglect temporal variations in these quantities. Depending on the materials in question, this can lead to significant variations in the measured reaction rates. In this work, we present two new analysis techniques for comparison between various kinetic models and isochoric gas measurement data obtained under varying temperature and pressure conditions in a high pressure Sievert system. We introduce the integral pressure dependence method and the temperature dependence factor as means of correcting for experimental variations, improving model-measurement fidelity, and quantifying the effect that such variations can have on measured reaction rates. We use measurements of hydrogen absorption in LaNi5 and TiCrMn to demonstrate the effect of each of these methods and show that their use can provide quantitative improvements in interpretation of kinetics measurements.

Volumetric apparatus for hydrogen adsorption and diffusion measurements: sources of systematic error and impact of their experimental resolutions

The development of a volumetric apparatus (also known as a Sieverts' apparatus) for accurate and reliable hydrogen adsorption measurement is shown. The instrument minimizes the sources of systematic errors which are mainly due to inner volume calibration, stability and uniformity of the temperatures, precise evaluation of the skeletal volume of the measured samples, and thermodynamical properties of the gas species. A series of hardware and software solutions were designed and introduced in the apparatus, which we will indicate as f-PcT, in order to deal with these aspects. The results are represented in terms of an accurate evaluation of the equilibrium and dynamical characteristics of the molecular hydrogen adsorption on two well-known porous media. The contribution of each experimental solution to the error propagation of the adsorbed moles is assessed. The developed volumetric apparatus for gas storage capacity measurements allows an accurate evaluation over a 4 order-of-magnitude pressure range (from 1 kPa to 8 MPa) and in temperatures ranging between 77 K and 470 K. The acquired results are in good agreement with the values reported in the literature.

In situ measurement of alternating current magnetic susceptibility of Pd-hydrogen system for determination of hydrogen concentration in bulk

An alternating current magnetic susceptometer for use as a hydrogen gauge for hydrogen-storage materials was designed and developed. The experimental system can simultaneously measure the hydrogen equilibrium pressure and the magnetic susceptibility of metal hydrides. The background voltage of the susceptometer was stabilized for a long period of time, without any adjustments, by attaching an efficient compensation circuit. The performance of the susceptometer at a static hydrogen concentration was demonstrated by measuring the magnetic susceptibility of a Pd-hydrogen system under equilibrium conditions. The in situ measurement of the magnetic susceptibility of Pd during hydrogen absorption was carried out using the susceptometer. Since the in situ magnetic susceptibility obtained at a lower initial hydrogen pressure agreed with the magnetic susceptibility measured at a static hydrogen concentration, the susceptometer could be used to determine the hydrogen concentration in Pd in situ. At a higher initial hydrogen pressure, enhancement of the magnetic susceptibility was observed at the beginning of hydrogen absorption because the magnetic moments induced by the large temporary strain generated in the Pd affected the magnetic susceptibility.

Catalytic effects of TiF3 on hydrogen spillover on Pt/carbon for hydrogen storage

Recent studies have shown that using the hydrogen spillover phenomena is a promising approach for developing new materials for hydrogen storage at ambient temperature. However, the rates need to be improved. Significant catalytic effects on both spillover (i.e., adsorption) and reverse spillover (i.e., desorption) on Pt-doped carbon by TiF(3) were found. By doping 2 wt % TiF(3) on the Pt-doped Maxsorb (a superactivated carbon), both adsorption and desorption rates were significantly increased while the storage capacity decreased only slightly due to decreased surface areas. The effect of the heat treatment temperature (473 K vs 673 K) of the doped TiF(3) on its catalytic effects was also studied. XPS analyses showed that C-F bonds were formed upon heat treatment and that the amount of C-F bonds increased with the heat treatment temperature. The catalytic effects also increased with the heat treatment temperature, indicating that the catalytic mechanism possibly involved the formation of C-F bonds on the carbon edge sites. In addition, the issue of proper sample preparation of Pt/carbon was briefly addressed; missteps in metal doping and consequently poor metal dispersion will result in significantly diminished spillover enhancements (Stadie et al.).

Hydrogen adsorption on ordered mesoporous carbons doped with Pd, Pt, Ni, and Ru

A soft-template synthesis and in situ doping were applied for dispersing transition metals palladium, platinum, nickel, and ruthenium on ordered mesoporous carbons as potential adsorbents for hydrogen storage. Three metal loadings (1, 5, and 10 wt %) on the carbons were obtained to study the effects of metal concentration on physical and chemical properties of the carbon adsorbents. The carbon adsorbents were characterized with TEM, XRD, Raman spectroscopy, and nitrogen adsorption apparatus for their physical and chemical properties, and evaluated for their hydrogen adsorption equilibria and kinetics at 298 K and hydrogen pressures up to 300 bar. The metal-doped carbons maintained the morphology of the pure ordered mesoporous carbon, although their specific surface area was significantly reduced. Hydrogen adsorption on the metal-doped carbons was enhanced by a factor 2.7-5.4 times over the pure carbon at hydrogen pressure of 800 Torr, and a factor of 1.38-3.69 at hydrogen pressure of 300 bar due to the spillover effect. Hydrogen adsorption on metal-doped carbons increases with metal loading for all metals except the Ni-doped carbons that showed a reverse trend. The 1 wt % Ni-doped carbon sample seems to be the best adsorbent for hydrogen adsorption; it adsorbs 0.13 wt % of hydrogen at 298 K and 800 Torr and 2.14 wt % of hydrogen at 298 K and 300 bar. Hydrogen adsorption/desorption hysteresis was observed in all metal-doped carbons, suggesting that part of the adsorbed hydrogen molecules/atoms did not spill over to the carbon surface and remained on the metal surface. All metal-doped carbons had equally faster adsorption kinetics at 298 K, and the metal loadings did not affect the hydrogen adsorption kinetics.

Catalyzed hydrogen spillover for hydrogen storage

A crucial bottleneck in developing a hydrogen economy is hydrogen storage. This is particularly true for transportation using hydrogen as the fuel for fuel cells. The U.S. Department of Energy has established specific R&D targets for on-board hydrogen storage. Among the most important targets are system gravimetric/volumetric capacities and charge/discharge rates. New sorbent materials based on hydrogen spillover have shown much promise recently. However, the rates of spillover are low and remain a major concern. Here it is shown that doping with 2 wt % TiCl(3) or VCl(3) can significantly increase the rates of both adsorption and desorption by spillover. Moreover, the small hysteresis loop in the hydrogen isotherms for the spillover system is eliminated upon doping with the metal salt. Both heats of adsorption and activation energies for spillover are decreased by doping with TiCl(3) or VCl(3). This result indicates that the binding energies between the spilled-over hydrogen and the sites on the carbon surface are decreased by doping.