Adsorption-Based Hydrogen Storage in Activated Carbons and Model Carbon Structures

Anatoly Fomkin,Oleg Aksyutin,Konstantin Romanov,Andrey Shkolin,Alexander Ishkov,Ilya Men’Shchikov,Anatoly Pribylov,Elena Khozina

doi:10.3390/reactions2030014

Abstract

The experimental data on hydrogen adsorption on five nanoporous activated carbons (ACs) of various origins measured over the temperature range of 303–363 K and pressures up to 20 MPa were compared with the predictions of hydrogen density in the slit-like pores of model carbon structures calculated by the Dubinin theory of volume filling of micropores. The highest amount of adsorbed hydrogen was found for the AC sample (ACS) prepared from a polymer mixture by KOH thermochemical activation, characterized by a biporous structure: 11.0 mmol/g at 16 MPa and 303 K. The greatest volumetric capacity over the entire range of temperature and pressure was demonstrated by the densest carbon adsorbent prepared from silicon carbide. The calculations of hydrogen density in the slit-like model pores revealed that the optimal hydrogen storage depended on the pore size, temperature, and pressure. The hydrogen adsorption capacity of the model structures exceeded the US Department of Energy (DOE) target value of 6.5 wt.% starting from 200 K and 20 MPa, whereas the most efficient carbon adsorbent ACS could achieve 7.5 wt.% only at extremely low temperatures. The initial differential molar isosteric heats of hydrogen adsorption in the studied activated carbons were in the range of 2.8–14 kJ/mol and varied during adsorption in a manner specific for each adsorbent.

Highlights

A global transformation of the energy sector involves decarbonization, which is intended to reduce greenhouse gas emissions by 25–40% by 2030 compared to 1990 or2005, as well as an increase in the share of renewable energy manifold [1]
The structural and energy characteristics (SEC) of the activated carbons, i.e., micropore volume (W 0), characteristic energy of adsorption (E), and effective half-width of micropores (x0), were calculated from the isotherms of adsorption of standard benzene vapors at 293 K represented in the coordinates of the well-known
The examination of hydrogen adsorption on the microporous carbon adsorbents of various origin with the specific micropore volumes from 0.46 to 2.00 cm3 /g at temperatures from 303 to 363 K and pressures up to 20 MPa revealed the following patterns:. Both at ambient and low temperatures, the highest gravimetric hydrogen density found for the AC sample (ACS) adsorbent at high pressures could be attributed to the largest micropore volume, bimodal pore size distribution, and specific BET surface among the rest samples

Summary

Introduction

A global transformation of the energy sector involves decarbonization, which is intended to reduce greenhouse gas emissions by 25–40% by 2030 compared to 1990 or2005 (as a part of the Paris agreement), as well as an increase in the share of renewable energy manifold [1]. Hydrogen offers one of the most efficient ways to provide long-term energy storage. Hydrogen is characterized by high specific energy on a mass basis (energy efficiency) and environmental safety; combined with the unlimited resource base, these features make it an advanced alternative for fossil fuel systems [2,3]. Hydrogen as an energy source can be used for a variety of applications such as power and manufacturing industries, transport, and housing maintenance and utilities. According to various estimates reported in [3], by 2050, the share of hydrogen in the global energy balance may be within the range of 7–24%. The extensive use of hydrogen as an environmentally friendly energy source depends on how successfully the problems of its efficient storage and transportation will be solved. Its high explosion hazard requires the development of efficient and safe facilities

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