Etching Physicochemical Adsorption Sites of Biochar by Steam for Enhanced Hydrogen Storage

Abstract

Enhancing the hydrogen storage capacity of carbon-based materials requires the precise synthesis of strong hydrogen adsorption sites. Consequently, this work suggests improving hydrogen storage capacity at low pressures (less than 50 bar) by employing H2O low-temperature etching technology. First, the simulation methods investigated the pore structure and oxygen-containing groups' adsorption properties on hydrogen. The findings demonstrated that carboxyl groups had the most significant influence on improving hydrogen adsorption. A suitable coupling of pores and oxygen-containing groups can improve the microporous region's hydrogen storage capacity. Moreover, biochar may form a new ultra-microporous region (less than 0.5 nm) by etching it at 700 °C and 30 vol% H2O. Additionally, the oxygen-containing groups content was equally adjusted. After etching 90 minutes, the surface oxygen concentration remained stable at 14 at.%. In conjunction with results from mass spectrometry, we discovered that the process influencing pore growth was the heterogeneous interaction between CO and H2 to create CH4. At 25 ℃ and -196 ℃, the KSBC-30-60 showed superior hydrogen storage capacity compared to KSB. Its total adsorption capacity was 0.49 wt.% and 5.28 wt.%, respectively, and increased by 1.32 and 1.2 times. This study proposes a novel approach to improving hydrogen storage by etching porous carbon structures with H2O. The strategy has the potential for large-scale application and can be further utilized in the design and optimization of related carbon adsorbents.

Keywords: Biochar；Hydrogen storage；H2O etching；Adsorption characteristics