Does boron or nitrogen substitution affect hydrogen physisorption on open carbon surfaces?

Area of Science:

• Materials Science
• Physical Chemistry
• Surface Science

Background:

• Heteroatom incorporation in carbon materials is widely studied for property modification.
• Previous research indicated significant effects on methane adsorption.
• The impact on hydrogen physisorption remains less understood.

Purpose of the Study:

• To investigate the effect of boron (B) and nitrogen (N) heteroatom substitution on hydrogen physisorption energies in carbon materials.
• To compare these effects with those observed for methane adsorption.
• To evaluate the technological significance of these modifications for hydrogen storage applications.

Main Methods:

• Computational chemistry methods, including a comprehensive set of levels of theory, were used for calculations.
• Physisorption energies were calculated for hydrogen on B- and N-substituted carbon surfaces.
• Experimental measurements of adsorption energies were also performed for comparison.

Main Results:

• No technologically significant effect of B- and N-substitution on hydrogen physisorption energies was identified.
• Calculated adsorption enthalpies (q_st = -ΔH_ads) were consistently around 4.1 ± 0.7 kJ mol^-1.
• Measured physisorption energies ranged from 4.1 to 4.6 kJ mol^-1, showing minimal variation with substitution.

Conclusions:

• Contrary to expectations based on methane adsorption studies, B- and N-substitution on mid-plane C-sites of open carbon surfaces do not significantly enhance hydrogen physisorption.
• The findings suggest that simple heteroatom substitution may not be an effective strategy for improving hydrogen storage capacity in these specific carbon materials.
• Further research may be needed to explore alternative modification strategies for optimizing hydrogen physisorption in carbon-based materials.