Sulfur Encapsulated in Microporous Carbon Composites for Improved Hydrogen Storage

As a sustainable, environmentally friendly energy vector, hydrogen is certain to play a significant role in meeting Net-Zero by 2050, with the International Energy Agency predicting a six times increase in demand[1]. Even though hydrogen possesses the highest gravimetric energy density of any known chemical fuel, its extremely low volumetric density is a significant drawback preventing widespread adoption. Current methods of storing hydrogen in a dense state require high pressures (&gt;70 MPa), cryogenic conditions (&lt; 20 K) or a combination of the two. These are often energy-intensive to achieve and maintain.<br/>The spontaneous adsorption process offers a low energy, materials based route to hydrogen storage and has even demonstrated densities greater than bulk solid hydrogen within highly microporous materials[2]. Many material properties determine the hydrogen storage performance, for instance, surface area, pore diameter and chemical functionalisation. Doping of porous materials with various heteroatoms can thus result in enhanced hydrogen sorption properties. For example, in some cases, empirical studies show sulfur or sulfur-containing groups can increase the total uptake and density of hydrogen[3, 4], while computational studies on sulfur-doped carbon nanotubes (CNTs) have predicted improved binding strength[5].<br/>Sulfur encapsulated within the narrow channels of carbon nanotubes (S@CNTs) represents a novel composite material hitherto unexplored for hydrogen storage. Interactions between sulfur and CNTs modulate the electronic properties of the composite, thus offering potential new avenues for improving hydrogen sorption in CNTs, towards achieving greater densities and increased binding strength. Here we will synthesise confined S@CNT composites and explore their potential application for hydrogen storage. Raman spectroscopy and N₂ sorption assays will prove the successful synthesis of the composite and characterise the surface area and porosity of the material. Furthermore, the performance of the composite material will be evaluated through semi-empirical modelling of high-pressure hydrogen sorption isotherms to gain estimations of hydrogen density, enthalpy of adsorption and total uptake.<br/><br/>1. IEA: Net Zero by 2050: A Roadmap for the Global Energy Sector. https://www.iea.org/reports/net-zero-by-2050 (2021). Accessed 27/10/2021 2021.<br/>2. Ting VP, Ramirez-Cuesta AJ, Bimbo N, Sharpe JE, Noguera-Diaz A, Presser V, et al. Direct evidence for solid-like hydrogen in a nanoporous carbon hydrogen storage material at supercritical temperatures. ACS nano. 2015;9(8):8249-54.<br/>3. Li D, Li W, Shi J, Xin F. Influence of doping nitrogen, sulfur, and phosphorus on activated carbons for gas adsorption of H 2, CH 4 and CO 2. RSC Advances. 2016;6(55):50138-43.<br/>4. Paraknowitsch JP, Thomas A. Doping carbons beyond nitrogen: an overview of advanced heteroatom doped carbons with boron, sulphur and phosphorus for energy applications. Energy & Environmental Science. 2013;6(10):2839-55.<br/>5. Mousavipour S, Chitsazi R. A theoretical study on the effect of intercalating sulfur atom and doping boron atom on the adsorption of hydrogen molecule on (10, 0) single-walled carbon nanotubes. Journal of the Iranian Chemical Society. 2010;7(2):S92-S102.