Abstract
The exploration and evaluation of new composites possessing both processability and enhanced hydrogen storage capacity are of significant interest for onboard hydrogen storage systems and fuel cell based electric vehicle development. Here we demonstrate the fabrication of composite membranes with sufficient mechanical properties for enhanced hydrogen storage that are based on a polymer of intrinsic microporosity (PIM-1) matrix containing nano-sized fillers: activated carbon (AX21) or metal–organic framework (MIL-101). This is one of the first comparative studies of different composite systems for hydrogen storage and, in addition, the first detailed evaluation of the diffusion kinetics of hydrogen in polymer-based nanoporous composites. The composite films were characterised by surface area and porosity analysis, hydrogen adsorption measurements, mechanical testing and gas adsorption modelling. The PIM-1/AX21 composite with 60 wt% AX21 provides enhanced hydrogen adsorption kinetics and a total hydrogen storage capacity of up to 9.35 wt% at 77 K; this is superior to the US Department of Energy hydrogen storage target. Tensile testing indicates that the ultimate stress and strain of PIM-1/AX21 are higher than those of the MIL-101 or PAF-1 containing composites, and are sufficient for use in hydrogen storage tanks. The data presented provides new insights into both the design and characterisation methods of polymer-based composite membranes. Our nanoporous polymer-based composites offer advantages over powders in terms of safety, handling and practical manufacturing, with potential for hydrogen storage applications either as means of increasing storage or decreasing operating pressures in high-pressure hydrogen storage tanks.
Highlights
Concerns over diminishing and dispersing resources and the environmental impact of burning fossil fuels have driven attention to the development of alternative and sustainable energy sources and to the management of intermittent renewable energies
The PIM-1 sample used for the fabrication of composite films with AX21 and MIL-101 was determined to have a BET surface area of 724 m2 g−1 from N 2 adsorption at 77 K
This was in good agreement with prior literature values (Budd et al 2004), but slightly lower than the surface area of the PIM-1 that was used for PIM-1/PAF-1 composite films (Rochat et al 2017; Polak-Kraśna et al 2017)
Summary
Concerns over diminishing and dispersing resources and the environmental impact of burning fossil fuels have driven attention to the development of alternative and sustainable energy sources and to the management of intermittent renewable energies. To form efficient composite films with enhanced porosity, storage performance and mechanical properties for use in storage tanks, it is essential to identify suitable high surface area, divided nanoporous fillers that are compatible with the polymer matrix. Based on the density and porosity of the composites, we identify the critical volume percentage of nanoporous filler of the PIM-1 based composites, which we define as the point at which a composite fails to form a self-standing film This critical volume can be used to determine the limitations of polymer-based composites and their functions; for example, as a coherent liner in a high-pressure hydrogen storage tank (Rochat et al 2017). This study provides a new design strategy for the selection and analysis of nanoporous fillers in polymer matrices using a broad range of characterisation techniques, including mechanical testing, high-pressure gas adsorption and kinetics investigations
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