Periodic Reporting for period 3 - UltimateMembranes (Energy-efficient membranes for carbon capture by crystal engineering of two-dimensional nanoporous materials)
Période du rapport: 2022-06-01 au 2023-11-30
The EU integrated strategic energy technology plan, SET-plan, in its 2016 progress report, has called for urgent measures on the carbon capture and storage (CCS). There are only 3 commercial (0.5-1 million tonnes CO2/year) CCS projects in Europe, all commissioned in offshore Norway for natural gas sweetening. Currently, the amine-based CO2 scrubbing is employed to capture CO2, leading to a high energy penalty (2.5–4.0 MJ/kg of captured CO2)2 attributing to thermal regeneration of the saturated amine stream. Moreover, the scrubbing technology suffers from the oxidative degradation of amines, and is not environmentally friendly due to loss of amines during the regeneration step. In comparison, the use of a high-performance membranes, defined as chemically and thermally stable films yielding a high gas permeance and selectivity, is environmentally friendly (no chemical is used, no waste is generated) and energy-efficient, and can reduce the energy-penalty for the carbon capture to less than 2 MJ/kg of CO2. Moreover, upon optimization, membranes modules can be installed in a decentralized fashion to a broad-range of emission sources (e.g. biogas plants, waste incinerators, residential and commercial heating, etc.).
This project seeks to develop the ultimate high-performance membranes for H2/CO2 (pre-combustion capture), CO2/N2 (post-combustion capture), and CO2/CH4 separations (natural gas sweetening). Based on calculations, these membranes will yield a gigantic gas permeance (1 and 0.1 million GPU for the H2 and the CO2 selective membranes, respectively), 1000 and 10-fold higher than that of the state-of-the-art polymeric and nanoporous membranes, respectively, reducing capital expenditure per unit performance and the needed membrane area. For this, we introduce three novel concepts, combining the top-down and the bottom-up crystal engineering approaches to develop size-selective, chemically and thermally stable, nanoporous two-dimensional membranes. First, exfoliated nanoporous 2d nanosheets will be stitched in-plane to synthesize the truly-2d membranes. Second, metal-organic frameworks will be confined across a nanoporous 2d matrix to prepare a composite 2d membrane. Third, atom-thick graphene films with tunable, uniform and size-selective nanopores will be crystallized using a novel thermodynamic equilibrium between the lattice growth and etching. Overall, the innovative concepts developed here will open up several frontiers on the synthesis of high-performance membranes for a wide-range of separation processes.
This project seeks to develop the ultimate high-performance membranes for H2/CO2 (pre-combustion capture), CO2/N2 (post-combustion capture), and CO2/CH4 separations (natural gas sweetening). Based on calculations, these membranes will yield a gigantic gas permeance (1 and 0.1 million GPU for the H2 and the CO2 selective membranes, respectively), 1000 and 10-fold higher than that of the state-of-the-art polymeric and nanoporous membranes, respectively, reducing capital expenditure per unit performance and the needed membrane area. For this, we introduce three novel concepts, combining the top-down and the bottom-up crystal engineering approaches to develop size-selective, chemically and thermally stable, nanoporous two-dimensional membranes. First, exfoliated nanoporous 2d nanosheets will be stitched in-plane to synthesize the truly-2d membranes. Second, metal-organic frameworks will be confined across a nanoporous 2d matrix to prepare a composite 2d membrane. Third, atom-thick graphene films with tunable, uniform and size-selective nanopores will be crystallized using a novel thermodynamic equilibrium between the lattice growth and etching. Overall, the innovative concepts developed here will open up several frontiers on the synthesis of high-performance membranes for a wide-range of separation processes.
We have obtained significant progress in three work packages of this project. The main results are discussed based on the objectives set out in each work package.
WP1 objective: To stitch exfoliated nanoporous 2d nanosheets in-plane to synthesize the truly-2d membranes.
Results: A major task here was to stitch 2d nanosheets with graphene at low temperatures. This required graphene synthesis at a lower temperature (typically 1000 ºC) mainly because 2d nanosheets are not stable at 1000 ºC. We have now achieved this by developing a crystallization protocol at 500 ºC on a Ni foil catalyst which promotes growth due to higher carbon solubility in the Ni matrix.
WP2 objective: confine metal-organic frameworks across a nanoporous 2d matrix to prepare a composite 2d membrane.
Results: We have been extremely successful in our project goal resulting in the synthesis of first two-dimensional metal-organic framework films with thickness down to 1 unit-cell. We have been able to synthesize such a film over a length scale of several centimeters at room temperature. Given that the film is so thin, we have been able to achieve a record-high H2/N2 and H2/CH4 separation performance. A manuscript on this subject is being prepared.
WP2/WP3 objectives: Understanding the formation of nanopores in graphene by Scanning Tunneling microscopy
Results: We are pleased to report that we have made several achievements in this regards: (i) we have decoded the formation mechanism of graphene nanopores by oxidation; (ii) we have develop methodologies to measure pore-size-distribution in graphene/graphite surfaces directly by STM which when combined with transmission electron microscopy studies is helping us to make robust conclusions on effect of etching parameters on the pore density, the pore-size-distribution, and more importantly pore functionalization; (iii) insights into pore generation mechanism has allowed us to engineer new methods to significantly improve the porosity generation in graphene in a reproducible and scalable manner.
WP3 objective: Understanding of etching kinetics of graphene with CO2 with and without the presence of CH4 to control the pore-size-distribution in graphene.
Result: We have now finished a systematic study on etching of graphene with CO2 where we have confirmed the theoretical finding that CO2 does not nucleate pores on the basal plane of graphene. We have also extracted the energy barrier for the expansion of graphene edges and demonstrated that nanopores expand much slowly attributing to the steric hinderance in chemisorption of CO2 in the nanopores. A manuscript on this topic is being submitted. We have also completed a study on competitive etching and growth of graphene in presence of both CO2 and CH4. A manuscript on this topic is being prepared.
WP1 objective: To stitch exfoliated nanoporous 2d nanosheets in-plane to synthesize the truly-2d membranes.
Results: A major task here was to stitch 2d nanosheets with graphene at low temperatures. This required graphene synthesis at a lower temperature (typically 1000 ºC) mainly because 2d nanosheets are not stable at 1000 ºC. We have now achieved this by developing a crystallization protocol at 500 ºC on a Ni foil catalyst which promotes growth due to higher carbon solubility in the Ni matrix.
WP2 objective: confine metal-organic frameworks across a nanoporous 2d matrix to prepare a composite 2d membrane.
Results: We have been extremely successful in our project goal resulting in the synthesis of first two-dimensional metal-organic framework films with thickness down to 1 unit-cell. We have been able to synthesize such a film over a length scale of several centimeters at room temperature. Given that the film is so thin, we have been able to achieve a record-high H2/N2 and H2/CH4 separation performance. A manuscript on this subject is being prepared.
WP2/WP3 objectives: Understanding the formation of nanopores in graphene by Scanning Tunneling microscopy
Results: We are pleased to report that we have made several achievements in this regards: (i) we have decoded the formation mechanism of graphene nanopores by oxidation; (ii) we have develop methodologies to measure pore-size-distribution in graphene/graphite surfaces directly by STM which when combined with transmission electron microscopy studies is helping us to make robust conclusions on effect of etching parameters on the pore density, the pore-size-distribution, and more importantly pore functionalization; (iii) insights into pore generation mechanism has allowed us to engineer new methods to significantly improve the porosity generation in graphene in a reproducible and scalable manner.
WP3 objective: Understanding of etching kinetics of graphene with CO2 with and without the presence of CH4 to control the pore-size-distribution in graphene.
Result: We have now finished a systematic study on etching of graphene with CO2 where we have confirmed the theoretical finding that CO2 does not nucleate pores on the basal plane of graphene. We have also extracted the energy barrier for the expansion of graphene edges and demonstrated that nanopores expand much slowly attributing to the steric hinderance in chemisorption of CO2 in the nanopores. A manuscript on this topic is being submitted. We have also completed a study on competitive etching and growth of graphene in presence of both CO2 and CH4. A manuscript on this topic is being prepared.
We have pushed the boundaries of the state-of-the-art in many aspects. These are listed below:
1) Synthesis of nanoporous graphene in one step by bottom-up synthesis at low temperature (500 ºC) in a rapid way which will improve the scalability of graphene membranes
2) Synthesis of first gas-sieving metal-organic frameworks film which is strictly two-dimensional (2 nm in thickness)
3) Post-synthetic adjustment of pore-size-distribution in graphene
1) Synthesis of nanoporous graphene in one step by bottom-up synthesis at low temperature (500 ºC) in a rapid way which will improve the scalability of graphene membranes
2) Synthesis of first gas-sieving metal-organic frameworks film which is strictly two-dimensional (2 nm in thickness)
3) Post-synthetic adjustment of pore-size-distribution in graphene