(579d) Pushing the Limit of Å-Scale Nanopore Engineering for Carbon Capture from Graphene Membrane

Energy and cost-efficient carbon capture is a highly urgent need in the current context due to the concerns of deteriorating global warming. An attractive CO₂/N₂ separation performance is needed to lower down the added penalty for carbon capture. The commercial thermally-driven capture technology from flue gas i.e., amine-based absorption, is limited by a high penalty, 48 - 111 $/ton CO₂^[1]. In this context, high-performance membranes, operating on the basis of chemical potential gradient, can be a good alternative especially when the flue gas more than 10% CO₂. Among the membranes, single-layer graphene is an ideal candidate, attributing to its atomic-thickness and short CO₂ transport pathway. Our recent techno-economic analysis showed that SLG (N-SLG) membranes with CO₂ permeance of 10000 gas permeation units (GPU, 1 GPU = 3.35 10^-10 mol m^-2 s^-1 Pa^-1) and CO₂/N₂ selectivity of 30 could cut down the capture penalty from flue gas with 14% CO₂ to 31.8 $/tonCO₂^[2].

Etching high density CO₂-sieving pores in the impermeable graphene lattice remains a challenge^[3], attributed to the competition between pore nucleation and expansion. Generally increasing the etching time to increase the pore density also leads to unwanted pore expansion, deteriorating the CO₂/N₂ selectivity. Unlike O₂ plasma^[4] and physical etching such as energetic ion or electron bombardment^[5], O₃ gasification has been shown to be quite effective in limiting pore expansion at a high pore density^[2]. We recently achieved CO₂ permeance of 2620 GPU and CO₂/N₂ selectivity of 27.6 by millisecond etching of graphene in an O₃ atmosphere.

In this presentation, I will introduce several new concepts for incorporating a high density CO₂-sieving pores in graphene, and will discuss nucleation-decoupled nanopore expansion regime (Figure 1A)^[6].I will discuss a novel multi-pulse millisecond route where pore expansion is limited by the availability of O₃ (Figure 1B). This method yielded CO₂ permeance of 4400 ± 2070 GPU and CO₂/N₂ selectivity of 33.4 ± 7.9, where the highest CO₂/N₂ separation factor was close to 40. In the nucleation-decoupled nanopore expansion regime, a low-concentration ozone supply is consumed by existing pores and fresh nucleation is avoided.

Next, I will discuss the functionalization of graphene nanopores with CO₂-philic polymers to enhance CO₂ adsorption over less absorbing gases such as N₂ and CH₄. Briefly, a ~10 nm thin polymeric layer was grafted on graphene lattice via the ring-opening chemistry between epoxy groups and amine groups^[7]. This led to high permeance membranes where the CO₂/N₂ selectivity was improved compared to over previous report, thanks to a much narrower pore-size-distribution compared to that yielded by the O₂ plasma. CO₂ permeance of 8730 GPU and CO₂/N₂ separation factor of 33.4 could be obtained from this strategy. Finally, we demonstrate that this approach to fabricate centimeter-scale membranes.

[1] E. S. Rubin, J. E. Davison, H. J. Herzog, Int. J. Greenh. Gas Control 2015.

[2] S. Huang, S. Li, L. F. Villalobos, M. Dakhchoune, M. Micari, D. J. Babu, M. T. Vahdat, M. Mensi, E. Oveisi, K. V. Agrawal, Sci. Adv. 2021, 7, eabf0116.

[3] L. Wang, M. S. H. Boutilier, P. R. Kidambi, D. Jang, N. G. Hadjiconstantinou, R. Karnik, Nat. Nanotechnol. 2017, 12, 509.

[4] J. Zhao, G. He, S. Huang, L. F. Villalobos, M. Dakhchoune, H. Bassas, K. V Agrawal, Sci. Adv. 2019, 5, eaav1851.

[5] K. Celebi, J. Buchheim, R. M. Wyss, A. Droudian, P. Gasser, I. Shorubalko, J.-I. Kye, C. Lee, H. G. Park, Science 2014, 344, 289.

[6] K.-J. Hsu, L. F. Villalobos, S. Huang, H.-Y. Chi, M. Dakhchoune, W.-C. Lee, G. He, M. Mensi, K.V. Agrawal, submitted.

[7] G. He, S. Huang, L. F. Villalobos, J. Zhao, M. Mensi, E. Oveisi, M. Rezaei, K. V. Agrawal, Energy Environ. Sci. 2019, 12, 3305.