Design of hyperporous graphene networks and their application in solid-amine based carbon capture systems

Abstract

We demonstrate a simple and fully scalable method for obtaining hierarchical hyperporous graphene networks of ultrahigh total pore volume by thermal-shock exfoliation of graphene-oxide (exfGO) at a relatively mild temperature of 300 C. Such pore volume per unit mass has not previously been achieved in any type of porous solid. We find that the amount of oxidation of starting graphene-oxide is the key factor that determines the pore volume and surface area of the final material after thermal shock. Specifically, we emphasize that the development of the hyperporosity is directly proportional to the enhanced oxidation of sp 2 C]C to form C]O/COO. Using our method, we reproducibly synthesized remarkable meso-/macroporous graphene networks with exceptionally high total pore volumes, exceeding 6 cm 3 g À1. This is a step change compared to #3 cm 3 g À1 in conventional GO under similar synthetic conditions.Moreover, a record high amine impregnation of >6 g g À1 is readily attained in exfGO samples (solid-amine@exfGO), where amine loading is directly controlled by the pore-structure and volume of the host materials. Such solid-amine@exfGO samples exhibit an ultrahigh selective flue-gas CO 2 capture of 30-40 wt% at 75 C with a working capacity of z25 wt% and a very long cycling stability under simulated flue-gas stream conditions. To the best of our knowledge, this is the first report where a graphene-oxide based hyperporous carbon network is used to host amines for carbon capture application with exceptionally high storage capacity and stability.The widespread implementation of clean energy technologies, such as CCS (carbon capture and sequestration), fuel cells, batteries, supercapacitors, water electrolysers, and/or molecular storage and transport, is critical to tackle climate change and energy security issues. [1][2][3][4][5] In this regard, nanoporous carbons, metal-organic frameworks (MOFs), polymers and zeolites have gained tremendous attention as storage, transport and conversion media.2-7 Considerable performance improvements have been achieved by synthesizing and manipulating their functional features and porous structures.6 In the case of CO 2 capture, obtaining high enough CO 2 uptake capacities by using sorbent based materials under ue-gas conditions is still a challenging task. Many sorbent materials show good CO 2 uptake capacities but only at 0 C or 25 C and for 100% dry CO 2 .Porous sorbents including zeolites, activated carbons and MOFs do not show desirable selective CO 2 uptake under humid conditions and/or at >50 C. 8 This is a major setback for the implementation of CCS. The recent efforts on the introduction of CO 2 -philic amine groups into nanoporous structures have led to a large enhancement in selective carbon (CO 2 ) capture and effluent ue-gas tolerance. 4,7,8 However, the practical feasibility of these materials for CO 2 capture is compromised by the lack of a simple and large-scale synthesis method. Substantial improvements in both the structural stability and scalable synthesis of these...

Superior Multifunctional Activity of Nanoporous Carbons with Widely Tunable Porosity: Enhanced Storage Capacities for Carbon‐Dioxide, Hydrogen, Water, and Electric Charge

“…These fascinating and versatile characteristics make carbons of special interest compared to other porous solids such as zeolites, metal‐organic frameworks (MOFs) or coordinated/cross‐linked polymers (CPs), and other layered materials. Therefore, these materials are being actively and continuously explored and numerous synthesis routes are proposed . For example, the templates of presynthesized molecular architectures of mesoporous silica, CPs, MOFs, and zeolites are often used to achieve control over porosities.…”

Design of 3D Graphene‐Oxide Spheres and Their Derived Hierarchical Porous Structures for High Performance Supercapacitors

“…[34,59] Briefly, graphite powder (1 g) was added to 9:1 mixture of concentrated H 2 SO 4 and H 3 PO 4 Small 2017, 13, 1702474 small NANO(22.5 mL:2.5 mL) under vigorous stirring at 0 °C. KMnO 4 (6 g) was then slowly added to the mixture under persistent stirring at a temperature below 5 °C.…”

“…[27][28][29][30] Direct solid-state exfoliation by microwave and thermal shock has also been applied. [31][32][33][34][35] Typical gravimetric capacitance (≈250 F g −1 ) of such structures is still less than the theoretical value of 550 F g −1 due to the strong overlapping/aggregation of graphene layers via π-π aromatic interactions, thus leading to reduced accessibility of the interlayer spacing. [36][37][38][39] Considerable efforts have been devoted to minimize the aggregation.…”

“…Thermal-shock is an ideal reduction strategy as GO decomposition is associated with large exothermic heat release, which in combination largely enhances the sudden volatility of the surface oxygen groups to create a substantial level of internal pressure, further props-up the GO sheets. [34] Therefore, the thermal-shock of GOS, conducted at 400 °C (in a preheated furnace) for less than 5 min, eventually produced a highly hierarchical porous graphene networks with a further enhanced degree of reduction (Figure 3 (Figure 3a,b). The C/O ratio is increased to ≈6.5 in HPG compared to ≈5.2 in srGOS, with respective oxygen content of ≈13.0 and ≈16.0 at%.…”

“…[1] Those are ideal for fast energy storage and delivery, e.g., for smart power grids and hybrid electric vehicles. [2] However, their energy density (3-5 Wh kg −1 ) is relatively low, compared with the traditional batteries (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35) Wh kg −1 ). In order to boost their performance, efforts have been devoted to increase the specific capacitance of the electrode material, both in terms of the power and the energy densities.…”