In-plane Nanopores Research Articles

Ultrahigh Performance of Novel Capacitive Deionization Electrodes based on A Three-Dimensional Graphene Architecture with Nanopores.

In order to achieve optimal desalination during capacitive deionization (CDI), CDI electrodes should possess high electrical conductivity, large surface area, good wettability to water, narrow pore size distribution and efficient pathways for ion and electron transportation. In this work, we fabricated a novel CDI electrode based on a three-dimensional graphene (3DG) architecture by constructing interconnected graphene sheets with in-plane nanopores (NP-3DG). As compared to 3DG, NP-3DG features a larger specific surface area of 445 m2 g−1 and therefore the higher specific capacitance. The ultrahigh electrosorptive capacity of NP-3DG predicted from Langmuir isotherm is 17.1 mg g−1 at a cell potential of 1.6 V. This can be attributed to the interconnected macropores within the graphene networks and nanopores on graphene sheets. Both of macropores and nanopores are favorable for enhancing CDI peroformance by buffering ions to reduce the diffusion distances from the external electrolyte to the interior surfaces and enlarging the surface area.

Extraordinarily high-rate capability of polyaniline nanorod arrays on graphene nanomesh

We report the high-rate capacitive performance of polyaniline (PANI) coated on graphene nanomesh (GNM). The PANI on GNM sheets shows vertical nanorod arrays that offer large electrochemically active surface area and numerous ion-accessible gaps. Benefiting from the highly pseudocapacitive PANI and ion-penetrable GNM, GNM-PANI with 70 wt% PANI exhibits a specific capacitance of 452 F g−1 at 1.0 A g−1, which remains at 404 F g−1 even at high discharge rate of 50 A g−1 in 1.0 M H2SO4. More importantly, a symmetric capacitor built with this electrode exhibits a relaxation time constant of 2.61 s, a value comparable to 2–5 s with activated carbon as electrode, and much shorter than 4–6 s of capacitors with chemically converted graphene as electrodes. The performance of GNM-PANI electrode reported herein is far superior to that of most other PANI-based electrodes, demonstrating that GNM is a promising scaffold that can help to realize the full potential of PANI due to its abundant in-plane nanopores.

Formation process of holey graphene and its assembled binder-free film electrode with high volumetric capacitance

Holey graphene with abundant in-plane nanopores is achieved through a mild defect-etching reaction between graphene oxide (GO) and hydrogen peroxide (H2O2) then followed by a reduction process in hydrazine solution. The porosity of the obtained holey graphene is systematically investigated by optimizing the reaction conditions between GO and H2O2. The optimum reaction conditions are that GO is hydrothermally treated in 0.4mL H2O2 at 100°C for 10h and the as-prepared holey graphene oxide (HGO) is refluxed in hydrazine solution at 100°C for 1h, by which holey reduced graphene oxide (HRGO) suspension with good dispersity is obtained. By vacuum filtration of the HRGO suspension, the binder-free porous graphene film electrodes are successfully assembled. The obtained film electrodes exhibit high specific capacitance (251Fg−1 at a current density of 1Ag−1), high volumetric capacitance (up to 216Fcm−3), and enhanced rate capability (73% capacitance retention from 1–60Ag−1) due to their high packing density (0.86gcm−3). The suitable porosity of the assembled porous graphene film keeps a balance between electrolyte ion diffusion rate and conductivity, which can bridge the gap between gravimetric capacitance and volumetric capacitance for the obtained electrode material.

Solution Processable Holey Graphene Oxide and Its Derived Macrostructures for High-Performance Supercapacitors.

Scalable preparation of solution processable graphene and its bulk materials with high specific surface areas and designed porosities is essential for many practical applications. Herein, we report a scalable approach to produce aqueous dispersions of holey graphene oxide with abundant in-plane nanopores via a convenient mild defect-etching reaction and demonstrate that the holey graphene oxide can function as a versatile building block for the assembly of macrostructures including holey graphene hydrogels with a three-dimensional hierarchical porosity and holey graphene papers with a compact but porous layered structure. These holey graphene macrostructures exhibit significantly improved specific surface area and ion diffusion rate compared to the nonholey counterparts and can be directly used as binder-free supercapacitor electrodes with ultrahigh specific capacitances of 283 F/g and 234 F/cm(3), excellent rate capabilities, and superior cycling stabilities. Our study defines a scalable pathway to solution processable holey graphene materials and will greatly impact the applications of graphene in diverse technological areas.

Activation of graphene aerogel with phosphoric acid for enhanced electrocapacitive performance

We present a facile and efficient route to introduce in-plane nanopores on the graphene sheets by activation of graphene aerogel (GA) with phosphoric acid (H3PO4). Results from N2 adsorption and TEM images showed that H3PO4 activation created mesopores with pore size of 2–8nm on the graphene sheets. With such nanopores on graphene sheets, the activated GA exhibits a specific capacitance of 204Fg−1, enhanced rate capability (69% capacitance retention from 0.2 to 30Ag−1), reduced equivalent series resistance (3.8mΩ) and shortened time constant (0.73s) when comparing with the hydrothermally-derived pristine GA and thermally annealed GA in the absent of H3PO4. The excellent capacitive properties demonstrate that introduction of nanopores on GA by H3PO4 activation not only provides large ion-accessible surface area for efficient charge storage, but also promotes the kinetics of electrolyte across the graphene two-dimensional planes.