Researchers from South-Korea's Pohang University of Science and Technology (POSTECH), Kumoh National Institute of Technology, Sungkyunkwan University, Yeungnam University, Konkuk University and University of Seoul have proposed a simple strategy for the fabrication of mesoporous graphene with applications in high-performance energy storage systems like electric double-layer supercapacitors (EDLCs).
Conventional energy storage systems made of activated carbons (ACs) tend to have a poor power density due to the insufficient specific contact area, leading to inadequate creation of an electric double layer between electrode material and electrolyte. Therefore, an active material with a high specific contact area could help obtain high energy densities and meet the needs of various energy storage systems. Graphene's remarkable electrical conductance naturally makes it a logical candidate, but the high van der Waals contact between the graphene sheets makes stacking unavoidable, producing a limited available surface area.
This inherent graphene disadvantage can be overcome by adding a three-dimensional (3D) porous microstructure, which increases the available surface area while retaining beneficial electrical properties. The resulting material, known as mesoporous graphene, combines the benefits of graphene, ultrathin 2D morphology, and mesoporous structures, significantly improving the power and energy densities of energy storage devices such as electric double-layer capacitors (EDLCs).
Several research groups have attempted synthesizing 3D mesoporous graphene using a catalytic template-assisted technique. However, due to a volatile catalytic template, the pore diameter and contact area were rather high. Therefore, developing an efficient technique for synthesizing 3D mesoporous graphene with a high contact area for high-energy-density EDLCs remains a major challenge.
In their recent work, the research team created 3D mesoporous graphene by employing block copolymers (BCPs) to construct the mesostructured active template and the carbon resource. An amphiphilic poly(styrene)-block-poly (2-vinyl pyridine) copolymer (PS-b-P2VP) was swelled in heated ethanol and then dehydrated to create a mesostructured template.
Electroless plating produced the reactive template by selectively depositing a nickel precursor as a graphene catalyst on the P2VP layer.
Interestingly, the highly porous architecture of mesoporous graphene was successfully preserved during catalytic decomposition even at high temperatures since the mechanical resilience of the PS-b-P2VP composite is adequate to act as rigid reinforcement and inhibit nickel catalyst aggregation.
The surface of as-prepared mesoporous graphene was studied using cutting-edge techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The Barrett-Joyner-Halenda (BJH) technique was used to compute the pore size distribution in mesoporous graphene particles from the adsorption and desorption branches.
The team reported that the mesostructured templates properly sustained their architectures without structural failure in high-temperature catalytic decomposition, allowing the synthesis of mesoporous graphene with a pore diameter of 3.5 nanometers. The as-prepared mesoporous graphene had a bi-continuous shape, with graphene assembling into 3D mesopores with a large contact area.
The large specific contact area and small pore diameter allowed a considerable number of electrolytes to enter mesoporous graphene. Moreover, the electrically conducting pathways in the mesoporous graphene sheets resulted in highly efficient interfacial electron transfer.
When mesoporous graphene and ionic fluids were utilized as electrode material and electrolytes, the resultant EDLC demonstrated high-voltage performance and remarkable energy storage efficiency, including high specific capacitance, high power density, and good cyclic stability.
These findings suggest that mesoporous graphene could be a promising carbon material for fabricating high-performance electrolytic energy storage systems.