A Simple Strategy for Constructing Hierarchical Composite Electrodes of PPy‐Posttreated 3D‐Printed Carbon Aerogel with Ultrahigh Areal Capacitance over 8000 mF cm^–2

Abstract

the specific capacitances of supercapacitor electrodes measured by area or volume are the primary consideration for electrochemical energy storage within miniaturized footprint area. [11][12][13] Besides, for supercapacitor electrodes, the design of more doses of active materials means that there exists plenty of active sites available for reversible redox reactions. [14] As a result, it seems desirable to configure a supercapacitor electrode with a high mass loading (per unit area or volume) of active materials, such as a relatively dense distribution or a large thickness. However, such designs usually tend to cause the sluggish electron/ion diffusion, as well as the insufficient use of active materials, which instead limits the overall performance of supercapacitors. [15,16] Carbon aerogel (CA) is a type of hierarchically porous material ranging from micropores to macropores, which exhibits excellent application prospects in catalysis, adsorption, sensing, water evaporation, bone regeneration, electromagnetic shielding, and energy storage. [17][18][19][20][21][22][23][24] Especially, because of the excellent properties such as abundant porosity, ultrahigh specific surface area, good electrical conductivity, excellent infiltration, and good mass transfer ability, CA is considered as a promising electrode material in supercapacitors. [13,[25][26][27] Over the past few years, many efforts have been focused on modifying the pore size distribution of CA to further improve specific capacitance. The abundant micropores and small mesopores for CA are beneficial to the increase of specific capacitance due to a significant increase in specific surface area and active sites. [28] Interestingly, larger mesopores (20-50 nm) are detrimental to the specific capacitance due to the barrier effect for ion diffusion. [29,30] The precise control of sol-gel process was usually used to avoid these larger mesopores. [31] In addition, macropores, as well as micrometer-level or even sub-millimeter-level channels are also conducive to the improvement of specific capacitance, because of the unimpeded channels for electrolyte entry and replacement. [25,28,[32][33][34][35] However, excessive larger channels are unfavorable for their mechanical properties and loading amount of active materials. [16,23] Therefore, the hierarchical pores ranging from nanometer to sub-millimeter scale other than larger mesopores A well-designed pore structure and optimized interface will improve specific capacitances of carbon-based supercapacitor electrodes significantly. Herein, a simple strategy is used to prepare the hierarchically porous 3D-printed carbon aerogel (CA) electrodes via combining direct ink writing, freezing drying, carbonization, and polypyrrole (PPy) posttreatment. The 3D-printed CA electrodes without PPy present a quasi-proportional increase in areal capacitance as thickness, achieving an extremely high areal capacitance of 6875 mF cm -2 under a thickness of 2.2 mm. Additionally, PPy posttreated 3D-printed CA (PPy@CA) electrode has improve...

A Facile and Versatile Post-Treatment Method to Efficiently Functionalize 3D-Printed Carbon Aerogels via Introducing Tailored Metal Elements

“…Empirically, we first evaluated the electrochemical performance of electrodes at a potential window of (−1.0–0) V . The cyclic voltammetry (CV) curves (Figures S9 and S10) of CA@Co electrodes at various scan rates exhibited profiles similar to those of the pure 3D-printed CA electrode Figures a and S10a presented the galvanostatic charge–discharge (GCD) curves of CA@Co electrodes at various current densities, displaying almost symmetrical triangular profiles.…”

“…Three-dimensional (3D) printing of aerogels combines the hierarchically nanoporous microstructure of aerogels and the well-designed macroscopic structure, attracting more and more interest from fundamental science and application engineering. Especially, carbon aerogels (CAs) have been extensively used in direct ink writing (DIW)-based 3D printing due to their specific electrical, electrochemical, and photothermal properties. , So far, 3D-printed CAs by using the DIW technique have demonstrated great promise in the development of high-capacitance supercapacitor electrodes, highly efficient solar evaporators, extremely stretchy strain sensors, and rapidly responsive shape memory devices . Normally, their fabrication process mainly involves four steps: ink preparation (transformation from raw material to a viscoelastic shear-thinning ink), printing (microneedles stack the ink layer by layer in the form of microfilaments), drying (freeze or supercritical drying), and carbonization (organic to inorganic conversion, depending on the ink formulation).…”

“…Very recently, we discovered that the well-designed hierarchically porous 3D-printed CAs can be created by precisely regulating rheology of conventional resorcinol-formaldehyde-based ink, along with DIW technology, freezing or supercritical drying, and carbonization. , The thus-resulted pure 3D-printed CAs have exhibited high performance for potential applications in electrochemical energy storage and solar steam generation. Moreover, the hierarchically porous nature allows a solution containing the customized ingredients to easily infiltrate the interior framework of 3D-printed CAs.…”

“…These impressive results may be attributed to two aspects: (i) the well-established great benefits of hierarchically porous electrode materials in energy storage applications and (ii) the pseudocapacitance and good dispersion of the specially designed functional targets ( i.e. , cobalt oxides). ,− This work effectively functionalizes 3D-printed CAs, compensating for the inadequacy of directly preparing inks to complete 3D-printed CAs and overcoming the limitation of the type of ink used for 3D-printed CAs from a distinctive standpoint.…”

“…Figures a and S10a presented the galvanostatic charge–discharge (GCD) curves of CA@Co electrodes at various current densities, displaying almost symmetrical triangular profiles. The EIS result (Figure S11a) showed that the increase in the deposition concentration was beneficial to reduce the equivalent series resistance but greater than that of the 3D-printed CA electrode . According to the GCD results, only the areal capacitances of the 0.2 M CA@Co electrode and 3D-printed CA (abbreviated as CA) electrode were virtually identical at all same current densities tested, but the electrodes with other deposition concentrations showed decreased areal capacitances, particularly the areal capacitances of the 0.1 M CA@Co electrode (Figure S11b).…”