High Areal Specific Capacitance Research Articles

3D Printed Ordered Hierarchically‐Porous Electrodes for Developing High‐Performance Quasi‐Solid‐State Aqueous Nickel‐Iron Batteries

AbstractStructural engineering offers a viable and broadly applicable approach for further enhancing the energy density of aqueous nickel‐iron (Ni‐Fe) batteries without changing the fundamental battery chemistries. Herein, the synthesis of 3D printed low‐tortuosity and ultra‐thick ordered hierarchically porous reduced graphene oxide (rGO)‐based microlattice electrodes for high‐performance aqueous Ni‐Fe batteries through direct writing (DIW) 3D printing technology is presented. Significantly, the areal specific capacitance of the 3D printed electrodes scales positively with electrode thickness, whereas the gravimetric capacitance remains relatively constant, indicating that the capacitive performance is not constrained by ion diffusion and exhibits rapid kinetic behavior, even at elevated mass‐loading levels and in the context of ultra‐thick electrodes. Based on a 3 m KOH aqueous electrolyte, the 3D printed aqueous Ni‐Fe cell (thickness: ≈2 mm) exhibits high areal specific capacity (≈0.353 mAh cm−2), high volumetric energy/power density (≈1.15 mWh cm−2 at 48.00 mW cm−2), and excellent long‐term cycling performance (≈81.25% capacitance retained after 5000 cycles). As a micro‐battery device, 3D printed quasi‐solid‐state Ni‐Fe battery (3DP QSS Ni‐Fe) device with 4 mm thickness still exhibits a high areal capacity of 0.525 mAh cm−2, and excellent cycle stability with ≈81.1% capacity retention after 10000 cycles. The promising 3D printed strategy provides a novel avenue for the controllable assembly of higher‐dimensional architectures, thereby paving the way for the advancement of next‐generation materials and devices.

A Nanofibrous Polypyrrole Membrane with an Ultrahigh Areal Specific Capacitance and Improved Energy and Power Densities.

For conductive polymers to be competitive with carbon-based electrode materials, it is critical to increase their surface area and electroactivity. In this work, a thick nanofibrous polypyrrole (PPy) membrane with communicating interfiber spaces was prepared through one-pot interfacial polymerization for the first time. The electrochemical properties and conductivity of the membrane were studied with cyclic voltammetry, electrochemical impedance spectroscopy, and a four-point probe. Its morphology, chemistry, and thermostability were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The areal specific capacitances measured between 0.0 and 0.8 V at 1 mA/cm2 were 19179, 13264, 7238, and 4458 mF/cm2 for the membranes doped with docusate sodium (AOT), camphor-10-sulfonic acid (β) (CSA), Cl-, and poly(sodium 4-styrenesulfonate) (PSS), respectively. The capacity retentions after 1000 cycles were 83, 74, 67, and 61% for the AOT-, CSA-, PSS-, and Cl--doped membranes, respectively. The Coulombic efficiency was above 99% for all of the membranes. They showed energy densities of 1.7, 1.2, 0.7, and 0.4 mWh/cm2 and power densities of 0.61, 0.75, 0.66, and 0.62 mW/cm2 for the AOT-, CSA-, Cl--, and PSS-doped membranes, respectively. The ultrahigh areal specific capacitance of PPy-AOT is due to its nanofibrous structure. A mechanism has been proposed to explain how this structure is formed based on the role of AOT as the surfactant. This nanofibrous PPy membrane is easy to prepare and metal-free and offers a very high areal specific capacitance, making it an excellent candidate to construct electrodes in pseudosupercapacitors.

Multifunctional Wearable Electronic Based on Fabric Modified by PPy/NiCoAl-LDH for Energy Storage, Electromagnetic Interference Shielding, and Photothermal Conversion.

With the rapid advancement of electronic technology, traditional textiles are challenged to keep up with the demands of wearable electronics. It is anticipated that multifunctional textile-based electronics incorporating energy storage, electromagnetic interference (EMI) shielding, and photothermal conversion are expected to alleviate this problem. Herein, a multifunctional cotton fabric with hierarchical array structure (PPy/NiCoAl-LDH/Cotton) is fabricated by the introduction of NiCoAl-layered double hydroxide (NiCoAl-LDH) nanosheet arrays on cotton fibers, followed by polymerization and growth of continuous dense polypyrrole (PPy) conductive layers. The multifunctional cotton fabric shows a high specific areal capacitance of 754.72 mF cm-2 at 5mA cm-2 and maintains a long cycling life (80.95% retention after 1000 cycles). The symmetrical supercapacitor assembled with this fabric achieves an energy density of 20.83µWh cm-2 and a power density of 0.23 mWcm-2. Moreover, the excellent electromagnetic interference shielding (38.83dB), photothermal conversion (70.2 °C at 1000mWcm-2), flexibility and durability are also possess by the multifunctional cotton fabric. Such a multifunctional cotton fabric has great potential for using in new energy, smart electronics, and thermal management applications.

Self-Assembled MXene Supported on Carbonization-Free Wood for a Symmetrical All-Wood Eco-Supercapacitor.

As an emerging two-dimensional (2D) material, MXene has garnered significant interest in advanced energy storage systems, yet the stackable structure, poor mechanical stability, and lack of moldability limit its large-scale applications. To address this challenge, herein, the self-assembly of MXene on carbonization-free wood was obtained to serve as high-performance electrodes for symmetrical all-wood eco-supercapacitors by a steam-driven self-assembly method. This method can be implemented in a low-temperature environment, significantly simplifying traditional high-temperature annealing processes and generating minimal impact on the environment, human health, and resource consumption. The environmentally friendly steam-driven self-assembly strategy can be further extended into various wood-based electrodes, regardless of the types and structures of wood. As a typical platform electrode, the optimized MXene@delignified balsa wood (MDBW) achieves high areal capacitance and specific capacitance values of 2.99 F cm-2 and 580.55 F g-1 at an extensive mass loading of 5.16 mg cm-2, respectively, with almost loss-free capacitance after 10,000 cycles at 50 mA cm-2. In addition, an all-solid-state symmetrical all-wood eco-supercapacitor was further assembled based on MDBW-20 as both positive and negative electrodes to achieve a high energy density of 19.22 μWh cm-2 at a power density of 0.58 mW cm-2. This work provides an effective strategy to optimize wood-based electrodes for the practical application of biomass eco-supercapacitors.

Ultrafast gelation of multifunctional β-cyclodextrin based hydrogel electrolyte for self-healing supercapacitor

The increasing attention towards flexible supercapacitors with self-healing ability can be attributed to their capacity to endure deformation and damage. However, the development of self-healing and adhesive hydrogel electrolytes, which serve as substrate materials for supercapacitors, remains a challenge. This work reports an ultrafast gelation method for fabricating multifunctional PAA-SL-CD hydrogels with ultrahigh stretchability, fast self-healing ability, superior adhesion, and high ionic conductivity (6.15 S/m). These excellent properties can be attributed to the hydrogen bonding between β-CD, the catechol groups and PAA chains, as well as metal-catechol coordination, metal-carboxyl coordination, and the unique truncated cone structure of the β-CD molecule. A flexible supercapacitor, fabricated using PAA-SL-CD hydrogel as electrolyte, demonstrates high areal specific capacitance (950 mF/cm2) and a capacitance retention rate of 76.3 % even after five cutting and healing cycles. With the well-designed adhesion of the hydrogel electrolyte, the device exhibits impressive specific capacitance retention after cyclic bending. Notably, a series supercapacitor retains the ability to power a clock for 28 min.

Electropolymerization of D-A-D type butterfly-shaped monomers based on triphenylamine-thiophene consisting of camphor substituted quinoxaline moiety for efficient electrochromism and supercapacitors

Two new butterfly-shaped monomers TTCQF and TTCQH consisting of camphor-substituted quinoxaline units as π-spacers were designed and synthesized, which were further electrochemical polymerized and deposited on ITO substrates for electrochromic energy storage devices. The present cross-linked polymer thin films PTTCQF and PTTCQH displayed prominent color changes with significant optical contrast in both the visible and near-infrared regions under external electrical stimuli. These two polymers showcased superior electrochromic performance, involving high optical contrast, fast switching speed, and good coloration efficiency. Additionally, both polymers demonstrated a high areal specific capacitance (12 mF/cm2 for PTTCQH and 9.97 mF/cm2 for PTTCQF) at a current density of 0.1 mA/cm2. Electrochromic energy storage devices based on these polymers were fabricated, and not only illuminated an LED bulb but also visually indicated the energy storage state, guaranteed their potential for applications in energy-saving smart windows. This work may provide valuable insights into the development of efficient cross-linked electrochromic energy storage polymers.

Construction and catalysis role of a kinetic promoter based on lithium-insertion technology and proton exchange strategy for lithium-sulfur batteries

The high theoretical energy density and specific capacity of lithium-sulfur (Li-S) batteries have garnered considerable attention in the prospective market. However, ongoing research on Li-S batteries appears to have encountered a bottleneck, with unresolved key technical challenges such as the significant shuttle effect and sluggish reaction kinetics. This investigation explores the catalytic efficacy of three catalysts for Li-S batteries and elucidates the correlation between their structure and catalytic impacts. The results suggest that the combined utilization of lithium-insertion technology and a proton exchange approach for δ-MnO2 can optimize its electronic structure, resulting in an optimal catalyst (H/Li inserted δ-MnO2, denoted as HLM) for the sulfur reduction reaction. The replacement of Mn sites in δ-MnO2 with Li atoms can enhance the structural stability of the catalyst, while the introduction of H atoms between transition metal layers contributes to the satisfactory catalytic performance of HLM. Theoretical calculations demonstrate that the bond length of Li2S4 adsorbed by the HLM molecule is elongated, thereby facilitating the dissociation process of Li2S4 and enhancing the reaction kinetics in Li-S batteries. Consequently, the Li-S battery utilizing HLM as a catalyst achieves a high areal specific capacity of 4.2 mAh cm−2 with a sulfur loading of 4.1 mg cm−2 and a low electrolyte/sulfur (E/S) ratio of 8 μL mg−1. This study introduces a methodology for designing effective catalysts that could significantly advance practical developments in Li-S battery technology.

Research and development of double layer P-doped laser induced graphene thin film electrode for flexible micro-supercapacitor applications

Laser-induced graphene (LIG) has garnered significant attention for its cost-effectiveness and high efficiency in fabricating flexible micro-energy storage devices. In this study, we devised a simple method to fabricate double layer P-doped LIG electrodes through repetitive laser induction technology for high-performance flexible energy storage applications. Instead of utilizing commercial polyimide (PI) thin film, we optimized the formation process of P-doped PI thin film and achieved a highly flexible double layer P-doped LIG thin film electrode with a uniformly porous structure and the high porosity through repeated laser induction processes. Experimental results demonstrated that the developed double layer P-doped LIG thin film electrode exhibits high porosity, high specific areal capacitance of 180 mF cm−2, and high energy density of 0.025 mWh cm−2. Furthermore, an all-solid-state micro-supercapacitor utilizing hydrogel electrolyte was assembled, demonstrating a high areal capacitance of 62 mF cm−2 and excellent cycling stability with 95% capacitance retention after 6000 charging/discharging cycles. Moreover, the developed all-solid-state micro-supercapacitor successfully powered a light-emitting diode, showcasing its significant potential for practical energy storage applications.

Enhancing sp3 content in diamond-like carbon thin film electrodes by pulsed laser annealing for durable charge storage performance

In this work, diamond-like carbon (DLC) thin film electrodes were grown on Si substrate by pulsed laser deposition (PLD) technique, and the implication of pulsed laser annealing (PLA) treatment on their electrochemical supercapacitor performance was examined by three electrode systems in 1 M Na2SO4 electrolyte solutions. The SEM micrographs exhibit a sheet-like wrinkled surface of DLC film on Si which later transformed into tiny hierarchical heap-like structures with enhanced surface roughness. The Raman spectra confirm signature of the D and G peaks of pristine DLC film at ∼1352 cm−1 (1356 cm−1 after PLA) and 1591 cm−1 (1589 cm−1 after PLA), and appearance of minor T2g (diamond) (1332 cm−1) peaks with an increment of the sp3 content after PLA treatment. The X-ray photoelectron spectroscopy (XPS) spectra were deconvoluted into three different contributions CC (sp2), CC (sp3), and CO, and their sp3 percentages were estimated ∼48.9 %, and 64.7 % before and after annealing. The area under cyclic voltammetry (CV) curve and galvanostatic charging discharging (GCD) performance of PLA-treated DLC film were improved and the highest areal-specific capacitance was obtained to be ∼48.25 mF/cm2 for scan rate of 5 mV/s and 36.01 mF/cm2 for current density of 2 mA/cm2, respectively. Excellent charging discharging cyclic stability of PLA treated electrode was observed over 5000 cycles, and Coulombic efficiency and capacitance retention were determined to be ∼93.5 % and ∼ 97.3 %, respectively. The electrochemical impedance spectroscopy (EIS) was performed to obtain the Nyquist plot (Z′vs.Z′′) of both electrodes before and after the stability test, and a small degradation in impedance was observed. The Nyquist plots were fitted with the well-known Randles equivalent circuit model Rs(Cdl(RctZw)) and substantial curtailment of Warburg resistance (Zw) in PLA-induced DLC electrode signifies the dominance of the diffusion-controlled region in the charging-discharging process. Minor changes in the Nyquist plot before and after the stability test manifest the enduring charge kinetics of both electrodes and PLA-treated DLC exhibits better cyclic stability. PLA techniques have a great impact on upgrading the areal-specific capacitance, capacitance retention with high Coulombic efficiency, and stability with negligible impedance loss of the DLC film electrodes.

A rigid free-standing supercapacitor electrode material made from fat coal-based activated carbon foam

A free-standing electrode material is a competitive candidate for supercapacitor due to its excellent capacity and volumetric energy density. Currently, most of the studies are focused on the preparations and performances of flexible free-standing electrode materials, whereas few on the development of rigid free-standing electrode materials. Herein, a vitrinite concentrate of fat coal is used as a raw material and carbon black as an addition agent to prepare a carbon foam by way of high-pressure pyrolysis. The prepared carbon foam is activated by KOH solution to further achieve an activated carbon foam by which we have fabricated a rigid free-standing electrode material. The assembled symmetric device with the rigid free-standing electrode material demonstrates an extremely high areal specific capacitance of 2304.41 mF cm−2 at 4 mA cm−2, an outstanding cycling stability of 100 % after 40 000 cycles, and an excellent volume energy density of 10.23 mWh cm−3 at 31.78 mW cm−3. These fascinating electrochemical performances of the electrode material are attributed to unique 3D interconnected porous structure of the activated carbon foam. The micron-sized 3D interconnected pores facilitate the transport of electrolyte ions within the electrodes. Meanwhile, micropores on the 3D interconnected pore wall provide abundant active sites for electrolyte ions.

Edge-rich reduced microcrystalline graphite oxide for Li-ion hybrid capacitors with ultrahigh volumetric energy density

Compact and high-performance carbon cathode materials are vital to improve the gravimetric and volumetric energy/power density of advanced energy storage devices such as lithium-ion hybrid capacitors (LIHCs). Graphite has a high mass density and the areal specific capacitance at the edge plane is far larger than that in the basal plane. Hence, increasing the proportion of edges can effectively improve the specific capacitance of the carbon material. However, it is challenging to expose more edges of graphite due to its high thermal and chemical stability. In this work, a compact cathode is prepared through a facile high-temperature ammonia treatment of microcrystalline graphite oxide (MGO). The obtained edge-rich reduced microcrystalline graphite oxide (ER-RMGO) demonstrates abundant edge sites, a high mass density of 1.48 g cm−3 and an extremely high areal specific capacitance of up to 319.3 μF cm−2. As a result, the fabricated Li-ion hybrid capacitor delivers an ultrahigh volumetric energy density of 392 Wh L−1 and power density of 9.49 W LkW L−1. This work sheds light on the great potential of microcrystalline graphite derived edge-rich carbon materials for compact capacitive energy storage.

An Environment-Tolerant Ion-Conducting Double-Network Composite Hydrogel for High-Performance Flexible Electronic Devices

HighlightsNovel double-network (DN) ion-conducting hydrogel (ICH) based on a poly(ionic liquid)/MXene/poly(vinyl alcohol) system (named PMP DN ICH) was synthesized using freeze–thawing and ionizing radiation technology.The PMP DN ICH possesses a multiple cross-linking mechanism and exhibits outstanding ionic conductivity (63.89 mS cm−1), excellent temperature resistance (−60–80 °C) and decent mechanical performance.The well-designed PMP DN ICH shows considerable potential in wearable sensing, energy storage, and energy harvesting.

Wood-derived flexible supercapacitors for anti-freezing green power sources

An anti-freezing flexible supercapacitor (−30 °C) with good mechanical flexibility and high specific areal capacitance is developed as a green renewable power source.

Synchronously promoting the electron and ion transport in high-loading Mn2.5V10O24∙5.9H2O cathodes for practical aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) are suitable candidates for stationary energy storage systems because of their inherent safety and affordability. However, the development of high-performance and high-loading ZIB cathode facing actual requirements is still a great challenge. Herein, we report Mn2.5V10O24∙5.9H2O (MVOH) as a high-loading cathode for aqueous ZIB. Combined experimental data and material simulations reveal that the inserted Mn2+ ions can regulate the electronic structure and defective state of the MVOH cathode, leading to high electric conductivity, reduced Zn2+ ion diffusion barrier, and good structural stability. Benefited from the synergistically enhanced electron and Zn2+ ion transport properties, the high-loading (11.7 mg cm−2) MVOH cathode obtains a high areal specific capacity of 3.74 mAh cm−2 and an outstanding capacity retaining rate of 91.4 % for 850 cycles at 0.5 A g−1. Noteworthy, a maximum areal capacity of 7.2 mAh cm−2 is reached at the active material mass loading of as high as 19.9 mg cm−2, exceeding most of the literature-reported results. The reversible Zn2+ ion storage behavior is also demonstrated by various ex-situ characterizations and pouch-type full cell evaluations. This work might deepen the Zn2+ ion storage knowledge of the high-loading vanadium-based cathodes and further promote the practical competitiveness of aqueous ZIBs.

Design of Hierarchical Nickel-Cobalt Phosphide/Nickel Oxide with Tunable Electronic Structure and Strong Chemical Interface for Advanced Supercapacitors

The design of a reasonable heterostructure electrode to achieve enhanced areal performance for supercapacitors remains a great challenge. Here, we constructed hierarchical porous NiCoP/NiO nanocomposites anchored on Ni foam with tunable electronic and structural properties, as well as robust interfacial interaction. In NiCoP/NiO, the interconnected NiO nanosheets serve as a carrier with enriched anchoring sites to confine the NiCoP and improve its stability. Meanwhile, the ultrathin NiCoP nanosheets with bimetallic centers are connected with porous NiO nanosheets to form a reliable heterojunction, enhancing the electrochemical reaction kinetics. Taking advantage of the synergistic contribution of bimetallic centers, phosphides and unique structure, the NiCoP/NiO delivers a high areal specific capacitance (1860 mF cm−2 at 5 mA cm−2), good rate performance of 78.5% at six times the increased current density, and remarkable durability (11.0% decrease after 10,000 cycles). Furthermore, the assembled hybrid supercapacitor NiCoP/NiO//porous-activated carbon (PAC) delivers a high areal energy density of 173.7 μWh cm−2 (116.4 μWh cm−2) at 1.6 mW cm−2 (32 mW cm−2). The results indicate that the design of the heterostructure interface with strong chemical interface and tunable electronic structure is an effective and promising approach to boost the electrochemical performance for advanced supercapacitors.

Anchoring polypyrrole on nitrogen and sulfur codoped graphene fibers to construct flexible supercapacitors

Graphene fiber-based flexible supercapacitors could function as flexible energy storage and supply equipment for wearable electronic devices. However, the future applications are restricted because of the low energy density for flexible supercapacitors. In this paper, the polypyrrole is anchored on nitrogen/sulfur co-doped graphene fibers (PPy/NSGF) by a hydrothermal self-assembly method and in situ polymerization process. The as-fabricated PPy/NSGF possess a high specific areal capacitance of 424.8 mF cm−2 and an excellent energy density of 43.3 μW h cm−2. The fiber-shaped supercapacitor assembled by PPy/NSGF can be utilized to power light. The improved properties of PPy/NSGF are mostly attributed to the increased electroactive sites from heteroatom nitrogen and sulfur codoping and in situ polymerization of polypyrrole. The produced graphene-based composite fibers are expected to become potential flexible electrode materials for fiber-shaped supercapacitors in future smart clothes and miniaturized flexible wearable electronics.

Remarkable chemical adsorption and catalysis of monodisperse metallic cobalt sulfide nanoparticles enable long-cycling Li–S battery with high areal capacity and low shuttle constant

High-energy density lithium-sulfur battery is considered as one of the most potential new-generation energy-storage technologies. Nevertheless, the capacity decays rapidly due to severe volumetric change of sulfur, dissolution and slow redox kinetics of intermediate polysulfides, and instability of lithium anode. Herein, a novel highly conductive porous sulfur cathode host composed of graphene aerogel and polar Co9S8 nanoparticle is designed to address these obstacles. The porous conductive framework not only provides channels for rapid conduction of electron and lithium ion, but also provides adequate space to physically confine the lithium polysulfides and accommodate the volume expansion. Both experimental and theoretical calculations demonstrate that the in-situ uniformly deposited Co9S8 nanoparticles can effectively bind polar lithium polysulfides and catalyze their interconversion, and the shuttle effect is therefore effectively suppressed. The Co9S8-GA/S cathode exhibits high specific discharge capacity (1219.1 mAh g−1) and high areal specific capacity (14.3 mAh m−2) at 0.1 C, low shuttle constant (0.15 h−1), excellent rate performance (625.6 mAh g−1/7.4 mAh m−2 at 5 C), outstanding long cyclic stability (low decay of 0.024 %/cycle during 1000 cycles at 2 C). This study demonstrates a promising aerogel strategy to design high-performance composite cathode for lithium-sulfur battery.

Conducting polymers/oxygen vacancies WO3 vertically nanowire arrays supported on carbon cloth as advanced electrodes for high-performance supercapacitors

The low energy density of supercapacitors (SCs) is one of the main factors restricting their development. WO3 with high theoretical capacitance is an ideal n-type material for anode electrode, but its narrow potential window and low conductivity are not conducive to the application of high-energy-density SCs. Herein, a high electrochemical activity poly(indole-5-carboxylic acid) (P5-ICA) as p-type material wrapping n-type oxygen vacancies WO3 vertically nanowire arrays supported on carbon cloth is prepared by hydrothermal method and subsequent electrodeposition method. This adhesive free flexible p/n-type hetero-structural P5-ICA@WO3 vertical nanowire array electrode has a three-dimensional porous nanostructure that not only provides a large surface area, but also promotes the penetration of electrolyte ions and the transmission of electrons. It is found that the P5-ICA@WO3 nanowire array with high areal specific capacitance (1430 mF cm−2 at 4 mA cm−2) and long cycle stability (94 % after 6000 cycles) exhibits a widened electrochemical activity window compared to individual material. The symmetrical SCs assembled using P5-ICA@WO3 can provide a high areal energy density of 137.6 μWh cm−2 at the power density of 1.4 mW cm−2, which is significantly higher than the SCs performance of previously used WO3-based electrode materials.

A macrocyclic amine-based electrolyte for lithium–sulfur batteries: Li ion encapsulation regulates electrode performance

The widespread use of lithium–sulfur (Li–S) batteries is hindered by slow cathode kinetics, the shuttle effect, and dendrite growth on the anode. We show that these challenges can be overcome by replacing a linear ether (i.e., 1,2-dimethoxyethane) in commonly used electrolytes with a macrocyclic amine, 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (TMTAC). Theoretical studies and experimental data indicate that the cavity of TMTAC matches a Li ion to form a robust solvation structure. Such a solvation structure not only leads to 3D deposition of Li2S on the cathode, which is responsible to the reduced overpotentials of Li2S nucleation and decomposition, but also suppresses Li dendrite growth on the anode. Moreover, the shuttle effect of polysulfides is effectively suppressed as the quantity of free TMTAC in the TMTAC-based electrolyte is substantially reduced. As a result, coin-type cells prepared with TMTAC-based electrolytes exhibit outstanding performance metrics for all key device parameters. Furthermore, pouch-type cells can be prepared with high sulfur loadings (e.g., 3.43 mg cm−2) and a low electrolyte to sulfur ratio (e.g., 6.16 μl mg−1) while maintaining a high areal specific capacity (3.38 mA h cm−2). This work demonstrates that the effective solvation of critical ions in energy storage devices is paramount to achieving peak performance.

Electrogeneration of N-substituted polyaniline micro/nanoparticles with potential for energy storage

In the pursuit to develop functionalized polyaniline (PANI) micro/nanoparticles suitable for electrical charge storage, the electrochemical copolymerization of N-(3-sulfopropyl) aniline (AnPS) and N-(2-hydroxyethyl) aniline (AnEtOH) was performed to generate electroactive N-substituted PANI layers directly deposited onto conductive substrates. A particular attention was focused on the impact of the comonomer's molar ratio and pH of the electrolysis solutions on the morphology and electrochemical properties of PANI electrodeposited layers. Thus, four mixtures of the monomers were subjected to electrochemical polymerization in two electrolyte solutions (1 M H2SO4 and acetate buffer solution, pH 4.5) that led to green, homogeneous copolymer deposition layers on the electrode surface. These provided different structural morphologies, that varied from spherical microparticles generated from solution with slightly acidic pH (4.5) to dense, granular morphological features in the case of the deposition layers electrogenerated from 1 M H2SO4. These were characterized in detail by FT-IR and UV–Vis spectroscopies, which confirmed their proposed chemical structure. The electrooxidative polymerization mechanism of the studied N-substituted aniline monomers was evidenced by spectroelectrochemical studies, which highlighted the influence of the monomer's molar ratio and solutions’ pH on the electrolysis process. Moreover, it was demonstrated that the particle dimensions and distributions can be controlled by the comonomer's molar ratio and electrolysis parameters. Considering that the high specific surface area of the obtained PANI micro/nanoparticles can contribute to a better wettability of the polymer molecules with electrolyte ions and their diffusion, the capacitive behaviour of these PANI films was investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD). The highest areal specific capacitance, of 5.32 mFcm−2, was obtained for the polymer electrogenerated from 1:1 molar ratio of the two monomers, that distinguished by the related polymers through a better ion diffusion at low scan rates and efficient charge transfer at high scan rates.