High-performance polydiacetylene organic cathode for zinc-ion batteries

Abstract

Organic cathodes are considered promising alternatives to metal-based electrodes in energy storage devices because of their versatile structural and electrochemical properties and benign environmental impact. Most organic cathodes in zinc ion batteries (ZIBs), however, exhibit small potential windows (<1.0 V vs. Zn²⁺/Zn) and display poor cycling performance as well as insufficient chemical stability, limiting their practical applicability. Here, we present a high-performance organic cathode, utilizing, for the first time, polydiacetylene (PDA) – a conjugated polymer exhibiting unique structural and electronic properties. Specifically, a ZIB comprising an anthraquinone-functionalized polydiacetylene cathode doped with polyaniline (PANI) and Zn(ClO₄)₂·6H₂O/acetonitrile as the electrolyte featured exceptionally high specific capacity (330 mAh g⁻¹ at 0.1 A g⁻¹) and energy density (277 Wh kg⁻¹ at 0.1 A g⁻¹), excellent rate capability, and long-term cycling stability. Structure/function analyses indicate that the superior electrochemical properties of the polydiacetylene-based cathode are ascribed to efficient diffusion and Zn²⁺ coordination with the redox-active quinone units of anthraquinone and benzenoid/quinoid residues of PANI. The polydiacetylene-based cathode, fabricated from inexpensive and readily synthesized building blocks, is environmentally friendly and resilient, and may be successfully utilized in commercially viable organic ZIBs.

---

1. Introduction

Energy storage devices are currently dominated by the lithium-ion technology, although challenges such as scarcity of lithium sources, safety risks, and environmental concerns have intensified the search for alternative battery technologies, particularly based on multivalent metal ions.¹ In particular, zinc-ion batteries (ZIBs) have attracted significant interest due to the natural abundance of zinc (nearly 300 times greater than that of lithium), high theoretical capacity, low redox potential (−0.76 V vs. SHE), intrinsic safety, and cost-effectiveness.² Advances in practical ZIB implementation largely depend on the design of high-performance cathodes, which critically affect energy density, cell capacity, rate capability, and cycling stability. While inorganic material-based cathodes employed in ZIBs are generally stable and exhibit high redox potential, they display low specific capacity, slow kinetics, and adverse environmental impact. Electrode volume expansion, structural damage, and sluggish ion transfer constitute additional challenges of inorganic-based ZIB cathodes, prompting the search for organic electrode materials as viable alternatives.³ Cathodes comprising organic materials offer attractive properties, including structural and electrochemical tunability, environmental friendliness, and low cost. Moreover, the redox-active functional groups of organic species in cathodes enable fast, surface-controlled, and reversible intercalation processes of the Zn²⁺ ions, thereby overcoming the solid-state diffusion constraints typically encountered in inorganic electrodes.⁴

Small organic molecules have been employed as cathode constituents in ZIBs, offering relatively high specific capacities.⁵ However, their practical applicability is hindered by poor cycling stability and low energy density, primarily due to dissolution in the aqueous electrolytes during prolonged cycling.⁶ n-type quinone derivatives offer high theoretical capacities and pronounced redox potentials.⁷ However, their typically low operating voltages (<1 V) and restricted solubility remain major limitations.⁵ Other studies have reported the use of covalent organic frameworks (COFs)⁸ and redox-active polymers⁹ as building blocks in ZIB organic cathodes. Conductive polymers have also been explored as cathode materials for ZIBs.¹⁰ Polyaniline (PANI) has received particular attention due to its electronic mobility, reversible redox behavior, facile charge-transfer characteristics, and mechanical robustness.¹¹ PANI, however, generally delivers limited capacity and moderate cycling stability.¹²

Polydiacetylenes (PDAs) are a distinctive class of conjugated polymers exhibiting unique structural and chromatic properties.¹³ PDAs, formed via topochemical polymerization, feature varied molecular architectures and dramatic color- and fluorescence-transformations.¹⁴ Indeed, the π-conjugated backbone of PDA and concomitant luminescent properties have underlined diverse applications in chemical sensing,¹⁵ molecular electronics,¹⁶ photonics,¹⁷ and others.¹⁸ PDAs functionalized with redox-active moieties have attracted particular interest in electrochemistry and energy storage, specifically as innovative supercapacitor electrodes.¹⁹

Herein, we present a new high-performance organic cathode for zinc-ion batteries, comprising polymerized anthraquinone (AQ)-functionalized diacetylene (AQ-DA) as the key structural and functional component, doped with polyaniline (PANI). Covalent tethering of the AQ units to the PDA backbone suppresses dissolution of redox-active species and minimizes structural rearrangement during repeated redox cycling. Importantly, the ubiquitous AQ moieties provide abundant redox-active sites for Zn²⁺ coordination, giving rise to high specific capacity and energy density. In parallel, the π-conjugated PDA backbone and the PANI network enhance electronic conductivity and structural stability. An electrochemical cell comprising the poly-AQ-DA/PANI cathode and a zinc anode exhibited a high specific capacity of 330 mAh g⁻¹ at 0.1 A g⁻¹, corresponding to an energy density of 277 Wh kg⁻¹ and a power density of 88 W kg⁻¹. Furthermore, even at 1 A g⁻¹, the cell retained an energy density of 135 Wh kg⁻¹ and a power density of 1190 W kg⁻¹. The poly-AQ-DA/PANI electrode displayed exceptional cycling stability, showing 93% capacity retention after 1000 cycles at 0.1 A g⁻¹ and 95% retention after 19 000 cycles at 1 A g⁻¹. Overall, the new polydiacetylene-based organic cathode charts new avenues for practical ZIB applications, harnessing for the first time conjugated polydiacetylenes as a versatile core element in battery applications.

2. Experimental section

2.1 Materials

1-Aminoanthraquionone (97%, Heysham, Lancashire, UK) and zinc sulphate heptahydrate (ZnSO₄·7H₂O, 98%, Belgium) were purchased from Thermo Fisher Scientific. Oxalyl chloride (98%) was purchased from Acros organics (India). N,N-Dimethylformamide (99.8%), zinc perchlorate hexahydrate (Zn(ClO₄)₂·6H₂O, >98%), Nafion perfluorinated resin solution (45–51%), and zinc trifluoromethane sulphonate (Zn(CF₃SO₃)₂, 98%) were purchased from Sigma-Aldrich (St. Louis, Missouri, USA). Acetonitrile (gradient grade) was purchased from J. T. Baker (Gliwice, Poland). Aniline (99%) and ammonium persulphate ((NH₄)₂S₂O₈, 98%) were purchased from Alfa Aesar (Heysham, England). Hydrochloric acid (32%) was procured from Bio-lab Ltd (Jerusalem, Israel). All the organic solvents were procured from Bio-lab Ltd 10, 12-Tricosadiynoic acid (98%) was purchased from Alfa Aesar (St. Louis, Missouri, USA) and purified before use by dissolving in dichloromethane, passing it through a 0.22 µm syringe filter and removing the solvent by rotary evaporation. Graphite sheets (0.25 mm, Dublin, Ireland) and zinc foil (99%, Ward Hill, MA, USA) were purchased from Farnell and Rhenium Israel.

2.2 Synthesis of anthraquinone-diacetylene (AQ-DA)

AQ-DA was synthesized using a previously reported procedure.²⁰ 10,12-Tricosadiynoic acid (1.04 g, 3.0 mmol) was dissolved in 20 mL of dichloromethane (DCM) in a round-bottom flask equipped with a magnetic stirrer. To this solution, oxalyl chloride (1 mL) was added, and the mixture was stirred for 30 min at room temperature. A catalytic amount of N,N-dimethylformamide (5–6 drops) was then added, and the reaction was continued for 4 hours. The solvents and excess oxalyl chloride were subsequently removed under reduced pressure using a rotary evaporator, producing the corresponding acyl chloride intermediate. The crude product was redissolved in 10 mL of DCM and immediately used for the subsequent step. Separately, 1-aminoanthraquinone (0.800 g, 3.6 mmol) was dissolved in a mixture of pyridine (20 mL) and dichloromethane (20 mL). The freshly prepared acyl chloride solution was added dropwise to this reaction mixture. Following complete addition, the mixture was stirred at room temperature for 12 h. After completion, the solvent (DCM) was removed under vacuum, and the residue was treated with 200 mL of doubly distilled water. The resulting precipitate was collected by filtration, washed twice with 100 mL of water and then suspended in 200 mL of ethanol. The suspension was heated in a hot water bath for 10 min, cooled to room temperature, and filtered again. The product was dissolved in chloroform, concentrated under vacuum, and purified by silica gel column chromatography using ethyl acetate/toluene (1 : 9) as the eluent, yielding AQ-DA as a yellow amorphous solid. Nuclear magnetic resonance (NMR) was employed to confirm purity.

2.2.1 Synthesis of polyaniline (PANI). PANI was synthesized using a previously reported procedure.¹⁹ Briefly, 3.1 mL of aniline was dissolved in a mixture of 20 mL of concentrated HCl and 190 mL of deionized water, and the solution was stirred continuously at room temperature for 24 h. Separately, an aqueous solution of ammonium persulfate (APS) was prepared by dissolving 7.6 grams in 10 mL of DI water. The APS solution was slowly added to the aniline solution and stirred for 6 hours in an ice bath. The obtained deep green precipitate was filtered and washed several times with ethanol and water. The product was dried at 60 °C overnight.

2.3 Preparation of the polymerized AQ-DA/PANI electrode

To prepare the AQ-DA and PANI integrated cathode for a zinc ion battery, 4 mg of AQ-DA was dissolved in 0.5 mL of chloroform. In parallel, 6 mg of PANI was dispersed in 0.5 mL of ethanol, and a 10 µL Nafion binder solution was added. The two suspensions were mixed and sonicated for 10 minutes to form a homogeneous solution, 30 µL of which was drop-cast on a circularly-shaped graphite sheet of 1 cm diameter. The coated sheet was dried at room temperature for 1 hour in the dark. Ultraviolet irradiation (UV) (254 nm) was applied for 5 minutes to induce diacetylene polymerization, affecting a yellowish-green to dark brown colour change. Mass loading optimization yielded a mass of 0.3 mg with the AQ-DA : PANI 2 : 3 mole ratio as the best electrode configuration (Fig. S2b and d).

2.4 Electrochemical measurements

Electrochemical measurements were carried out on a complete zinc-ion battery using the poly-AQ-DA/PANI-coated graphite sheet as the cathode, a zinc anode, and 2 M Zn(ClO₄)₂·6H₂O in acetonitrile as the electrolyte. The anode and cathode were sandwiched in a CR2032 coin cell (Neware Technology Limited, Kowloon Bay, Hong Kong) using Whatman filter paper as a separator. The batteries were assembled under ambient conditions. Electrochemical experiments were conducted on a Bio-Logic (SP-300) system (Seyssinet-Pariset, Grenoble, France) for cyclic voltammetry and electrochemical impedance spectroscopy. The measurements of galvanostatic charge/discharge, self-discharge profile, and cycling stability, and the galvanostatic intermittent titration technique (GITT) were conducted on a Neware battery testing system (CT-4008Tn-5V50mA-HWX) (Shenzhen, China).

2.5 Characterization

Scanning electron microscopy (SEM) images of the films on a graphite sheet were acquired after air-drying overnight in a vacuum at room temperature. The dried sample was covered with 10 nm of Au by sputtering. The samples were imaged using SEM (Thermo Fisher Verios, XHR 460L, Brno, Czech Republic). The images were viewed at different magnifications, using an acceleration voltage of 5 kV. Ultraviolet-visible (UV-vis) absorbance spectra were recorded on a Thermo Scientific Evolution 220 spectrophotometer (Madison, WI, USA) in the range of 320–700 nm at room temperature. Fourier Transform Infrared (FTIR) spectra were recorded using a Nicolet 6700 laboratory FT-IR spectrometer. X-ray diffraction (XRD) patterns were recorded using a PANalytical Empyrean II system (Almelo, Netherlands) with the Cu-Kα radiation of λ = 1.54 Å. X-ray photoelectron spectroscopy (XPS) measurements were performed on a Thermo Fisher Scientific (ESCALAB Xi) (Waltham, MA USA). STEM-EDS experiments were carried out using a JEM-2100F fitted with a JEOL HAADF (Tokyo, Japan) detector.

3. Results

3.1 Electrode construction

Synthesis and co-assembly of the electrode components are depicted in Fig. 1. The aminoanthraquinone-functionalized diacetylene (AQ-DA) monomer was synthesized via amide coupling between 1-aminoanthraquinone and 10,12 tricosadiynoyl chloride (Fig. 1a); the purity of the synthesized compound was verified by NMR (Fig. S1). AQ-DA was deposited on a graphite sheet serving as a current collector, and UV irradiation induced the formation of the conjugated polymerized diacetylene (PDA) network (Fig. 1b). Electrode layer organization and stabilization were both aided by π–π stacking between the anthraquinone residues, as well as hydrogen bonding involving the anthraquinones' amides. Importantly, both anthraquinone and conjugated PDA display electron delocalization, thus contributing to enhanced charge storage capabilities.^21,22

Fig. 1 Fabrication of the polymerized anthraquinone-diacetylene/polyaniline cathode. (a) Synthesis of the AQ-functionalized diacetylene monomers through reaction of 10,12-tricosadiynoic acid and 1-aminoanthraquinone. (b) Formation of the poly-AQ-DA/PANI composite cathode upon deposition of the diacetylene monomers and PANI, followed by UV irradiation, inducing formation of the conjugated polydiacetylene network. (c) UV-vis absorbance spectra of the non-polymerized AQ-DA/PANI film (blue spectrum) and polymerized AQ-PDA/PANI film (red). Photographs of the non-polymerized (left) and polymerized film (right) are shown. (d) SEM image of poly-AQ-DA/PANI. The scale bar corresponds to 5 µm.

As illustrated in Fig. 1b, the cathode further comprises PANI, a well-known dopant that enhances electron transport within organic electrodes.²³ The UV-vis absorbance spectra in Fig. 1c confirm that co-dispersion of PANI did not hinder the ene-yne polymerization of the diacetylene backbone, producing the conjugated PDA network. Specifically, the as-deposited polymerized-AQ-DA/PANI (poly-AQ-DA/PANI) film (2 : 3 mole ratio of AQ-DA and PANI; this mole ratio yielded the best electrochemical performance, Fig. S2a and c) displayed a broad absorbance band at 400–500 nm, ascribed to intramolecular charge transfer between the electron-rich amide group of AQ-DA and the electron-deficient anthraquinone.^24,25 Upon UV irradiation (at 254 nm), the appearance of a typical pronounced absorbance peak at 650 nm and a shoulder at around 600 nm corresponding to the PDA network²⁴ indicates that incorporation of PANI did not adversely affect the formation of the conjugated PDA backbone.

The scanning electron microscopy (SEM) image in Fig. 1d shows the morphology of the composite poly-AQ-DA/PANI film, complementing the UV-vis absorbance analysis. Specifically, the SEM image features distinct domains of PANI^19,26 interspersed within the elongated thread-like assemblies of poly-AQ-DA (Fig. S3 presents SEM micrographs of the individual components).²⁷ The spectroscopic and structural analyses in Fig. 1c and d attest that the two electrode constituents, poly-AQ-DA and PANI, adopt their distinctive molecular organizations, forming interspersed microdomains upon deposition on the graphite electrode surface. FTIR and XPS analyses (Fig. S4a and b) demonstrate that incorporation of PANI does not alter the molecular structure of poly-AQ-DA, as the composite preserves the characteristic vibrational signatures and exhibits C 1s and N 1s spectra dominated by the poly-AQ-DA framework with overlapping contributions from PANI, confirming their homogeneous coexistence.

3.2 Electrochemical properties of the poly-AQ-DA/PANI cathode

Fig. 2 presents the electrochemical characterization of the poly-AQ-DA/PANI cathode in a complete zinc ion cell, employing zinc foil as the anode and poly-AQ-DA/PANI (2 : 3 mole ratio) as the cathode. We tested several zinc ion species and solvents; Zn(ClO₄)₂·6H₂O/acetonitrile featured the best electrochemical performance (Fig. S5a). Fig. 2a depicts cyclic voltammetry (CV) curves of the poly-AQ-DA/PANI cathode, recorded at 0.2 mV s⁻¹. The CV curves display three pairs of distinct redox peaks, accounting for specific redox reactions undergone by Zn²⁺ ions upon interactions with the poly-AQ-DA/PANI matrix. Specifically, the peak at 0.53 V vs. Zn²⁺/Zn in the cathodic scan likely corresponds to the reaction of Zn²⁺ ions with the quinone moieties of AQ-DA.²¹ The higher potential peaks at 0.87 and 1.38 V are attributed to redox reactions of Zn²⁺ with the benzenoid/quinoid and amide units in AQ-DA and PANI, respectively.^28,29 The anodic scans display negative peaks in similar voltage values, accounting for the stepwise release of Zn²⁺ ions, confirming the reversible storage behavior of the poly-AQ-DA/PANI cathode. Importantly, the pronounced 1.7 V potential window is significantly higher than that of most reported ZIB cathodes.^30,31 Furthermore, the CV curves were almost identical in the five cycles recorded, attesting to the reversibility and stability of the poly-AQ-DA/PANI electrode.

Fig. 2 Electrochemical properties of the polymerized-AQ-DA/PANI cathode. (a) CV curves recorded for the poly-AQ-DA/PANI (2 : 3) cathode at 0.2 mV s⁻¹. (b) CV curves for poly-AQ-DA/PANI recorded at different scan rates. (c) Relationship between peak current and scan rates calculated for the distinct redox peaks in the CV curves, unveiling the relative contributions of capacitive-controlled versus diffusion-controlled capacity. The b values indicated were extracted according to eqn (1), see text. (d) CV curve with capacitive contribution quantified by using eqn (2) at 0.2 mV s⁻¹ (grey: capacitive and dark cyan: diffusive contribution). (e) Bar diagram depicting the contribution ratio between diffusion-controlled and capacitive-controlled capacities at different scan rates (grey: capacitive contribution, dark cyan: diffusive contribution). (f) EIS of poly-AQ-DA/PANI. The equivalent electrical circuit utilized for extracting the resistance values from the EIS curve is illustrated.

To investigate the redox reaction kinetics of the poly-AQ-DA/PANI cathode, CV curves were recorded at different scan rates (Fig. 2b). Importantly, the redox peak positions were largely retained upon varying the scan rate, confirming reaction reversibility.³²Fig. 2c depicts the relationship between the peak current and scan rates for each redox peak in the CV scans, calculated according to eqn (1):

i = av^b (1)

where i is the specific peak current extracted from the CV curves, v is the scan rate, while a and b can be calculated from the intercept and slope of the linear relationships shown in Fig. 2c. The calculated b-values for the poly-AQ-DA/PANI cathode were 0.85, 0.90, and 0.78 (oxidation peaks), and 0.79, 0.79, and 0.81 (reduction peaks), indicating that the redox behavior of the poly-AQ-DA/PANI cathode is governed by a hybrid mechanism involving both capacitive and diffusion-controlled contributions.³³

The capacitive and diffusive contributions to the total current were calculated according to eqn (2).³⁴

where i, k₁v, and k₂v^1/2 are the total current, non-diffusive-controlled, and diffusive-controlled currents, respectively. Fig. 2d and e depict the relative capacitive and diffusive contributions to the total capacity. The bar diagram in Fig. 2e illustrates the relative contributions of capacitive and diffusion-controlled processes, calculated using eqn (2). As the scan rate increases from 0.2 to 5 mV s⁻¹, the capacitive contribution increases from 44% to 82%, reflecting that the reaction is predominantly capacitive-controlled charge storage associated with fast diffusion dynamics.³⁵

Electrochemical impedance spectroscopy (EIS) analysis in Fig. 2f furnishes insight into the interfacial charge transport and ion diffusion processes within the poly-AQ-DA/PANI cathode. The Nyquist plot displays a distinctive semicircle in the high-frequency region, accounting for the charge-transfer resistance. The Warburg-type tail in the low-frequency region is tilted towards the x-axis, accounting for efficient Zn²⁺ ion diffusion in the bulk electrolyte. Fitting the data according to an equivalent electrical circuit (Fig. 2f, inset) yields a solution resistance (R_s) of 8 Ω, a charge-transfer resistance (R_ct) of 156 Ω, and a Warburg factor (σ) of 142 Ω s⁻¹. These relatively low resistance values reflect fast electrochemical reaction kinetics and charge transfer efficiency.³⁶

We further calculated the diffusion coefficient D_Zn²⁺ using eqn (3):

where R is the gas constant, T is the working temperature, n is the number of electrons transferred per molecule, F is the Faraday constant, A is the electrode area, C is the ion concentration, and σ is the Warburg factor obtained from the EIS results.³⁷ The calculated diffusion coefficient value was 1.09 × 10⁻¹² cm² s⁻¹, confirming efficient Zn²⁺ ion transport at the interface between the electrolyte and the poly-AQ-DA/PANI cathode.³⁸

Fig. 3 portrays the Zn²⁺-ion storage performance of the poly-AQ-DA/PANI cathode. Fig. 3a depicts the galvanostatic charge–discharge (GCD) curves recorded at different current densities. Notably, the charge and discharge curves display almost identical capacities at the various current densities, indicating reversible Zn²⁺ storage. Fig. 3a demonstrates that the poly-AQ-DA/PANI cathode exhibits an excellent capacity of 330 mAh g⁻¹ at 0.1 A g⁻¹ and approximately 60 mAh g⁻¹ at 5 A g⁻¹. Importantly, these values surpass those recorded in electrodes comprising the individual components (Fig. S5b and Table S1). Moreover, the performance of poly-AQ-DA/PANI exceeds that of many reported quinone-containing organic cathodes^30,39,40 and organic cathodes, in general.^32,41

Fig. 3 Electrochemical Zn²⁺ ion storage performance. (a) GCD curves recorded at different current densities. (b) Rate capability and coulombic efficiency (values in the rate capability graph correspond to the indicated current densities, A g⁻¹). (c) GITT measurements at 0.1 A g⁻¹ (red curves), and the corresponding ion diffusion coefficients (blue). (d) Energy density vs. power density of the poly-AQ-DA/PANI cathode (red data points), compared to other organic cathode battery systems (1) HATN-PNZ,⁴¹ (2) Cu-TCNQ,⁴² (3) 3TANC,⁴³ (4) HATTA,⁴⁴ (5) PNZ-PTO,⁴⁵ and (6) PMPT.⁴⁶ (e) Self-discharge profile of the cathode: charging at 0.1 A g⁻¹ (black); open circuit for 350 h (red); discharge (blue). (f) Charge–discharge profile corresponding to the self-discharge experiment.

Fig. 3b depicts the discharge capacities at different current densities, and the coulombic efficiencies of the poly-AQ-DA/PANI cathode recorded over multiple cycles. The experimental data indicate that the cell delivered 330 mAh g⁻¹ at 0.1 A g⁻¹, retaining a capacity of 325 mAh g⁻¹ after a complete cycle (increasing the current density to 5 A g⁻¹ and reverting to 0.1 A g⁻¹), confirming its excellent rate capability. Notably, the coulombic efficiencies recorded were greater than 99.9% during the entire cycling experiments, underscoring the reversibility of the electrochemical reactions.

To further elucidate the diffusion dynamics of Zn²⁺ ions within the poly-AQ-DA/PANI electrode, diffusion coefficients were calculated by the galvanostatic intermittent titration technique (GITT, Fig. 3c). The diffusion coefficient (D_Zn²⁺) calculations were based upon the GITT measurements (Fig. 3c, red), according to eqn (4):²²

where τ is the current relaxation time (1200 s), L is the average thickness of the electrode (3 µm), ΔE_s is the voltage change induced by the current pulse, and ΔE_τ is the voltage change induced by the galvanostatic charge/discharge.⁴⁷Fig. 3c (blue) demonstrates that the calculated diffusion coefficients were in the range of 6.1 × 10⁻¹³ cm² s⁻¹ to 7.8 × 10⁻¹¹ cm² s⁻¹, indicating fast Zn²⁺ ion diffusion kinetics and low polarization with extensive interfacial interactions of the poly-AQ-DA/PANI cathode.^48,49 The narrow range of the calculated ion diffusion coefficients further accounts for the excellent rate capability of the electrode. Notably, the ion diffusion coefficients calculated at the highest charge voltage (6.8 × 10⁻¹³ cm² s⁻¹) and lowest discharge voltage (6.1 × 10⁻¹³ cm² s⁻¹) reflect hindered diffusion kinetics, particularly at the fully intercalated and de-intercalated states.⁵⁰

The excellent specific capacity and rate capability of the poly-AQ-DA/PANI cathode are further reflected in the energy density vs. power density graph, calculated from the active mass loading on the cathode (Fig. 3d). Specifically, the poly-AQ-DA/PANI electrode exhibited a high energy density of 277 Wh kg⁻¹ at 135 W kg⁻¹ (0.1 A g⁻¹), while an energy density of 61 Wh kg⁻¹ was obtained at a power density of 1415 W kg⁻¹ (5 A g⁻¹). These values are superior to numerous previously reported organic cathodes (values for representative reported organic cathodes are indicated in Fig. 3d).

The self-discharge profile of the Zn‖poly-AQ-DA/PANI cell is depicted in Fig. 3e. In the experiment, the battery was fully charged to 1.8 V after three cycles at 0.1 A g⁻¹, and the open circuit voltage (OCV) was recorded for 350 hours. As shown in Fig. 3e, the OCV decreased from 1.8 to 1.58 V within 5 hours (decay rate of 44 mV h⁻¹) due to the relaxation of ions at the electrode–electrolyte interface, transforming to a relative equilibrium state.⁵¹ The OCV further decreased to 1.11 V within approximately 100 hours (corresponding to a decay rate of 4.6 mV h⁻¹). After an additional 250 hours, the voltage decreased to 1.04 V (decay rate of 0.3 mV h⁻¹). The slow decay rate indicates significant charge retention over a long period. The GCD curves in Fig. 3f reveal that the Zn//poly-AQ-DA/PANI battery exhibited 11% specific capacity loss after 350 hours. The excellent anti-self-discharge profile of the Zn//poly-AQ-DA/PANI-based battery is likely attributed to the suppression of cathode dissolution⁵¹ (Fig. S6 and S7), redox selectivity for Zn²⁺ ions,⁵² and minimal occurrence of parasitic side reactions. The Zn(ClO₄)₂·6H₂O/acetonitrile electrolyte likely also contributes to an even deposition of zinc on the anode following cell discharge.⁵³

Fig. 4 shows the practical applicability of a Zn‖poly-AQ-DA/PANI battery. Fig. 4a and b depict the cycling stabilities of the Zn‖poly-AQ-DA/PANI cell at 1 A g⁻¹ and 0.1 A g⁻¹, respectively (stability of the zinc anode was confirmed in cycling experiments employing a symmetric Zn‖Zn cell, Fig. S8). Excellent cycling performance was observed at both current densities. At 1 A g⁻¹, 99.8% retention of the coulombic efficiency was recorded after 19 000 cycles (Fig. 4a). In parallel, the specific capacity retention was 95% after 19 000 cycles. The GCD curves recorded at the 1, 5000, 10 000, and 19000th cycles yielded specific capacities of 118, 116, 113, and 112 mAh g⁻¹, respectively (Fig. 4a, right), indicating negligible capacity decay over 19 000 cycles, underscoring the outstanding cycling stability and high reversibility of Zn²⁺ insertion/extraction in the cathode.

Fig. 4 Stability and practical application of a Zn‖poly-AQ-DA/PANI battery. (a) Long-term cycling performance at 1 A g⁻¹ (violet: coulombic efficiency, red: specific discharge capacity); GCD curves recorded at the indicated cycles (right). (b) Long-term cycling performance at 0.1 A g⁻¹ (violet: coulombic efficiency, red: specific discharge capacity); GCD curves at the indicated cycles (right panel). (c) Three cells linked in series according to the electric circuit diagram (left); photographs of LEDs turned on by the circuit: (i) white LED (3.4 V forward voltage), (ii) green LED (3 V), (iii) blue LED (3.2 V), and (iv) red LED (1.8 V). (d) Red LEDs (1.8 V and 120 mA) connected in parallel, according to the electric circuit diagram shown. (e) Commercial 20 LED's fairy string lights powered by three cells assembled in series.

High cycling stability was also observed at a lower current density of 0.1 A g⁻¹ (Fig. 4b). After 1000 cycles, a coulombic efficiency retention of >98% and a capacity retention of 93% were observed, reflecting the excellent stability of the poly-AQ-DA/PANI cathode. The GCD curves (Fig. 4b, right) recorded at different cycle numbers exhibit nearly identical profiles, accounting for the structural stability and reversible redox kinetics of the cathode under high-rate cycling conditions. SEM images in Fig. S9, recorded after 1000 cycles (at 0.1 A g⁻¹) and 19 000 cycles (at 1 A g⁻¹), reveal that the poly-AQ-DA/PANI cathode preserved its structural integrity and morphology, highlighting its stability and long-term cycling performance.

Practical utilization of the Zn‖poly-AQ-DA/PANI battery is illustrated in Fig. 4c–e. In the experiments presented in Fig. 4c, we fabricated coin cell batteries and connected three cells in series to generate sufficient voltage. The batteries successfully turned on light-emitting diodes (LEDs) requiring different forward voltages and operating at typical currents (∼20 mA) and power (35–70 mW). To further assess the battery performance under higher load conditions, the 3-coin cell power source successfully turned on six LEDs (1.8 V and 120 mA) connected in parallel, requiring a current of ∼120 mA (Fig. 4d). Similarly, the 3-coin cell source could successfully turn on 20 commercial LEDs on a fairy string (Fig. 3e).

3.3 Charge storage mechanism of the poly-AQ-DA/PANI cathode

Fig. 5 presents experiments designed to elucidate the charge storage mechanism of the poly-AQ-DA/PANI cathode. Fig. 5a depicts a charge–discharge curve recorded in Zn‖poly-AQ-DA/PANI cells; in each of the indicated voltage points, the cells were disassembled, and the cathodes were retrieved and analyzed using different techniques (Fig. 5b–f). Importantly, cells were prepared under identical conditions for each measured point. The EIS analysis in Fig. 5b yields the charge transfer resistance values for the poly-AQ-DA/PANI cathode at each voltage point. Specifically, according to the EIS data in Fig. 5b, the charge transfer resistance markedly decreased from 643 Ω to 195 Ω on charging from 0.1 to 1.8 V, indicating efficient charge transport and effective release of Zn²⁺ ions from the cathode matrix into the bulk electrolyte. Upon discharging, R_ct increased from 195 Ω to 655 Ω, reflecting intercalation of Zn²⁺ ions in the cathode. Similar to other ZIBs, the relatively pronounced R_ct during low-voltage discharge likely accounts for the large ionic radius and strong electrostatic interactions of Zn²⁺ ions upon intercalation in the polymer matrix,⁵⁴ ultimately leading to sluggish diffusion in the cathode.⁵⁵

Fig. 5 Structural and mechanistic analyses of the poly-AQ-DA/PANI cathode. (a) Charge/discharge profile of Zn‖poly-AQ-DA/PANI cells; the cells were disassembled at the indicated points, and the cathodes were characterized (panels b–f). (b) EIS measurements. (c) XRD patterns; black diamonds correspond to ZnCl₂ peaks; red stars indicate Zn(ClO₄)₂·6H₂O. (d) XPS spectra of the cathodes at the indicated charge and discharge potentials. (e) SEM images (scale bars 5 µm) recorded for the cathodes at the indicated charge and discharge potentials. (f) HAADF-STEM images and corresponding EDS mapping of the cathodes: charged at 1.8 V (left) and discharged at 0.1 V (right).

The X-ray diffraction (XRD) patterns shown in Fig. 5c furnish important structural information on the zinc species during the charge/discharge process. Notably, XRD peaks at 8.3°, 16.7°, and 34.4°, corresponding to the (001), (002), and (110) crystal planes are ascribed to ZnCl₂ (JCPDS no. 01-072-0538).⁵⁶ The ZnCl₂ peaks arise from the reduction of Zn²⁺ in the presence of ClO₄⁻, contributing to the formation of a Cl⁻-rich interfacial layer. Importantly, this behavior does not indicate a dual-ion storage mechanism but reflects interfacial side reactions that help stabilize the electrode surface. Upon charging from 0.1 to 1.8 V, the ZnCl₂ peaks disappear, confirming their dissolution back into the bulk electrolyte. The Zn(ClO₄)₂·6H₂O electrolyte peaks are marked in red asterisks (JCPDS no. 00-006-0197), indicating that residual electrolyte species are also present in the poly-AQ-DA/PANI cathode. Overall, the XRD data confirm the reversible intercalation and release of Zn²⁺ ions during discharging and charging.

Ex situ X-ray photoelectron spectroscopy (XPS) analysis, as shown in Fig. 5d, provides important information on the interactions of Zn²⁺ ions with the poly-AQ-DA/PANI framework during charging and discharging. The pronounced Zn 2p peaks, accounting for Zn²⁺ ions⁵⁷ following discharge at 0.1 V, correspond to the intercalated Zn²⁺ ions within the cathode matrix. Notably, in the charged state (1.8 V), significantly lower zinc intensities are apparent (Fig. 5d), attesting to the almost complete release of the Zn²⁺ ions and reversible storage by the poly-AQ-DA/PANI cathode.

The oxygen and nitrogen XPS data shown in Fig. 5d further illuminate the Zn²⁺ binding modes within the poly-AQ-DA/PANI cathode. In the case of O 1s XPS, three main peaks are observed, accounting for C=O (531 eV, blue), C–O (532.6 eV, red), and C=O–H⁺ (535.6 eV, green). Notably, the new peak emerging at 530 eV upon discharge at 0.1 V indicates the formation of C–O–Zn bonds.³⁰ Concurrently, the intensity of C=O (531 eV) significantly decreased, while that of the C–O peak at 532.6 eV was enhanced, confirming interactions of Zn²⁺ with the quinone oxygen during discharge. Following recharging, the O 1s XPS peaks mostly reverted to their initial intensity modes, underscoring the reversibility of Zn²⁺ uptake by the poly-AQ-DA/PANI matrix.

The N 1s XPS spectra shown in Fig. 5d reveal that Zn²⁺ ions were also coordinated with the benzenoid/quinoid units of PANI during discharging. Specifically, upon 0.1 V discharge, a new N 1s peak at 398.8 eV, corresponding to C–N–Zn appeared.⁸ The formation of C–N–Zn units also accounts for the considerable intensity reduction and spectral shift of the C=N peak (from 400.2 eV to 399.7 eV, Fig. 5d), and, in parallel, the appearance of a more prominent C–N peak at 401.2 eV. Like the O 1s XPS results, in the fully charged state, the N 1s spectrum almost fully reverted to the initial state, underscoring the reversibility of Zn²⁺ ion intercalation and redox reactions within the poly-AQ-DA/PANI cathode matrix.

The SEM images in Fig. 5e illuminate the morphology of the poly-AQ-DA/PANI cathode, indicating that no significant morphological changes occurred following the charge/discharge process. The scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDS) images in Fig. 5f further illuminate the enhanced, homogeneous distribution of zinc upon discharging, attesting to efficient Zn²⁺ incorporation within the poly-AQ-DA/PANI matrix.⁵⁸ Upon charging, a significantly lower concentration of zinc ions was apparent (Fig. 5f), confirming reversibility and effective cycling.

4. Discussion

This study presents the construction of an organic ZIB cathode, comprising anthraquinone-functionalized polydiacetylene and PANI, exhibiting excellent electrochemical properties. Specifically, the poly-AQ-DA/PANI cathode operates over a wide potential window between 0.1 and 1.8 V, further displaying high capacity and energy density, while retaining stable cycling. Furthermore, the battery comprising the poly-AQ-DA/PANI cathode exhibits an excellent anti-self-discharge profile, high specific capacity, and rate capability. The superior electrochemical performance of the poly-AQ-DA/PANI cathode is summarized in Table 1, which provides a comprehensive comparison with previously published organic cathode systems in ZIBs.

Table 1 Comparative electrochemical performance of the poly-AQ-DA/PANI cathode

	Type of organic cathode	Electrolyte	Potential window	Specific capacity (mAh g^−1) @ current density (A g^−1)	Energy density (Wh kg^−1)/power density (W kg^−1)	Number of cycles @ current density (A g^−1)/capacity retention (%)
1	Thianthrene (TT)	1 M Zn(OTF)2 electrolyte in acetonitrile	1.7 V	118.7 @ 0.5	67/2740	8000 cycles at 1/82% (ref. 59)
2	5,6,11,12-Tetraazanaphthacene (TANC)	3 M Zn(OTf)2 electrolyte	1.15 V	240/0.2C	245/—	47 500 cycles at 10C/71% (ref. 32)
3	Dibenzo[bi]thianthrene-5,7,12,14-tetraone (DTT)	2 m ZnSO4 in water	1.05 V	210.9 @ 0.05	126.5/31.6	150 cycles @ 0.1 and 23 000 cycles 2/89% (ref. 60)
4	Anthraquinone-quinoxaline derivative (HATAN)	3 m Zn(ClO4)2 in H2O	1.2 V	187 @ 0.1 in H2O and 128 @ 0.1 in acetonitrile	—	1000 cycles @ 1/56% (ref. 22)
5	Polytriphenylamine CMP (denoted as m-PTPA)	2 M ZnCl2 in water	1.1 V	210.7 @ 0.5	236/600	1000 cycles @ 6/87.6% (ref. 61)
6	Poly(phenazine-alt-pyromellitic anhydride) (PPPA)	2 M Zn(OTf)2/gelatin-based gel electrolyte	1.6 V	210 @ 0.5	—	20 000 cycles @ 5/70.6% (ref. 30)
7	Bipolar poly(thionine)	1 M zinc perchlorate (Zn(ClO4)2)	1.2 V	109 @ 0.5	—	5000 cycles @ 5/66.32% (ref. 62)
8	5,12-Dihydro-5,6,11,12-tetraazatetracene (DHTAT)	3 M Zn(ClO4)2	1.6 V	200.3 @ 0.1	105.1/53.4	100 cycles @ 1/94% (ref. 63)
9	poly(2H,11H-bis[l,4]triazino[3,2-b:3′,2′-m]triphenodithiazine-3,12-diyl-2,11-diyli-dene-11,12-bis[methyldene]) (PTL)	1 M Zn(OTf)2	1.4 V	120 @ 1	—	100 cycles @ 1/98% (ref. 64)
10	5,6,11,12,17,18-Hexaazatrinaphthylene-2,8,14-tricarboxylic acid (HATTA)	1 M Zn(CF3SO3)2	1.4 V	225.3 @ 0.1	142.7/34.7	10 000 cycles @ 25/84.07% (ref. 44)
11	AQ-DA/PANI (this work)	2 M Zn(ClO4)2·6H2O in acetonitrile	1.7 V	328.79 @0.1	277.4/135.07	Over 1000 cycles @ 0.1 and 19 000 cycles @ 1/93% and 95%

---

The excellent electrochemical performance of the poly-AQ-DA/PANI cathode is attributed to the unique features of the anthraquinone-functionalized polydiacetylene and integrated PANI constituents. Specifically, the redox-active anthraquinone residues, complemented by the extensive electron delocalization within both AQ and the conjugated PDA framework, result in abundant active sites for reversible Zn²⁺ ion intercalation and redox reactions. The conjugated PDA network particularly enhances charge transport while simultaneously providing a robust and stable framework, minimizing electrode degradation. Furthermore, the porous structure of the polymer facilitates ion diffusion during multiple charge–discharge processes. Importantly, the poly-AQ-DA scaffold likely constitutes a key factor contributing to the wide operation voltage, owing to the highly π-conjugated PDA backbone, which stabilizes the molecular framework by suppressing redox-induced structural degradation of the anthraquinone units. Furthermore, the extended ordered π-conjugated framework minimizes polarization and enables fast, reversible charge transfer.

Structural analyses provided insight into the electrode performance and its mechanistic features, particularly the occurrence of a highly efficient and reversible Zn²⁺ ion intercalation/extraction process. The Zn²⁺ storage mechanism in the poly-AQ-DA/PANI cathode is governed by a synergistic interplay between the redox-active anthraquinone moieties and π-conjugated PDA and PANI framework. During discharge, Zn²⁺ ions reversibly coordinate with quinone (C=O) and imine (C=N) units, forming Zn–O and Zn–N bonds without disrupting the overall electrode structure. In parallel, both PDA and PANI contribute to overall electron mobility, together affecting rate capability and cycling stability. The electrochemical properties and energy storage performance of the Zn‖poly-AQ-DA/PANI battery are intimately linked to the interplay between the cathode material, electrolyte, and ion transport dynamics.

Quinone-based organic cathode materials for ZIBs are compatible with both aqueous and organic electrolytes. Although aqueous ZIBs offer advantages like environmental friendliness, high safety, and low toxicity, superior electrochemical performance can be achieved in organic electrolytes. This improvement mainly arises from more effective electrode wetting and interfacial contact, which is particularly beneficial for the hydrophobic polydiacetylene-based framework employed here. In this context, Zn(ClO₄)₂·6H₂O/acetonitrile electrolyte features high ionic conductivity⁶⁵ and contributes to a wider potential window as it minimizes hydrogen evolution and electrode decomposition reactions in general.⁶⁶ Furthermore, the electrolyte also supports uniform zinc stripping/plating behavior at the anode, overall aiding longer lifetime and better rate capability of the ZIB.⁶⁷ The selection of acetonitrile as a solvent, in particular, enhances Zn²⁺ ion transport and minimizes the occurrence of parasitic reactions, and aids the reversible redox processes at the poly-AQ-DA/PANI electrode.⁵⁹

5. Conclusions

We demonstrate the construction of a novel, high-performance cathode for zinc ion batteries, comprising anthraquinone-functionalized polydiacetylene and PANI. The experiments reported indicate that the exceptional electrochemical and charge storage properties of the cathode are likely ascribed to the structural resilience and electron delocalization of the conjugated PDA framework and the abundant redox-active sites within the AQ moieties and PANI domains, as well as the overall high surface area and microporous structure of the poly-AQ-DA/PANI electrode. Specifically, we constructed a Zn‖poly-AQ-DA/PANI cell, exhibiting a particularly wide operating potential window of 1.7 V and a high specific capacity of 330 mAh g⁻¹ at 0.1 A g⁻¹, corresponding to an energy density of 277 Wh kg⁻¹ and a power density of 88 W kg⁻¹. Even at a higher current density of 1 A g⁻¹, the cell retained an energy density of 135 Wh kg⁻¹ and a power density of 1190 W kg⁻¹. The battery demonstrated minimal self-discharge, losing merely 11% of its initial capacity over 350 hours, highlighting its excellent electrochemical stability. The poly-AQ-DA/PANI electrode also exhibited remarkable cycling stability, showing 93% capacity retention after 1000 cycles at 0.1 A g⁻¹ and 95% retention after 19 000 cycles at 1 A g⁻¹ with >99% of coulombic efficiency. In summary, the new poly-AQ-DA/PANI organic cathode may usher new avenues for the utilization of zinc ion battery technologies for practical energy storage solutions.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information: NMR spectra, electrochemical data, FTIR, XPS, SEM and further experimental details. See DOI: https://doi.org/10.1039/d6ta01184e.

Acknowledgements

We are grateful to the Ministry of Energy for financial support, grant no. 2022/34. A. Samage acknowledges the Kreitman scholarship for Post-Doctoral studies. We acknowledge Dr Nitzan Shauloff for his valuable inputs. The authors are grateful to Dr Nitzan Maman for assistance with STEM sample preparation, Dr Lee Shelly and Dr Natalya Froumin for assistance with the XPS measurements, and Dr Alex Upcher and Dr Lonia Friedlander for STEM and p-XRD measurements.

References

1. Y. Liang, H. Dong, D. Aurbach and Y. Yao, Nat. Energy, 2020, 5, 822.
2. H. Wang, K. Lai, F. Guo, B. Long, X. Zeng, Z. Fu, X. Wu, Y. Xiao, S. Dou and J. Dai, Carbon Neutralization, 2022, 1, 59–67.
3. J. Park, A. M. Houser and S. Zhang, Adv. Mater., 2024, 36, 2409946.
4. H. Cui, L. Ma, Z. Huang, Z. Chen and C. Zhi, SmartMat, 2022, 3, 565–581.
5. Z. Tie and Z. Niu, Angew. Chem., Int. Ed., 2020, 59, 21293–21303.
6. N. T. H. Luu, A. S. Ivanov, T.-H. Chen, I. Popovs, J.-C. Lee and W. Kaveevivitchai, J. Mater. Chem. A, 2022, 10, 12371–12377.
7. S. Bian, Y. Yang, S. Liu, F. Ye, H. Tang, Y. Wu and L. Hu, Chem.–Eur. J., 2024, 30(13), e202303917.
8. W. Wang, V. S. Kale, Z. Cao, Y. Lei, S. Kandambeth, G. Zou, Y. Zhu, E. Abouhamad, O. Shekhah, L. Cavallo, M. Eddaoudi and H. N. Alshareef, Adv. Mater., 2021, 33(39), 2103617.
9. N. Patil, C. de la Cruz, D. Ciurduc, A. Mavrandonakis, J. Palma and R. Marcilla, Adv. Energy Mater., 2021, 11, 2100939.
10. Y. Zhao, M. Wei, H. Zhang, H. Zhang, Y. Zhu, H. Ma and M. Xue, ChemSusChem, 2024, 18(2), e202401354.
11. C. Yin, C. Pan, Y. Pan, J. Hu and G. Fang, Small Methods, 2023, 7(11), 2300574.
12. X. Liao, C. Pan, H. Yan, Y. Zhu, Y. Pan and C. Yin, Chem. Eng. J., 2022, 440, 135930.
13. N. N. Kadamannil, A. I. Shames, R. Bisht, S. Biswas, N. Shauloff, H. Lee, J.-M. Kim and R. Jelinek, ACS Appl. Mater. Interfaces, 2024, 16, 22593–22603.
14. B. H. A. Tasiman, R. Aflaha, W. P. Wicaksono, G. Fadillah, Y. D. Prabowo, J. D. Prades, E. Peiner, K. Triyana and H. S. Wasisto, Commun. Chem., 2026, 9(1), 60.
15. A. K. M. M. Alam and C. Xiang, ACS Omega, 2025, 10, 12346–12356.
16. J. Seo, M. I. Khazi, K. Bae and J. M. Kim, Small, 2023, 19(18), 2206428.
17. A. Maulik, V. C. Chandran, R. De, D. Nath, J. Ralhan, S. Sil, S. K. Pal and A. Pal, Small, 2025, 21(35), 2504051.
18. A. D. Tjandra, A.-H. Pham and R. Chandrawati, Chem. Mater., 2022, 34, 2853–2876.
19. S. Biswas, N. Shauloff, R. Bisht and R. Jelinek, Adv. Sustainable Syst., 2023, 7(6), 2300035.
20. N. Shauloff, R. Bisht, Y. Turkulets, R. Manikandan, A. Morag, A. Lehrer, J. H. Baraban, I. Shalish and R. Jelinek, Small, 2022, 19, 2206519.
21. J. Liu, Y. Zhou, G. Xing, M. Qi, Z. Tang, O. Terasaki and L. Chen, Adv. Funct. Mater., 2024, 34, 2312636.
22. Y. Zhai, C. Ji, R. Wang, Q. Ma, L. Zhang, H. Li, C. Zhang and Q. Zhang, Adv. Energy Mater., 2024, 15, 2403011.
23. R. Li, F. Xing, T. Li, H. Zhang, J. Yan, Q. Zheng and X. Li, Energy Storage Mater., 2021, 38, 590–598.
24. R. Bisht, V. Dhyani and R. Jelinek, Adv. Opt. Mater., 2020, 9, 2001497.
25. M. Umadevi and V. Ramakrishnan, J. Raman Spectrosc., 2002, 34, 13–20.
26. S. Xing, C. Zhao, S. Jing and Z. Wang, Polymer, 2006, 47, 2305–2313.
27. W. Song, Y. Li, L. Geng, G. Feng, J. Ren and X. Yu, Mater. Des., 2021, 205, 109744.
28. H. Dong, L. Wang, F. Zhang, H. Li, X. Zhao, W. Wei, Y. Kang, C. Yan, Y. Sang, H. Liu and S. Wang, Nano Energy, 2024, 128, 109768.
29. K. Hua, Q. Ma, Y. Liu, P. Xiong, R. Wang, L. Yuan, J. Hao, L. Zhang and C. Zhang, ACS Nano, 2025, 19, 14249–14261.
30. F. Ye, Q. Liu, H. Dong, K. Guan, Z. Chen, N. Ju and L. Hu, Angew. Chem., 2022, 134, e202214244.
31. C. Li, L. Hu, X. Ren, L. Lin, C. Zhan, Q. Weng, X. Sun and X. Yu, Adv. Funct. Mater., 2024, 34, 2313241.
32. D. Du, J. Zhou, Z. Yin, G. Feng, W. Ji, H. Huang and S. Pang, Adv. Energy Mater., 2024, 14, 2400580.
33. L. Ma, N. Li, C. Long, B. Dong, D. Fang, Z. Liu, Y. Zhao, X. Li, J. Fan, S. Chen, S. Zhang and C. Zhi, Adv. Funct. Mater., 2019, 29, 1906142.
34. A. Samage, M. Halakarni, H. Yoon and N. Sanna Kotrappanavar, Carbon, 2024, 219, 118774.
35. Y. Zhao, Y. Huang, F. Wu, R. Chen and L. Li, Adv. Mater., 2021, 33, 2101733.
36. Z. Zhou, J. Tong, X. Zou, Y. Wang, Y. Bai, Y. Yang, Y. Li, C. Wang and S. Liu, J. Mater. Chem. A, 2024, 12, 10923–10931.
37. X. Cui, Y. Li, Y. Zhang, Z. Sun, Y. Liu, J. Zhang, E. Xie and J. Fu, Chem. Eng. J., 2023, 478, 147197.
38. V. Soundharrajan, B. Sambandam, S. Kim, M. H. Alfaruqi, D. Y. Putro, J. Jo, S. Kim, V. Mathew, Y.-K. Sun and J. Kim, Nano Lett., 2018, 18, 2402–2410.
39. O. Buyukcakir, R. Yuksel, F. Begar, M. Erdogmus, M. Arsakay, S. H. Lee, S. O. Kim and R. S. Ruoff, ACS Appl. Energy Mater., 2023, 6, 7672–7680.
40. Y. Wang, S. Niu, S. Gong, N. Ju, T. Jiang, Y. Wang, X. Zhang, Q. Sun and H. b. Sun, Small Methods, 2024, 8, 2301301.
41. S. Li, J. Shang, M. Li, M. Xu, F. Zeng, H. Yin, Y. Tang, C. Han and H. M. Cheng, Adv. Mater., 2022, 35, 2207115.
42. L. Zhang, Y. Chen, Z. Jiang, J. Chen, C. Wei, W. Wu, S. Li and Q. Xu, Energy Environ. Mater., 2024, 7(1), e12507.
43. R. Wang, Y. Zhang, C. Ma, X. Wang, M. Cai, H. Du, Z. Yang, D. Chao and Y. Wang, Adv. Funct. Mater., 2025, 35, 2505318.
44. J. Li, L. Huang, H. Lv, J. Wang, G. Wang, L. Chen, Y. Liu, W. Guo, F. Yu and T. Gu, ACS Appl. Mater. Interfaces, 2022, 14, 38844–38853.
45. T. Xu, L. Su, C. Ku, Y. Zhang, L. Chen, Q. Gou, S. Fang, P. Xue, M. Tang, C. Wang and Z. Wang, Chem. Eng. J., 2024, 502, 158169.
46. Y. Liu, Z. Li, C. Li, Y. Wei, S. Yan, Z. Ji, S. Zou, H. Li, Y. Liu, C. Chen, X. He and M. Wu, Chem. Eng. J., 2024, 488, 150778.
47. L. Jiang, Z. Wu, Y. Wang, W. Tian, Z. Yi, C. Cai, Y. Jiang and L. Hu, ACS Nano, 2019, 13, 10376–10385.
48. S. Zhang, W. Zhao, H. Li and Q. Xu, ChemSusChem, 2019, 13, 188–195.
49. X. Cheng, Z. Xiang, C. Yang, Y. Li, L. Wang and Q. Zhang, Adv. Funct. Mater., 2023, 34, 2311412.
50. Q. Zong, W. Du, C. Liu, H. Yang, Q. Zhang, Z. Zhou, M. Atif, M. Alsalhi and G. Cao, Nano-Micro Lett., 2021, 13, 116.
51. J. Sun, J. Zhang, S. Wang, P. Sun, J. Chen, Y. Du, S. Wang, I. Saadoune, Y. Wang and Y. Wei, Energy Environ. Sci., 2024, 17, 4304–4318.
52. Q. Yang, Z. Huang, X. Li, Z. Liu, H. Li, G. Liang, D. Wang, Q. Huang, S. Zhang, S. Chen and C. Zhi, ACS Nano, 2019, 13, 8275–8283.
53. Z. Huang, T. Wang, H. Song, X. Li, G. Liang, D. Wang, Q. Yang, Z. Chen, L. Ma, Z. Liu, B. Gao, J. Fan and C. Zhi, Angew. Chem., 2020, 133, 1024–1034.
54. H. Zhang, Z. Zeng, F. Ma, X. Wang, Y. Wu, M. Liu, R. He, S. Cheng and J. Xie, Adv. Funct. Mater., 2022, 33, 2212000.
55. J. Xie, Z. Jia, H.-S. Tsai, M. Qian and X. Zhang, Chem. Eng. J., 2025, 518, 164660.
56. Y. Chen, K. Zhang, Z. Xu, F. Gong, R. Feng, Z. Jin and X. Wang, Energy Environ. Sci., 2025, 18, 713–727.
57. Q. Zong, Y. Zhuang, C. Liu, Q. Kang, Y. Wu, J. Zhang, J. Wang, D. Tao, Q. Zhang and G. Cao, Adv. Energy Mater., 2023, 13, 2301480.
58. M. Y. Rusanova, P. Polášková, M. Muzikař and W. R. Fawcett, Electrochim. Acta, 2006, 51, 3097–3101.
59. H. Cui, T. Wang, Z. Huang, G. Liang, Z. Chen, A. Chen, D. Wang, Q. Yang, H. Hong, J. Fan and C. Zhi, Angew. Chem., 2022, 134, e202203453.
60. Y. Wang, C. Wang, Z. Ni, Y. Gu, B. Wang, Z. Guo, Z. Wang, D. Bin, J. Ma and Y. Wang, Adv. Mater., 2020, 32, 2000338.
61. H. Zhang, L. Zhong, J. Xie, F. Yang, X. Liu and X. Lu, Adv. Mater., 2021, 33, 2101857.
62. S. Zhan, C. Wang, L. Zhong, L. Zhao, X. Yang, A. X. Y. Guo, W. Xiong, L. Cheng, R. Li, Z. Tang, S. C. Cao, C. Zhi and H. Lv, Small, 2024, 20, 2402767.
63. Y. Zhang, M. Li, Z. Li, Y. Lu, H. Li, J. Liang, X. Hu, L. Zhang, K. Ding, Q. Xu, H. Liu and Y. Wang, Angew. Chem., 2024, 63(48), e202410342.
64. L. Zhao, Y. Jia, Y. Wu, T. Gu, X. Zhou, X. Wang, L. Zhong, S. Zhan, H. Lv, C. Zhi and J. Liu, Angew. Chem., Int. Ed., 2025, 64, e202425082.
65. Y. Sun, B. Liu, L. Liu, J. Lang and J. Qiu, Small Struct., 2023, 4, 2200345.
66. Z. Wu, Y. Li, A. Amardeep, Y. Shao, Y. Zhang, J. Zou, L. Wang, J. Xu, D. Kasprzak, E. J. Hansen and J. Liu, Angew. Chem., Int. Ed., 2024, 136(19), e202402206.
67. Z. Song, L. Miao, L. Ruhlmann, Y. Lv, L. Li, L. Gan and M. Liu, Angew. Chem., Int. Ed., 2023, 62(13), e202219136.

---