Abstract
Supercapacitors are well-known as promising energy storage devices capable of bridging the gap between conventional electrolytic capacitors and batteries to deliver both high power and energy densities for applications in electric vehicles and a smart energy grid. However, many reported instances of high-capacitance pseudocapacitors employ strong Faradaic reactions that hinder fast charge–discharge cycles and long-term stability, limiting their commercial viability. In this study, we utilise an economical and solution-processable procedure to fabricate a Cs3Bi2I9-based symmetric supercapacitor employing both electric double layer capacitance and pseudocapacitance with an aqueous NaClO4 electrolyte to deliver an outstanding device areal capacitance of 2.4 F cm−2 and specific capacitance of 280 F g−1. The Cs3Bi2I9 device achieves an excellent 88% capacitance retention after 5000 charge–discharge cycles, proving its long-term cycle stability and promise as a practical supercapacitor. We characterise the time-dependent charge storage mechanisms through cyclic voltammetry and electrochemical impedance spectroscopy to find that electrostatic charge accumulation predominates at high potentials (0.3–0.6 V) whereas weak, Faradaic charge adsorption and pore penetration bolster charge storage at lower potentials (0.0–0.2 V).
Highlights
Supercapacitors can be subdivided into two classifications depending on their predominant charge storage mechanism: electric double layer capacitors (EDLC) store charge primarily through non-Faradaic electrostatic interactions between a polarized electrolyte and charged electrodes, whereas pseudocapacitors combine the electrostatic behaviour of EDLCs with typically reversible Faradaic reactions between the electrolytic solution and the electrode surface, which is often coated with metal oxides and other inorganic/organic hybrid materials.[8,9,10]
The electrodes were characterized through X-ray diffraction (XRD) and scanning electron microscopy (SEM)
We evaluated the electrochemical behavior and capacitive performance of the Cs3Bi2I9-based supercapacitor in varying voltage and time regimes through cyclic voltammetry (CV) and galvanostatic charge-discharge measurements, aiming to identify its primary charge storage mechanisms
Summary
The recent proliferation of renewable but variable solar and wind energy technologies, as well as the growing market for hybrid electric vehicles, has spurred research efforts to develop a new generation of high performing and sustainable energy storage devices.[1,2,3] So-called supercapacitors (ultracapacitors, electrochemical capacitors) have accrued particular research attention for their high energy densities compared to conventional capacitors and rapid chargedischarge rates and long-life cycle stabilities compared to batteries and fuel cells.[4,5,6,7] Supercapacitors can be subdivided into two classifications depending on their predominant charge storage mechanism: electric double layer capacitors (EDLC) store charge primarily through non-Faradaic electrostatic interactions between a polarized electrolyte and charged electrodes, whereas pseudocapacitors combine the electrostatic behaviour of EDLCs with typically reversible Faradaic reactions between the electrolytic solution and the electrode surface, which is often coated with metal oxides and other inorganic/organic hybrid materials.[8,9,10] While EDLCs xxxx-xxxx/xx/xxxxxxJournal XX (XXXX) XXXXXX boast optimal power densities and long-life stabilities necessary for commercial applications due to the highlyreversible nature of electrostatic charge storage, EDLCs often lack suitable energy densities for real world applications.[11,12] In contrast, pseudocapacitors can achieve capacitances 10-100 times greater than EDLCs while preserving high power densities by constraining electron transfer to the electrodes’ surfaces and near-surface pores.[13,14] Popular pseudocapacitor electrode materials have included RuO2, MnO2, and other inorganic/organic hybrids that acclaim extremely high gravimetric capacitances (> 1000 F g-1) and areal capacitances (>100 mF cm-2).[15,16,17,18,19,20,21,22] Many such pseudocapacitive materials undergo strong Faradaic reactions that inhibit longterm stability and prevent fast discharge.[23]. Claims of deceptively ultrahigh gravimetric capacitances are often calculated from electrodes with extremely low mass loadings (
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