Symmetric All-Solid-State Supercapacitor Operating at 1.5 V Using a Redox-Active Gel Electrolyte

Abstract

The charge storage characteristics of a symmetric, all-solid-state supercapacitor device composed of redox-active PVA−K 3 Fe(CN) 6 −K 4 Fe(CN) 6 gel electrolyte and carbon nanotube paper electrodes are investigated in this study. Threeelectrode tests performed with aqueous K 3 Fe(CN) 6 /K 4 Fe(CN) 6 electrolyte exhibit an area-normalized specific capacitance 5 times larger than conventional aqueous H 3 PO 4 electrolyte due to pseudocapacitive contribution of the redox ions. The all-solidstate device composed of binder-free, carbon nanotube paper electrodes is thin and lightweight and has superior electrochemical performance. It exhibits a high area-normalized capacitance of 390 mF cm −2 at a low current density of 2 mA cm −2 , which is twice and four times that of devices composed of conventional PVA−H 3 PO 4 and PVA−KOH gel electrolytes, respectively. Furthermore, cyclic voltammetry tests and long-term stability tests demonstrate a large stability voltage window of 1.5 V, compared to only 1.0 and 0.4 V, respectively, for the PVA−H 3 PO 4 and PVA−KOH devices. High capacitance combined with a wide voltage window leads to a maximum volumetric energy density value of 2.47 mWh cm −3 and maximum power density value of 0.6 W cm −3 . It is expected that this novel, symmetric, lightweight, binder-free, all-solid-state supercapacitor system may provide a scalable strategy towards powering future wearable electronic devices.

Synergistic Interface‐Assisted Electrode–Electrolyte Coupling Toward Advanced Charge Storage

“…Impressively, the HCO-PFC// FG full cell delivers outstandingly high volumetric energy densities well beyond the reported values at all power rates, for the cobalt or nickel-based redox cells, [13,[42][43][44] manganese-based redox cells, [45] and even RE-based cells. [46][47][48] In summary, we demonstrate a facile decoration of K 4 Fe(CN) 6 onto Co 3 O 4 as a "smart" interface to boost the energy storage capability of both electrode and RE, which further leads to a coupled electrode-electrolyte system. The grafting of Fe(CN) 6 4− groups on Co 3 O 4 is implemented via Co-N bonding, which effectively modulates the electronic structure of Co 3 O 4 and dramatically enhances the adsorption of redox moieties in the electrolyte.…”

“…Impressively, the HCO‐PFC//FG full cell delivers outstandingly high volumetric energy densities well beyond the reported values at all power rates, for the cobalt or nickel‐based redox cells, [ 13,42–44 ] manganese‐based redox cells, [ 45 ] and even RE‐based cells. [ 46–48 ]…”

Thermogalvanic and Thermocapacitive Behavior of Superabsorbent Hydrogels for Combined Low-Temperature Thermal Energy Conversion and Harvesting

“…29 Redox-ionbased supercapacitors have also been previously reported but notably in the absence of a temperature gradient. 31,32 To the best of our knowledge, there have only been two true thermogalvanic cells that have inherently stored energy for later release. The first of these used an aqueous K 3 / K 4 [Fe(CN) 6 ] solution with a ion-exchange membrane, allowing K + ion transport, but frustrating [Fe(CN) 6 ] 3−/4− transfer; when thermogalvanically generating electricity, the redox states became unbalanced, and this "stored energy" could be released by removal of the temperature difference, allowing a flow of current in the opposite direction.…”

“…Another method is through exploiting the Soret effect to attain a form of thermally induced double-layer capacitance. − Neither of these methods utilize redox-active electrolytes, and therefore, these cannot be classed as thermogalvanic, given that the energy is stored and released via double-layer capacitance . Redox-ion-based supercapacitors have also been previously reported but notably in the absence of a temperature gradient. , …”

Preparation of Composite Monolith Supercapacitor Electrode Made from Textile-Grade Polyacrylonitrile Fibers and Phenolic Resin

“…An electrochemical supercapacitor consists of two electrodes, an electrolyte, and a separator [3]. There are four types of electrolytes: aqueous electrolytes (e.g., H 2 SO 4 and KOH), organic electrolytes (e.g., acetonitrile and propylene carbonate), ionic liquids (e.g., liquid salts) [4], solid state electrolytes (e.g., polyvinyl alcohol mixed with potassium ferrocyanide and potassium ferricyanide gel) [5,6].…”