Graphene Hydrogel Supercapacitor for Wider Aqueous Voltage Window
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Solution Overview
Problem
Supercapacitors with aqueous electrolytes are limited by the breakdown of water, restricting their operational voltage window to around 1.3-1.5 V, while those with organic electrolytes offer higher voltage but are more costly and toxic.
Innovation Solution
A symmetric supercapacitor design using graphene electrodes enveloped in a hydrogel electrolyte, which enhances the operational voltage window to beyond 2.6 V, achieved by the synergy between graphene and hydrogel, allowing for a flexible and efficient energy storage device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aqueous electrolyte is used in supercapacitor, then cost is reduced and toxicity is reduced, but operational voltage window is limited to 1.3-1.5 V
Solution Approach 1:
The patent uses a composite structure combining graphene electrodes with hydrogel electrolyte. The graphene material provides high surface area and excellent electrical conductivity, while the hydrogel electrolyte (containing PVA and LiClO4) enables enhanced voltage operation. This composite approach allows the supercapacitor to achieve operational voltage windows exceeding 2.6 V, overcoming the traditional 1.3-1.5 V limitation of aqueous electrolytes without incurring the cost and toxicity issues of organic electrolytes.
2Reliability
If organic electrolyte is used in supercapacitor, then operational voltage window is increased to 2.5-2.7 V, but cost increases and toxicity increases
Solution Approach 1:
The patent changes the physical and chemical parameters of the electrolyte by using a hydrogel system with specific composition (PVA concentration, LiClO4 concentration) and cross-linking density. This parameter optimization allows the aqueous-based hydrogel electrolyte to achieve voltage stability comparable to organic electrolytes (2.6-2.7 V operational window) while maintaining the environmental and cost advantages of aqueous systems. The graphene electrode structure further enhances this by providing stable interface chemistry.
3Reliability
If graphene electrodes are used with hydrogel electrolyte, then operational voltage window is enhanced beyond 2.6 V, but device complexity increases
Solution Approach 1:
The patent employs porous graphene electrodes with high surface area that are enveloped by the hydrogel electrolyte. The porous structure of graphene provides numerous active sites for charge storage and facilitates electrolyte penetration. The hydrogel electrolyte fills the pores and provides ionic conductivity. This porous architecture enables the device to achieve enhanced voltage operation (>2.6 V) while maintaining a relatively simple overall device structure and fabrication process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device achieves an unexpectedly large operational voltage window akin to organic solvent-based supercapacitors, overcoming the limitations of aqueous electrolytes, with improved stability and efficiency.
Implementation Method 1
Each capacitor is positioned at the interface between electrode and the electrolyte, and is formed from the supercapacitor electrode, a dielectric layer formed from solvent molecules present in the electrolyte (called the inner Helmholtz plane), and a layer of charge carriers supplied by the electrolyte as counter-charges to charge on the electrode (called the outer Helmholtz plane). This triple structure of electrode, inner Helmholtz plane and outer Helmholtz plane forming a capacitive system at each electrode is referred to as the double layer, or electrical double layer.
Implementation Method 2
A hydrogel is a gel in which the liquid constituent is water and which may be formed from a network of polymer chains.
Implementation Method 3
Electrodes based on carbon have been associated with supercapacitors since the early days of their development. Initially carbon was of interest as an electrode material because it provided the possibility to manufacture electrodes with large surface areas. It was only later in the development of supercapacitor devices that the importance of the so-called double layer at the electrode surfaces was realised. This complex and often ill-understood phenomenon, which is linked to the use of carbon as an electrode material, is at the heart of the high capacitance values associated with supercapacitors.
Implementation Method 4
a layer of charge carriers supplied by the electrolyte as counter-charges to charge on the electrode
Data Source
AI summary
A symmetric supercapacitor device comprising two electrodes, wherein each electrode comprises graphene, and a hydrogel electrolyte enveloping the electrodes in an active area, produces an enhanced operational voltage window. The graphene may be 3D graphene. The electrolyte may comprise a high molarity salt. The electrodes may have an interdigitated geometry.