Investigation into Pseudo-Capacitance Behavior of Glycoside-Containing Hydrogels

Abstract

Electrochemical pseudocapacitors are an attractive choice for energy storage applications because they offer higher energy densities than electrostatic or electric double layer capacitors. They also offer higher power densities in shorter durations of time, as compared to batteries. Recent efforts on pseudocapacitors include biocompatible hydrogel electrolytes and transition metal electrodes for implantable energy storage applications. Pseudocapacitive behavior in these devices has been attributed to the redox reactions that occur within the electric double layer, which is formed at the electrode-electrolyte interface. In the present study, we describe a detailed investigation on redox reactions responsible for pseudocapacitive behavior in glycoside-containing hydrogel formulations. Pseudocapacitive behavior was compared among various combinations of biocompatible hydrogel electrolytes, using carbon tape electrodes and transition metal electrodes based on fluorine-doped tin oxide. The hydrogels demonstrated a pseudocapacitive response only in the presence of transition metal electrodes but not in the presence of carbon electrodes. Hydrogels containing amine moieties showed greater energy storage than gels based purely on hydroxyl functional groups. Furthermore, energy storage increased with greater amine content in these hydrogels. We claim that the redox reactions in hydrogels are largely based on Lewis acid-base interactions, facilitated by amine and hydroxyl side groups along the electrolyte chain backbones, as well as hydroxylation of electrode surfaces. Water plays an important role in these reactions, not only in terms of providing ionic radicals but also in assisting ion transport. This understanding of redox reactions will help determine the choice of transition metal electrodes, Lewis acid-base pairs in electrolytes, and medium for ionic transport in future biocompatible pseudocapacitors.

Repulsion of Polar Gels From Water: Hydration‐Triggered Actuation, Self‐Folding, and 3D Fabrication

“…Amikagel films were generated by cross‐linking between amines in aminoglycoside amikacin with epoxide groups present in PEGDE or BDDE, resulting in gels that contain both amine and hydroxyl groups (Figure S1, Supporting Information). [ 32,45 ] Figure shows various 3D objects that were fabricated following hydration‐triggered actuation and folding of different 2D shapes of AM‐PEGDE films. After placing the film on the surface of water, each shape was seen to curl such that the actuation resulted in minimization of the contact area between the film and the water.…”

“…Here, we report hydration‐triggered activation of a single‐component cationic hydrogel, “Amikagel,” [ 31,32 ] derived from an aminoglycoside antibiotic, amikacin (AM), cross‐linked with diglycidyl ethers. The hydrogel is homogeneous in that no gradients of cross‐linking or porosity are intentionally engineered into its morphology.…”

Diamond Supercapacitors: Towards Durable, Safe, and Biocompatible Aqueous-Based Energy Storage

“…Biomedical applications are also suggested by the diamond electrode’s ability to operate in physiological solution ( Garrett et al, 2012 ; Falahatdoost et al, 2021 ). This approach has previously been demonstrated with other materials and could be used to power small biomedical devices within the body ( Chae et al, 2017 ; Raravikar et al, 2017 ; Sim et al, 2018 ). It has been suggested that supercapacitors can be used in hybrid devices where batteries or energy harvesting devices provide baseload power and supercapacitors can provide peak power ( Wang et al, 2020b ).…”

“…This window can be widened by using ionic liquids, or organic and “water-in-salt” electrolytes (for example [EMIM][BF 4 ], TEABF4/CAN, and LiTFSI, respectively); however, many of these chemicals are flammable or toxic ( Martínez-Casillas et al, 2019 ). Highly toxic electrolytes present a significant health hazard for biomedical applications even if hermetically sealed, and so safer aqueous electrolytes are preferred ( Raravikar et al, 2017 ). Aqueous electrolytes also have high conductivity at room temperature enabling higher P densities, while are generally less expensive than organic electrolytes or ionic liquids ( Simon and Gogotsi, 2013 ; Gao and Nebel, 2016 ; da Silva et al, 2018 ).…”

“…These properties suggest the use of diamond in surgically implantable supercapacitors, which are attractive power sources for biomedical devices due to high power density, long lifespan, and small dimensions ( Chae et al, 2017 ; Sim et al, 2018 ; Liu et al, 2021 ). Diamond-based supercapacitors are able to use safer aqueous electrolytes while retaining an extended potential window, or could possibly even use the physiological electrolyte itself, as has been done previously with other materials [see ( Chae et al, 2017 ; Raravikar et al, 2017 ; Sim et al, 2018 )].…”