School of Engineering of Matter, Transport and Energy, Arizona State University , Tempe, Arizona 85287, United States.
School of Biological and Health Systems Engineering, Arizona State University , Tempe, Arizona 85287, United States.
ACS Appl Mater Interfaces. 2017 Feb 1;9(4):3554-3561. doi: 10.1021/acsami.6b11113. Epub 2017 Jan 19.
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.
电化学赝电容器是储能应用的理想选择，因为它们比静电电容器或双电层电容器具有更高的能量密度。与电池相比，它们在更短的时间内提供更高的功率密度。最近在赝电容器方面的研究包括用于可植入储能应用的生物相容性水凝胶电解质和过渡金属电极。这些器件中的赝电容行为归因于在电极-电解质界面处形成的双电层内发生的氧化还原反应。在本研究中，我们详细研究了含糖苷的水凝胶配方中负责赝电容行为的氧化还原反应。使用碳带电极和基于掺氟氧化锡的过渡金属电极，比较了各种生物相容性水凝胶电解质组合之间的赝电容行为。只有在存在过渡金属电极的情况下，水凝胶才表现出赝电容响应，而在存在碳电极的情况下则没有。含有胺基的水凝胶比仅基于羟基官能团的凝胶具有更大的储能能力。此外，这些水凝胶中胺含量越高，储能能力就越高。我们声称，水凝胶中的氧化还原反应主要基于路易斯酸碱相互作用，这是由电解质链主链上的胺和羟基侧基以及电极表面的羟化作用促进的。水在这些反应中起着重要的作用，不仅提供离子自由基，而且还帮助离子传输。对氧化还原反应的这种理解将有助于确定在未来的生物相容性赝电容器中选择过渡金属电极、电解质中的路易斯酸碱对以及离子传输的介质。
