Engineered Conductive Proteins for Supercapacitors

Abstract

Proteins can be used as building blocks of functional materials for electrochemical applications due to their structural properties and the possibility to tailor their ionic and electronic conductive properties.[1] One of the most attractive applications is in the bioelectronics field, for example as energy storage devices such as Electrical Double Layer Capacitors (EDLCs), due to the nontoxicity and biocompatibility of the materials.[2] EDLCs are primarily used for applications where high power is required during a short period of time. They present several advantages, such as fast charge-discharge cycling, high power density, and outstanding long-term stability.[3]Traditionally, the incorporation of biomaterials in EDCLs is limited because they can be denaturalized in contact with organic solvents or salts. In addition, they easily interact with other cell components resulting in parasitic reactions and their complex purification processes hinder their commercialization.[4] These drawbacks can be overcome by introducing engineered proteins, since their amino acid sequences can be tuned resulting in 3D structures with varying degrees of complexity. Based on this approach, engineered proteins with improved conductivity will be introduced as interlayers with good stability and wettability, to ensure that the ions can shuttle freely between the two electrodes.In our case, consensus tetratricopeptide repeat (CTPR) proteins have been chosen [5] and engineered with the aim of increasing the ionic conductivity of the resulting variants. CTPR variants have been mixed with 5% PEG solutions and drop cast to obtain self-standing films. After being cross-linked, the films have been sandwiched in a two electrodes Swagelok-cell configuration between two electrodes made of activated carbon. KCl (3M) aqueous solution has been used as electrolyte for evaluating the electrochemical performance of the devices.The electrochemical characterization of the EDLC devices has been carried out using cyclic voltammetry (CV) and galvanostatic cycling (GC) to study the effect of the of the engineering strategy of the CTPR proteins on the EDLC performances. The CV curves of the devices using thin films of proteins with distinct mutations show quadratic capacitive responses for all the assembled EDLCs, demonstrating both its ability to isolate the two electrodes and to allow the diffusion of ions. The EDLCs capacitances were calculated and analyzed from the GC characteristics at different charge-discharge currents and compared with commercial glass fiber separators confirming their feasibility as safe and environmentally friendly separators. The ionic diffusive behavior of the devices has been also studied by electrochemical impedance spectroscopy (EIS). Finally, the effect of the thickness, porosity, polarity, wettability, and ionic conductivity of the different protein separators has been addressed to explore the role of the engineered proteins in EDLC devices. Acknowledgements This abstract is part of R&D&I project TED2021-131641B-C44, funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGenerationEU/PRTR. This project has received funding from the European Union’s Horizon 2020 FET Open under the grant agreement No: 964593