Hydroxide ion-conducting viologen–bakelite organic frameworks for flexible solid-state zinc–air battery applications. Issue 2 (13th December 2022)

• Record Type: Journal Article
• Authors: Rase, Deepak; Illathvalappil, Rajith; Singh, Himan Dev; Shekhar, Pragalbh; Leo, Liya S; Chakraborty, Debanjan; Haldar, Sattwick; Shelke, Ankita; Ajithkumar, Thalasseril G.; Vaidhyanathan, Ramanathan
• Is Part Of: Nanoscale horizons. Volume 8:Issue 2(2023)
• Page Start: 224
• Page End: 234
• Publication Date: 2022-12-13
• Subjects: Nanoscience -- Periodicals; Nanotechnology -- Periodicals; 620.505
• DOI: 10.1039/d2nh00455k
• Languages: English
• ISSNs: 2055-6756

Abstract

Abstract : A cationic bakelite–viologen polymer with counter-balancing hydroxide ions serves as a solid-state electrolyte for zinc–air battery. Abstract : Adaptable polymer-based solid-state electrolytes can be a game-changer toward safe, lightweight flexible batteries. We present a robust Bakelite-type organic polymer covalently decked with viologen, triazine, and phenolic moieties. Its flexible structure with cationic viologen centers incorporates counter-balancing free hydroxide ions into the polymeric framework. By design, the aromatic groups and heteroatoms in the framework can be activated under an applied potential to prompt a push–pull drive, setting off the towing of hydroxide ions via weak electrostatic, van der Waals, and hydrogen-bond interactions. The frontier orbitals from a DFT-modeled structure certify this. The hydroxyl-polymer requires minimal KOH wetting to maintain a humid environment for Grotthuss-type transport. The hydroxide ion conductivity reaches a value of 1.4 × 10 −2 S cm −1 at 80 °C and 95% RH, which is retained for over 15 h. We enhanced its practical utility by coating it as a thin solid-state separator-cum-electrolyte on readily available filter paper. The composite exhibits a conductivity of 4.5 × 10 −3 S cm −1 at 80 °C and 95% RH. A zinc–air battery (ZAB) constructed using this polymer-coated paper as electrolyte yields a maximum power density of 115 mW cm −2 and high specific capacitance of 435 mA h g −1 . The power density recorded for our ZAB is among the best reported for polymer electrolyte–based batteries. Subsequently, the flexible battery fabricated with IISERP-POF11_OH@FilterPaper exhibits an OCV of 1.44 V, and three batteries in series power a demo traffic signal. To underscore the efficiency of hydroxide ion transport through the complex multifunctional backbone of the polymer, we calculated the diffusion coefficient for OH − (Exp: 2.9 × 10 −5 cm 2 s −1 ; Comp. 5.2 × 10 −6 cm 2 s −1 ) using electrochemical methods and MD simulations. Climbing-edge NEB calculations reveal a large energy barrier of 2.11 eV for Zn 2+ to penetrate the polymer and identify hydroxide ions within the polymer, suggesting no undesirable Zn 2+ crossover. Our findings assert the readily accessible C–C-linked cationic polymer's capacity as a solid-state electrolyte for ZABs and any anion-conducting membrane.