Lignin-Based Electrolytes for Redox Flow Batteries

Abstract

Redox flow batteries (RFBs) are promising candidates for long duration energy storage applications thanks to their unique feature of independent scaling of energy and power. Organic electrolytes and an alternative to the present metal-based have been proposed as potentially low-cost and environmentally friendly electrolytes to alleviate the capital costs of RFBs. Lignin, the second most abundant bio-based polymer in nature, demonstrates the advantages of high carbon content, rich in aromatic groups and is a potential electrolyte basefor RFBs [1] [2] [3] [4]. In this work, soda lignin was considered as redox species modified in optimum oxidative conditions. The cyclic voltammetry analysis confirmed its electrochemical reversibility, so that for RFB tests, modified soda lignin was used on the negative side versus ferrocyanide on the positive at highly alkaline media.Following RFB cycling tests, a substantial improvement was achieved in the charge/discharge capacities and coulombic efficiency of RFB using modified soda lignin compared to pristine. For further performance optimization, it was found that the flow ratehas a substantial influence. This is more likely due to the thixotropic behaviour of the lignin electrolyte. Further explorations are under way of studying different membranes/electrolyte additives and cycling with higher concentration of lignin towards enhancing the RFB performance by improving the conductivity thus voltage efficiencies. Thecurrent approach of introducing bio-based electrolytes could enlighten a new path in the future research direction of organic RFBs and add a valuable point towards the carbon neutralization. Keywords: Lignin, Bio-based electrolyte, Organic redox flow battery, Sustainability, Energy storageAcknowledgement:The authors acknowledge Miscancell, Hondiusstraat 28, 6827 DE Arnhem, Netherlands for providing the lignin material for this work.