A Total Organic Aqueous Redox Flow Battery Employing a Low Cost and Sustainable Methyl Viologen Anolyte and 4‐HO‐TEMPO Catholyte

TLDR

Renewable integration demands new storage; redox flow batteries offer high power density, scalability, and safety, yet resource limits and high costs hinder widespread adoption. The study reports a total organic aqueous redox flow battery using low‑cost, sustainable methyl viologen anolyte and 4‑HO‑TEMPO catholyte with a benign NaCl electrolyte. The authors characterized the electrochemical behavior of MV and 4‑HO‑TEMPO via cyclic voltammetry and rotating disk electrode measurements. The MV/4‑HO‑TEMPO ARFB delivers a 1.25‑V cell voltage, operates at 20–100 mA cm⁻², maintains stable capacity over 100 cycles with nearly 100 % Coulombic efficiency, and represents a major advance in organic ARFBs.

Abstract

Increasing worldwide energy demands and rising CO 2 emissions have motivated a search for new technologies to take advantage of renewables such as solar and wind energies. Redox flow batteries (RFBs) with their high power density, high energy efficiency, scalability (up to MW and MWh), and safety features are one suitable option for integrating such energy sources and overcoming their intermittency. However, resource limitation and high system costs of current RFB technologies impede wide implementation. Here, a total organic aqueous redox flow battery (OARFB) is reported, using low‐cost and sustainable methyl viologen (MV, anolyte) and 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (4‐HO‐TEMPO, catholyte), and benign NaCl supporting electrolyte. The electrochemical properties of the organic redox active materials are studied using cyclic voltammetry and rotating disk electrode voltammetry. The MV/4‐HO‐TEMPO ARFB has an exceptionally high cell voltage, 1.25 V. Prototypes of the organic ARFB can be operated at high current densities ranging from 20 to 100 mA cm 2 , and deliver stable capacity for 100 cycles with nearly 100% Coulombic efficiency. The MV/4‐HO‐TEMPO ARFB displays attractive technical merits and thus represents a major advance in ARFBs.