A Hexacyanomanganate Negolyte for Aqueous Redox Flow Batteries

Abstract

Aqueous redox flow batteries (RFBs) have emerged as promising largescale energy storage devices due to their high scalability, safety, and flexibility. Manganese-based redox materials are promising sources for use in RFBs owing to their earth abundance, affordability, and variety of oxidation states. However, the instability of Mn redox couples, attributed to the unstable d-orbital configuration of Mn 3+ (d 4 ) known to involve strong Jahn−Teller effects, has hindered their practical use. Here, we discover that the [Mn(CN) 6 ] 5−/4−/3− negolyte offers advantages in terms of reversibility, stability, and reaction kinetics owing to the addition of NaCN supporting electrolyte, which inhibits ligand exchange reactions, resulting in high performance. [Mn(CN) 6 ] 5−/4−/3− negolyte possesses stable multielectron reactions from Mn(I) to Mn(III), leading to a high capacity of 133.7 mAh after 100 cycles. We provide chemical evidence obtained from in situ Raman analysis for unprecedented Mn(I) stability during electrochemical cycling, opening up new avenues for the design of low-cost Mn-based redox systems.

Lead-Based Flow Battery Based on New Pb-Based Anolyte Chemistry

“…Cathodic peak current versus the square root of the scan rate (v 1/2 ) for the different scan rates with a linear fit. (c) Comparison of the diffusion coefficient and potential of metal-based redox couples. − (d) Charge curves of static Pb symmetric batteries using 0.4 mol L –1 PbBr 2 + 4 mol L –1 HBr anolyte and 0.4 mol L –1 PbMSA + 4 mol L –1 MSA anolyte, respectively. The corresponding plating morphology of metallic Pb was determined using (e) PbMSA anolyte and (f) PbBr­(H 2 O) n + anolyte.…”

Surpassing water-splitting potential in aqueous redox flow batteries: insights from kinetics and thermodynamics

“…Nonetheless, aqueous electrolytes consist of common salts dissolved in water, making them cost-effective and affordable for large-scale applications. 35 Moreover, they are less toxic than organic electrolytes, posing a lower risk in terms of toxicity and being more environmentally friendly. Furthermore, the relatively high dielectric constant of water positions it as an ideal solvent for aqueous electrolytes, enhancing its solubility.…”

A perspective on manganese-based flow batteries

“…Therefore, the use of ligands to coordinate with the Mn 3+ ion and alter the electron distribution has the potential to enhance its stability. For example, CN − can coordinate with Mn ions to form a hexacyanomanganate complex ([Mn(CN) 6 ] 5−/4−/3− ) [42]. The strong coordination field leads to a low-spin state of Mn 3+ , which helps to reduce disproportionation reactions and stabilize the Mn 3+ ion.…”