Optimized Charge Storage in Aza-Based Covalent Organic Frameworks by Tuning Electrolyte Proton Activity

Abstract

Proton activity in electrolytes plays a crucial role in deciding the electrochemical performance of aqueous batteries. On the one hand, it can influence the capacity and rate performance of host materials because of the high redox activity of protons. On the other hand, it can also cause a severe hydrogen evolution reaction (HER) when the protons are aggregated near the electrode/electrolyte interface. The HER dramatically limits the potential window and the cycling stability of the electrodes. Therefore, it is critical to clarify the impact of electrolyte proton activity on the battery macro-electrochemical performance. In this work, using an aza-based covalent organic framework (COF) as a representative host material, we studied the effect of electrolyte proton activity on the potential window, storage capacity, rate performance, and cycle stability in various electrolytes. A tradeoff relationship between proton redox reactions and the HER in the COF host is revealed by utilizing various in situ and ex situ characterizations. Moreover, the origin of proton activity in near-neutral electrolytes is discussed in detail and is confirmed to be related to the hydrated water molecules in the first solvation shell. A detailed analysis of the charge storage process in the COFs is presented. These understandings can be of importance for utilizing the electrolyte proton activity to build high-energy aqueous batteries.

Regulating the solvation structure with N,N-dimethylacetamide co-solvent for high-performance zinc-ion batteries

“…25 These coordinated water molecules, due to the polarizing effect, exhibit higher reduction reactivity compared to free water molecules, thereby leading to issues such as H + co-insertion and hydrogen evolution, which in turn limit the cycle life of batteries. 26,27 To overcome these challenges, it is necessary to regulate the coordination environment of zinc ions in the electrolyte by minimizing the number of coordinated water molecules. 28–30 Although the water-in-salt electrolytes (WISE) can significantly reduce the number of coordinated water molecules by involving a large number of anions in the solvation shell of zinc ions, the high cost associated with this approach makes it impractical for the industrialization of AZIBs.…”

Tailoring Localized Electrolyte via a Dual-Functional Protein Membrane toward Stable Zn Anodes

“…When hydrated Zn 2+ diffuses into the electric double-layer regions at the electrode/electrolyte interface, overcoming the energy barrier is a necessity to release bonded water for subsequent ion diffusion . This has been evidenced by recent studies showing the ease of Zn 2+ -solvated water in the solvation shell in dissociating into H + and OH – , which accordingly exacerbates hydrogen evolution, corrosion occurrence, and zincate accumulation (Scheme a). , These bottlenecks are mutually reinforcing and are closely interrelated. Continuous side reactions consume the active metal anode and increase the local pH value.…”