Exploring Hex-Aza-COFs for Advanced Aqueous Batteries—A Case Study

Due to their merits such as safety, lower cost and reliability over non-aqueous batteries; aqueous batteries (ABs) have attracted a lot of attention recently. Particularly compared to lithium-ion batteries which are prone to violently react with exposed air and use of flammable organic solvents as electrolytes; water based traditional aqueous batteries are safer. Organic electrodes have their own benefits of use over inorganic electrodes and additionally their extended conjugation can enhance storage properties in ABs applications. 2D-COFs are recently emerged as a promising type of organic electrodes but still there is lack of performance in terms of the energy density and long term cycling capacity of (ABs). We have developed highly conjugated, electroactive phenazine and phenazine with quinone functionalities containing a series of 2D-COFs (Hex-Aza-COF-1 to 4).[1-2] Particularly, highly conjugated Hex-Aza-COF-3 was synthesized and used as a cathode for aqueous zinc-ion battery which showed a high capacity of 247 mAh g−1 (at a current density of 0.1 A g−1) with only 0.38% capacity decay per cycle during 10 000 cycles (at a current density of 1.0 A g−1), cointercalation of Zn2+ (60%) and H+ (40%) was evidenced by various spectroscopic techniques.[3] Further, we found that Zn2+ storage capacity is boosted in phenazine and quinone containing Hex-Aza-COF-2 compared to its non-quinone analogue Hex-Aza-COF-1.[4] To extend our interest in other non-metallic charge carriers, we used ammonium ions (NH4+) for the charge storage in Hex-Aza-COF-2 (quinone containing COF) where mechanism for the reaction of nitrogen and oxygen bridged by hydrogen bonds is revealed.[5] Interestingly we further revealed the synergistic charge storage mechanism of Hex-Aza-COF-2 involving the reaction of nitrogen and oxygen bridged by Mg2+ ions.[6] Later, the tradeoff between proton redox reactions and the HER in the Hex-Aza-COF-4 host material is revealed in detail. As a result, by balancing the electrolyte proton activity, an aqueous K+-assisted proton battery was assembled with a high energy density of 62.3 Wh kg−1.[7] In this series of Hex-Aza-COF, recently we have synthesized a novel HATP-PT COF which as an anode for aqueous NH4+ battery showed a high capacity and superior cycling performance.[8] Our understanding of 2D Hex-Aza-COF series will help to design and develop new organic materials particularly COFs.

References:
[1] Husam N. Alshareef and Mohamed Eddaoudi et. al.
Covalent Organic Frameworks as Negative Electrodes for High Performance Asymmetric Supercapacitors
Adv. Energy Mater. 2020, 10(38), 2001673
[2] Husam N. Alshareef and Mohamed Eddaoudi et. al.
2D Covalent-Organic Framework Electrodes for Supercapacitors and Rechargeable Metal-Ion Batteries
Adv. Energy Mater. 2022, 12(4), 2100177
[3] Husam N. Alshareef and Mohamed Eddaoudi et. al.
Phenanthroline Covalent Organic Framework Electrodes for High Performance Zinc-ion Supercapattery
ACS Energy Lett. 2020, 5(7), 2256-2264
[4] Husam N. Alshareef and Mohamed Eddaoudi et. al.
Molecular Engineering of Covalent Organic Framework Cathode for Enhanced Zinc-ion Batteries
Adv. Mater. 2021, 33(39), 2103617
[5] Husam N. Alshareef and Mohamed Eddaoudi et. al.
High Capacity NH4+ Charge Storage in Covalent Organic Frameworks
J. Am. Chem. Soc. 2021, 143(45), 19178-19186
[6] Husam N. Alshareef and Mohamed Eddaoudi et. al.
A Symmetric Aqueous Magnesium Ion Supercapattery Based on Covalent Organic Frameworks
Adv. Energy Mater. 2023, 13(7), 2203193
[7] Husam N. Alshareef and Mohamed Eddaoudi et. al.
Optimized Charge Storage in Aza-Based Covalent Organic Frameworks by Tuning Electrolyte Proton Activity
ACS Nano 2023, 17(14), 13961-13973
[8] Husam N. Alshareef and Mohamed Eddaoudi et. al.
An Ultrastable Aqueous Ammonium-Ion Battery Using a Covalent Organic Framework Anode
Adv. Mater. 2024, 36(47), 2409354