A Phenothiazine-Derived Organic Cathode for High-Capacity Aqueous Aluminum Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aqueous aluminum batteries (AABs) offer inherent safety and high theoretical volumetric capacity.
• Challenges with inorganic cathodes in AABs include Al3+ charge density issues causing structure collapse.
• Organic cathodes present a viable alternative due to sustainability, designability, and reactive sites.

Purpose of the Study:

• To investigate methylene blue (MB) as an organic cathode material for advanced AABs.
• To elucidate the charge storage mechanism in MB-based AABs.
• To demonstrate the potential of phenothiazine derivatives for reversible aluminum storage.

Main Methods:

• Electrochemical testing of methylene blue as a cathode in AABs.
• Analysis of ion co-insertion/extraction mechanisms.
• Evaluation of cycling stability and rate performance.
• Comparative study using neutral red (NR) as a structural analogue.

Main Results:

• MB cathode demonstrated reversible co-insertion/extraction of Al3+ with OTF- anions.
• Achieved reversible capacities of 138.8 mAh g-1 at 50 mA g-1 and 57.0 mAh g-1 at 200 mA g-1.
• Maintained 82.0 mAh g-1 after 110 cycles at 50 mA g-1.
• Neutral red confirmed the universality of the phenothiazine framework for aluminum storage.

Conclusions:

• Methylene blue is a high-performance organic cathode for aqueous aluminum batteries.
• The phenothiazine framework offers a promising platform for developing advanced organic cathode materials.
• This research highlights potential for next-generation, safe, and sustainable aqueous battery systems.