Redox Cofactor from Biological Energy Transduction as Molecularly Tunable Energy-Storage Compound

Influence of Magnetic Fields on Electrochemical Reactions of Redox Cofactor Solutions

Redox cofactors mediate many enzymatic processes and are increasingly employed in biomedical and energy applications. Exploring the influence of external magnetic fields on redox cofactor chemistry can enhance our understanding of magnetic-field-sensitive biological processes and allow the application of magnetic fields to modulate redox reactions involving cofactors. Through a combination of experiments and modeling, we investigate the influence of magnetic fields on electrochemical reactions in redox cofactor solutions. By employing flavin mononucleotide (FMN) cofactor as a model system, we characterize magnetically induced changes in Faradaic currents. We find that radical pair intermediates have negligible influence on current increases in FMN solution upon application of a magnetic field. The dominant mechanism underlying the observed current increases is the magneto-hydrodynamic effect. We extend our analyses to other diffusion-limited electrochemical reactions of redox cofactor solutions and arrive at similar conclusions, highlighting the opportunity to use this framework in redox cofactor chemistry.

Bioderived Molecular Electrodes for Next-Generation Energy-Storage Materials

Nature-derived organic small molecules, as energy-storage materials, provide low-cost, recyclable, and non-toxic alternatives to inorganic and polymer electrodes for lithium-/sodium-ion batteries and beyond. Some organic carbonyl compounds have met or exceeded the voltages and gravimetric storage capacities achieved by traditional transition metal oxide-based compounds due to the metal-ion coupled redox and facile electron-transport capability of functional groups. Stability issues that previously limited the capacity of small organic molecules can be remediated with reactions to form insoluble salts, noncovalent interactions (hydrogen bonding and π stacking), loading onto substrates, and careful electrolyte selection. The cost-effectiveness and sustainability of organic materials may further be improved by employing porphyrin-based electrodes and multivalent-ion batteries utilizing abundant metals, such as aluminum and zinc. Finally, redox flow batteries take advantage of the solubility of organics for the development of scalable, high power density, and safe energy-storage devices based on aqueous electrolytes. Herein, the advantages and prospects of small molecule-based electrodes, with a focus on nature-derived organic and biomimetic materials, to realize the next-generation of green battery chemistry are reviewed.

Sustainable Battery Materials from Biomass

Sustainable sources of energy have been identified as a possible way out of today's oil dependency and are being rapidly developed. In contrast, storage of energy to a large extent still relies on heavy metals in batteries. Especially when built from biomass-derived organics, organic batteries are promising alternatives and pave the way towards truly sustainable energy storage. First described in 2008, research on biomass-derived electrodes has been taken up by a multitude of researchers worldwide. Nowadays, in principle, electrodes in batteries could be composed of all kinds of carbonized and noncarbonized biomass: On one hand, all kinds of (waste) biomass may be carbonized and used in anodes of lithium- or sodium-ion batteries, cathodes in metal-sulfur or metal-oxygen batteries, or as conductive additives. On the other hand, a plethora of biomolecules, such as quinones, flavins, or carboxylates, contain redox-active groups that can be used as redox-active components in electrodes with very little chemical modification. Biomass-based binders can replace toxic halogenated commercial binders to enable a truly sustainable future of energy storage devices. Besides the electrodes, electrolytes and separators may also be synthesized from biomass. In this Review, recent research progress in this rapidly emerging field is summarized with a focus on potentially fully biowaste-derived batteries.

Cross-Conjugated Polycatechol Organic Cathode for Aqueous Zinc-Ion Storage

The rapid development of aqueous zinc-ion batteries poses a challenge for the exploration of cathode materials with high capacity and long cycle life. Organic materials are considered an appropriate choice owing to their structural flexibility and tunable surface chemistry. However, most organic cathode materials still have some shortcomings, such as low electrical conductivity, high cost, and limited cycling durability. Here, a facile synthesis of a novel organic composite cathode composed of cross-conjugated polycatechol (PC) combined with graphene (PC/G) is reported. The PC/G cathode is used for aqueous zinc-ion storage, wherein many hydroxy groups in the PC/G composite cathode can be converted into redox-active carbonyl groups at the initial discharge-charge. This composite cathode can deliver a high specific capacity of 355 mAh g^-1 at 0.1 C and a specific capacity of 171 mAh g^-1 at 10 C. Moreover, the composite cathode can retain 74.4 % of its initial capacity after 3000 discharge-charge cycles at 2 C. This coordination route to zinc ions within the PC/G composite cathode can avoid the destruction of the cathode material during discharge-charge. This organic cathode shows great promise for reversible zinc-ion storage, bringing aqueous zinc-ion batteries a step closer to future practical applications.

Biological Nicotinamide Cofactor as a Redox-Active Motif for Reversible Electrochemical Energy Storage

Nicotinamide adenine dinucleotide (NAD⁺ ) is one of the most well-known redox cofactors carrying electrons. Now, it is reported that the intrinsically charged NAD⁺ motif can serve as an active electrode in electrochemical lithium cells. By anchoring the NAD⁺ motif by the anion incorporation, redox activity of the NAD⁺ is successfully implemented in conventional batteries, exhibiting the average voltage of 2.3 V. The operating voltage and capacity are tunable by altering the anchoring anion species without modifying the redox center itself. This work not only demonstrates the redox capability of NAD⁺ , but also suggests that anchoring the charged molecules with anion incorporation is a viable new approach to exploit various charged biological cofactors in rechargeable battery systems.

Organic Carbonyl Compounds for Sodium-Ion Batteries: Recent Progress and Future Perspectives

Sodium-organic batteries, which use organic materials as the electrodes in sodium-ion batteries, are an attractive alternative to conventional lithium-ion batteries for next-generation sustainable and versatile energy storage devices owing to the abundant sodium resources and environmental friendly features. However, organics used in sodium-ion batteries also encounter some issues such as low redox potential, high solubility in the electrolyte, and low conductivity. In response, altering the aromatic system/attaching electron-withdrawing groups, constructing polymers, and incorporating a conductive matrix are effective strategies. This review summarizes and briefly discusses recent organic carbonyl compounds for sodium-organic batteries from the viewpoint of function-oriented design, including function evolution from small-molecule compounds to polymers, then composites, and finally flexible electrodes. In particular, as a timely overview, carbonyl-based organic flexible electrodes for sodium-organic batteries are also highlighted for the first time.