The development of green flexible micro-supercapacitors (MSCs) is one of the biggest challenges in future wearable electronics. Flexible MSCs are mainly produced from non-biodegradable synthetic polymers, resulting in massive electronic waste. Moreover, complex multi-step fabrication increases their production cost. Here, the direct fabrication of highly conductive, intrinsically flexible, and green microelectrodes from naturally fallen leaves in ambient air using femtosecond laser pulses without any additional materials is reported. Hierarchically porous graphene is patterned on different types of leaves via a facile, mask-less, scalable, and one-step laser writing. Leaves consist of biominerals, which decompose into inorganic crystals that serve as nucleation sites for the growth of 3D mesoporous few-layer graphene. The femtosecond laserinduced graphene (FsLIG) microelectrodes formed on leaves have lower sheet resistance (23.3 Ω sq −1 ) than their synthetic polymer counterparts and exhibit an outstanding areal capacitance (34.68 mF cm −2 at 5 mV s −1 ) and capacitance retention (≈99% after 50 000 charge/discharge cycles). The FsLIG MSCs on a single leaf could easily power a light-emitting diode or a table clock and could be applied in wearable electronics, smart houses, and Internet of Things.
A rechargeable
aluminum-ion battery based on chloroaluminate electrolytes
has received intense attention due to the high abundance and chemical
stability of aluminum. However, the fundamental intercalation processes
and dynamics in these battery systems remain unresolved. Here, the
energetics and dynamics of chloroaluminate ion intercalation in atomically
thin single crystal graphite are investigated by fabricating mesoscopic
devices for charge transport and operando optical
microscopy. These mesoscopic measurements are compared to the high-performance
rechargeable Al-based battery consisting of a few-layer graphene–multiwall
carbon nanotube composite cathode. These composites exhibit a 60%
capacity enhancement over pyrolytic graphite, while an ∼3-fold
improvement in overall ion diffusivity is also obtained exhibiting
∼1% of those in atomically thin single crystals. Our results
thus establish the distinction between intrinsic and ensemble electrochemical
behavior in Al-based batteries and show that engineering ion transport
in these devices can yet lead to vast improvements in battery performance.
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