Green Flexible Graphene-Inorganic-Hybrid Micro-Supercapacitors Made of Fallen Leaves Enabled by Ultrafast Laser Pulses

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 laser-induced graphene (FsLIG) microelectrodes formed on leaves have lower sheet resistance (23.3 ohm 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 (approximate to 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.