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

Abstract

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.

Research Progress on the Preparation and Applications of Laser-Induced Graphene Technology

“…The MSC fabricated by this technology had ultra-high energy density (0.23 Wh cm −3 ), ultra-small time constant (0.01 ms), excellent specific capacitance (128 mF cm −2 and 426.7 F cm −3 ), and long-term cycling performance, overcoming the current limitations of low efficiency fabrication and low energy density of micro-supercapacitors. Recently, Le et al [ 38 ] prepared high-quality graphene on fallen leaves using a femtosecond UV laser ( Figure 12 c). The spatial resolution of the laser pattern was improved due to the ultra-short pulse duration that reduced the thermal diffusion in the heat-affected region.…”

“…( b ) Environmental protection, adapted with permission from [ 35 , 36 , 37 ]. ( c ) Energy storage, adapted with permission from [ 38 , 39 , 40 ].…”

“…( b ) The fabrication and performance of J-LIGP-MSCs, adapted with permission from [ 144 ]. ( c ) The fabrication and application of FsLIG microelectrodes on fallen leaves, adapted with permission from [ 38 ].…”

Multiple Quartz Crystals Connected in Parallel for High-Resolution Sensing of Capacitance Changes

“…The step variation in 𝐿𝐿 𝑙𝑙𝑙𝑙 was achieved by laser trim capacitors [52][53][54][55][56]. For this measurement, the capacitors with capacitance 𝐿𝐿 𝑙𝑙𝑙𝑙 and coils with inductance 𝐿𝐿 𝑐𝑐𝑐𝑐𝑐𝑐 , both with a tolerance of 0.2 %, were selected [47] by measurements with the Keithley 4200A-SCS parameter analyser equipped with a 4215 CVU (high-resolution capacitance-voltage unit), the resolution of which is 1 aF in the measuring range 10 aF do 10 pF.…”

Recent Development of Integrated Systems of Microsupercapacitors

“…In addition, exploration of biodegradable and environmentally friendly materials for MSCs is one of the important directions for development of safe and nontoxic micropower supplies in vivo [40][41][42][43][44]. Lee et al [21] successfully prepared a biodegradable MSC by using metal electrodes (e.g., Mo, W, and Fe) on poly(lactic-co-glycolic acid) substrate obtained by electron beam evaporation deposition and NaCl/agarose gel as electrolyte.…”