UV laser processing of super-hydrophilic graphene films with good electrical conductivity for high-voltage micro-capacitors

Laser-induced graphene (LIG) technique has significant advantages in the applications of micro energy storage devices including micro-supercapacitors (MSCs) due to its low cost, high efficiency and scalability. However, it is still a big challenge to simultaneously achieve super-hydrophilic graphene films with good conductivity, especially using efficient and low-cost methods. In this work, a two-step laser processing technique was proposed to address this issue. The technique employs a UV picosecond laser to scan twice on a KOH-coated polyimide film to in-situ fabricate LIG films with unique microstructures and rich oxygen-containing groups. The resulting LIG films have super-hydrophilic (a contact angle of 0°) and even capillary properties. The capillary rise height reaches 30 mm after a LIG sample strip comes into contact with water for 3.2 seconds. Moreover, the low sheet resistance (78.6 Ω square
⁻¹
) of resulting LIG films demonstrate its good conductivity. Thus, 10 series-connected LIG electrodes can be used for high-voltage MSCs of 10 V with an areal capacitance of 0.32 mF cm
⁻²
. Therefore, the super-hydrophilic LIG electrodes with rapid response characteristics are expected to extend their applications to the field of micro-electronics and beyond.