Direct laser-reduction of graphene oxide (GO), as a lithography-free approach, has been proven effective in manufacturing in-plane micro-supercapacitors (MSCs) with fast ion diffusion. However, the power density and the charge/discharge rate are still limited by the relatively low conductivity of electrodes. Here, we report a facile approach by exploiting femtolaser in situ reduction of the hydrated GO and chloroauric acid (HAuCl₄) nanocomposite simultaneously, which incorporates both the patterning of rGO electrodes and the fabrication of Au current collectors in a single step. These flexible MSCs boast achievements of one-hundred fold increase in electrode conductivities of up to 1.1 × 10⁶ S m⁻¹, which provide superior rate capability (50% for the charging rate increase from 0.1 V s⁻¹ to 100 V s⁻¹), sufficiently high frequency responses (362 Hz, 2.76 ms time constant), and large specific capacitances of 0.77 mF cm⁻² (17.2 F cm⁻³ for volumetric capacitance) at 1 V s⁻¹, and 0.46 mF cm⁻² (10.2 F cm⁻³) at 100 V s⁻¹. The use of photo paper substrates enables the flexibility of this fabrication protocol. Moreover, proof-of-concept 3D MSCs are demonstrated with enhanced areal capacitance (up to 3.84 mF cm⁻² at 1 V s⁻¹) while keeping high rate capabilities. This prototype of all solid-state MSCs demonstrates the broad range of potentials of thin-film based energy storage device applications for flexible, portable, and wearable electronic devices that require a fast charge/discharge rate and high power density.

With the ever-increasing demand for power sources of high energy density and stability for emergent electrical vehicles and portable electronic devices, rechargeable batteries (such as lithium-ion batteries, fuel batteries, and metal–air batteries) have attracted extensive interests. Among the emerging battery technologies, metal–air batteries (MABs) are under intense research and development focus due to their high theoretical energy density and high level of safety. Although significant progress has been achieved in improving battery performance in the past decade, there are still numerous technical challenges to overcome for commercialization. Herein, this mini-review summarizes major issues vital to MABs, including progress on packaging and crucial manufacturing technologies for cathode, anode, and electrolyte. Future trends and prospects of advanced MABs by additive manufacturing and nanoengineering are also discussed.

Porous graphene (PG) and graphene quantum dots (GQDs) are attracting attention due to their potential applications in photovoltaics, catalysis, and bio-related fields. We present a novel way for mass production of these promising materials. The femtosecond laser ablation of highly oriented pyrolytic graphite (HOPG) is employed for their synthesis. Porous graphene (PG) layers were found to float at the water–air interface, while graphene quantum dots (GQDs) were dispersed in the solution. The sheets consist of one to six stacked layers of spongy graphene, which form an irregular 3D porous structure that displays pores with an average size of 15–20 nm. Several characterization techniques have confirmed the porous nature of the collected layers. The analyses of the aqueous solution confirmed the presence of GQDs with dimensions of about 2–5 nm. It is found that the formation of both PG and GQDs depends on the fs-laser ablation energy. At laser fluences less than 12 J cm⁻², no evidence of either PG or GQDs is detected. However, polyynes with six and eight carbon atoms per chain are found in the solution. For laser energies in the 20–30 J cm⁻² range, these polyynes disappeared, while PG and GQDs were found at the water–air interface and in the solution, respectively. The origin of these materials can be explained based on the mechanisms for water breakdown and coal gasification. The absence of PG and GQDs, after the laser ablation of HOPG in liquid nitrogen, confirms the proposed mechanisms.