With the development of wearable electronics, the use of engineered functional inks with printing technologies has attracted attention owing to its potential for applications in low-cost, high-throughput, and high-performance devices. However, the improvement in conductivity and stretchability in the mass production of inks is still a challenge for practical use in wearable applications. Herein, a scalable and efficient fluid dynamics process that produces highly stretchable, conductive, and printable inks containing a high concentration of graphene is reported. The resulting inks, in which the uniform incorporation of exfoliated graphene flakes into a viscoelastic thermoplastic polyurethane is employed, facilitated the screen-printing process, resulting in high conductivity and excellent electromechanical stability. The electrochemical analysis of a stretchable sodium ion sensor based on a serpentine-structured pattern results in excellent electrochemical sensing performance even under strong fatigue tests performed by repeated stretching (300% strain) and release cycles. To demonstrate the practical use of the proposed stretchable conductor, on-body tests are carried out in real-time to monitor the sweat produced by a volunteer during simultaneous physical stretching and stationary cycling. These functional graphene inks have attractive performance and offer exciting potential for a wide range of flexible and wearable electronic applications.

Manganese dioxide (MnO 2 ) materials have received much attention as promising pseudocapacitive materials owing to their high theoretical capacitance and natural abundance. Unfortunately, the charge storage performance of MnO 2 is usually limited to commercially available mass loading electrodes because of the significantly lower electron and ion migration kinetics in thick electrodes. Here, an alternatively assembled 2D layered material consisting of exfoliated MnO 2 nanosheets and nitrogen-doped carbon layers for ultrahighmass-loading supercapacitors without sacrificing energy storage performance is reported. Layered birnessite-type MnO 2 is efficiently exfoliated and intercalated by a carbon precursor of dopamine using a fluid dynamic-induced process, resulting in MnO 2 /nitrogen-doped carbon (MnO 2 /C) materials after self-polymerization and carbonization. The alternatively stacked and interlayer-expanded structure of MnO 2 /C enables fast and efficient electron and ion transfer in a thick electrode. The resulting MnO 2 /C electrode shows outstanding electrochemical performance at an ultrahigh mass loading of 19.7 mg cm −2 , high gravimetric and areal capacitances of 480.3 F g −1 and 9.4 F cm −2 at 0.5 mA cm −2 , and rapid charge/discharge capability of 70% capacitance retention at 40 mA cm −2 . Furthermore, asymmetric supercapacitor based on high-mass-loading MnO 2 /C can deliver an extremely high energy of 64.2 Wh kg −1 at a power density of 18.8 W kg −1 in an aqueous electrolyte.

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