Versatile and low-cost manufacturing processes/materials are essential for the development of paper electronics. Here, a direct-write laser patterning process is developed to make conductive molybdenum carbide-graphene (MCG) composites directly on paper substrates. The hierarchically porous MCG structures are converted from fibrous paper soaked with the gelatin-mediated inks containing molybdenum ions. The resulting Mo C and graphene composites are mechanically stable and electrochemically active for various potential applications, such as electrochemical ion detectors and gas sensors, energy harvesters, and supercapacitors. Experimentally, the electrical conductivity of the composite is resilient to mechanical deformation with less than 5% degradation after 750 cycles of 180° repeated folding tests. As such, the direct laser conversion of MCGs on papers can be applicable for paper-based electronics, including the 3D origami folding structures.

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Supercapacitors with high power density and life cycles are an important family of power supplies among energy storage systems. The operating voltage window of a supercapacitor is determined by both the chemistry of electrode materials and the electrochemical kinetics of electrolytes while the water hydrolysis potential of 1.23 V is the typical limit for capacitors based on aqueous electrolytes. Here, we briefly outline the working mechanism of electrochemical supercapacitors, including electron double layer capacitors (EDLC) and pseudo-capacitors, and investigate the limitations of their working voltages. The principles and examples of different designs of electrodes and electrolytes for high-voltage supercapacitors beyond the hydrolysis limit are discussed, such as asymmetric electrodes, high concentration electrolytes, and electrolytes with different pH values. Insights into high voltage capacitor cells and future prospects are provided for the development of electrochemical energy storage systems.[a] Dr.