A moisture-enabled fully printable power source inspired by electric eels.

Great efforts have been made to build integrated devices to enable future wearable electronics; however, safe, disposable, and cost-effective power sources still remain a challenge. In this paper, an all-solid-state power source was developed by using graphene materials and can be printed directly on an insulating substrate such as paper. The design of the power source was inspired by electric eels to produce programmable voltage and current by converting the chemical potential energy of the ion gradient to electric energy in the presence of moisture. An ultrahigh voltage of 192 V with 175 cells in series printed on a strip of paper was realized under ambient conditions. For the planar cell, the mathematical fractal design concept was adapted as printed patterns, improving the output power density to 2.5 mW cm-3, comparable to that of lithium thin-film batteries. A foldable three-dimensional (3D) cell was also achieved by employing an origami strategy, demonstrating a versatile design to provide green electric energy. Unlike typical batteries, this power source printed on flexible paper substrate does not require liquid electrolytes, hazardous components, or complicated fabrication processes and is highly customizable to meet the demands of wearable electronics and Internet of Things applications.