Rare-metal-free high-performance water-activated paper battery: a disposable energy source for wearable sensing devices†

Lightweight, thin paper-based devices are attracting attention due to their portability, lower metal and plastic use, and smaller environmental impact when discarded. For example, paper-based thin diagnostic devices can be mass-produced and their environmental impact after disposal is low, making them promising rapid diagnostic devices for diseases and infectious diseases, especially in developing countries. This report describes a high-performance paper battery activated by water composed of a Mg–air battery with a neutral electrolyte and a safe, high-performance pigment-based electrocatalyst. The paper battery was fabricated by bonding Mg foil to paper and forming a cathode catalyst and gas diffusion layer (GDL) directly on the opposite surface. The fabricated paper battery achieved an OCV of 1.8 V, a 1.0 V current density of 100 mA cm⁻², and a maximum output of 103 mW cm⁻². The safety of materials used in the paper battery was also examined. Furthermore, applications of the battery in wearable sensing devices, such as a pulse oximeter (SpO₂ sensor) and a GPS logger, were also demonstrated.