Powering Electronics by Scavenging Energy from External Metals

This article demonstrates a new approach for powering robots and electronics by electrochemically scavenging energy from metal surfaces. This approach overcomes energy storage scaling laws by allowing robots and electronics to extract energy from large volumes of energy dense material without having to carry the material on-board. We show that a range of hydrogel electrolyte compositions can be combined with air cathodes to extract 159, 87, and 179 mAh/cm² capacities from aluminum, zinc, and steel surfaces at up to 130, 81, and 25 mW/cm² power densities, which exceed the power density of the best energy harvesters by 10×. When moving across a metal surface, metal scavenging exceeds the energy densities of lithium-ion and metal–air batteries by 13× and 2×. Metal scavenging is especially beneficial for small robots and electronics, whose size and performance are severely limited by the low energies provided by microenergy storage technologies.