‘Express lanes’ for ions
Actuators are devices that convert electrical energy into mechanical energy, such as the battery-powered device inside a cell phone that causes the phone to vibrate. When this process is reversed — when a device converts mechanical energy into electrical energy — the device is called an energy harvester, and that electrical energy is often stored for future use. An example would be a device inside a pacemaker that converts mechanical energy created by the motion of a pair of breathing lungs into electrical energy that can be used to charge the pacemaker’s batteries. Both devices typically contain electromechanical materials, such as electroactive polymers, that are made of chainlike molecules that change in size or shape when stimulated by an electric field. But their efficiency and speed depend on how quickly ions, or electrically charged particles, can move between electrodes, or the conductors that electric current passes through, to change the...