For this project, you need an inductive charging system. This kind of system uses a transmitter circuit to convert electricity from a wall outlet into electromagnetic energy that is wirelessly sent to the receiver. The receiver then converts the electromagnetic energy into electricity that it uses to charge mobile devices.
I am using the PowerMat inductive charger. In this model the transmitter is a thin plate that the receiver sits on. The receiver is a small disk with a mini USB power cord that plugs into the device that you want to charge. When the transmitter detects the presence of a receiver unit, it automatically turns on and begins sending power to the receiver.
You don't need to use this exact model. Other inductive chargers can also work. If you are interested in building an inductive charger from scratch, you can check out this Instructable from user Inducktion