A wheel includes a metal rim, an electrically conductive hub, a thermoelectric device, and a battery. The metal rim is exposed out of a circumference surface of the wheel for contacting with the ground. The thermoelectric device is connected between the metal rim and the electrically conductive hub for generating electric energy using temperature difference between the metal rim and the electrically conductive hub. The battery has two electrodes connected to the metal rim and the electrically conductive hub, respectively. The battery is configured for collecting electric energy generated by the thermoelectric device.