A controlled-release fuel cell comprising (a) a proton exchange membrane having a first surface and a second surface, a fuel electrode or anode being coupled to the first surface, and an oxidant electrode or cathode being coupled to the second surface; (b) a fuel flow field plate having surface channels positioned in front of the anode with the channels containing therein a controlled-release material that retains a liquid fuel at or below an ambient temperature, but releases the fuel at a temperature higher than an activation temperature to deliver a fuel vapor to the anode; (c) heating means in heat-supplying relation to the controlled-release material to activate fuel vapor release on demand at a desired rate; and (d) fuel supply means that feeds the liquid fuel to the controlled-release material. The invented fuel cell is compact and lightweight, with significantly reduced fuel crossover and improved fuel utilization efficiency. The fuel cell is particularly useful for powering small vehicles and portable devices such as a notebook computer, a personal digital assistant, a mobile phone, and a digital camera.