An integrated fuel cell assembly is described. The integrated fuel cell assembly includes a polymer membrane; an anode electrode and a cathode electrode on opposite sides of the polymer membrane; a pair of gas diffusion media on opposite sides of the polymer membrane, the gas diffusion media comprising a microporous layer and a gas diffusion layer, the anode electrode and the cathode electrode positioned between the polymer membrane and the pair of gas diffusion media; a subgasket positioned around a perimeter of one of the gas diffusion media, the subgasket defining an active area inside the perimeter, the subgasket having a layer of thermally activated adhesive thereon; and a bipolar plate sealed to the subgasket by the layer of thermally activated adhesive. Methods of making the integrated fuel cell assembly and assembling fuel cell stacks are also described.