NOVELTY - The device (10) comprises micro fuel cells (1), a microreactor (2) having a reaction chamber including a catalyst for producing hydrogen gas to be fed to the micro fuel cells, a fuel solution for reacting with the catalyst, a tank for storing the fuel solution and by-products of hydrogen production that occurs inside the microreactor, and piezoelectric microfluidic units for sending the fuel solution to the reaction chamber and for expelling the by-products from the reaction chamber after the hydrogen production is complete. The microreactor comprises a composite material substrate (6).    USE - The device is useful for producing electric energy for portable applications/portable electronic devices such as mobile telephone, personal digital assistant, palmtop computer, laptops, digital video cameras, battery chargers, global positioning system units, MP3 players, video games consoles, computer notebooks and even remote sensors.    ADVANTAGE - The device is capable of efficiently, rapidly and stably producing the electric energy for a long period of time, is compact, and can be reliably, economically and simply designed with high performance.    DETAILED DESCRIPTION - The device (10) comprises micro fuel cells (1), a microreactor (2) having a reaction chamber including a catalyst for producing hydrogen gas to be fed to the micro fuel cells, a fuel solution for reacting with the catalyst, a tank for storing the fuel solution and by-products of hydrogen production that occurs inside the microreactor, and piezoelectric microfluidic units for sending the fuel solution to the reaction chamber and for expelling the by-products from the reaction chamber after the hydrogen production is complete. The microreactor comprises a composite material substrate (6), a semipermeable membrane adjacent to the composite material substrate, and an upper layer (9) over the composite material substrate and the semipermeable membrane. The composite material substrate and the semipermeable membrane are coupled to the micro fuel cell to define a single body. The composite material substrate comprises a microchannel having trapping seats for particles of the catalyst. The trapping seats are transverse with respect to an axis of the microchannel. The upper layer has a through opening. The micro fuel cell comprises first and second layers, each of which comprises a composite material and has a membrane electrode assembly (MEA) membrane arranged between the layers. The micro fuel cell comprises a third intermediate layer between the first layer and the second layer. The MEA membrane is completely embedded between the first layer and the third layer. The composite material substrate, the first and second layers, the upper layer and the third intermediate layer each comprise a composite material. The composite material comprises a flame retardant 4 and composite epoxy material type 1. The catalyst comprises VIIIB group metal. The device defines a monolithic structure. An INDEPENDENT CLAIM is included for a method of forming a device for producing energy for portable applications.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic exploded view of a device for producing energy.    Micro fuel cells (1)    Microreactor (2)    Substrate (6)    Upper layer (9)    Device. (10)