NOVELTY - A high-pressure hydrogen producing system comprises a first stack of electrochemical hydrogen generating cell integrated with a second stack of electrochemical hydrogen compressor cell. The compressor cell includes a second anode oxidizing hydrogen generated by the first stack, and a second cathode evolving hydrogen at pressure greater than in the generating cell.    USE - The device is used for producing high-pressure hydrogen to fill a gas storage cylinder for stationary and transportation applications, including on board a vehicle and at refueling stations.    ADVANTAGE - Provides safety of operation and relative simplicity of constructing a differential-pressure hydrogen compressor cell compared to an electrolyzer with the same pressure difference, which translates into cost savings. The two-cell system allows for the use of thinner membranes, resulting in lower voltage. Less risk of explosion exists in recirculating water accumulated at the anode or cathode side of the compressor than in feeding a pressurized reactor with cathode water, even if the water contains hydrogen. A high-pressure proton-exchange membrane electrolyzer is also more expensive than an integrated low-pressure electrolyzer and electrochemical hydrogen compressor.    DETAILED DESCRIPTION - A high-pressure hydrogen producing system (10) comprises a first stack of electrochemical hydrogen generating cell (12) including a first anode (16) and a first cathode (20), for generating hydrogen at a first pressure; and a second stack integrated with first stack of electrochemical hydrogen compressor cell (14) including a second anode (22) oxidizing hydrogen generated by the first stack, a second cathode (26) evolving hydrogen at a second pressure, and an ionic conductive membrane in intimate contact with and separating the second anode and the second cathode. The first pressure is atmospheric or moderate pressure and the second pressure is greater than the first pressure.    An INDEPENDENT CLAIM is included for a method of producing high-pressure hydrogen in a system comprising applying power to the first stack, producing protons and electrons at the first anode, transporting the protons across the first ionic conductive membrane, reducing the protons with externally transported electrons at the first cathode to produce hydrogen at the first pressure, feeding the hydrogen produced by the first stack to the second stack, oxidizing the hydrogen at the second anode to produce protons and electrons, transporting the protons across the second ionic conductive membrane, and reducing the protons with externally transported electrons at the second cathode to evolve hydrogen at the second pressure.    DESCRIPTION OF DRAWING(S) - The figure is a schematic diagram of an integrated electrolyzer stack and electrochemical hydrogen compressor stack.    System (10)    Electrochemical hydrogen generating cell (12)    Electrochemical hydrogen compressor cell (14)    First anode (16)    First cathode (20)    Second anode (22)    Second cathode (26)