TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Gas: The gaseous species is oxygen, hydrogen, nitrogen monoxide, or carbon dioxide. Preferred Ratio: The ratio of the amount of dissolved gaseous reactant (in moles) to the surface area (mm2) is 3x109-3x1012.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The microfluidic channel has sidewalls extending between the electrode and membrane. At least two microfluidic channels are on the electrode. The microfluidic channels are portion of a microfluidic network (104). An electrolyte is provided in the channel. A gaseous reactant is dissolved in the electrolyte and the membrane, and the electrode has a surface area that is exposed to the microfluidic channel. Alternatively, the electrochemical reactor comprises an electrode, and at least two microfluidic channels on the electrode. The microfluidic channels include a top gas-permeable polymer membrane having a thickness of 1 microns - 2 mm, and sidewalls extending between the electrode and membrane. Preferred Dimensions: The microfluidic channels are separated by a distance of 1 microns - 1 mm. The distance between the sidewalls is 1 microns - 1 mm. The distance between the electrode and the membrane is 1-500 microns. The membrane has a thickness of 1 microns - 2 mm.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Method: Formation of gas-permeable polymer layer includes covering a master pattern with an elastomer precursor which solidifies into a silicon-containing elastomer, removably attaching the silicon-containing elastomer to a transfer pad material, and removing the silicon-containing elastomer from the master. Removable attachment of silicon-containing elastomer to transfer pad material includes oxidizing the silicon-containing elastomer, applying an adhesion control agent to the oxidized elastomer, and contacting the oxidized elastomer to a transfer pad material; or applying a stimulus-responsive adhesive between the silicon-containing elastomer and the transfer pad. The strength of attachment between the silicon-containing elastomer and the transfer pad is reduced by a change in a property, e.g. temperature, irradiation, or electric field. The method includes separating the silicon-containing elastomer from the transfer pad after contacting the first side of gas-permeable polymer layer with the electrode and the substrate, and filling the microfluidic network with an electrolyte.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Gas: The gaseous species is oxygen, hydrogen, nitrogen monoxide, or carbon dioxide. Preferred Ratio: The ratio of the amount of dissolved gaseous reactant (in moles) to the surface area (mm2) is 3x109-3x1012.    TECHNOLOGY FOCUS - POLYMERS - Preferred Materials: The gas-permeable polymer is silicon-containing polymer, fluorinated polymer, polypropylene, or polymer comprising diene monomer units. Preferred Properties: The gas-permeable polymer has a permeability coefficient for gaseous species of greater than or equal to5x10-13 cm3cm/cm3-s-Pa at 0degreesC and 1.013x105 Pa.