NOVELTY - An electrochemical device for converting carbon dioxide to a reaction product comprises cathode (51) and a component located within 1 mm of the cathode, where the component comprising at least one of (a) an electrolyte (53), (b) Helper catalyst, (c) solution, (d) a liquid, (e) functional unit, and (f) solid, where the component comprises a substance having a pH having a value of 1.1-5.5.    USE - As electrochemical device for converting carbon dioxide to a reaction product, used in carbon dioxide sensor, fuel cell, where the reaction product comprises CO, HCO-, H2CO, (HCO2)-, HCOOH, CH3OH, CH4, C2H4, CH3CH2OH, CH3COO-, CH3COOH, C2H6, (COOH)2, (COO-)2, CH2=CHCOOH, CF3COOH or (C6H5O)2CO (claimed).    ADVANTAGE - The electrochemical device decreases carbon dioxide emissions from industrial facilities; and converts into useful products.    DETAILED DESCRIPTION - An electrochemical device for converting carbon dioxide to a reaction product comprises cathode (51) and a component located within 1 mm of the cathode, where the component comprising at least one of (a) an electrolyte (53), (b) Helper catalyst, (c) solution, (d) a liquid, (e) functional unit, and (f) solid, where the component comprises a substance having a pH having a value of 1.1-5.5 when the pH of the substance is measured according to at least one of the following tests: Test I: measuring the pH of the substance directly, using a pH meter; Test II: mixing a given volume of the substance with an equal volume of water and agitating, then measuring the pH of the resultant water-rich phase; Test III: mixing a given volume of the substance with an equal volume of isopropanol and stirring, then measuring the pH of the resultant alcohol-rich phase; and Test IV: mixing a given volume of the substance with an equal volume of isopropanol and agitating, adding 20% water by volume to the alcohol-rich phase, then measuring the pH of the resultant alcohol-rich phase. An INDEPENDENT CLAIM is included for making a reaction product involving introducing carbon dioxide, a carbonate and a bicarbonate to the cathode of the electrochemical device, and applying electrical energy to the electrochemical device to effect electrochemical conversion of the carbon dioxide, a carbonate and a bicarbonate to the reaction product.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of Electrochemical device.    Anode (50)    Cathode (51)    Electrolyte (53)