NOVELTY - The process comprises introducing an acidic anolyte into an anolyte compartment of an electrochemical reactor, where the anolyte compartment partially contains an anode, introducing carbon dioxide gas from a gas compartment (28) into a diffuser (48), and introducing the carbon dioxide gas from the gas compartment into a catholyte compartment of the electrochemical reactor, where the catholyte compartment is separated from the anolyte compartment by a membrane and partially contains a porous, catalytically coated cathode (16a).    USE - The process is useful for the electrochemical reduction of carbon dioxide to formate and formic acid, which is useful: for replacing hydrochloric acid in steel pickling, traditional tanning of leather, and formic acid-based fuel cells; as a storage medium for hydrogen and carbon monoxide that are useful as fuels and chemical feedstocks for airport runway deicing, preservatives and antibacterial agents, an ingredient in bleaching pulp and paper, and as a precursor for organic synthesis including pharmaceuticals.    ADVANTAGE - The process ensures efficient and economical electrochemical reduction of the carbon dioxide to formate and formic acid with reduced energy requirements.    DETAILED DESCRIPTION - The process comprises introducing an acidic anolyte into an anolyte compartment of an electrochemical reactor, where the anolyte compartment partially contains an anode, introducing carbon dioxide gas from a gas compartment (28) into a diffuser (48), introducing the carbon dioxide gas from the gas compartment into a catholyte compartment of the electrochemical reactor, where the catholyte compartment is separated from the anolyte compartment by a membrane and partially contains a porous, catalytically coated cathode (16a), flowing the gaseous carbon dioxide from the gas compartment through the cathode, introducing a catholyte into the catholyte compartment, impressing a direct current (DC) voltage across the anode and the cathode, where a portion of the carbon dioxide is converted to formate, removing a deposit from the cathode by periodically applying anodic polarization and/or deep cathodic polarization, and introducing a portion of the catholyte into a porous, absorbent non conductive pad. The diffuser is adjacent to a gas compartment side of the cathode. The cathode comprises a manufacture such as a porous, electrically conductive substrate and a carbon fiber paper substrate with a tin catalyst deposited on the substrate, where the catalyst is formulated to electrochemically reduce carbon dioxide to formate, and separates the cathode compartment from the gas compartment. The gas compartment is in fluid communication with the cathode and in fluid communication with the catholyte. The catholyte is formulated for the electrochemical reduction of carbon dioxide to formate. The anolyte is acidic and/or alkaline and formulated for the electrochemical reduction of carbon dioxide to formic acid and/or to formate. The anode comprises a substrate, and a metal oxide catalyst deposited on the substrate. The application of anodic and cathodic polarizations is superimposed on top of the DC voltage and the total periodic application is 0.3-1.7 % of a maximum time interval between applications. The combination of deep cathodic polarization and anodic polarization is applied in every 2-10 hours for 5-30 seconds and 15-120 seconds respectively. The current density of the anodic polarization is a positive current density of 10 times of the current density effected by the impressed DC voltage across the anode and the cathode. The current density of the deep cathodic polarization is a negative current density of 10 times of the current density effected by the impressed DC voltage across the anode and the cathode. The cathode and the membrane partially define the catholyte compartment. The catholyte compartment contains the porous, absorbent, nonconductive pad, which is adjacent to a catholyte compartment side of the membrane. The tin deposits substantially cover the outer surface of the substrate, penetrate the carbon fiber substrate to a depth of 30-50 microns, and have a grain size of 0.5-5 microns. INDEPENDENT CLAIMS are included for:    (1) an apparatus for electrochemical reduction of carbon dioxide;    (2) a solution;    (3) a process for depositing tin onto a porous cathode; and    (4) a manufacture including a porous, electrically conductive substrate.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a three-compartment electrochemical reactor.    Cathode (16a)    Catholyte compartment mixture (26)    Gas compartment (28)    Carbon dioxide gas feed (32)    Diffuser. (48)