Abstract: The invention relates to a cathode based on a transition metal (M) for reduction of carbon dioxide into formate in a hydro-organic or purely aqueous medium, particularly for air decarbonation applications for industry and in general for atmospheric pollution control and regeneration of breathable air in a confined or unconfined environment, characterized by including a transition metal molecular complex formed of:a bidentate ligand functional by identical or different electroattractive groups A and A', the ligand comprising a basic molecular group allowing the reduction redox potential of the complex to be reduced in a range of -1.40 to +0.80 V relative to an Ag/Ag.sup.+ reference electrode, at least one of the groups A or A' being electropolymerizable;two identical or different labile groups Y and Y' with trans stereochemistry taken from the following series: halide anion (Cl.sup.-, Br.sup.-, I.sup.-), acetate anion (CH.sub.3 COO.sup.