The composition of the cathode has a significant effect on the efficiency of electrocarboxylation of aromatic halides which are relatively difficult to reduce in N,N-dimethylformamide. At low temperatures (< O degrees C) and controlled current conditions, aromatic bromides and iodides are carboxylated with much greater efficiency than aromatic chlorides at a silver electrode, while at stainless steel the chlorides are carboxylated more efficiently. At silver the efficiency depends on the ease of reduction of the halides relative to CO2, while at stainless steel passivation effects, which are more serious for the bromides and iodides, primarily influence the efficiency. Experiments with added D2O provide no evidence for production of aromatic radical intermediates via CO2-mediated one-electron reduction of the halides.