Pulsed electroreduction of CO2 on silver electrodes

A large degree of selectivity of reduction products of CO2 has been achieved on Ag electrodes by a pulsed technique in which the anodic (V-a) and the cathodic (V-c) bias were found to be key parameters. The maximum faradaic efficiencies for CO, CH4, C2H4, and C2H5OH were, respectively, 70% (V-c = -2.0 V, V-a = -0.125 V), 55% (-2.25 V, -0.4 V), 3.1% (-2.25 V, -0.4 V), 3.1% (-2.25 V, -0.4 V), and 22% (-2.25 V, -0.5 V). The total value of 58.1% for CH4 and C2H4 formation recorded on the Ag electrode is comparable with that for CH4 and C2H4 formation on the Cu electrode, which has long been considered as a unique metal for CH4 and C2H4 formation. In addition, in the potential range where CH4 and C2H4 are preferentially produced, the formation of HCOOH was found to be almost zero. The selectivity was ascribed to be due to the extent of the surface coverage of adsorbed hydrogen, which can be controlled by the anodic bias.