The Electrochemical Conversion of Carbon Dioxide on Cu−Ni Stacked Bilayer Electrodes

The electrochemical reduction of carbon dioxide (CO2) has gained popularity as a novel technique to realize a sustainable carbon cycle owing to improvements in power generation using renewable energy sources, such as solar and wind energy [1−2]. Recent progress of CO2 conversion utilizing the crystalline copper surfaces offers a promising approach to produce the useful hydrocarbon products. In our previous works, we demonstrated the fabrication of the single-crystal copper membranes by sputtering copper onto the specific support substrates, such as c-plane sapphire (Al2O3) and magnesium oxide (MgO). The electrochemical reduction of CO2 on these copper surfaces was produced selective hydrocarbons as compared with the commercially available copper plates [3]. In addition, these sputtered single-crystal copper membranes have been successfully peeled away from the support substrates, and thus it is able to fabricate repeatedly onto the identical support substrate [4]. The electrochemical reduction of CO2 on these crystalline copper electrodes is an effective route toward the practical use of the CO2 conversion process, however this methodology of homogeneous copper membrane deposition is essential to the complicated process. On the other hand, it has been demonstrated that the electrochemical reduction of CO2 to hydrocarbon on a copper surface is due to moderate surface adsorption of a carbonate intermediate by theoretically calculations [5]. Binary metal electrodes, such as copper and another metal, are expected to allow to the carbonate intermediate to adsorb to the appropriate surface and achieve the more effective CO2 conversion to hydrocarbon production as compared with pristine copper electrodes. In this work, we study the electrochemical conversion of CO2 on Cu−Ni stacked bilayer electrodes. Hydrocarbon emissions for the electrochemical reduction of CO2 were strongly dependent on the amount of nickel deposited on the copper electrodes. However, excess deposition of nickel on the copper electrodes suppressed the CO2 conversion. This is suggested that the surface adsorption of the carbonate intermediate is improved on the Cu−Ni stacked bilayer electrodes, compared with pristine copper electrodes, due to the interactions between copper and nickel. Additionally, we also show the selectivity of the hydrocarbon products formed via CO2 conversion on the Cu−Ni stacked bilayer electrodes in terms of the crystal structure underneath the copper electrodes. Reference [1] Y. Hori et al., J. Mol. Catal. A Chem., 199, 39–47 (2003). [2] K. J. P. Schouten et al., ACS Catal., 3(6), 1292–1295 (2013). [3] N. Yoshihara et al., ECS Trans., 66(24), 83-89 (2015). [4] N. Yoshihara et al., ECS Trans., 75(43), 33-38 (2017). [5] A. A. Peterson et al., J. Phys. Chem. Lett., 3, 251−258 (2012).