Surface Atomic Arrangement Dependence of Electrochemical CO2 Reduction on Gold: Online Electrochemical Mass Spectrometric Study on Low-Index Au(hkl) Surfaces

We evaluated the electrochemical CO2 reduction reaction (ECR) on low-index Au single crystal surfaces (Au(111), (100), and (110); Au(hkl)) and discussed the surface-atomic-arrangement-dependence of Au on the ECR. Online-electrochemical mass spectrometry (OLEMS) results revealed that the onset potential of the quadrupole mass spectrometer (Q-mass) ion signal for the reduction product carbon monoxide (CO; m/z = 28) is ca. 0.3 V lower on the Au(110) surface than on the Au(111) and (100) surfaces. Furthermore, the Au(110) surface showed the highest selectivity for CO generation in the potential region of -0.4 V to -1.4 V vs reversible hydrogen electrode (RHE); the relative, OLEMS-corrected ECR partial current density for generated CO at -0.76 V was ca. 20-fold higher compared with the Au(100) and (111) surfaces. The Tafel slope of Au(110) at the onset potential region (around -0.4 V) was much smaller than that of the Au(111) and (100) surfaces, suggesting that Au(110) shows the fastest ECR kinetics among the low-index Au surfaces. The results obtained in this study reveal that the ECR efficiency as well as the selectivity for CO generation on Au electrode surfaces can be dominated by the surface atomic arrangements and that relative Faradaic selectivity evaluation by OLEMS is helpful for discussion of the ECR process.