Surface processes and kinetics of CO2 reduction on Pt(100) electrodes of different surface structure in sulfuric acid solutions

The reduction of CO2 on a Pt(100) electrode in CO2 saturated 0.5 M H2SO4 solutions was studied by in situ FTIR reflection spectroscopy and a programmed potential step technique. Different surface structures of Pt(100) electrode were prepared by different treatments including fast potential cycling (200 V s(-1)) for a known time. The Pt(100) surface was characterized by a parameter gamma that designates the relative amplitude of the current peak of hydrogen adsorption on (100) sites distributed on the one-dimensional surface domains to that on the two-dimensional surface domains. The in situ FTIR spectroscopic results demonstrated that the reduction of CO2 on the Pt(100) dominated by two-dimensional surface domains produced only bridge-bonded CO (COB) species, which give rise to IR absorption near 1840 cm(-1). However both bridge- and linear-bonded CO (COL, yielding IR absorption at around 2010 cm(-1)) species are found for CO2 reduction on the Pt(100) dominated by one-dimensional surface domains. The small intensity of the COL and COB bands indicates that coverage by reduced CO2 species (r-CO2. or COL and COB species) is low. The cyclic voltammetric (CV) studies confirmed quantitatively the in situ FTIRS results, and revealed that the r-CO2 species adsorb preferentially on (100) sites distributed on the two-dimensional surface domains. The initial rate of CO2 reduction upsilon (i), i.e., the rate of CO2 reduction on a clean Pt(100) surface, has been determined quantitatively from studies using a programmed potential step technique. It has been demonstrated that the maximum values of upsilon (i)(upsilon (m)(i)) measured on Pt(100) electrodes with different surface structures all appeared at -0.19 V. From analysis of the relationship between upsilon (m)(i) and gamma we have determined that the upsilon (m)(i) of CO2 reduction on (100) sites distributed on the two-dimensional surface domains is 0.53 x 10(-11) mol cm(-2) s(-1) and that on (100) sites distributed on the one-dimensional surface domains is approximately 2.66 x 10(-11) Mol cm(-2) s(-1). Based on in situ FTIRS and electrochemical studies a migration process of the r-CO2 from the one-dimensional surface domains to the two-dimensional surface domains has been proposed to be involved in CO2 reduction. The present study has thrown new light on the electrocatalytic activity of different surface structures of a Pt(100) electrode and the surface processes and kinetics of CO2 reduction.