Langmuir 2004, 20, 2807-2807
2807
Comment on On the Existence of Ordered Organic Adlayers at the Cu(111)/Electrolyte Interface
This comment concerns the paper entitled “On the Existence of Ordered Organic Adlayers at the Cu(111)/ Electrolyte Interface” by Friebel et al.1 We repeated their experiments, obtained the same experimental results as they reported, and found that their observations could be from Cl- contaminated surfaces. Results and Interpretation Cyclic Voltammogram (CV). The CV of Cu(111) in 0.1 M HClO4 by Friebel et al. (in Figure 1)1 is obviously different from that by Brisard and our groups not observing the “X” peak (Friebel et al. assignment) near the hydrogen evolution peak.2,3 The peak in the negative potential region can be produced by Cl-. However, it is noted that the peak potential in the CV by Friebel et al. is different from those in the CVs of the literature.2b,3 The “X” peak appeared at -280 mV (versus the reversible hydrogen electrode). Cu dissolution starts at 350 mV. Copper dissolution was previously reported to start near 0.2 V in acidic solutions.2-4 Our Figure 1a shows the CV after Cu(111) was electropolished in a commecial H3PO4 solution usually containing a trace of Cl-, which is consistent with the CV by Friebel et al. The negative “X” peak appears at about -280 mV. Copper dissolution starts at 350 mV. To demonstrate the existence of a contaminant such as Cl-, we added a 1 mM HCl solution into H3PO4. The “X” peak increases, while the overall shape of the CV stays unchanged. This suggests that the CV by Friebel et al. was recorded from a Cl- contaminated surface. More details have to be studied in the future using other techniques. However, the contaminated layer can be removed by the method described in our previous papers.2 STM Observation. We repeated the scanning tunneling microscopy (STM) experiment of Friebel et al.1 and * Corresponding authors:
[email protected] (L.-J.W.); itaya@ atom.che.tohoku.ac.jp (K.I.). † Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan. (1) Friebel, D.; Mangen, T.; Obliers, B.; Schlaup, C.; Broekmann, P.; Wandelt, K. On the Exsistence of Ordered Organic Adlayers at the Cu(111)/Electrolyte Interface. Langmuir 2003, 20, 2803. (2) Wan, L. J.; Itaya, K. Langmuir 1997, 13, 7173. (b) Inukai, J.; Osawa, Y.; Itaya, Y. J. Phys. Chem. B 1998, 102, 10034. (c) Sugimasa, M.; Inukai, J.; Itaya, K. J. Electrochem. Soc. 2003, 150, E266. (d) Xu, Q. M.; Wang, D.; Wan, L. J.; Bai, C. L.; Wang, Y. J. Am. Chem. Soc. 2002, 124, 14300. (3) Brisard, G. M.; Zenati, E.; Gasteiger, H. A.; Markovic´, N. M.; Ross, P. N. Langmuir 1995, 11, 2221. (4) Broekmann, P.; Wilms, M.; Spaenig, A.; Wandelt, K. Prog. Surf. Sci. 2001, 67, 59.
Figure 1. (a) CV of Cu(111) in 0.1 M HClO4. The Cu(111) surface was electropolished in a commercial H3PO4 solution containing a trace of Cl-. The potential scan rate was 50 mV s-1. (b) STM image of Cu(111) in 0.1 M HClO4 with Clcontaminant. Tunneling current was 40 nA.
obtained the same STM images as they recorded. Our Figure 1b is a typical STM image in 0.1 M HClO4 after Cu(111) was electropolished in a commercial H3PO4 containing a trace of Cl-. The image is almost the same as that shown in Figure 2b by Friebel et al. The structure can be defined as a (4 × 4). Other images similar to those of Friebel et al. in Figures 2 and 4 were also observed in a wide potential region, even from -150 to +50 mV, where Friebel et al. (Figure 3a) reported a rhombus lattice called “(1 × 1)”. The same images as those by Friebel et al. were also seen on clean Cu(111) in 0.1 M HClO4 with the presence of a trace of HCl (less than 10-5 M). On the contaminated electrode, no cinchonidine or other molecules were observed.2a,d From the reinvestigation, we can reach the conclusion that all findings by Friebel et al. are influenced by contaminants such as Cl-. Mei-Juan
Han,
Yu-Xia Diao, Hui-Min Zhang, Li-Jun Wan,* and Kingo Itaya*,†
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
10.1021/la0497548 CCC: $27.50 © 2004 American Chemical Society Published on Web 02/28/2004
Received January 27, 2004 LA0497548
