Hydrogen absorption into electrodeposited metal films is largely influenced by the depositing conditions. We have been investigating the hydrogen absorption into electrodeposited platinum (Pt) films that depends on a change in hydrogen adsorption state with applied potential.¹ The microstructure of electrodeposited Pt films was affected by the absorbed hydrogen.² In this study, we investigate an atomistic state of absorbed hydrogen in electrodeposited Pt films.

Pt films were potentiostatically deposited on a gold foil from a solution containing 0.024 mol dm^-3 K₂PtCl₄ at pH of 0.8. A Ag/AgCl electrode was used as the reference electrode and a Pt plate was used as the counter electrode. The amount of hydrogen in samples was measured by thermal desorption spectroscopy (TDS) in a temperature range between 300 and 1100 K. The amount of hydrogen in deposited Pt films was calculated by subtracting the total amount of desorbed hydrogen of the gold foil substrates from that of the samples.

The amount of hydrogen in potentiostatically deposited Pt films (+0.1 ~ -0.3 V vs. Ag/AgCl) as a function of film thickness is summarized in Fig. 1. The amount of hydrogen was nearly 0 for Pt films deposited at +0.1 V (Fig. 1 ●). It was 1 ~ 2×10^-7 mol cm^-2 and independent of the film thickness at 0 V (Fig. 1 ◇). For the Pt films deposited at -0.1 and -0.2 V, a positive correlation was observed between the amount of hydrogen and the film thickness (Fig. 1 ○ and △), respectively. The positive correlation of ca. 1.7×10^-7 mol cm^-2 µm^-1 indicates that hydrogen was uniformly contained at atomic ratio ([H]/[Pt]) of 0.015 in the Pt films. For the Pt films deposited at ‑0.3 V, the positive slope, that is, content of uniformly absorbed hydrogen was much larger than that for the films deposited at -0.1 and ‑0.2 V (Fig. 1 □). Positive vertical intercepts of 2 ~ 6×10^-7 mol cm^-2 for -0.1 ~ -0.3 V indicate that a certain amount of hydrogen was contained even in the initial deposits. Pt deposition at +0.1 V onto the Pt film deposited at 0 V reduced the amount of hydrogen to nearly 0. The Pt deposition at 0 V onto the Pt film deposited at +0.1 V increased the amount of the hydrogen to ca. 1×10^-7 mol cm^-2. These results suggest the possibility that the certain amount of hydrogen indicated by the vertical intercepts of Fig. 1 exists near film surface.

Acknowledgements

The present work was partly supported by JSPS KAKENHI (JP26289276 and JP17K06864).

References

1. A. Yokoyama, S. Karatsu, M. Sumikawa, N. Fukumuro, and S. Yae, ECS Trans., 75(52) 55 (2017).
2. N. Hisanaga, N. Fukumuro, S. Yae, and H. Matsuda, ECS Trans., 50(48), 77 (2013).