Various Effects of Alkali Metal Ions on H 2 O 2 Reduction Reactions at Pt Electrodes
The hydrogen peroxide reduction reaction (HPRR) has attracted much attention because it is involved in the oxygen reduction reaction which is an important cathode reaction in several fuel cell systems. Pt has an excellent electrocatalytic activity toward the HPRR. Thus, the HPRR at Pt electrodes has...
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| Published in | Meeting abstracts (Electrochemical Society) Vol. MA2020-02; no. 58; p. 2893 |
|---|---|
| Main Authors | , |
| Format | Journal Article |
| Language | English |
| Published |
23.11.2020
|
| Online Access | Get full text |
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| Summary: | The hydrogen peroxide reduction reaction (HPRR) has attracted much attention because it is involved in the oxygen reduction reaction which is an important cathode reaction in several fuel cell systems. Pt has an excellent electrocatalytic activity toward the HPRR. Thus, the HPRR at Pt electrodes has been widely studied including effects of electrolyte components and additives on it.
Katsounaros and Mayrhofer have reported that alkali metal cations such as Li
+
, Na
+
, and K
+
inhibit the HPRR in basic media [1]. The hydrated alkali metal cations and chemisorbed OH species on Pt, denoted as M
+
(H
2
O)
x
and OH
ads
respectively, non-covalently stabilize each other, leading to the formation of quasi-specifically adsorbed hydrated metal ion clusters that blocks electrochemical reactions. The inhibition becomes stronger as the strength of the non-covalent interaction increases (K
+
< Na
+
< Li
+
), and consequently the rest potential decreases in this order, as reproduced in Figure 1a.
We have recently found that the HPRR in strongly acidic media is also affected by the alkali metal ions. As shown in Figure 1b, the HPRR is inhibited at
U
< 0.7 V in the presence of the ions. This indicates that the alkali metal ions inhibit the transport of electroactive species, namely, H
+
and H
2
O
2
, toward the electrode surface. The HPRR current becomes smaller (in absolute value) in the following order: Li
+
< Na
+
< K
+
, that is, the inhibition becomes stronger in the reverse order of the strength of the non-covalent interaction. In this work, to explain this inhibition, we study the HPRR by electrochemical impedance method.
Interestingly, the metal ions induce a significance increase in the local pH at the electrode surface (pH
s
) during the HPRR when the concentration of H
2
O
2
is relatively high, that is, when the HPRR consumes a large amount of H
+
[2]. For instance, the pH
s
becomes strongly basic when 0.01 M H
2
SO
4
+ 0.05 M H
2
O
2
+ 0.05 M M
2
SO
4
(where M stands for Li, Na, and K) is used as the electrolyte solution. We thus think that the non-covalent interaction can be induced during the HPRR even in the acidic media. Note that the pH
s
remains acidic in the case of Figure 1b because of the lower concentration of H
2
O
2
. In this work, we summarize the above-mentioned effects of the alkali metal ions on the HPRR.
REFERENCES
[1] I. Katsounaros and K. J. J. Mayrhofer,
Chem. Commun.
,
48
, 6660-6662 (2012).
[2] Y. Mukouyama, H. Kawasaki, D. Hara, Y. Yamada, S. Nakanishi,
J. Electrochem. Soc.,
164
(2017) H675.
FIGURE CAPTION
Figure 1. The current (
I
) – potential (
E
) curves for a Pt-plate electrode in basic and acidic solutions measured under potential controlled conditions at a scan rate of 0.01 Vs
-1
. The basic solutions are 0.05 M alkali hydroxide (denoted as MOH) + 0.01 M H
2
O
2
, and the acidic ones are 0.05 M H
2
SO
4
+ 0.01 M H
2
O
2
with or without 0.05 M alkali sulfate (denoted as M
2
SO
4
).
Figure 1 |
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| ISSN: | 2151-2043 2151-2035 |
| DOI: | 10.1149/MA2020-02582893mtgabs |