147
of Pt/C and Pt ML Pd/C, respectively; the Pt mass activity of Pt ML PdIr/C is more than
20 times and 25% higher than that of Pt/C and Pt ML Pd/C, respectively. The influence
of the Ir sublayer on the ORR activity could be explained by the position of the Pt ML
d-band center (ε d ). A surface characterized by a higher-lying ε d tends to bind adsorbates more strongly, thereby enhancing the kinetics of dissociation reactions
Cu monolayer
Cu monolayer
Pd
CuPd
Ir 2/3 monolayer
IrPd
Annealing 350°C
Pt monolayer
CuPdIr
Pt ML PdIr
Iridium
Platinum
Palladium
Copper
PdIr
0.15
0.1
0.05
0
–0.05
–0.1
–0.15
–0.2
0
0.2
0.4
0.6
0.8
1
1.2
E (V) versus RHE
E (V) versus RHE
Pt/C
Pt ML Pd/C
Pt ML PdIr/C
Pt/C
Pt ML Pd/C
Pt ML PdIr/C
Pt ML PdIr/C
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
–1
–2
–3
–4
–5
–6
j (mA/cm
2
)
j (mA/cm
2
)
1600 rpm
(a)
(b)
Fig. 8.35 (a) Voltammetry curves for Pt ML Pd/C (blue), Pt ML PdIr/C (red), and Pt/C (black) in a
deaerated 0.1  M HClO 4 solution. Scan rate, 20 mVs
−1
. (b) Polarization curves for the ORR on
Pt ML IrPd/C (green), Pt ML Pd/C (blue), Pt ML PdIr/C (red), and Pt/C (black) at 1600 rpm in oxygensaturated 0.1 M HClO 4 solution. Scan rate, 10 mVs
−1 [19] with permission from Springer Nature
8.4 Ethanol Electrooxidation on Platinum Monolayer Electrocatalysts