Page 96 - MODERN ASPECTS OF ELECTROCHEMISTRY

Direct Methanol Fuel Cells

Figure 8. SPAIR spectra of the adsorbed intermediates 79
involved in the oxidation of 0.1 M CH OH in 0.5 M
3
HCIO on a Pt Ru alloy dispersed electrode (p-polar-
4
0.1
0.9
ized light; modulation potential ∆E= 0.3 V; reference
spectrum taken at 50 mV/RHE; averaging of 128 inter-
ferograms). Electrode potential (mV/RHE): (1) 100,(2)
150, (3) 200, (4) 250, (5) 300, (6) 350, (7) 400, (8) 450,
(9) 500, (10) 550.
•
or Pt–(CH O ) → Pt–( CHO) ads +H aq +e – (20′)
+
2 • ads
The different species formed by steps (18) to (20) or (18′) to (20′)
have been detected by in situ infrared reflectance spectroscopy, and such
dissociative steps are now widely accepted even if the exact nature of the
species formed during (20) or (20′) is still a subject of discussion. Several
groups proposed the species (COH) as the main, strongly adsorbed
ads
species on the platinum surface, 30,33 even though no absorption infrared
band can be definitely attributed to (COH) . However, the formyl-like
ads
•
species ( CHO) ads has been formally identified, since it gives an IR
absorption band at around 1690cm .
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