Methanol current-potential curves

Exchange reactions between bulk and adsorbed substances can be studied by on-line mass spectroscopy and isotope labeling. In this section the results on the interaction of methanol and carbon monoxide in solution with adsorbed methanol and carbon monoxide on platinum are reported [72], A flow cell for on-line MS measurements (Fig. 1.2) was used. 13C-labeled methanol was absorbed until the Pt surface became saturated. After solution exchange with base electrolyte a potential scan was applied. Parallel to the current-potential curve the mass intensity-potential for 13C02 was monitored. Both curves are given in Fig. 3.1a,b. A second scan was always taken to check the absence of bulk substances. 

Fig. 2.6 Current-potential curves for (A) p-InP, (B) p-GaAs, and (C) p-Si electrodes in 0.3 M TBAP in methanol (40 atm C02) (b) in the dark and (a, c) under illumination. Curves a and c correspond to the behavior corrected and uncorrected for ohmic losses, respectively. Curve d was obtained for a metallic Cu electrode. (QRE stands for quasi-reference electrode).

Figure 7. Current-potential curves for methanol under Ar and CO2 atmospheres using p-InP and p-GaAs photocathodes.

The current-potential curve for the p-InP photocathode under illumination in CO2 (40 atm)-methanol exhibited a relatively large photocurrent (solid line), while the dark current was negligibly small (dotted line, < 1 mA cm 2) at potentials down to -2.0 V vs. Ag-QRE (Fig. 1). The onset photopotential was approximately -0.6 V. When CO2 was replaced with Ar, the onset of the cathodic photocurrent shifted toward the negative direction by 0.4 V (dashed line). This indicates that, in the highly concentrated CO2 solution, CO2 reduction on the p-InP surface occurs in preference to the reaction occurring under Ar atmosphere, which is predominantly hydrogen evolution. The cathodic photocurrent reached 20 mA (approximately 100 mA cm 2) at a potential of -2.4 V vs. Ag-QRE. 

Muller and his co-workers made the first mechanistic investigation of methanol, determining current-potential curves on several noble metals. In 1954, Pavela studied methanol oxidation using galvanostatic steady-state methods. Recent investigations have been carried out almost exclusively with non-steady state... 

Fig. 93. Steady-state current-potential curves of the methanol oxidation in 6 M KOH -h 4 M CH3OH at 40 °C on different porous carbon electrodes impregnated with platinum (curves a, b, c, e, f) and on platinized platinum (curve d)...

The current-time response of the system during Sn(Il) addition presents the same features as the mass intensity-time curve. For comparison the i-t curve for a blank experiment (only adsorbed methanol being present, no tin addition) is also shown in Fig. 4.6a. The observed response is not simply the sum of the individual responses of Sn(II) (Fig. 4.2b) and adsorbed methanol (see dashed curve in Fig. 4.6a), to the applied potential step. 

Figure 3.31 Current/time curve for methanol adsorption. The methanol concentration was 0.5 M. Adsorption occurred after holding the potential at -I- 1.55 V for 20 ms, and then stepping the potential to 0.37 V. The step from 1.55 V to 0.37 V takes place 40 ms in from the right-hand edge. The x-nxis scale is 200 ms cm the y-axis scale is 3.33pAcm. After Bciglcr and Koch...

Potentiodynamic Technique. Adsorption of methanol on Pt in acid solution was studied by Breiter and Gilman (3) using a potentiostatic technique. The anodic sweep, with a sweep rate of 800 V/s, was started at rest potential and extended to 2.0 V with respect to a hydrogen reference electrode in the same solution. As shown in Figure 10.8, the current was recorded as a function of potential (time) in the absence (curve A) and in the presence (curve B) of methanol. The increase in current in curve B is due to oxidation of the adsorbed methanol on the platinum electrode. Thus, shaded area 2 minus shaded area 1 (Fig. 10.8) yields the change 2m (C/cm ) required for oxidation of the adsorbed methanol ... 

Fig. 51.4. Normalized feedback current-distance curves obtained with a 25 pm Pt UME in ImM ferrocene methanol in 0.1M Na2S04. The substrate potential was varied to control the feedback effect (1) 150 mV, (2) 100 mV, (3) 50 mV, (4) OmV, (5) —50 mV, (6) —100 mV, (7) —150 mV and (8) —200 mV vs. Ag/AgCl reference electrode. (9) and (10) are the limiting curves for conductor and insulator substrate, respectively. The tip was held at 0.4 V where the oxidation was diffusion-controlled.

Pt/Ru alloys exhibit lower susceptibility to poisoning than does pure platinum, as can be shown by a slower decay in current-time curves following a potential step. The reaction of methanol on Pt/Ru alloys results in CO2 production at lower potential than does reaction on pine Pt, indicating enhanced complete oxidation by die ruthenium. When a high coverage of adsorbed CO develops on the Pt sites, the Ru sites facilitate its oxidation. 

Figure 5.10b presents RDE curves obtained for the ORR in 0.5 mol H2SO4 electrolyte in the absence and presence of 1.0 mol methanol. The ORR curves for Pt/C was included in the absence of methanol for comparison. As can be observed, RuSe/C shows an increase in overpotential of c.a.lO mV, in the presence of methanol which corroborates with its low observed for methanol oxidation. For Rh cSy/C, a current contribution from methanol oxidation was seen at potentials above 0.7 V, resulting in a net positive current at above 0.8 V. As discussed by the authors [31], modifying ruthenium with selenium results in a significant enhancement of oxygen reduction activity and almost an entirely suppressing of its methanol oxidation activity, in contrast to rhodium modified by sulfur. 

Figure 4.3.12. The effect of surface preparation of the current-potential response curves of n-CuInSc2 in a solution of 6M KI -I- 0.1 M InT -l- 0.0125M I2 at pH 6.0. The square-wave response results from using a chopped white light source of intensity lOOmW/cm. Etching was in a 2% Br2-methanol solution for 60s oxidation was for 2h at 150°C. (Shen et al. [1986].) Reprinted by permission of the publisher, The Electrochemical Society, Inc.

Anodic Reactions in Electrocatalysis -Methanol Oxidation, Fig. 2 Current density versus electrode potential curves for electrochemical reactions involved in a PEMFC and in a DMFC... 

Current voltage curves for p-Si v/ith methanol and acetonitrile containing redox couples above the conduction band edge as determined from flat-band potential measurements. 

Fig. 37. Analyses of current-time curves during the initial interaction of methanol with platinum in O.5MH2SO4 + XMCH3OH at different potentials.

Fig. 25 Structure of PtRu model electrodes and catalytic activity for methanol oxidation after a potential step from 300 to 500 mV RHE current/time curves under conditions as in Fig. 24 [103] (A) Two layer Ru island formation on Pt(l 11) by Ru evaporation at 400 K (B) Smooth Ru/Pt(l 11) surface alloy (C) Ru evaporated on smooth Pt(l 11) (D) Ru evaporated on a rough Pt(l 11) surface (E) Ru evaporated on Pt(l 11) and roughened via ion bombardment (E) Sputtered PtRu alloy (85 15), STM image not possible.

The electrocatalytic activity of the nanostructured Au and AuPt catalysts for MOR reaction is also investigated. The CV curve of Au/C catalysts for methanol oxidation (0.5 M) in alkaline electrolyte (0.5 M KOH) showed an increase in the anodic current at 0.30 V which indicating the oxidation of methanol by the Au catalyst. In terms of peak potentials, the catalytic activity is comparable with those observed for Au nanoparticles directly assembled on GC electrode after electrochemical activation.We note however that measurement of the carbon-supported gold nanoparticle catalyst did not reveal any significant electrocatalytic activity for MOR in acidic electrolyte. The... 

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