Effect of Surface Composition on Electrochemical Oxidation Reaction of Carbon Monoxide and Ethanol of PtxRh1−x Solid Solution Electrodes

Kien, Nguyen Trung; Yara, Haruki; Chiku, Masanobu; Higuchi, Eiji; Inoue, Hiroshi

doi:https://doi.org/10.1155/2023/2386013

International Journal of Electrochemistry

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Abstract Introduction Experimental Results and Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2023 | Article ID 2386013 | https://doi.org/10.1155/2023/2386013

Effect of Surface Composition on Electrochemical Oxidation Reaction of Carbon Monoxide and Ethanol of Pt_xRh_1−x Solid Solution Electrodes

Nguyen Trung Kien,¹Haruki Yara,¹Masanobu Chiku,¹Eiji Higuchi,¹and Hiroshi Inoue¹

Academic Editor: Hamish Andrew Miller

Received27 Jul 2023

Revised02 Nov 2023

Accepted06 Nov 2023

Published15 Nov 2023

Abstract

Pt_xRh_1−x (x = 0.76, 0.54, and 0.27) solid solutions were prepared by arc-melting. For these solid solutions, the lattice constant was linearly related to the Pt content. The surface compositions of the solid solutions determined by X-ray photoelectron spectroscopy were quite similar to their bulk compositions estimated by energy dispersive X-ray spectroscopy. The CO-stripping voltammograms demonstrated that the onset potential of CO oxidation current density (E_onset) shifted negatively as the surface Pt content decreased, suggesting an increased CO-poisoning resistance. Linear sweep voltammograms of the solid solution electrodes in an Ar-saturated (1 M ethanol + 0.1 M HClO₄) solution exhibited that the onset potentials of ethanol oxidation reaction (EOR) current for all solid solution electrodes were lower than of a Pt electrode, and Pt_0.54Rh_0.46 gave the highest specific activity (SA) of 312 μA·cm⁻², which was about 1.8 and 2.5 times higher than the SAs of Pt and Rh, respectively. In situ infrared reflection-absorption spectra exhibited that the Pt_0.54Rh_0.46 electrode had the bands due to the linear-bonded CO on Pt and bridge-bonded CO on Rh as EOR intermediates around 0.2 V vs. the reversible hydrogen electrode, but the band due to the linear-bonded CO on Rh was not observed even at 0.6 V, suggesting that the existence of the adjacent Pt-Rh sites and the preferential formation of bridge-bonded CO on Rh accelerated the C-C bond cleavage and improved the EOR activity.

1. Introduction

Ethanol has a high energy density (8.0 kWh·kg⁻¹) [1, 2] and can be mass-produced from biofuels generated from plant-based waste materials such as biomass. Thus, direct ethanol fuel cell (DEFC) is attracting attention as carbon-neutral power sources. However, to improve the slow rate of ethanol oxidation reaction (EOR) in DEFC, the research and development of electrocatalysts with high activity and high durability have been performed [3–5]. The CO species as an EOR intermediate is known to poison electrocatalysts, resulting in a significant decrease in EOR catalytic activity [1, 6–8]. In addition, the cleavage reaction of the C-C bond required for the complete EOR to CO₂ is difficult [1, 9–14].

Pt nanoparticle catalysts exhibit excellent EOR activity, but their surfaces are easily poisoned by intermediately-generated CO species. Binary alloys of Pt with foreign metals such as Ru [15, 16], Sn [12, 14, 17–19], and Rh [1, 10, 20–27] exhibit high EOR activity in acidic media. Among them, PtRh alloys had the highest EOR activity [1, 20–23, 26]. Wang et al. evaluated the EOR activity of Pt_xRh_100−x (x = 91, 76, 52, 24) alloys whose compositions were determined by energy dispersive X-ray spectroscopy (EDX) and found that the Pt₇₆Rh₂₄ alloy showed the highest EOR activity [20]. Piwowar et al. reported that the amount of produced CO₂ per electrochemical active surface area (ECSA) of Pt_xRh_1−x (x = 0.71, 0.51, and 0.36) nanoalloys loaded on carbon black (Pt_xRh_1−x/C) at 0.95 V vs. RHE was independent of the surface Rh content [26]. The CO₂ selectivity was also improved for PtRh/C [24] and Pt overlayer on Rh [25]. Zhu et al. reported that PtRh nanowires loaded on carbon black (PtRh NW/C) had significantly high C-C breaking ability to promote the complete EOR [1]. In addition, they found that the EOR activity and durability of the PtRh NW/C at 1.0 V vs. RHE in (0.1 M HClO₄ + 0.5 M C₂H₅OH) aqueous solution evaluated by cyclic voltammetry were nearly three times as high as those of Pt/C, and the faradaic efficiency for CO₂ production in potentiostatic electrolysis at 1.0 V vs. RHE for the former was 57%, which was much higher than that of Pt/C (17%), clearly indicating that the Rh component is effective for improving the CO₂ selectivity [1]. Delpeuch et al. also reported that PtRh nanodendrites had high EOR activity in acidic media, and the EOR activity strongly depended on surface composition, in contrast to the results of Piwowar and Lewera [26].

So far, the EOR activity of PtRh alloy catalysts has been evaluated at potentials over 1.0 V vs. RHE [1, 20–25] that was higher than the potential of oxidative Rh dissolution (0.8 V vs. RHE) [28, 29]. So, the surface composition of PtRh alloys must be changed during the EOR activity evaluation. As a matter of course, the EOR activity evaluation of the PtRh catalysts should be carried out at potentials less than 0.8 V where surface alloy composition is maintained. Meanwhile, for alloy nanoparticles, the surface composition often does not match the bulk composition. Therefore, the surface composition with the highest EOR activity cannot be predicted from the bulk composition. In the present study, Pt_xRh_1−x (x = 0.76, 0.54, and 0.27) solid solutions whose surface compositions were almost the same as bulk compositions were prepared by an arc-melting method. Their EOR activity in an acidic solution was evaluated at 0.6 V vs. RHE, where Rh does not dissolve oxidatively, and a relationship between surface composition and EOR activity was reevaluated. In addition, the EOR mechanism on the Pt_xRh_1−x solid solutions was discussed based on in situ infrared reflection-absorption spectra at different potentials.

2. Experimental

2.1. Preparation of Rh and Pt_xRh_1−x Solid Solution Electrodes

Ingots (diameter: 3 mm) of Pt, Rh, and Pt_xRh_1−x solid solutions with bulk compositions of x = 0.76, 0.54, and 0.27 were prepared from constituent elements (99.98% Pt plate and 99.9% Rh wire, Nilaco) by induction melting under an Ar atmosphere. Each solid solution ingot was turned over and remelted four times to ensure homogeneity. The resultant polycrystalline Rh and each Pt_xRh_1−x solid solution ingot with a diameter of 3 mm were polished into a hemisphere. The flat side of the hemisphere was used as an electrode, and the other side was connected to a lead wire. The side of the hemisphere was covered with a Teflon tube to prevent contact with an electrolyte solution. On the other hand, a commercial polycrystalline Pt electrode with a diameter of 5 mm (BAS Inc.) was polished with alumina suspensions, followed by sonicating in ultrapure water and ethanol.

2.2. Characterization of Pt, Rh, and Pt_xRh_1−x Solid Solution Electrodes

Crystallographic characterization of each ingot was carried out with an X-ray diffractometer (Cu K_α/λ = 1.5405 Å, 40 kV, 30 mA, XRD-6100, Shimadzu). The bulk composition of each solid solution was determined by EDX (JED-2300, JEOL Ltd.). The evaluation of the electronic state and the determination of surface composition for each solid solution were performed by XPS (ESCA-3400 instrument, Shimazu, Mg K_α radiation 1253.6 eV, 10 kV, and 20 mA). Each XPS spectrum was calibrated using an Au 4f_7/2 peak of gold powder (99.999%, Strem Chemicals) as 84.0 eV.

2.3. Electrochemical Measurements

The polycrystalline Pt electrode has two couples of redox peaks due to hydrogen adsorption/desorption between 0.05 and 0.4 V vs. the reversible hydrogen electrode (RHE) [30, 31]. The electric charge for the desorption of atomic hydrogen (Q_H-des) for polycrystalline Pt is 210 μC·cm⁻² [30], assuming that atomic hydrogen is adsorbed on a Pt atom. The Q_H-des for polycrystalline Rh is 221 μC·cm⁻² [31]. The redox peaks due to hydrogen desorption for a pure Rh electrode partly overlap with those for the polycrystalline Pt electrode [32, 33]. Rh has a face-centered cubic (fcc) structure, and its atomic radius is similar to that of Pt. So, assuming that Rh has a stoichiometric composition of Rh : H = 1 : 1 like Pt, a Q_H-des value of 210 μC·cm⁻² was used [31]. The ECSAs of the Pt_xRh_1−x electrodes were calculated as follows:

To evaluate the CO poisoning of the Pt, Rh, and Pt_xRh_1−x solid solution surfaces, CO was bubbled through the 0.1 M HClO₄ aqueous solution for 5 min with applying a constant potential of 0.30 V vs. RHE. After that, Ar gas was bubbled through the electrolyte solution for approximately 15 min to remove the dissolved CO while keeping the constant potential of 0.30 V. Two cycles of CVs were recorded at 10 mV·s⁻¹ between 0.05 and 1.2 V. These operations were performed at 25°C.

CVs and linear sweep voltammograms (LSVs) of each electrode were recorded at 20 mV·s⁻¹ in Ar-saturated 0.5 M H₂SO₄ and (1 M ethanol + 0.1 M HClO₄) solutions at 30°C, respectively. A platinized Pt electrode and an RHE were used as counter and reference electrodes, respectively.

2.4. Qualitative Analysis of EOR Products and Intermediates

The products and intermediates of EOR were identified by in situ IRAS (FT/IR 6100, HgCdTe (MCT) detector, JASCO). The cell is coupled at its bottom with a CaF₂ prism beveled at 60° from the surface normal. The spectra were recorded with a resolution of 4 cm⁻¹. IR spectra were drawn due to the absorbance calculated from reflectance intensities at 0.1–0.6 V (R) and 0.05 V (R⁰) for reference.

3. Results and Discussion

3.1. Structure and Compositions of Pt_xRh_1−x Solid Solutions

Figure 1(a) shows XRD patterns for Pt_0.76Rh_0.24, Pt_0.54Rh_0.46, and Pt_0.27Rh_0.73 ingots. The diffraction pattern of each Pt_xRh_1−x ingot was similar to the diffraction patterns of Pt and Rh with a face-centered cubic (fcc) structure, suggesting that each Pt_xRh_1−x ingot also has the fcc structure. All diffraction peaks of these Pt_xRh_1−x ingots were located between the corresponding diffraction peaks of Pt and Rh, as shown in Figure 1. The (111) peak shifted to the higher angles with increasing the Rh content or decreasing the Pt content due to the shrinkage of the unit cell, and the other diffraction peaks also showed the similar tendency. Figure 1(b) shows the lattice constant as a function of the bulk Pt content evaluated by EDX. As can be seen from this figure, the lattice constant linearly increased with the Pt content, suggesting that Vegard’s law holds. Thus, the Rh atoms were uniformly incorporated into the Pt crystallites, and binary solid solutions were formed, as expected from the XRD patterns.

(a)

(b)

Figure 2 shows the Pt4f and Rh3d core-level spectra for Pt, Rh, Pt_0.76Rh_0.24, Pt_0.54Rh_0.46, and Pt_0.27Rh_0.73. The Pt4f spectrum for each solid solution exhibited intense doublets at 71.0 and 74.4 eV, which were assigned to metallic Pt (Pt⁰) [1, 27], and there were not any peaks assigned to Pt oxides. On the other hand, the Rh3d spectrum for each solid solution exhibited the 3d_3/2 peak (312.1 eV) and the 3d_5/2 peak (307.3 eV) for Rh⁰ [27]. Figure 2 clearly shows that each solid solution had positive shifts of the Pt4f peaks and negative shifts of the Rh3d peaks. The positive and negative peak shifts are related to the downshift and upshift of the d-band center, causing the decrease and increase in the CO adsorption energy [34], respectively, suggesting that the adsorbed CO on Pt is destabilized, whereas that on Rh is stabilized. So, the positive shift of Pt4f peaks for each Pt_xRh_1−x solid solution will cause the destabilization of CO adsorbed on the Pt sites.

(a)

(b)

The surface composition of each Pt_xRh_1−x solid solution was determined by XPS, and the relationship between the surface composition and bulk composition for the Pt_xRh_1−x solid solutions is shown in Figure 3. As can be seen from Figure 3, the surface Pt content was in good agreement with the bulk Pt content.

3.2. CO Oxidation Behaviors of Pt, Rh, and Pt_xRh_1−x Electrodes

To investigate the adsorption/desorption behavior of CO species, CO-stripping voltammograms of the solid solution electrodes were measured. Figures 4(a) and 4(b) show CO-stripping voltammograms of Pt, Rh, Pt_0.76Rh_0.24, Pt_0.54Rh_0.46, and Pt_0.27Rh_0.73 solid solution electrodes. For Pt and Rh electrodes, no hydrogen desorption waves were observed in a potential range of 0.05–0.4 V during the first forward sweep, indicating that the formation of atomic hydrogen on both electrode surfaces was hindered by adsorbed CO. In addition, the CO-stripping current began flowing around 0.62 V for the Rh electrode and 0.74 V for the Pt electrode, suggesting that the adsorbed CO on the Pt surface is more stable than that on the Rh surface. In the second cycle, the CVs of the Pt and Rh electrodes almost agreed with those in an Ar-saturated solution, respectively. Therefore, adsorbed CO on both electrode surfaces was almost removed in the first cycle.

(a)

(b)

(c)

(d)

(e)

(f)

Figure 4(c) shows the onset potential of CO-stripping current (E_{onset, CO}) as a function of surface Pt content. The E_{onset, CO} was evaluated using a compensated CV that was obtained by subtracting the CV in the 1st cycle from that in the 2nd cycle. As can be seen from Figure 4(c), the E_{onset, CO} value shifted negatively as the surface Pt content decreased. In a proposed CO oxidation mechanism in the PtRh alloy electrode [20], water is oxidized at the Rh sites to form adsorbed OH (OH_ad) (equation (2)), which binds to the adsorbed CO (CO_ad) at the adjacent Pt sites (equation (3)).

Rh, a highly oxophilic transition metal, initiates water dissociation at a lower potential than Pt, as expected from Figure 4(a). The adsorption energy of CO on Pt decreases with the downward shift of the d-band center due to the ligand effect of Rh [1, 34–37], and as expected from Figure 2(a), the d-band center will shift downwardly for each Pt_xRh_1−x solid solution. In this way, the ligand effect and bifunctional effect improve the oxidation of adsorbed CO.

Figures 4(d)–4(f) show CVs of Pt_0.76Rh_0.24, Pt_0.54Rh_0.46, and Pt_0.27Rh_0.73 solid solution electrodes in an Ar-saturated 0.1 M HClO₄ solution before and after CO-stripping voltammetric measurements. Irrespective of solid solution composition, the hydrogen adsorption/desorption waves did not change after each CO-stripping voltammetric measurement, suggesting that the surface composition of each solid solution did not change during this measurement.

3.3. EOR Activity for the Pt, Rh, and Pt_xRh_1−x Electrodes

LSVs of the Pt, Rh, Pt_0.76Rh_0.24, Pt_0.54Rh_0.46, and Pt_0.27Rh_0.73 solid solution electrodes in Ar-saturated (1.0 M C₂H₅OH + 0.1 M HClO₄) solution were performed to investigate their EOR activity. The results are shown in Figure 5(a). In addition, the specific activity (SA) of each electrode was evaluated by dividing the EOR current at 0.6 V vs. RHE by ECSA_Pt+Rh and shown in Figure 5(b). As can be seen from Figure 5(b), the Pt_0.54Rh_0.46 electrode had the highest SA (312 μA·cm⁻²) among the three solid solution electrodes. Figure 5(c) shows the onset potential (E_onset) of the EOR current density evaluated from Figure 5(a) as a function of the surface Pt content. The E_onset values of the Pt_0.76Rh_0.24, Pt_0.54Rh_0.46, and Pt_0.27Rh_0.73 solid solution electrodes were 0.337, 0.335, and 0.339 V, respectively, each of which was lower than that of Pt (0.342 V). In this way, the Pt_xRh_1−x solid solution electrodes improved the EOR activity of Pt and Rh electrodes.

(a)

(b)

(c)

3.4. IRAS Spectra and EOR Mechanism of the Pt, Rh, and Pt_xRh_1−x Electrodes

Many EOR mechanisms on Pt electrodes in acidic media have been proposed. In a typical EOR mechanism in acidic media, ethanol molecules are dissociatively adsorbed at the Pt sites with O-adsorption or C-adsorption, and then oxidized to acetaldehyde. Acetaldehyde is dissociatively oxidized to acetyl (CH₃CO_ad), which is still oxidized to acetic acid, the final partial oxidation product, by OH_ad. In another pathway, it has been proposed that acetaldehyde was dehydrated to form adsorbed enolate, followed by dissociating adsorbed CO and CH_x species through C-C bond cleavage in the potential region of hydrogen desorption [38].

Figure 6 shows in situ IRAS spectra at various potentials in an Ar-saturated (1 M ethanol + 0.1 M HClO₄) solution for the Pt, Rh, Pt_0.76Rh_0.24, Pt_0.54Rh_0.46, and Pt_0.27Rh_0.73 solid solution electrodes. For the Pt electrode, the band around 2051 cm⁻¹ assigned to linearly bonded CO (CO_L), which is a precursor of CO₂ formation, was observed at about 0.2 V, and the band intensity increased with potential, suggesting that the C-C bond was cleaved [38]. A band assigned to the asymmetric stretch vibration of CO₂ around 2343 cm⁻¹ [39, 40] was not distinctly observed even at 0.6 V, suggesting that the oxidation of adsorbed CO does not occur. A band assigned to carbonyl around 1714 cm⁻¹ due to the formation of acetaldehyde [41] appeared at 0.5 V. Therefore, the oxidation current observed at the Pt electrode (Figure 5(a)) is mainly attributed to the partial oxidation of ethanol to intermediates, not CO₂.

(a)

(b)

(c)

(d)

(e)

For the Rh electrode (Figure 6(b)), the bands assigned to linearly bonded CO (Rh-CO_L, 2016 cm⁻¹) and bridged CO on Rh (Rh-CO_B, 1900 cm⁻¹) [42] were observed around 0.2 V. The band assigned to carbonyl (1714 cm⁻¹) appeared at 0.5 V, whereas the band due to CO₂ (2343 cm⁻¹) was clearly observed at 0.6 V, as expected from the onset of CO-stripping on Rh at lower potentials (Figure 4(a)). This indicates that the CO₂ production on Rh occurs at lower potentials than that on Pt, but intermediates and/or CO₂ can poison the Rh surface, causing a significant decrease in EOR current (Figure 5(a)).

According to the EOR mechanism study [1], the EOR of the Pt_xRh_1−x (x = 0.76, 0.54, and 0.27) solid solutions are summarized in equations (2)–(8).

Rh in Pt_xRh_1−x (x = 0.76, 0.54, 0.27) solid solution has two important functions. First, Rh can promote the cleavage of C-C bonds in EOR and inhibit the dehydrogenation process to form CH₃COOH and CH₃CHO. Second, Rh can provide the OH_ads species needed to oxidize intermediates such as CO adsorbed on adjacent Pt sites and avoid catalytic poisoning.

For the Pt_0.54Rh_0.46 solid solution electrode (Figure 6(d)), which had the highest SA in this study, the bands around 2051 cm⁻¹ (Pt-CO_L) and 1900 cm⁻¹ (Rh-CO_B) appeared around 0.2 V, whereas the band around 2016 cm⁻¹ (Rh-CO_L) was not observed, suggesting that the C-C bond cleavage occurs at the adjacent Pt-Rh sites. The band around 1714 cm⁻¹ due to carbonyl was observed around 0.4 V, and the band for CO₂ appeared at 2343 cm⁻¹ was observed around 0.5 V, suggesting that EOR was accelerated due to the appearance of the Pt-Rh sites, as expected from Figure 5(a).

For the Pt_0.76Rh_0.24 solid solution electrode (Figure 6(c)), the band due to Pt-CO_L (2051 cm⁻¹) and the small shoulder around 2016 cm⁻¹ due to Rh-CO_L appeared at 0.4 V, while the band for Rh-CO_B was not observed because the Rh sites were isolated surrounded by Pt sites, suggesting that the surface Pt and Rh atoms were uniformly arranged, as expected from Figure 1(b). Interestingly, similar to the Pt electrode, CO₂ and carbonyl were not detected even at 0.6 V. The oxidation of Rh-CO_L seems to be more difficult than that of Rh-CO_B, which is supported by the positive shift of E_onset of CO-stripping with increasing Pt content (Figure 4(c)). The EOR on the Pt_0.76Rh_0.24 solid solution electrode seems to mainly occur at Pt sites modified electronically by alloying with Rh, improving the EOR activity.

For the Rh-rich Pt_0.27Rh_0.73 solid solution electrode (Figure 6(e)), the bands due to Rh-CO_B (1900 cm⁻¹) and Rh-CO_L (2016 cm⁻¹) appeared around 0.2 V, while the small band due to Pt-CO_L was also observed as a shoulder around 0.4 V because the Pt sites were isolated surrounded by Rh sites. The bands due to carbonyl (1714 cm⁻¹) and CO₂ (2343 cm⁻¹) were observed around 0.4 V, and the strong band for CO₂ appeared at 0.6 V, similar to the Rh electrode. The Pt_0.27Rh_0.73 solid solution has the fewer adjacent Pt-Rh sites than Pt_0.54Rh_0.46, reducing the C-C bond cleavage at the Pt-Rh sites. The appearance of Rh-CO_L may be responsible of the delayed CO₂ production.

4. Conclusions

We prepared Pt_xRh_1−x (x = 0.76, 0.54, and 0.27) solid solutions by the arc-melting method. Their lattice constant and bulk composition followed the Vegard equation. For each solid solution, the surface composition estimated by XPS was quite similar to the bulk composition estimated by EDX. The CO-stripping voltammograms demonstrated that the E_onset value of CO oxidation shifted negatively as the Pt content in the solid solutions decreased, which indicated an enhancement of CO-poisoning resistance for the solid solutions with lower Pt contents. From the LSV analysis of each solid solution electrode in an Ar-saturated (1 M ethanol + 0.1 M HClO₄) solution, it was found that the Pt_0.54Rh_0.46 electrode gave the highest specific activity of 312 μA·cm⁻², which was about 1.8 and 2.5 times higher than the SAs of the Pt and Rh electrodes, respectively. From the in situ IRAS analysis, no band of CO₂ was observed even at 0.6 V for Pt and Pt_0.76Rh_0.24 electrodes, but band of CO₂ was clearly observed at 0.5 or 0.6 V for Rh, Pt_0.27Rh_0.73, and Pt_0.54Rh_0.46 electrodes. In addition, the in situ IRAS clearly illustrated the increase of a peak at 2343 cm⁻¹ assigned to CO₂ at potentials above 0.5 V for the Pt_0.54Rh_0.46 solid solution electrode, suggesting the EOR activity of the Pt_0.54Rh_0.46 electrode was higher than that of Pt_0.76Rh_0.24 and Pt_0.27Rh_0.73 electrodes.

Data Availability

The data used to support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare that they have no conflicts of interest regarding the publication of this paper.

Acknowledgments

This research was supported by the research funds provided by Osaka Metropolitan University.

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Copyright © 2023 Nguyen Trung Kien et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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International Journal of Electrochemistry

Effect of Surface Composition on Electrochemical Oxidation Reaction of Carbon Monoxide and Ethanol of PtxRh1−x Solid Solution Electrodes

Abstract

1. Introduction

2. Experimental

2.1. Preparation of Rh and PtxRh1−x Solid Solution Electrodes

2.2. Characterization of Pt, Rh, and PtxRh1−x Solid Solution Electrodes

2.3. Electrochemical Measurements

2.4. Qualitative Analysis of EOR Products and Intermediates

3. Results and Discussion

3.1. Structure and Compositions of PtxRh1−x Solid Solutions

3.2. CO Oxidation Behaviors of Pt, Rh, and PtxRh1−x Electrodes

3.3. EOR Activity for the Pt, Rh, and PtxRh1−x Electrodes

3.4. IRAS Spectra and EOR Mechanism of the Pt, Rh, and PtxRh1−x Electrodes

4. Conclusions

Data Availability

Conflicts of Interest

Acknowledgments

References

Copyright

Effect of Surface Composition on Electrochemical Oxidation Reaction of Carbon Monoxide and Ethanol of Pt_xRh_1−x Solid Solution Electrodes

2.1. Preparation of Rh and Pt_xRh_1−x Solid Solution Electrodes

2.2. Characterization of Pt, Rh, and Pt_xRh_1−x Solid Solution Electrodes

3.1. Structure and Compositions of Pt_xRh_1−x Solid Solutions

3.2. CO Oxidation Behaviors of Pt, Rh, and Pt_xRh_1−x Electrodes

3.3. EOR Activity for the Pt, Rh, and Pt_xRh_1−x Electrodes

3.4. IRAS Spectra and EOR Mechanism of the Pt, Rh, and Pt_xRh_1−x Electrodes