Unusually High Activity of Pt Islands on Rh(1 1 1) Electrodes for Ethanol Oxidation

Abstract

The electrooxidation of ethanol has been widely studied since its possible application in PEM cells. Many efforts have been devoted to disentangle its oxidation mechanism and how this mechanism depends on the ethanol concentration and the surface structure and composition of the electrode. [1][2][3][4] The goal is to obtain CO2 as final product at the lowest potential and the highest current. In the oxidation mechanism, three different products can be obtained: acetaldehyde, acetic acid and CO2, exchanging 2, 4 and 12 electrons respectively. Acetic acid is a stable product since its oxidation takes place at very high potentials [5] , thus the challenge is to break the C-C bond either in ethanol [6,7] or acetaldehyde [8] to obtain CO2.Among pure metals, platinum has the highest catalytic activity in acid media, but the final product in the oxidation is mixture of CO2 and acetic acid, whose ratio strongly depends on the surface structure. [9] In order to increase the activity of platinum, other metals, namely, Ru, [8,10] Os, [11,12] Sn [7] and Rh [13] have been added to the surface to diminish the overpotentials and to increase the selectivity of the oxidation towards the formation of CO2. The effect of these metals in the oxidation mechanism has been explained on the basis of the bifunctional mechanism [14] and ligand effect. [15] From previous results, it seems clear that the only surface modifier that increases the CO2/acetaldehyde ratio is Rh, [13] although the overall reaction rate is lower. On the other hand, the opposite combination, Pt deposited on Rh electrodes has not been studied yet. Rh electrodes are not active for the oxidation of ethanol. However, it has been shown that a single layer (or submonolayer) of a metal deposited on a different substrate can have electrocatalytic activities larger than any of the two bulk metals. [16,17] In general, the metal overlayer has interatomic distances that are different from the bulk metal, since it accommodates its structure to that of the underneath substrate. This effect causes a change in the electronic properties of the overalyer and can increase (or decrease) the catalytic properties.[18] The aim of this work is to determine the electrochemical behaviour of Rh electrodes modified by Pt (sub)monolayers for ethanol oxidation, analysing the effect of the surface composition on the mechanism using in situ FTIR spectroscopy. [19] For the clean Rh(111) electrode, the voltammogram in sulphuric acid solution shows a pair of quasi-reversible peaks at 0.15 and 0.06 V, which are associated to the competitive adsorption of hydrogen/sulphate on the electrode surface. [20,21] In the initial deposition stages of Pt, these peaks become significantly sharper and more reversible. Although the explanation on the origin of such change is beyond the scope of this manuscript, it should be recalled that the interaction of water with adsorbates is different on platinum and rhodium. For instance water and CO adsorbed on Pt(111) show repulsive interactions whereas attractive interac...

Structurally ordered high‐entropy intermetallic nanoparticles with enhanced C–C bond cleavage for ethanol oxidation

“…The EOR activity of the structurally ordered HEIs is superior to that of most current electrocatalysts under the same test conditions 10,35,36 . Meanwhile, the electrocatalytic activity of Rh/C was also tested under the same conditions, and we found Rh had much less capacity for dehydrogenation than Pt (Figure ), which was consistent with the results reported in the literature 37,38 . In the process of electrochemical testing, we clearly observed that there were two peaks during the forward scanning.…”

Adatom modified shape-controlled platinum nanoparticles towards ethanol oxidation

“…In all cases, the current diminishes significantly and no change in the onset potential can be detected. Although it has been reported that PtRh alloys increase the CO2/acetaldehyde ratio in ethanol oxidation [15,23], the net effect observed here is a diminution of the total current. At this respect, it is worth noting that Rh atoms are exclusively adsorbed at the surface of Pt nanoparticles, that is, Rh decorated Pt surface is formed, whose behavior can be different from that observed for a PtRh surface alloy.…”

“…In previous studies, Sn and Ru deposition on stepped surfaces showed some enhancement for the oxidation to CO2 [21,22], whereas Pt deposited on Rh electrodes also shows increased activity for the C-C bond scission [23]. In addition, some works have demonstrated the improvement in the carbonate formation when Pb atoms are adsorbed on polycrystalline Pt surfaces in alkaline solutions [24,25].…”

Replicating the Defect Structures on Ultrathin Rh Nanowires with Pt to Achieve Superior Electrocatalytic Activity toward Ethanol Oxidation

“…Figure a and Figure S11 (Supporting Information) show the ethanol electrooxidation curves of different electrocatalysts with the current density normalized to the Pt mass and the ECSA, respectively. The Rh wavy NWs are inactive for EOR (Figure S12, Supporting Information), because Rh has much less capacity for dehydrogenation than Pt . Therefore, the activities for ethanol electrooxidation on these Rh@Pt n L NW/C catalysts are completely stemmed from the outer Pt shells.…”

“…Also, the onset potential for generating CO 2 was lower on the catalysts with less Pt atomic layer numbers. In Rh‐Pt bimetallic heterosystems, the strain and ligand effects from the Rh subsurface is a key factor for weakening Pt–intermediate binding strength (such as PtCO) to ease their oxidation . As the in situ FTIR spectra shown, no obvious CO L band can be observed on the Rh @ Pt 1L NW/C and Rh @ Pt 3.5L NW/C catalysts, while a tiny CO L signal and a larger one can be found on the Rh @ Pt 5.3L NW/C and the Pt/C, respectively.…”