Propene Oxidation and Hydrogenation on a Porous Platinum Electrode in Acidic Solution

Abstract

The electrochemical reactivity of propene at the polycrystalline Pt/acidic solution interface was studied by on line differential electrochemical mass spectrometry (DEMS). It was shown that a relatively fast adsorption of hydrocarbon molecules on the electrode surface preceded their electroreduction and electrooxidation at E < 0.2 V and E > 0.6 V, respectively. The adsorbate consisted of associatively bonded propene, partially dehydrogenated C3-hydrocarbon residues, as well as C3-, C2-, and/or C1-oxygen-containing species in relative amounts dependent on the adsorption potential and the subsequent potential sequence. The maximum electrode coverage of 0.58 nmol cm-2 was achieved in the potential range 0.3−0.5 V, where the major part of the surface species was propene itself, oriented with the carbon chain almost parallel relative to the electrode/solution interface. The oxygenated C3-species were formed favorably in the presence of coadsorbed water and/or OH species, at 0.5 V < E < 0.8 V. Propane was identified as the main volatile product of the cathodic hydrogenation of the adsorbate. Additionally, the reductive decomposition of the oxygenated C3-species yielded methane along with the C2-oxygen-containing moieties remaining on the Pt surface and/or undergoing further fragmentation to the C1-oxygen-containing residues. The only final volatile oxidation product of all the adsorbates was CO2.

PEMFC Cathode Catalyst Contamination Evaluation with a RRDE- Propene and Naphthalene

“…In the reverse scan, the PtO reduction peak is suppressed, indicating the incomplete oxidation of C 3 H 6 at the potential limit of 1.03 V and/or the occurrence of C 3 H 6 re-adsorption during cycling. In the H UPD region, an apparent increase in the H UPD adsorption peak is noticed, which can be ascribed to the hydrogenation of the C = C bond [14] and the formation of propane. In the following cycles, the ECSA value increases back to 90% of its initial value, indicating a decrease in the coverage by C 3 H 6 , due to the oxidation/reduction process.…”

“…1c. With the lack of interference from C 3 H 6 reduction, the total C 3 H 6 oxidation current decreases to lower value with increase in cycling numbers, indicating the accumulation of C 3 H 6 oxidation residuals at potential up to 1.03 V. The incomplete oxidation of C 3 H 6 is associated with the difficulty in C-C bond rupture and the complicated 18-electron transfer reaction, in which the peak potential of oxidation is located at approximately 1.1 V [14].The accumulation of the oxidative residuals limits the adsorption of oxygen-containing species and impedes the new C 3 H 6 molecules to be adsorbed and oxidized. The increase in C 3 H 6 coverage, due to the change in potential window, is in agreement with the CV measurements shown in Fig.…”

“…1a were measured in a quasistatic solution, the RRDE measurements for ORR are taken under different hydrodynamic circumstances. Considering that C 3 H 6 can be oxidized and reduced (the final product for oxidation is CO 2 and the reduction product is C 3 H 8 [14]) during cycling, the effect of C 3 H 6 mass transfer on surface coverage must be considered to compare the surface area loss with the ORR kinetic loss. CV measurements with an electrode rotation rate of 1600 rpm are shown in Fig.…”

“…1b, where the coverage of C 3 H 6 is found to be potential dependent. The lower surface coverage in low potential region can be attributed to the easier removal of C 3 H 6 and its oxidative intermediate through hydrogenation process, which forms the volatile C 3 H 8 , a compound with much weaker affinity for the Pt surface and leads to a lower surface coverage [14]. The mass transfer effect of C 3 H 6 is further considered with CV measurements taken at different rotation rates, the results are shown in Fig.…”

“…Among the 7 contaminants, propene (C 3 H 6 ) and naphthalene (C 10 H 8 ) are the ones for which C = C double bond interactions are expected, with the molecules bonded to the Pt surface through a C = C bridge configuration [14,15]. However, differences in behavior are also expected, due to the differences in molecule structure (e.g., the linear structure of C 3 H 6 vs. the rigid, aromatic structure of C 10 H 8 ) and adsorption energy on Pt surface (-89.7 kJ mol −1 for C 3 H 6 and -126 kJ mol −1 for C 10 H 8 ) [15,16].…”