OperandoNear Ambient Pressure XPS (NAP-XPS) Study of the Pt Electrochemical Oxidation in H₂O and H₂O/O₂Ambients

Abstract

Oxides on the surface of Pt electrodes are largely responsible for the loss of their electrocatalytic activity in the oxygen reduction and oxygen evolution reactions. In this work we apply near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study in operando the electrooxidation of a nanoparticulated Pt electrode integrated in a membrane-electrode assembly of a high temperature proton-exchange membrane under water and water/oxygen ambient. Three types of surface oxides/hydroxides gradually develop on the Pt surface depending on the applied potential at +0.9, + 2.5, and +3.7 eV relative to the 4f peak of metal Pt and were attributed to the formation of adsorbed O/OH, PtO, and PtO2, respectively. The presence of O2 in the gas-phase results in the increase of the extent of surface oxidation, and in the growth of the contribution of the PtO2 oxide. Depth profiling studies, in conjunction with quantitative simulations, allowed us to propose a tentative mechanism of the Pt oxidation at high anodic polarization, consisting of adsorption of O/OH followed by nucleation of PtO/PtO2 oxides and their subsequent three-dimensional growth.

From Bad Electrochemical Practices to an Environmental and Waste Reducing Approach for the Generation of Active Hydrogen Evolving Electrodes

“…The analysis of the peak areas after background subtraction reveals that the platinum at the surface of sample comprises around 94.5 % metallic Pt (blue) and 5.5 % can be attributed to Pt(OH) 2 (green). The Pt 4f7/2 binding energy of 72.2 eV found from the deconvolution for Pt(OH) 2 is in excellent agreement with the result for chemisorbed O/OH on Pt reported by Saveleva et al [45] These findings made us believe that platinum-oxide species are formed on the Pt counter electrode whilst HER on Ni42, for a given cell voltage of about 2.1 V (Pt: anode and Ni42: cathode), at E cathode = À400 mV vs. RHE (E anode =+ 1700 mV vs. RHE). Thus, oxygen evolution took place on the Pt surface.…”

“…Whereas the 4f 7/2 core level energy is expected to be located at 70.7 eV for the metallic Pt "bulk" state of a polycrystalline Pt foil, [43] binding energies of 71.0 eV to 71.3 eV have been obtained for Pt electrodes with the platinum being in polycrystalline and nanostructured form. [44,45] The features, which we associate to metallic Pt (blue), show a rather pronounced tail (asymmetry) to higher binding energies ( Figure 6 f), another strong indication for metallicity. The analysis of the peak areas after background subtraction reveals that the platinum at the surface of sample comprises around 94.5 % metallic Pt (blue) and 5.5 % can be attributed to Pt(OH) 2 (green).…”

Recovery of Active Surface Sites of Shape-Controlled Platinum Nanoparticles Contaminated with Halide Ions and Its Effect on Surface-Structure

“…Oxygen evolution reaction (OER) is evident at further higher potential of 1.6 V. Conway et al documented these findings with Pt electrodes. 51 Recently, Savaleva et al established three types of surface species using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) 52 at potentials close to the onset of Pt electrooxidation: (i) adsorbed O/OH, (ii) PtO and (iii) PtO 2 . The pre-adsorbed or chemisorbed (HSO 4 − ) solution anions will be replaced by the formation of 2D-array of adsorbed O/OH at the onset of the electroxidation of Pt.…”

Periodic Transition between Breathing Spots and Synchronous Sulfur Deposition/Dissolution in Transpassive Region of the Electro‐Oxidation of Sulfide on Platinum

“…It is widely known that a passivated metal film starts to rapidly dissolve if the electrode potential of the metal becomes too positive. It was believed that in the transpassive region the passive film turned into higher valence oxides such as Pt 3 O 4 and PtO 2 and evolving oxygen . Therefore, transpassivation is generally regarded as a type of corrosion damage to a passivated metal or alloy.…”

“…It was believed that in the transpassive region the passive film turned into higher valence oxides such as Pt 3 O 4 and PtO 2 and evolving oxygen. [10] Therefore, transpassivation is generally regarded as a type of corrosion damage to a passivated metal or alloy. Investigation of the transpassive dynamics have mainly focused on iron, [11][12][13][14] chromium, [15][16] nickel, [17][18][19][20][21][22][23][24] copper, [25] and also alloys; [26][27] but little attention has been paid to noble metals, such as platinum and gold.…”