Degradation kinetics of Pt during high-temperature PEM fuel cell operation Part III: Voltage-dependent Pt degradation rate in single-cell experiments

Boosting the Electrolysis of Monosaccharide-Based Streams in an Anion-Exchange Membrane Cell

A systematic study on the electrochemical reforming of monosaccharides (fructose, glucose, and xylose) using Pt-based anodic electrocatalysts is here presented for the first time to completely optimize the anodic catalyst and electrolyzer operating conditions. First, the electro-oxidation of each molecule was studied using a monometallic (Pt) and two bimetallic (PtNi and PtCo) anodic electrocatalysts supported on graphene nanoplatelets (GNPs). Tests in a three-electrode cell showed superior electrochemical activity and durability of PtNi/GNPs, especially at potentials higher than 1.2 V vs RHE, with the highest electrocatalytic activity in d-xylose electro-oxidation. Then, monometallic (Pt and Ni) and bimetallic electrocatalysts with different Pt:Ni mass ratios (1:1 and 2:1) were studied for d-xylose electro-oxidation, with the 2:1 mass ratio presenting the best results. This electrocatalyst was selected as the most suitable for scale-up to an anion-exchange membrane electrolyzer, where the optimal operating potential was determined. Additionally, stable operating conditions of the electrolyzer were achieved by cyclic H2 production and cathodic regeneration polarization steps. This led to suitable and reproducible H2 production rates throughout the production cycles for renewable hydrogen production from biomass-derived streams.

Elucidating the Complex Oxidation Behavior of Aqueous H3PO3 on Pt Electrodes via In Situ Tender X-ray Absorption Near-Edge Structure Spectroscopy at the P K-Edge

In situ tender X-ray absorption near-edge structure (XANES) spectroscopy at the P K-edge was utilized to investigate the oxidation mechanism of aqueous H3PO3 on Pt electrodes under various conditions relevant to high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) applications. XANES and electrochemical analysis were conducted under different tender X-ray irradiation doses, revealing that intense radiation induces the oxidation of aqueous H3PO3 via H2O yielding H3PO4 and H2. A broadly applicable experimental procedure was successfully developed to suppress these undesirable radiation-induced effects, enabling a more accurate determination of the aqueous H3PO3 oxidation mechanism. In situ XANES studies of aqueous 5 mol dm-3 H3PO3 on electrodes with varying Pt availability and surface roughness reveal that Pt catalyzes the oxidation of aqueous H3PO3 to H3PO4. This oxidation is enhanced upon applying a positive potential to the Pt electrode or raising the electrolyte temperature, the latter being corroborated by complementary ion-exchange chromatography measurements. Notably, all of these oxidation processes involve reactions with H2O, as further supported by XANES measurements of aqueous H3PO3 of different concentrations, showing a more pronounced oxidation in electrolytes with a higher H2O content. The significant role of water in the oxidation of H3PO3 to H3PO4 supports the reaction mechanisms proposed for various chemical processes observed in this work and provides valuable insights into potential strategies to mitigate Pt catalyst poisoning by H3PO3 during HT-PEMFC operation.

Voltage Readjustment Methodology According to Pressure and Temperature Applied to a High Temperature PEM Fuel Cell

The operating conditions can have uncontrolled effects on the voltage of a High-Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC). For instance, the HT-PEMFC can be used at ambient pressure, i.e., without having a back pressure regulator. In this case, the variation in the atmospheric pressure directly affects pressures inside the fuel cell, which induces voltage variation. Moreover, in transient phases, several coupled phenomena can have an uncontrolled effect on the voltage. For example, following a change in the current operating point, thermal conditions in the fuel cell can vary, and the temperature stabilization then leads to a voltage variation. This article introduces a readjustment method for the fuel cell voltage to compensate for the effects of the pressure and temperature variations that are undergone and to decouple their effects. This methodology is based on the realization of a design of experiments to characterize the voltage sensitivity to pressure ([1; 1.5 bar]) and temperature ([120; 180 °C]) between 0.2 and 1 A/cm2 of an Advent PBI MEA (formerly BASF Celtec®-P 1100 W). The data obtained allowed identifying an empirical model that takes into account the aging caused by the experiment. Finally, the methodology is criticized before proposing an alternative method.

Activation of bimetallic PtFe nanoparticles with zeolite-type cesium salts of vanadium-substituted polyoxometallates toward electroreduction of oxygen at low Pt loadings for fuel cells

The catalytic activity of commercial carbon-supported PtFe (PtFe/C) nanoparticles admixed with mesoporous polyoxometalate Cs3H3PMo9V3O40, (POM3-3–9), has been evaluated towards oxygen reduction reaction (ORR) in acid medium. The polyoxometalate cesium salt co-catalyst/co-support has been prepared by titration using the aqueous solution of phosphovanadomolibdic acid. The synthesized material has been characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results confirm formation of the polyoxometalate salt with the characteristic Keggin-type structure. The composite catalyst has been prepared by mixing the POM3-3–9 sample with the commercial PtFe/C by sonication. The diagnostic rotating ring-disk voltammetric studies are consistent with good performance of the system with low Pt loading during ORR. The fuel cell membrane electrode assembly (MEA) utilizing the PtFe/POM-based cathode has exhibited comparable or better performance (at relative humidity on the level of 100, 62, and 17%), in comparison to the commercial MEA with higher Pt loading at the cathode. Furthermore, based on the cell potential and power density polarization curves, noticeable improvements in the fuel cell behavior have been observed at the low relative humidity (17%). Finally, the accelerated stress test, which uses the potential square wave between 0.4 V and 0.8 V, has been performed to evaluate MEA stability for at least 100 h. It has been demonstrated that, after initial losses, the proposed catalytic system seems to retain stable performance and good morphological rigidity.