Water transport across the membrane of a direct toluene electro-hydrogenation electrolyzer: Experiments and modelling

Toluene/methylcyclohexane is a promising liquid organic hydride for hydrogen storage and transport under ambient conditions. Direct toluene electro-hydrogenation electrolyzers, utilizing proton exchange membrane technology, offer benefits in reducing the reversible decomposition voltage and eliminating theoretical heat losses associated with conventional hydrogenation methods. Nevertheless, water transport across the membrane can inhibit the supply of toluene to reaction sites at the cathode. This study investigates water transport across the Nafion™ 117 membrane of an in-house electrolyzer cell, employing sulfuric acid and toluene solutions as the anode and cathode reactant, respectively, and operating at current densities from 0.1 to 0.8 A/cm2. The experiments show that the cathode toluene concentration has a negligible effect on drag water, while water flux increases with electric current and decreases with higher anode sulfuric acid concentrations. The modelling approach assumes electro-osmosis and diffusion mechanisms govern water transport. Simulations predict a linear decrease in the electro-osmotic drag coefficient from 2.3 to 1.6 as the sulfuric acid concentration rises from 0.1 to 1.5 mol/L, while the back diffusion flux increases linearly up to 2 mg/(min·cm2). These findings closely align with experimental data and previous literature, despite the high complexity of water transport in polymer electrolyte membranes.Funding for open access charge: Universidad de Málaga / CBU

Study on Morphological Properties and Mass Transport Parameters of ORR in Recast Ion- exchange Polymer Electrolyte Membranes

ABSTRACT We have investigated the effect of the recast temperature, i.e., heat treatment of a polymer electrolyte, on the diffusion coefficient and solubility of oxygen in the electrolyte and also on the morphological properties of recast ion-exchange membranes for improving the cathode activity in PEFCs. The recast membranes were prepared at different recast temperatures from Nafion ® and Aciplex ® solutions. Based on the chronoamperometric measurements, it was found that the diffusion coefficient and solubility of oxygen were deeply affected by the recast temperature. The diffusion coefficient increased with the decreasing recast temperature while the solubility had the opposite tendency. The water uptakes and ionic cluster size also varied with the recast temperature. Based on the X-ray measurements, it is considered that the differences in the mass transport parameters, the cluster sizes and water uptakes are due to the growth of clusters and crystallinity in the electrolyte

Kinetics of Toluene Electrohydrogenation on Pt/C Catalyst

International audienceThe kinetics of the toluene (TL) electrohydrogenation on a carbon-supported platinum catalyst (Pt/C) have been investigated as a fundamental study of the cathode reaction in an electrolyzer with water decomposition. Since the TL electrohydrogenation on a Pt wire and Pt/C catalyst is a fast kinetic reaction with a low solubility, and slow mass transfer in an aqueous electrolyte, a potential step sequence was employed to determine its kinetic performance. Based on this method, a non-faradic current and faradic current could be identified and thereafter separated by a capacitance simulation. This experiment was performed in a TL-saturated sulfuric acid electrolyte to minimize the effect of the TL mass transfer. Based on the mass transfer-free TL electrohydrogenation experimental results, the exchange current densities of the TL electrohydrogenation on the Pt/C were 0.48, 0.49, 0.72, and 0.8mAcm(-2) at 25, 40, 50, and 60 degrees C, respectively. We found that the carbon support has a high impact towards the TL electrohydrogenation on the Pt-supported material. The carbon material works as a sponge by absorbing TL from the solution, and providing a large TL coverage for the Pt surface. Finally, a Tafel plot of the TL electrohydrogenation on the Pt/C catalyst was obtained and the kinetic performance was determined. The apparent active energy of the TL electrohydrogenation on the Pt/C was then calculated as 13.1kJmol(-1)

Heat and Mass Balance Analysis of 130-W Active-type Direct-methanol Fuel Cell

A “heat- and mass-balance analysis” for a direct-methanol fuel cell (DMFC) system, accounting for actual experimental data and the heat- and mass transfer of the DMFC, is proposed to facilitate the usage of general spreadsheet software. The spreadsheet software enables the use of various functions on the data and visualizes the data using graphs. In addition, this application has a light computational load and is thus easy to implement in system control. The output of the analysis is the transfer of material and heat within the DMFC, as well as the heat balance and electrical efficiency of the DMFC. The analysis was verified using experimental data of the DMFC system, and the results of the verification indicated that the analysis could predict heat balance and system efficiency with accuracies of approximately 3.7 and 2.5 %, respectively. Further, the analysis was used to investigate the effect of stack temperature on the electrical efficiency of the system, and the results showed that the optimum stack temperature at a system power of 130 W was 60 °C and the electrical efficiency at that temperature was 21.8 % HHV

Practical and Reliable Methanol Concentration Sensor for Direct Methanol Fuel Cells

An electrochemical methanol concentration sensor with practicality and reliability has been developed to apply for a direct methanol fuel cell (DMFC) system. The methanol concentration can be estimated simply by the original algorithm based on the Arrhenius law and diffusion limiting current, even though the complex oxidation current characteristics for the methanol concentration and temperature. The oxidation current of methanol shows linearity against the methanol concentration up to 10 wt% (15 mgPt cm−2 at anode) with quick response. The sensor also has a high durability for 6500 h in the simulated DMFC operating temperature

The Effect of Li x Ni2-x O2/Ni with Modification Method on Activity and Durability of Alkaline Water Electrolysis Anode

International audienceWater electrolysis requires durability during a fluctuating power supply in power-to-gas application with renewable energies. The previously developed lithiated NiO modified Ni (Li (x) Ni2-x O-2/Ni) has a high catalytic activity and durability during potential cycling, whereas the relatively high surface oxide resistance due to preparation of the oxidation at high temperature with a LiOH coating. In order to improve the catalytic activity, we proposed optimization of the oxide layer by thermal decomposition with various precursor coatings. The oxide layers prepared with acetate and nitrate precursors were dense and porous, respectively. The initial activity obtained from the acetate precursor electrode was higher than that of the nitrate precursor and the oxidation with the LiOH coating. Although the nitrate precursor electrode suffered from the same degradation as the Ni anode during potential cycling, the activity of the acetate precursor electrode as well as the oxidized electrode with the LiOH coating increased, and the activity for the former was almost the same as the initial Ni anode after 20,000 cycles. The lower preparation temperature of the acetate precursor would suppress the formation of the electron resistive nickel oxide between the base nickel and lithiated NiO, which was observed for the oxidized electrode with the LiOH coating as well. While the double-layer capacitance and redox peak around 1.3 V vs. RHE of the Ni and the nitrate precursor electrode significantly increased with Ni(IV) formation during potential cycling, those of the acetate precursor electrode slightly increased without any Ni(IV) formation. Therefore, the dense Li (x) Ni2-x O-2 prepared with acetate has a good electric conductivity and catalytic activity with a high durability during potential cycling as the anode of an alkaline water electrolyzer for renewable power sources