Electric-field-aligned functionalized-layered double hydroxide/polyphenyl ether composite membrane for ion transport

To address the insufficient ion conductivity of hydroxide exchange membranes (HEMs) used in alkali membrane fuel cells (AMFCs), we present a series of aligned layered double hydroxide (LDH)/polyphenyl ether (PPO) composite membranes based on the electrorheological effect. The hexagonal LDH was functionalized with N-spirocyclic ammonium (ASU-LDH) to enhance the electrorheological effect of the ASU-LDH as well as improve the ion conductivity of the ASU-LDH. The aligned ASU-LDH/triple-cation-functionalized PPO (ASU-LDH/TC-PPO) composite membranes were prepared by applied-electric field. The effective electric-induced ion channels (EICs) were constructed by aligned ASU-LDH nanosheets in HEMs, which are distinctly observed by scanning electron microscope (SEM). Notably, these EICs-contained ASU-LDH/TC-PPO composite membranes exhibit the higher ion conductivity and alkaline stability than those of normal TC-PPO and ASU-LDH/TC-PPO membranes. It is worth noticing that these EICs are different with the traditional phase-induced ion channels, the EICs show the shorter ion transport distances and broader water channels in HEMs. Attributing to EICs, the longitudinal ion conductivity of aligned ASU-LDH/TC-PPO membrane shows 32.2% and 18.7% improvement compared to pristine TC-PPO and normal ASU-LDH/TC-PPO membrane. The maximum ion conductivity of the aligned ASU-LDH/TC-PPO composite membrane reaches to 109.8 mS/cm at 80 °C. The long-term stability test shows that the aligned ASU-LDH/TC-PPO membranes still exhibit enhancing alkali resistance (83.2%) in 1 M KOH at 80 °C for 500 h. In brief, this work provides a novel and effective approach to prepare high-performance HEMs.     

Catalytic enhancement of formic acid electro-oxidation through surface modifications with gold on supported Pt nanoparticles

The Formic Acid Electro-oxidation (FAEO) on Pt/Au Nanoparticles (PtAu NP) supported on Hierarchical Porous Carbon (HPC), was studied by cyclic voltammetry and chronoamperometry. The supported HPC-Pt nanoparticles were surface modified by Au spontaneous deposits. The morphological and compositional characterization was performed by Scanning Electron Microscopy (SEM) coupled with Electron Dispersive Spectroscopy (EDS). A significant increase of the current densities for FAEO in the potential region 0.1–0.75 V_RHE was observed on HPC-PtAu catalysts. The comparison with HPC-Pt electrodes results show that Au atoms presence on Pt nanoparticles is a key factor to improve the catalysts performance. Based on our results, a clear change in FAEO mechanism on HPC-PtAu catalysts with respect to HPC-Pt was evidenced.     

Thermal management in PEMFCs: The respective effects of porous media in the gas flow channel

This study aims to evaluate the convective heat transfer enhancement of the proton exchange membrane fuel cells (PEMFC) numerically. As the higher heat transfer surfaces lead to higher heat transfer rates, a flat plate porous layer is utilized in the gas flow channel (GFC). This enhancement in heat transfer stems from the corresponding modification in the temperature and velocity profiles. The influencing parameters on these profiles are the thickness, permeability, and porosity of the GFC porous layer. After performing the simulations, the results indicate that convective heat transfer has a direct relationship with GFC porous layer's thickness and permeability. However, lower values of porosity lead to the higher Nusselt numbers. Previous investigations have also mentioned the positive impact of the microporous layer (MPL) on the water management of these fuel cells. Therefore, six different sizes of MPL and the gas diffusion layer (GDL) are utilized to evaluate their impacts on the thermal management. Results indicate that although these sizes have negligible effects on the heat transfer, Nu increases by enhancing the total size of MPL and GDL. The results also show that thicker MPLs lead to higher heat transfer rates. The evaluation of the friction factor also indicates the adverse effect of the GFC porous layer, although this undesirable effect is negligible. Finally, all the simulated values are utilized to train an artificial neural network (ANN) model with high precision. This ANN model can produce more data for sensitivity analysis and presenting respective 3D diagrams of the influencing parameters on heat transfer.     

Understanding mass and charge transports to create anion-ionomer-free high-performance alkaline direct formate fuel cells

The disadvantage of anion ionomer that possesses low hydroxide conductivity, and thermal and chemical instability hinders the development of the high-performance anion-exchange membrane direct liquid fuel cells. Instead of adding additional base and synthesizing high-conductivity ionomer material, by gaining insight into species transports, herein, we propose an anion-ionomer-free anion-exchange membrane direct formate fuel cell (AEM DFFC). Experimental result reveals that this conceptual anion-ionomer-free AEM DFFC can operate stably within a 6-h constant-current discharge at 10 mA cm⁻², mainly because formate hydrolysis renders a high OH⁻ conductivity. It was also found that the anion-ionomer-free AEM DFFC yields a peak power density as high as 41 mW cm⁻² at 40 °C, 40% higher than that of the conventional quaternary ammonia polysulfone anion-ionomer AEM DFFC. This can be attributed to the fact that the OH⁻-containing formate solution facilitates the mass and charge transports, thereby enlarging the triple-phase boundary for both anodic formate oxidation reaction and cathodic oxygen reduction reaction.     

Assessing anodic microbial populations and membrane ageing in a pilot microbial electrolysis cell

First large-scale experiences of bioelectrochemical systems (BES) are underway. However, there is still little knowledge on how the different elements that integrate a BES behave in near real-life conditions. This paper aims at assessing the impact of long-term operation on the cation exchange membrane and on the anodic biofilm of two 16 L Microbial Electrolysis Cells (MEC) designed for hydrogen production and ammonia recovery from pig slurry. Membrane deterioration was examined by physical, chemical and microscopy techniques at different locations, revealing a strong attachment of microorganisms and a significant decay in membrane properties such as ion exchange capacity and thermal stability. Anode microbial communities did not show a dramatic shift in the eubacteria composition at different sampling areas, although the relative abundance of some bacterial groups showed a clear vertical stratification. After 100 days of continuous operation, MEC performance did not declined significantly maintaining ammonium transport rates and H₂ production rates of 15.3 gN d⁻¹ m⁻² and 0.2 LH₂·L⁻¹_reactor·d⁻¹ respectively.     

A completely slot die coated membrane electrode assembly

This work shows how to manufacture completely coated membrane electrode assemblies (CC-MEAs) for PEM water electrolysis by only using a slot die. Platinum, Nafion^®, and IrO₂ dispersions are successively coated to the respective dried layer. For comparison reasons, MEAs with the same Iridium loading of 2.1 mg cm⁻² and Platinum loading of 0.4 mg cm⁻², assembled with a commercial membrane of the same 20 μm thickness, were produced via decal method. Differences in polarization curves are attributed to the lower high frequency resistance of CC-MEAs determined by impedance spectroscopy. The easy-to-scale CC-MEA method presented here offers the advantages of direct membrane deposition (DMD) without the challenge of homogenously coating a porous transport layer (PTL). Therefore, it allows a free choice of different PTLs – regardless if in sintered form or as expanded metal. The comparability between the produced CC-MEAs and published DMD results is shown by means of cross-sectional and electrochemical measurements.     

Simulation of 12-bed vacuum pressure-swing adsorption for hydrogen separation from methanol-steam reforming off-gas

This study focuses on analysis of a 12-bed vacuum pressure-swing adsorption (VPSA) process capable of purifying hydrogen from a ternary mixture (H₂/CO₂/CO 75/24/1 mol%) derived from methanol-steam reforming. The process produces 9 kmol H₂/h with less than 2 ppm and 0.2 ppm of CO2 and CO, respectively, to supply a polymer electrolyte membrane fuel cell. The process model is developed in Aspen Adsorption® using the “uni-bed” approach. A parametric study of H₂ purity and recovery with respect to adsorption pressure, adsorbent height, activated carbon:zeolite ratio, feed composition, and number of beds is performed. Results show 12-bed VPSA can meet the H₂ purity goals, with H₂ recovery as high as 75.75%. Adsorption occurs at 7 bar, the column height is 1.2 m, and the adsorbent ratio is 70%:30%. A 4-bed VPSA can achieve the same purity goals as the 12-bed process, but H₂ recovery decreases to 61.34%.     

In-situ repair of composite palladium membranes with macro defects: A case study

A new method was developed for repairing Pd/Al₂O₃ membranes with macro defects without the need of disassembling the membrane from the module. In order to target and fill the membrane defect automatically with solid particles, a TiO₂ powder was firstly tested by flowing high-pressure nitrogen as a carrier gas, followed by a heat treatment. A filter cake was found on the membrane defect but still porous. A glass powder was selected instead of TiO₂, and the membrane defect was successfully sealed by glazing. The in-situ repair of a waste commercial Pd/Al₂O₃ membrane separator was carried out with the glass powder, and the hydrogen flux and H₂/N₂ selectivity of the membrane separator at 450 °C under 100 kPa reached 12.6 m³m⁻²h⁻¹ and 1600, respectively.     

Pre-activation of SBA-15 intermediate barriers with Pd nuclei to increase thermal and mechanical resistances of pore-plated Pd-membranes

Thermal and mechanical resistances of palladium composite membranes prepared by Electroless Pore-Plating (ELP-PP) and containing SBA-15 as intermediate layer were improved by doping the silica material with Pd nuclei before its incorporation on the composite membrane. Textural properties of synthesized SBA-15 materials (both raw and doped ones) were analyzed by XRD, N₂ adsorption-desorption at 77 K and TEM, while the main properties of the composite membrane were determined by SEM and gravimetric analyses. Moreover, membrane permeation tests were also carried out with pure gases, hydrogen and nitrogen, and binary mixtures of them at temperature of 400 °C and pressure driving forces in the range of 0.5–2.5 bar. The use of bare SBA-15 intermediate layer leads to the appearance of cracks on the Pd layer during permeation experiments at high temperature. In contrast, the use of Pd-doped SBA-15 particles avoids this problem, thus improving both thermal and mechanical resistances of the composite ELP-PP Pd-membrane. Following this preparation method, an estimated Pd thickness of 7.1 μm was obtained, reaching a hydrogen permeance of 3.81·10^?4 mol s^?1 m^?2 Pa^?0.5 and ensuring an ideal H₂/N₂ separation factor higher than 2550 at 400 °C.