A multi-electrode probe is employed to distinguish the bulk and contact resistances of the catalyst layer (CL) and the gas diffusion layer (GDL) with the bipolar plate (BPP). Resistances are compared ...for Vulcan carbon catalyst layers (CL), carbon paper and carbon cloth GDL materials, and GDLs with microporous layers (MPL). The Vulcan carbon catalyst layer bulk resistance is 100 times greater than the bulk resistance of carbon paper GDL (Toray TG-H-120). Carbon cloth (CCWP) has bulk and contact resistances twice those of carbon paper. Compression of the GDL decreases the GDL contact resistance, but has little effect on the bulk resistance. Treatment of the GDL with polytetrafluoroethylene (PTFE) increases the contact resistance, but has little effect on the bulk resistance. A microporous layer (MPL) added to the GDL decreases the contact resistance, but has little effect on the bulk resistance. An equivalent circuit model shows that for channels less than 1 mm wide the contact resistance is the major source of electronic resistance and is about 10% of the total ohmic resistance associated with the membrane electrode assembly.
Display omitted
•Direct measurement of gas diffusion layer bulk and contact resistances.•Teflon treatment increases GDL contact resistance with no change of bulk resistance.•Microporous layer decreases contact resistance.•Uneven compression under channels and ribs deforms GDL, breaking electrical contact.
Fragrances have been widely used in many customer products to improve the sensory quality and cover flavor defects. The key to the successful application of fragrance is to realize controlled ...fragrance release, which relies on the use of an appropriate carrier for fragrance. An ideal fragrance carrier helps to achieve the stable storage and controlled release of fragrance. In this work, a novel composite fragrance carrier with MIL-101 (Cr) as the fragrance host and cellulose acetate fiber (CAF) as the protective shell was developed. The encapsulation effect of MIL-101 (Cr) and the protective function of the CAF shell significantly improved the storage stability of L-menthol (LM). Only 5 wt % of LM was lost after 40 days of storage at room temperature. Encapsulated LM could also be effectively released upon heating due to the thermal responsiveness of CAF. In addition, the composite carrier was highly stable with neglectable Cr leaching under different conditions. The results of this work showed that the developed composite carrier could be a promising carrier for the thermally triggered release of fragrance.
Electrochemical water splitting has wide applicability in preparing high-density green energy. The Proton exchange membrane (PEM) water electrolysis system is a promising technique for the generation ...of hydrogen due to its high electrolytic efficiency, safety and reliability, compactness, and quick response to renewable energy sources. However, the instability of catalysts for electrochemical water splitting under operating conditions limits their practical applications. Until now, only precious metal-based materials have met the requirements for rigorous long-term stability and high catalytic activity under acid conditions. In this review, the recent progress made in this regard is presented and analyzed to clarify the role of precious metals in the promotion of the electrolytic decomposition of water. Reducing precious metal loading, enhancing catalytic activity, and improving catalytic lifetime are crucial directions for developing a new generation of PEM water electrolysis catalysts. A summary of the synthesis of high-performance catalysts based on precious metals and an analysis of the factors affecting catalytic performance were derived from a recent investigation. Finally, we present the remaining challenges and future perspectives as guidelines for practical use.
•We found for the first time that the performance of fuel cells will be improved by anoxic cathode, mainly due to the hydrogen pump phenomenon.•We found for the first time that hydrogen permeation ...due to cathode hypoxia is closely related to current density.•Hydrogen pump phenomenon can improve the performance of fuel cells and can be used for rapid activation or performance recovery of fuel cell.
Air starvation occurring in a proton exchange membrane fuel cell will result in voltage drop and even a slightly reversal. However, a short period of air starvation may have a beneficial effect on the cell. In this paper, single cells are used to simulate the air starvation of a single cell in the stack and the related phenomena are studied. The experimental results show that when the starvation occurs in a single cell, the larger the output current, the more negative the voltage, the more obvious the hydrogen pumping; When the starvation occurs in the whole stack, the current and voltage of the cell and the amount of hydrogen pumping are only related to the hydrogen concentration on both sides of the cell. Subsequent research on single starved cell found that after a short period of 100 s of starvation, the cell's performance has improved, with an average increase of 22.3%@1500 mA/cm2, and ECSA of the catalyst increased slightly. The characterization of the catalyst before and after the air starvation found that the catalyst was not destroyed, indicating that the short-term air starvation will not damage the cell, but will improve the performance of it.
The water generated in the catalyst layer flows through the GDL (gas diffusion layer) and passes through the microfluidic channels of fuel cells. In this study, characteristics of water motion in the ...microfluidic channels are investigated corresponding to various Reynolds numbers and compression ratios of GDL. Gas can bypass the rib to the adjacent channel and flows through the GDL underneath the slug. To remove the slug, the bypass distance (%) and gas flow rate should be larger than 13%. The cross-section shape of the slug in 1-wall hydrophobic GDL and 3-walls hydrophilic acrylic channel is an analogous upside-down trapezoid. Since the required GDL compression ratio should be over 13% to eliminate liquid water instead of simply increasing the volumetric gas flow, the residual droplets are received at the vertical corner in the channel, compared to the arc corner. The regimes of liquid water flow in the 1-wall hydrophobic GDL and 3-walls hydrophilic acrylic channel are summarized as slug motion, compressed drop motion, elongate droplet motion, drop oscillation, and cap drop motion. These results provide improved physical models predicting the state of water hold-up and flooding in PEM fuel cells.
The development of solid oxide fuel cell (SOFC) operated at low and intermediate temperatures is limited by the poor performance of inorganic ionic conductors. Oxide-based ion conductors have ...attracted much attention due to their excellent stability and tunable ion conduction behavior. In this study, we propose a new approach for the construction of regulated ionic transport pathways in a composite oxide ionic conductor made of WO3/ZrO2 (WZ) and (Li0.68K0.32)2CO3. The interfacial reaction between WO3/ZrO2 and (Li0.68K0.32)2CO3 is used to enhance the interaction between the oxide and carbonate interfaces and introduce hydrophilic phases for water retention, thus achieving ultra-high ionic conductivity of the oxide/carbonate composites at low and intermediate temperatures. The optimal ionic conductor, 13WZ-30(Li0.68K0.32)2CO3 (13WZ-30C), has a superior ionic conductivity of 25.8-6.28 mS cm−1 from room temperature to 250 °C. The ion conduction mechanism of the composite is investigated. This study emphasizes the significance of interfacial chemistry regulation between oxides and carbonates for achieving superior ion conduction performance.
Display omitted
•Interfacial reaction of oxide and carbonate is designed to tailor ionic conductivity.•13WZ-30C exbibits a conductivity of 25.8-6.28 mS cm−1 from room temperature to 250 °C.•The superior performance is a result of synergy among the components in 13WZ-30C.
Amorphous carbon (α-C) nano-coatings are the most commonly used coating materials for the metal bipolar plates in fuel cells due to their low cost, excellent electrical conductivity, and good ...corrosion resistance. However, α-C usually forms a columnar structure during the deposition process, which seriously affects its performance and service life. This study proposes that the columnar structure of α-C nano-coatings can be controlled by modifying the deposition temperature during magnetron sputtering. Further, the effects of deposition temperature on the composition, microstructure, electrochemical corrosion behavior, interfacial conductivity and hydrophilicity of α-C nano-coatings were systematically studied. The results show that the columnar structure of α-C nano-coatings is inhibited by increasing the deposition temperature. When the deposition temperature is above 300 °C, the microstructure of the α-C nano-coatings changes from columnar to denser microcrystalline. At the same time, a higher deposition temperature leads to a higher proportion of sp2 carbon in the α-C nano-coatings; resulting in significant improvement in the corrosion resistance, interfacial conductivity and hydrophobicity of the coatings.
Display omitted
A rational design of the structure of catalyst layer (CL) is required for proton exchange membrane fuel cells to attain outstanding performance and excellent stability. It is crucial ...to have a profound comprehension of the correlations existing between the properties (catalyst ink), network structures of CL and proton exchange membrane fuel cells’ performance for the rational design of the structure of CL. This study deeply investigates the effects of a series of alcohol solvents on the properties and network structure of CL. The results demonstrate that the CL aggregates in higher ε solution show smaller particle sizes, and the sulfonic acid groups (∼SO3H) tend to extend more outward due to the strong dissociation. A more continuous and homogeneous ionomer distribution around Pt/C aggregates is observed in the CL, which improves the electrochemically active surface area (ECSA) and performance of the electrode. But, the electrode has a poor performance at high current density regions due to the mass transfer resistance. Based on this, a two-step solvent control strategy is proposed to maintain uniform ionomer and aggerates distribution and optimize the mass transfer for CL. The performance of the cell improves from 0.555 V to 0.615 V at 2000 mA·cm−2.
