Collection of Fuel Cell(202312)
The gas diffusion layer (GDL) is a critical component of proton exchange membrane fuel cells (PEMFCs) and accounts for 40%-50% of the fuel cell membrane's cost. Developing a low-cost and high-performance GDL is imperative to advance the commercialization of PEMFCs. In this study, we generated a flexible carbon cloth with high electrical conductivity and porosity from cellulose cloth at a low temperature (1500 ℃). The carbon cloth is composed of micron-sized carbon fibers with a porosity of up to 76.93%. Through catalytic graphitization of iron-based compounds, massive carbon nanotube clusters were formed in situ on the surface of carbon fibers, which effectively enhanced the electrical conductivity of the carbon cloth. The in-plane resistance was as low as 34 mΩ·cm while the through-plane resistance was 2.8 mΩ·cm under a pressure of 2 MPa, meeting the performance standard of commercial carbon cloth. Furthermore, the PEMFC with the prepared carbon cloth as GDLs exhibits a power density of 0.4 W·cm-2 at current density of 0.7 A·cm-2, exceeding the device with commercial carbon cloth (0.34 W·cm-2 at 0.7 A·cm-2). This study demonstrates that the prepared biomass-derived carbon cloth with low-cost and high- performance holds great potential for advanced GDLs for PEMFCs.
Oxygen reduction reaction (ORR) is an important electrochemical reaction process at the cathode of fuel cell, but its spontaneous reaction process is slow, and its catalysts, though efficient in catalyzing the ORR reaction, are facing problems of expensive price, complicated synthesis process, and polluting environment. Therefore, it is of great significance to explore the method of synthesizing a simple and environmentally friendly catalyst for the preparation of ORR catalysts. Fe-N co-doped mesoporous carbon substrate (Fe-N/MC) is a kind of non-precious metal catalysts for oxygen reduction reaction with great application value. In this work, mesoporous carbon substrate (MCM) was obtained by high-temperature carbonization of small molecule precursors in a semi-closed system in a muffle furnace, and then Fe-N co-doped mesoporous carbon substrate (Fe-N/MCMT) was prepared by mixing the obtained MCM with iron salts in a tube furnace at a high temperature. This method only needs simple pyrolysis conditions, requiring no template agents and toxic substances such as NH3 and HF. MCM is beneficial to enhance the hydrophilicity and coordination ability of the mesoporous carbon substrate surface due to its high element contents of nitrogen and oxygen. Fe-N/MCMT, prepared by MCM and iron salts, contains abundant and catalytic ORR Fe-Nx active sites with onset potential and half-wave potential of 0.941 and 0.831 V(vs RHE), respectively, which are 34 and 16 mV more positive than those of commercial Pt/C catalyst, respectively. ORR can be divided into two-electron or four-electron type according to the reaction process, and the transfer electron numbers of Fe-N/MCMT and Pt/C are 3.77 and 3.91, respectively, indicating a four-electron reaction process.
Oxygen reduction reaction (ORR) is the key reaction in cathode for fuel cells. Because of the sluggish kinetics, platinum (Pt) is widely used as the electrocatalysts for ORR. However, the high cost of Pt and poor stability of carbon black support under high voltage limit the commercialization and durability of fuel cells. Two-dimensional transition metal dichalcogenides (2D TMDs) possess large specific area, tunable electronic structure, and high chemical stability, making them a good candidate for ORR catalysts with high activity and durability. This paper reviews the recent progress of 2D TMDs-based ORR electrocatalysts. First, crystal structure, electronic properties, and ORR reaction mechanism are briefly introduced. Then some strategies for adjusting ORR performance of 2D TMDs are summarized, including heteroatom doping, phase conversion, defect engineering, and strain engineering. Meanwhile, the ORR activity enhancement arising from 2D TMDs-based heterostructures is also analyzed. Finally, perspectives are given for current issues and their possible solutions.
This work investigated the influence of Li2O as a sintering aid on the sintering behavior of La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolytes in solid oxide fuel cells, which systematically presented the effects of sintering aid content and sintering temperature on the density, microstructure, phase composition, and the ionic conductivity of sintered LSGM bulk. The results show that addition of Li2O sintering aid not only reduces the sintering temperature, but also eliminates the LaSrGa3O7 impurity phase in the sintered LSGM and suppresses the formation of MgO impurity phase which is easily generated during the conventional sintering process. Moreover, the addition of Li2O increases the ionic conductivity of sintered LSGM electrolytes. When 1% (molar percentage) Li2O is added, the LSGM bulk sintered at 1400 ℃ for 4 h reaches 99% of the theoretical density and presents a single perovskite stracture. When tested at 800 ℃, the ionic conductivity of the sintered bulk reaches 0.17 S/cm, which is 20% higher than that of the sample without sintering aid. All results demonstrate that adding an appropriate amount of Li2O as sintering aid is of great significance for the application of high ionic conductivity electrolyte in intermediate- temperature solid oxide fuel cells (IT-SOFCs).
Direct ethanol fuel cell (DEFC) has been widely studied because of its advantages of easy fuel availability, green and high effiency. However, DEFC catalysts are still frustrated with low catalytic efficiency and poor catalyst stability, which restrict its rapid development. In this work, XC-72R carbon black-loaded Pt1Cox/C high-index crystalline nanocatalysts were prepared in one step by liquid-phase hydrothermal synthesis, using polyvinylpyrrolidone (PVP k-25) as dispersant and reducing agent, glycine as surface control agent and co-reducing agent, and modulating the molar ratio of Pt-Co metal precursors to achieve the in-situ growth of catalyst particles on carbon carriers. The exposed high index crystalline facets of the Pt1Co1/3/C nanocatalyst mainly consisted of (410), (510) and (610) crystalline facets. The growth pattern of the Pt1Co1/3/C nanocatalyst grains varied from 'sphere-like' to cubic, and eventually to concave with high index grain orientation. The Pt1Co1/3/C nanocatalyst with high index crystalline surface has the highest electrocatalytic activity with an electrochemically active surface area of 18.46 m2/g, a current density of 48.70 mA/cm2 for the ethanol oxidation peak, a steady state current density of 8.29 mA/cm2 and a potential of 0.610 V for the CO oxidation peak. This indicates that the defect atoms such as steps and kinks on the surface of the catalyst with high index crystal plane can increase the active sites, thus showing excellent electrocatalytic performance. This study may provide a theoretical basis for the development and industrial application of high index crystalline catalyst materials.
Intermediate-temperature solid oxide fuel cell (IT-SOFC) is promising for carbon neutrality, but its cathode is limited by the contradiction between thermal compatibility and catalytic activity. Herein, we propose a high-entropy double perovskite cathode material, GdBa(Fe0.2Mn0.2Co0.2Ni0.2Cu0.2)2O5+δ (HE-GBO) with improved compatibility and activity, in view of the high-entropy strategy by multi-elemental coupling, which possesses double perovskite structure and excellent chemical compatibility with state-of-the-art Gd0.1Ce0.9O2-δ (GDC). The polarization resistance (Rp) of the symmetrical cells with HE-GBO cathode is 1.68 Ω·cm2 at 800 ℃, and the corresponding Rp of HE-GBO-GDC (mass ratio 7:3) composite cathode can be greatly reduced (0.23 Ω·cm2 at 800 ℃) by introducing GDC. Dendritic microchannels anode-supported single cells with HE-GBO and HE-GBO-GDC cathodes realize maximum power densities of 972.12 and 1057.06 mW/cm2 at 800 ℃, respectively, indicating that cell performance can be enhanced by high-entropy cathodes. The results demonstrate that high-entropy double perovskite cathode material HE-GBO has a high potantial to solve the conflict problem of thermal compatibility and catalytic activity in IT-SOFCs.
Ammonia with low cost, easily liquefied and high volumetric energy density is an attractive carbon-free fuel. Utilizing ammonia as anodic fuel, direct ammonia fuel cells are showing great interests to researchers. However, such amazing fuel cell device is limited by the sluggish anodic ammonia oxidation reaction. In this work, PtIr alloy aerogels with a three-dimensional porous network structure were prepared by nanoparticles (NPs) self-assembled under a simple and surfactant-free conditions. This structure provided a rich open interconnected proton transport channel and additional catalytically active sites which contributed to the dehydrogenation process of NH3 molecules in ammonia electrocatalytic oxidation. An optimal AOR activity was achieved at the 80/20 molar ratio of Pt/Ir. Effects of NH3 concentration and operating temperature on catalyst's ammonia oxidation performance were studied, which revealed that the AOR performance of Pt80Ir20 alloy aerogel was improved with the increase of ammonia concentration or operating temperature. For example, the mass specific activity, at 0.50 V of the Pt80Ir20 alloy aerogel, was estimated to be 44.03 A·g-1, which was about 4 times as that of the ammonia concentration at 0.05 mol/L. In the case of operating temperature effect, the mass activity was estimated to be 148.73 A·g-1, which was almost 12 times as that of the temperature rising (from 25 ℃) to 80 ℃. Encouragingly, the onset potential of the optimal Pt80Ir20 alloy aerogel catalyst displayed about 40 mV reduction during such a temperature change. Further calculations using the Arrhenius equation showed that its activation energy was reduced by about 9.43 kJ·mol-1 as compared with commercial Pt/C. Moreover, its AOR stability was improved as evidenced by a loss of ~50.6% mass activity after 2000 potential cycles when compared with commercial Pt/C (~74.9%).