Frontiers in Energy最新文献

The frame of membrane electrode assembly (MEA) influences the durability of proton exchange membrane fuel cell (PEMFC). In this paper, the thermal shock bench was applied as an accelerated aging test to explore the effect of frame sealing structure on MEA durability at different temperatures. Analysis of scanning electron microscope (SEM) images reveals that thermal shock results in the formation of cracks on the exposed proton exchange membrane (PEM) at the gap between the frame and the active area. Moreover, it breaks the bonding interface between the frame and the membrane and leads to the debonding of the adhesive, which exacerbates the risk of crossover of the reactant gas. A comparison of the single-layer and improved double-layer frame structures reveal that the mechanical damage is caused by frequent membrane wrinkles in the gap under temperature shock. However, addition of a cushion layer improves the continuity between the frame and the active area, and reduces deformation of the membrane, thereby preventing membrane damage.

Fe-N-C catalysts are potential substitutes to displace electrocatalysts containing noble chemical elements in the oxygen reduction reaction (ORR). However, their application is hampered by unsatisfactory activity and stability issues. The structures and morphologies of Fe-N-C catalysts have been found to be crucial for the number of active sites and local bonding structures. In this work, dicyandiamide (DCDA) and polyaniline (PANI) are shown to act as dual nitrogen sources to tune the morphology and structure of the catalyst and facilitate the ORR process. The dual nitrogen sources not only increase the amount of nitrogen doping atoms in the electrocatalytic Fe-C-N material, but also maintain a high nitrogen-pyrrole/nitrogen-graphitic: (N-P)/(N-G) value, improving the distribution density of catalytic active sites in the material. With a high surface area and amount of N-doping, the Fe-N-C catalyst developed can achieve an improved half-wave potential of 0.886 V (vs. RHE) in alkaline medium, and a better stability and methanol resistance than commercial Pt/C catalyst.

The undesired side reactions at electrode/electrolyte interface as well as the irreversible phase evolution during electrochemical cycling significantly affect the cyclic performances of nickel-rich NMCs electrode materials. Electrolyte optimization is an effective approach to suppress such an adverse side reaction, thereby enhancing the electrochemical properties. Herein, a novel boron-based film forming additive, tris(2,2,2-trifluoroethyl) borate (TTFEB), has been introduced to regulate the interphasial chemistry of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) cathode to improve its long-term cyclability and rate properties. The results of multi-model diagnostic study reveal that formation lithium fluoride (LiF)-rich and boron (B) containing cathode electrolyte interphase (CEI) not only stabilizes cathode surface, but also prevents electrolyte decomposition. Moreover, homogenously distributed B containing species serves as a skeleton to form more uniform and denser CEI, reducing the interphasial resistance. Remarkably, the Li/NMC811 cell with the TTFEB additive delivers an exceptional cycling stability with a high-capacity retention of 72.8% after 350 electrochemical cycles at a 1 C current rate, which is significantly higher than that of the cell cycled in the conventional electrolyte (59.7%). These findings provide a feasible pathway for improving the electrochemical performance of Ni-rich NMCs cathode by regulating the interphasial chemistry.

Utilizing plasmonic effects to assist electrochemical reactions exhibits a huge potential in tuning the reaction activities and product selectivity, which is most appealing especially in chemical reactions with multiple products, such as CO₂ reduction reaction (CO₂RR). However, a comprehensive review of the development and the underlying mechanisms in plasmon-assisted electrocatalytic CO2RR remains few and far between. Herein, the fundamentals of localized surface plasmonic resonance (LSPR) excitation and the properties of typical plasmonic metals (including Au, Ag, and Cu) are retrospected. Subsequently, the potential mechanisms of plasmonic effects (such as hot carrier effects and photothermal effects) on the reaction performance in the field of plasmon-assisted electrocatalytic CO₂RR are summarized, which provides directions for the future development of this field. It is concluded that plasmonic catalysts exhibit potential capabilities in enhancing CO₂RR while more in situ techniques are essential to further clarify the inner mechanisms.

In recent years, the dry reforming of methane (DRM) reaction has gained widespread attention due to its effective utilization of two major greenhouse gases. Supported Ni-based catalysts for DRM exhibit a strong dependence on particle size, however, the reaction mechanisms involved remain unclear. In this work, the effect of metal particle size on CO₂ activation and CO formation was explored in the DRM reaction using the density functional theory. Nix/MgO (x = 13, 25, 37) was constructed to investigate the CO₂ activation and the formation of CO during the DRM reaction. It is found that CO₂ is more inclined to undergo chemisorption on Nix/MgO before activation. With the variation in particle size, the main activation pathway of CO₂ on the catalyst changes. On the smallest Ni13/MgO, CO₂ tends to directly dissociate, while on the larger Ni25/MgO and Ni37/MgO, the hydrogenation dissociation of CO₂ is more kinetically favorable. Compared to Ni13/MgO and Ni37/MgO, the oxidation of surface C atoms and the oxidation of CH occur more readily on Ni25/MgO. This indicates that C atoms are less likely to form on Ni25 particle and are more easily to be oxidized. To some extent, the results suggest that Ni25/MgO exhibits superior resistance to carbon formation.

Ammonia, with its high hydrogen storage density of 17.7 wt.% (mass fraction), cleanliness, efficiency, and renewability, presents itself as a promising zero-carbon fuel. However, the traditional Haber–Bosch (H–B) process for ammonia synthesis necessitates high temperature and pressure, resulting in over 420 million tons of carbon dioxide emissions annually, and relies on fossil fuel consumption. In contrast, dielectric barrier discharge (DBD) plasma-assisted ammonia synthesis operates at low temperatures and atmospheric pressures, utilizing nitrogen and hydrogen radicals excited by energetic electrons, offering a potential alternative to the H-B process. This method can be effectively coupled with renewable energy sources (such as solar and wind) for environmentally friendly, distributed, and efficient ammonia production. This review delves into a comprehensive analysis of the low-temperature DBD plasma-assisted ammonia synthesis technology at atmospheric pressure, covering the reaction pathway, mechanism, and catalyst system involved in plasma nitrogen fixation. Drawing from current research, it evaluates the economic feasibility of the DBD plasmaassisted ammonia synthesis technology, analyzes existing dilemmas and challenges, and provides insights and recommendations for the future of nonthermal plasma ammonia processes.

Developing efficient anode catalysts for direct ammonia solid oxide fuel cells (NH₃-SOFCs) under intermediate-temperatures is of great importance, in support of hydrogen economy via ammonia utilization. In the present work, the pyrochlore-type La₂Zr_2−xNi_xO_7+δ (LZN_x, x = 0, 0.02, 0.05, 0.08, 0.10) oxides were synthesized as potential anode catalysts of NH₃-SOFCs due to the abundant Frankel defect that contributes to the good conductivity and oxygen ion mobility capacity. The effects of different content of Ni²⁺ doping on the crystal structure, surface morphology, thermal matching with YSZ (Yttria-stabilized zirconia), conductivity, and electrochemical performance of pyrochlore oxides were examined using different characterization techniques. The findings indicate that the LZN_x oxide behaves as an n-type semiconductor and exhibits an excellent high-temperature chemical compatibility and thermal matching with the YSZ electrolyte. Furthermore, LZN_0.05 exhibits the smallest conductive band potential and bandgap, making it have a higher power density as anode material for NH₃-SOFCs compared to other anodes. As a result, the maximum power density of the LZN_0.05-40YSZ composite anode reaches 100.86 mW/cm² at 800 °C, which is 1.8 times greater than that of NiO-based NH₃-SOFCs (56.75 mW/cm²) under identical flow rate and temperature conditions. The extended durability indicates that the NH₃-SOFCs utilizing the LZN_0.05-40YSZ composite anode exhibits a negligible voltage degradation following uninterrupted operation at 800 °C for 100 h.