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燃料电池作为一种清洁高效的能量转换装置，被认为是构建未来社会可再生能源结构的关键一环。不同于质子交换膜燃料电池(PEMFC)，碱性聚合物电解质燃料电池(APEFC)的出现使非贵金属催化剂的使用成为可能，因而受到了日益广泛的关注和研究。APEFC的关键结构是膜电极，主要由聚合物电解质膜和阴阳极(含催化层、气体扩散层)组成，膜电极是电化学反应发生的场所，其优劣直接决定着电池性能的好坏。因此，基于现有的碱性聚合物电解质及催化剂体系，如何构筑更加优化的膜电极结构，使APEFC发挥出更高的电池性能是亟待开展的研究。本文首先通过模板法在碱性聚合物电解质膜的表面构建出有序的锥形阵列，再将具有阵列结构的一侧作为阴极来构筑膜电极，同时，作为对比，制备了由无阵列结构的聚合物电解质膜构筑而成的膜电极，最后对基于两种不同膜电极的APEFC的电化学性能进行了对比研究。实验结果表明，锥形阵列结构可以将APEFC的峰值功率密度由1.04 W·cm−2显著提高到1.48 W·cm−2，这主要归因于在APEFC的阴极侧具有锥形阵列结构的聚合物电解质膜的亲水性的提升和催化剂电化学活性面积的增加。本工作为碱性聚合物电解质燃料电池的膜电极结构设计与优化提供了新思路。
Solar cells, which are excellent alternatives to traditional fossil fuels, can efficiently convert sunlight into electricity. The intensive development of high-performance photovoltaic materials plays an important role in environmental protection and the utilization of renewable energy. Organic–inorganic hybrid perovskite materials, with a formula of ABX3 (A = methylammonium (MA) or formamidinium (FA); B = Pb or Sn; X = Cl, I, or Br), have exhibited remarkable commercial prospects in high-performance photovoltaic devices owing to their long carrier diffusion length, excellent light absorption properties, high charge carrier mobility, and weak exciton binding energy. Recently, perovskite solar cells, fabricated using halide perovskite materials as light-absorbing layers, have achieved remarkable results; their certified power conversion efficiency has continuously improved and reached 25.7%. However, high-performance devices are usually fabricated using spin-coating methods with active areas below 0.1 cm2. Hence, long-term research goals include achieving a large-scale uniform preparation of high-quality photoactive layers. The current one-step preparation of perovskite films involves the nucleation-crystalline growth process of perovskite. Auxiliary processes, such as using an anti-solvent, are often required to increase the nucleation rate and density of the film, which is not suitable for industrial large-area preparation. Additionally, the large-area preparation of perovskite films by spin-coating will result in different film thicknesses in the center and edge regions of the film due to an uneven centrifugal force. This will cause intense carrier recombination in the thicker area of the film and weak light absorption in the thinner area, which will reduce the performance of the device. To address these problems, the development of a large-area fabrication method for high-performance perovskite light-absorbing layers is essential. In this study, a two-step sequential blade-coating strategy was developed to prepare the FA-based perovskite layer. In general, PbI2 easily forms a dense film; therefore, formamidinium iodide (FAI) cannot deeply penetrate to completely react with PbI2. The PbI2 residue is therefore detrimental to charge transportation. To fabricate the desired porous PbI2 film, tetrahydrothiophene 1-oxide (THTO) was introduced into the PbI2 precursor solution. By forming PbI2·THTO complexes, PbI2 crystallization is controlled, resulting in the formation of vertically packed PbI2 flaky crystals. These crystals provide nanochannels for easy FAI penetration. The 5 cm × 5 cm modules fabricated through this strategy achieved a high efficiency of 18.65% with excellent stability. This indicates that the two-step sequential blade-coating strategy has considerable potential for scaling up the production of perovskite solar cells.
The ever-increasing carbon dioxide (CO2) emissions caused by excessive fossil fuel consumption induce environmental issues such as global warming. To overcome this, the electrocatalytic CO2 reduction (ECR) under ambient conditions offers an appealing approach for converting CO2 to value-added chemicals and realizing a closed carbon loop. Among the ECR products, ethylene (C2H4), an important building block for plastics and other chemicals, has attracted considerable attention owing to its compatibility with existing infrastructure and the promising substitution of industrial steam cracking. In recent years, numerous efforts have been devoted to developing highly active and selective catalysts for converting CO2 to C2H4, with most studies having focused on Cu-based materials. Despite the significant advancements made to date, the development of the ECR-to-C2H4 process is still hindered by the lack of suitable catalysts that can effectively activate CO2 and strengthen the surface binding of *CO and *COH species. In this study, an amorphous copper oxide (CuOx) nanofilm that is rich in oxygen vacancies was prepared via a facile vacuum evaporation method for the efficient electrocatalytic conversion of CO2 to C2H4. It was expected that the nano-scale electrode thickness would greatly accelerate charge- and mass-transfer during CO2 electrolysis. Moreover, the introduction of oxygen vacancies favored the adsorption of CO2 and intermediates. As a result, in a typical H-cell, the synthesized defective catalyst delivered a maximum Faradaic efficiency of 85 ± 3% at −1.3 V versus the reversible hydrogen electrode and maintained a stable C2H4 selectivity over 48 h in a 0.1 M potassium bicarbonate solution. Interestingly, the performance observed with the synthesized electrocatalyst in this study is comparable with that of state-of-the-art Cu-based ECR catalysts. Additional structural and chemical characterizations confirmed the robust nature of the as-prepared catalyst. Moreover, when the catalyst was utilized in a membrane electrode assembly cell, it achieved a maximum C2H4 partial current density of approximately 115.4 mA∙cm−2 at a cell voltage of −1.95 V and Faradaic efficiency of 78 ± 2% at a cell voltage of −1.75 V. Furthermore, theoretical and experimental analyses revealed that oxygen defects not only favored CO2 adsorption but also enabled strong affinities for *CO and *COH intermediates, which synergistically contributed to a high selectivity for C2H4 formation. We believe that our present work will motivate the exploration of amorphous Cu-based materials for achieving efficient CO2-to-C2H4 electrolysis and be a guide towards fundamentally understanding the mechanism of catalytic CO2 reduction.
Hydrogen is considered as a desirable clean energy source for supporting human life in the future. Electrochemical water splitting is a promising method for generating carbon-free hydrogen. However, the relatively high overpotential of anodic oxygen evolution reaction (OER) is the main obstacle hindering the widespread popularity of water electrocatalysis technology. Recently, urea oxidation reaction (UOR) has gained significant attention as a potential alternative to OER for hydrogen production since the equilibrium potential of UOR is 0.86 V lower than that of OER. Transition metal-based layered double hydroxides (TM-LDHs) have been explored as promising UOR electrocatalysts, with the advantages of diversified metal species, stable two-dimensional layered structure and exchangeability of interlayer anions. To date, most studies have focused on TM-LDHs of late transition metals (e.g., Ni, Co, and Fe). In this work, by combining early and late transition metals, CoV-LDHs nanosheets were fabricated via a simple one-step coprecipitation method as high-performance UOR electrocatalysts. Additionally, cobalt hydroxide (Co(OH)2), with a similar lamellar structure, was synthesized via the same method. When compared with Co(OH)2, CoV-LDHs nanosheets exhibited better UOR performance owing to the following advantages: 1) The nanosheet structure of the as-fabricated CoV-LDHs electrocatalyst exposed a high number of active sites for the electrocatalytic conversion of urea. 2) The introduction of V enhanced the wettability of the CoV-LDHs electrocatalyst; thus, increasing its intrinsic electrocatalytic kinetics. 3) The d-electron compensation effect between Co (3d74s2) and V (3d34s2) was conducive to promoting the adsorption of urea. Therefore, the CoV-LDHs electrocatalyst exhibited a low electrochemical potential (1.52 V vs. the reversible hydrogen electrode, RHE) to achieve a current density of 10 mA∙cm−2 in 1 mol∙L−1 of potassium hydroxide containing 0.33 mol∙L−1 urea, which was 70 mV less than that of Co(OH)2. The Tafel slope value of the CoV-LDHs electrocatalyst (99.9 mV∙dec−1) was lower than that of Co(OH)2 (115.9 mV∙dec−1), indicating faster UOR kinetics over the CoV-LDHs electrocatalyst. Furthermore, the CoV-LDHs electrocatalyst displayed high stability, with a negligible potential increase after a 10-h chronopotentiometry test by maintaining the current density of 10 mA∙cm−2. In conclusion, the present work not only shows that the d-electron compensation effect between early and late transition metals could adjust the local electronic structure of TM-LDHs to improve the UOR efficiency, but also provides a feasible route to design dedicated nanostructured TM-LDHs as high-performance UOR electrocatalysts.
水系锌离子电池(ZIBs)因安全性高、成本低、环境友好，以及负极锌高的理论容量(820 mAh∙g−1)和低的氧化还原电位(−0.76 V vs. SHE)等优点而受到研究者们的广泛关注，有望应用于大规模储能领域，但循环寿命仍是限制其规模化应用的瓶颈之一。通过电解液优化调控策略，可有效抑制正极材料的溶解、结构坍塌和界面副反应等问题，从而提高水系ZIBs的电化学性能。本文综述了电解液调控策略提升水系ZIBs正极材料电化学性能的研究进展，讨论了该策略所解决的具体问题和局限性，并对电解液体系的发展方向进行了展望。