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PbTiO3 as Electron-Selective Layer for High-Efficiency Perovskite Solar Cells: Enhanced Electron Extraction via Tunable Ferroelectric Polarization
No full textPbTiO3 (PTO) is explored as a versatile and tunable electron-selective layer (ESL) for perovskite solar cells. To demonstrate effectiveness of PTO for electron-hole separation and charge transfer, perovskite solar cells are designed and fabricated in the laboratory with the PTO as the ESL. The cells achieve a power conversion efficiency (PCE) of approximate to 12.28% upon preliminary optimization. It is found that the PTO ferroelectric layer can not only increase the PCE, but also tune the photocurrent via tuning PTO's ferroelectric polarization. Moreover, to understand the physical mechanism underlying the carrier transport by the ferroelectric polarization, the electronic structure of PTO/CH3NH3PbI3 heterostructure is computed using the first-principles methods, for which the triplet state is used to simulate charge transfer in the heterostructure. It is shown that the synergistic effect of type II band alignment and the specific ferroelectric polarization direction provide the effective extraction of electrons from the light absorber, while minimize recombination of photogenerated electron-hole pairs. Overall, the ferroelectric PTO is a promising and tunable ESL for optimizing electron transport in the perovskite solar cells. The design offers a different strategy for altering direction of carrier transport in solar cells
Economical synthesis strategy of RHO zeolites with fine-tuned composition and porosity for enhanced trace CO2 capture
No full textDelicate modification of the silica contents and porous structures within RHO zeolites has been readily realized by adopting a variety of alkali metal-crown ether (AMCE) complexes as the templates. Compared to the previous protocols, up to 70% of the Cs+ cations could be substituted by much cheaper K+ cations and thus the synthesis costs of RHO zeolites could be impressively reduced. The subsequent Cs-133 and Na-23 MAS NMR spectra further reveal that the Cs+ cations may aggregate with crown ether in a form of monomer or dimer complex, which then plays a significant role in the structural direction of RHO zeolites, whereas the hydrated Na+ cations mainly serve as the charge balancing cations. Meanwhile, the addition of different amount of K+ cation could result in varying degrees of template-framework interaction and consequently generates RHO zeolites with diverse compositions. Finally, the proton-type RHO zeolites were applied to the adsorptive separation of CO2/CH4/N-2 mixture. Therein, the medium-silica ones achieve fine trade-off for the adsorption capacity, selectivity and heat even under ultralow CO2 concentration, which makes them potential candidates for trace CO2 capture
Biochemical characterization of three new α-olefin-producing P450 fatty acid decarboxylases with a halophilic property
No full textAbstractBackgroundThe CYP152 family member OleTJE from Jeotgalicoccus sp. ATCC 8456 has been well-known to catalyze the unusual one-step decarboxylation of free fatty acids towards the formation of terminal alkenes. Efforts to tune up its decarboxylation activity for better production of biological alkenes have been extensively explored via approaches such as site-directed mutagenesis and electron source engineering, but with limited success. To gain more insights into the decarboxylation mechanism and reaction bifurcation (decarboxylation versus hydroxylation), we turned to an alternative approach to explore the natural CYP152 resources for a better variety of enzyme candidates.ResultsWe biochemically characterized three new P450 fatty acid decarboxylases including OleTJH, OleTSQ and OleTSA, with respect to their substrate specificity, steady-state kinetics, and salt effects. These enzymes all act as an OleTJE-like fatty acid decarboxylase being able to decarboxylate a range of straight-chain saturated fatty acids (C8–C20) to various degrees. Site-directed mutagenesis analysis to the lower activity P450 enzyme OleTSA revealed a number of key amino acid residues within the substrate-binding pocket (T47F, I177L, V319A and L405I) that are important for delicate substrate positioning of different chain-length fatty acids and thus the decarboxylation versus hydroxylation chemoselectivity, in particular for the mid-chain fatty acids (C8–C12). In addition, the three new decarboxylases exhibited optimal catalytic activity and stability at a salt concentration of 0.5?M, and were thus classified as moderate halophilic enzymes.ConclusionThe P450 fatty acid decarboxylases OleTJE, OleTJH, OleTSQ and OleTSA belong to a novel group of moderate halophilic P450 enzymes. OleTJH from Jeotgalicoccus halophilus shows the decarboxylation activity, kinetic parameters, as well as salt tolerance and stability that are comparable to OleTJE. Site-directed mutagenesis of several key amino acid residues near substrate-binding pocket provides important guidance for further engineering of these P450 fatty acid decarboxylases that hold promising application potential for production of α-olefin biohydrocarbons
