Abstract The performance of quasi‐2D perovskite light emitting diodes (LEDs) with mixed small cations, cesium and formamidinium (FA), is significantly affected by their ratio. The best devices obtained for Cs:FA ratio of 1:1 exhibit a maximum external quantum efficiency (EQE) of 12.1%, maximum luminance of 15 070 cd m −2 and maximum current efficiency of 46.1 cd A −1 , which is significantly higher (about 3 times) compared to devices with FA only (maximum EQE of 4.1%, maximum luminance of 4521 cd m −2 ) and Cs‐only (maximum EQE of 4.0%, maximum luminance of 4886 cd m −2 ). The photoluminescence quantum yield of the Cs:FA 1:1 sample is similarly enhanced, 21.3% compared 5.4% and 6%, for FA‐only and Cs‐only samples, respectively. It can be observed that the Cs:FA ratio significantly affects the crystallization of the perovskite, with the optimal 1:1 ratio resulting in the formation of tetragonal Cs 0.5 FA 0.5 PbBr 3 phase (different from cubic FAPbBr 3 and orthorhombic CsPbBr 3 ) with pronounced preferential orientation as well as a significant reduction in the trap density, which leads to a substantial improvement in the light‐emitting performance.
M-N-C single-atom catalysts (SACs) have emerged as a potential substitute for the costly platinum-group catalysts in oxygen reduction reaction (ORR). However, several critical aspects of M-N-C SACs in ORR remain poorly understood, including their pH-dependent activity, selectivity for 2- or 4-electron transfer pathways, and the identification of the rate-determining steps. Herein, analyzing >100 M-N-C structures and >2000 sets of energetics, we unveil a pH-dependent evolution in ORR activity volcanos from a single-peak in alkaline media to a double-peak in acids. We found that this pH-dependent behavior in M-N-C catalysts fundamentally stems from their moderate dipole moments and polarizability for O* and HOO* adsorbates, as well as unique scaling relations among ORR adsorbates. To validate our theoretical discovery, we synthesized a series of molecular M-N-C catalysts, each characterized by well-defined atomic coordination environments. Impressively, the experiments matched our theoretical predictions on kinetic current, Tafel slope, and turnover frequency in both acidic and alkaline environments. These new insights also refine the famous Sabatier principle by emphasizing the need to avoid an "acid trap" while designing M-N-C catalysts for ORR or any other pH-dependent electrochemical applications.
Iron–nitrogen–carbon (Fe–N–C) single-atom catalysts are promising precious-metal-free catalysts for various essential reactions. However, poor stability is a roadblock to their practical applications. Recent studies suggested that introducing electron-donating or -withdrawing substituents near their catalytic active sites may improve their stability. However, standard M–N–C catalysts synthesized by high-temperature pyrolysis have inhomogeneous structures, making it challenging to understand their degradation mechanisms. Here, we use a series of heterogeneous molecular catalysts with well-defined structures as model Fe–N–C catalysts to map their degradation for oxygen reduction reaction in acidic electrolytes, relevant to M–N–C catalysts' applications in proton-exchange hydrogen fuel cells. Iron phthalocyanine molecules with different types of electron-donating and -withdrawing substituents (i.e., –H, –tBu, –NH2 at α-position, or β-position, –NO2, and –F) are adsorbed on purified carbon nanotubes and exhibit varied oxygen reduction reaction (ORR) activity and stability in acidic electrolytes. Detailed characterizations identify five degradation paths and reveal the beneficial role of electron-withdrawing substituents, i.e., –F and –NO2, by quantifying the Fe distribution. We find that direct Fe leaching from Fe–N4 sites plays a crucial role in early-stage degradation, and it can be significantly suppressed by –F and –NO2 substituents. The oxidative degradation becomes dominant with time, forming FeOx nanoclusters on a carbon nanotube substrate, which the electron-withdrawing substituents can partially alleviate. This work provides insights into the degradation of Fe–N–C single-atom catalysts, which can accelerate the development of robust catalysts for hydrogen fuel cells and beyond.
We investigated the influence of native defects on the adsorption and photocatalytic degradation of anionic and cationic dyes for different ZnO nanoparticles. We found that there was no relationship between the dye adsorption onto ZnO nanoparticles and their photocatalytic activity. Fast photocatalytic degradation could be observed for samples having a low concentration of nonradiative defects (and thus low recombination losses of photogenerated carriers), regardless of the amount of dye adsorbed onto the surface. While the absorption of cationic dyes was not significantly affected by ZnO nanoparticle properties, dye adsorption of several anionic dyes was strongly affected by native defects in ZnO. The defects involved in the dye adsorption are likely shallow donor centers exhibiting an electron spin resonance peak at g ≈ 1.957, resulting in positively charged sites at the surface.
Abstract Understanding how phytoplankton response to elevated CO2 and/or warming through long-term genotypic adaptation is critical for predicting future phytoplankton distribution and community structure. In this study, we conducted a 4.5-year experimental evolution with the model marine diatom Phaeodactylum tricornutum Bohlin under four environmental regimes: ambient conditions, high CO2, warming, and combined high CO2 + warming. Following this long-term adaptation, we exposed the populations to a broad CO2 gradient in a short-term (7-day) experiment, assessing their multi-trait responses. Our results demonstrate that P. tricornutum Bohlin populations adapted to different regimes exhibit significant multi-trait variation across CO2 gradients. Notably, the variability driven by long-term adaptation exceeded that induced by short-term CO2 changes. Furthermore, both long-term adaptation and short-term CO2 exposure altered trait co-variations, highlighting the complex interplay between environmental history and immediate conditions. This study emphasizes the importance to assess long-term genetic changes in marine phytoplankton under global change, as short-term experiments alone may underestimate their capacity for adaptation and the broader implications for marine ecosystems under future climate scenarios.
Abstract Lead‐free 2D antimony‐based halide perovskites with excellent optoelectronic properties, low toxicity, and good intrinsic stability are promising for photovoltaic devices. However, the power conversion efficiency (PCE) of antimony‐based perovskite solar cells (PSCs) is still lower than 3% due to the poor crystallinity and random orientation. Herein, it is found that the Cs 3 Sb 2 Cl x I 9‐x films prepared by adding methylamine chloride as an additive to the precursor solution can form a mixed intermediate phase with 0D dimer phase and 2D layered phase after low pressure treatment. During the annealing process, the 0D dimer phase will completely transition to 2D layered phase due to the partial replacement of I by Cl. Compared to adding SbCl 3 directly, this method considerably increases the crystallinity of Cs 3 Sb 2 I x Cl 9‐x films. The obtained films have a preferential orientation along the (201) direction, which is beneficial for charge carrier transportation. Consequently, the champion device shows a PCE of 3.2%, which is one of the highest efficiencies achieved for inorganic Sb‐based PSCs with the n‐i‐p architecture to date.
Abstract Fenton processes allow to degrade and mineralize toxic organic contaminants, yet classical Fenton processes require continuously adding hydrogen peroxide and ferrous ions, costly solution pH adjustment, and treatment of secondary iron sludge pollution. Heterogeneous electro-Fenton processes deliver oxidizing radicals with only oxygen and electricity consumed. Bifunctional catalysts allow the synthesis and activation of hydrogen peroxide simultaneously, eliminate additional chemical reagents, and yield no metal residues in treated water. Here, we review bifunctional catalysts for heterogeneous electro-Fenton processes. We describe the mechanisms of oxidizing radical generation from oxygen. Then, we compare different types of bifunctional catalysts based on their elemental compositions: (1) metal/carbon composite catalysts, i.e., monometallic iron/carbon composite catalysts, bimetallic/trimetallic carbon composite catalysts, and transition metal single-atom catalysts; (2) metal composite catalysts without carbon; and (3) metal-free carbon catalysts. Then, we present five other approaches beyond electrocatalysts, which have been used to improve the performance of heterogeneous electro-Fenton processes.
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