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Solute structure and its evolution in supersaturated aqueous solutions are key clues to understand Ostwald’s step rule. Here, we measure the structural evolution of solute molecules in highly supersaturated solutions of KH2PO4 (KDP) and NH4H2PO4 (ADP) using a combination of electrostatic levitation and synchrotron X-ray scattering. The measurement reveals the existence of a solution-solution transition in KDP solution, caused by changing molecular symmetries and structural evolution of the solution with supersaturation. Moreover, we find that the molecular symmetry of H2PO4- impacts on phase selection. These findings manifest that molecular symmetry and its structural evolution can govern the crystallization pathways in aqueous solutions, explaining the microscopic origin of Ostwald’s step rule.The molecular symmetry of solute structure in aqueous solutions is a key clue to understand Ostwald’s step rule. Here, the authors show that molecular symmetry and its structural evolution can govern the crystallization pathways in aqueous solutions. [ABSTRACT FROM AUTHOR]

Extensive research on bulk‐heterojunction (BHJ) optimization has advanced organic photovoltaics (OPVs). However, the need for research addressing the issue of morphological instability and ensuring long‐term durability remains a priority. Herein, a diffusion‐governed morphological modification methodology via a sequential deposition (SD) process comprising ternary components with low miscibility is demonstrated. Sequential coating of a high glass transition temperature (Tg) material and a host binary blend induces a concentration difference between successively coated layers, allowing for effective blending of immiscible materials during solvent evaporation. The enhanced miscibility of the SD‐processed BHJ layer facilitates molecular interactions between the high Tg material and the host materials, thereby increasing the Tg of the BHJ blend. The SD‐processed OPVs exhibit superior photovoltaic performance and suppressed glass transition under thermal stress compared to reference OPVs fabricated via a conventional method. After 500 h of thermal aging at 85 °C, the SD‐BHJ OPV retains over 80% of its initial efficiency, whereas the reference device shows a drastic drop to below 80% of its initial efficiency after only 80 h. This study provides a step toward efficient, long‐term stable OPVs by overcoming the limitations of blend miscibility and poor thermal durability of conventional BHJ systems via a SD process. [ABSTRACT FROM AUTHOR]

Achieving highly effective catalytic activity in photoelectrochemical (PEC) water splitting has become a challenge in the fabrication of Fe2O3 photoanodes due to their poor electrical conductivity and surface charge recombination. This study outlines a one-step hydrothermal route for the design of surfactant-assisted in situ Au nanoparticle (NP)-integrated Zr-doped Fe2O3 photoanodes for PEC water splitting. A cetyltrimethylammonium bromide (CTAB) surfactant and Au-incorporated Zr-doped Fe2O3 photoanode achieved a photocurrent density of 2.30 mA cm−2 at 1.23 V vs. RHE (1.23 VRHE). CTAB promoted the adsorption of Au NPs on the Zr-FeOOH during the synthesis, while Au NPs accelerated the charge transfer kinetics. The loaded Au NPs enhanced the separation of photo-generated electron–hole pairs; as a consequence, Au NPs effectively shuttled the holes from the hematite to the photoelectrode/electrolyte interface, leading to improved photocatalytic activity. Further, the optimized Zr-HT/CTAB/Au photoanode exhibited an intrinsic solar-to-chemical conversion (ISTC) efficiency of 1.034%. Moreover, impressively, the deposition of a NiCo(OH)x cocatalyst enhanced the PEC performance to 2.72 mA cm−2 at 1.23 VRHE. This study presents a potentially fruitful strategy for simultaneous in situ decoration of a surfactant and Au NPs with photoanodes for PEC water splitting. [ABSTRACT FROM AUTHOR]

Distribution of Zn 2 + , Al 3 + , and Fe 3 + ions on tetrahedral and octahedral sites in Fe 3 + -doped ZnAl 2 O 4 nanocrystals is studied through detailed x-ray diffraction (XRD) analysis. Significant changes in the intensity ratio of (220), (311), (400), and (422) diffraction peaks upon Fe addition were perceived, whose correlation with lattice inversion, Fe 3 + ions distribution, and ionic vacancies is probed through simulations and Rietveld refinement. Fe 3 + ions were found to be occupying tetrahedral sites in increasing proportion with the doping concentration, leading to decreased spinel inversion. However, different orders of defects, viz., cation and anion vacancies were also found to be playing their part in the statistical distribution of cations on octahedral/tetrahedral interstices. Fe L 2 , 3 -edge x-ray absorption near edge structure spectroscopy indicated Fe 3 + ions being present on tetrahedral as well octahedral interstices and distortion in cation polyhedra, while O K-edge inferred formation of different orders of ionic vacancies upon Fe addition, thereby corroborating the results from XRD. The photoluminescence study illustrated the quenched emission intensity upon Fe doping, with almost no change in emission color, and signatures of tetrahedral/octahedral Fe 3 + occupancy in the lattice. Thus, this study highlights the variation in degrees of freedom associated with atomic arrangements in spinel ZnAl 2 O 4 lattice upon Fe 3 + addition. [ABSTRACT FROM AUTHOR]