查看更多>>摘要：? 2022 Elsevier B.V.This study reports the effect of the Ti source (Ti foil or TiO2 thin layer) and NaOH concentration on the growth of sodium titanate nanostructures via hydrothermal treatment to improve the photoelectrochemical (PEC) water splitting performance. An optimal condition to grow sodium titanate nanoflower composed of ultrathin nanosheets on the surface of the thin TiO2 film led to the formation of a novel nanocomposite TiO2/Na2Ti3O7 photoelectrode with great adhesion of the two phases. The Ti/TiO2/Na2Ti3O7 photoanode demonstrated a significant enhancement in photocurrent density and shifted the onset potential to a more negative value compared to the pure Ti/TiO2 and Ti/Na2Ti3O7 samples. This noticeable improvement is attributed to the suitable band alignment between the TiO2 and Na2Ti3O7 phases and their direct contact with the Ti foil, as well as the large surface area of nanoflower sodium titanate, which significantly facilitate the generation, separation, and transfer of photogenerated electrons from the active phases to the substrate. More interestingly, the prepared photoanode retained its initial photocurrent density even after 16 h. An ion-exchange method and calcination treatment were used at different temperatures to convert the Na2Ti3O7 phase in the Ti/TiO2/Na2Ti3O7 photoanode to TiO2 to investigate the role of type II heterojunction for efficient photogenerated charge carrier separation in this photoanode. It was concluded that converting Na2Ti3O7 into TiO2 in the Ti/TiO2/Na2Ti3O7 system would reduce its PEC performance due to the formation of a pure phase of TiO2 in the Ti/TiO2/TiO2 photoanode.
查看更多>>摘要：? 2022 Elsevier B.V.The direct seawater electrolysis requires the robust oxygen evolution reaction (OER) catalysts with high activity and stability. Co-based perovskites with superior durability can be used as the promising OER catalysts for the direct seawater electrolysis, though their OER catalytic activity still needs to be improved. In this work, we propose a novel top-down phase evolution method to synthesize a Co-based perovskite hybrid (P/RP-SNCF) compositing the ABO3-type SrNb0.1Co0.7Fe0.2O3-δ (P-SNCF) and Ruddlesden-Popper Sr3NbCoO7-δ (RP-SNCF) perovskite by a facile annealing method. Compared with P-SNCF, the OER process of P/RP-SNCF prefers the lattice oxygen oxidation (LOM) pathway. The P/RP-SNCF hybrid shows significantly enhanced OER catalytic activity with the overpotential being as low as 335 mV at 10 mA cm-2. By the active surface reconstruction of P/RP-SNCF with electrochemical reduction, the optimized ER-P/RP-SNCF-5 shows the further improved OER activity. Furthermore, by using ER-P/RP-SNCF-5 as the anode for the direct seawater electrolysis, the electrolytic voltage reaches 1.57 V to yield a current density of 10 mA cm-2 and keeps stable for 100 h. The proposed strategy provides a new insight into the design of the high-performance perovskite hybrid for the direct seawater electrolysis.
查看更多>>摘要：? 2022 The AuthorsAdditive manufacturing offers the opportunity to produce complex geometries from novel alloys with improved properties. Adapting conventional alloys to the process-specific properties can facilitate rapid implementation of these materials in industrial practice. Nevertheless, the processing of conventional alloys by laser powder bed fusion is challenging, particularly in cases of pronounced susceptibility to hot cracking. Previous studies have demonstrated the positive influence of zirconium on the susceptibility to hot cracking of high-strength aluminum alloys, although its influence on precipitation formation, which is immensely important for 2xxx alloys, remains largely unexplored. This work investigates the optimum process parameters and precipitation formation of 2618 modified by zirconium in laser powder bed fusion. The addition of zirconium results in the production of a crack-free, high-density (~99.9%) material. The microstructure is characterized by a trimodal grain size distribution. Very fine (~0.5 μm) equiaxed grains, nucleated by L12-Al3Zr precipitation at the melt pool boundary, followed by columnar-dendritic grains (5–15 μm long, 1–3 μm wide) and coarser equiaxed grains (1–3 μm) form during solidification. The grain boundaries are populated predominantly by (Al,Cu)9FeNi, but also by Mg2Si, Al2CuMg, and AlCu, which presumably impede grain growth and promote a very fine-grained, low-textured microstructure, even in regions where L12-Al3Zr are absent. The as-built microhardness of 1360 ± 74 MPa exceeds that of the known high-strength Al alloys tailored to additive manufacturing, Addalloy? and Scalmalloy?. The results provide a better understanding of precipitate formation in Zr-modified 2xxx series alloys and pave the way for the commercialization of further 2xxx alloys adapted to additive manufacturing.
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