Structural/Compositional-Tailoring of Nickel Hexacyanoferrate Electrodes for Highly Efficient Capacitive Deionization.

Prussian blue analogs (PBAs) represent a crucial class of intercalation electrode materials for electrochemical water desalination. It is shown here that structural/compositional tailoring of PBAs, the nickel hexacyanoferrate (NiHCF) electrodes in particular, can efficiently modulate their capacitive deionization (CDI) performance (e.g., desalination capacity, cyclability, selectivity, etc.). Both the desalination capacity and the cyclability of NiHCF electrodes are highly dependent on their structural/compositional features such as crystallinity, morphology, hierarchy, and coatings. It is demonstrated that the CDI cell with hierarchically structured NiHCF nanoframe (NiHCF-NF) electrode exhibits a superior desalination capacity of 121.38 mg g-1 , a high charge efficiency of up to 82%, and a large capacity retention of 88% after 40 cycles intercalation/deintercalation. In addition, it is discovered that coating of carbon (C) film over NiHCF can lower its desalination capacity owing to the partial blockage of diffusion openings by the coated C film. Moreover, the hierarchical NiHCF-NF electrode also demonstrates a superior selectivity toward monovalent sodium ions (Na+ ) over divalent calcium (Ca2+ ) and magnesim (Mg2+ ) ions, allowing it to be a promising platform for preferential capturing Na+ ions from brines. Overall, the structural/compositional tailoring strategies would offer a viable option for the rational design of other intercalation electrode materials applied in CDI techniques.

Low loss and high extinction ratio all-silicon TM-pass polarizer with reflection removal enabled by contra-mode conversion Bragg-gratings.

Bragg-gratings have been frequently used to design compact and high extinction ratio (ER) on-chip polarizers. However, the strong reflection of the unwanted polarization may deteriorate the performance of the light source or cause unwanted interferences. In this paper, we propose a Bragg-grating-based all-silicon TM-pass polarizer with low reflection, low insertion loss (IL) and high ER. Unlike previously reported polarizers based on single mode waveguides, we construct the Bragg grating with a multimode waveguide, which not only acts as a Bragg reflector, but also a mode-order converter to convert the reflected TE light into higher order modes to be eventually filtered out by utilizing a tapered transition. On the other hand, the grating has little adverse influence on the TM input light since it works at sub-wavelength-guided wave propagation regime. Finally, the polarizer obtained has a length of 30µm, an ER of 51.83dB, an IL of 0.08dB, and an operating bandwidth of ∼61nm for ER > 30dB at the wavelength of 1.55µm. More importantly, the reflection of the unwanted polarization is suppressed to -12.6dB, which can be further lowered via additional design optimization. Our work points to a new direction for making better on-chip polarizers.

Single Pt atoms stabilized on Mo2TiC2O2 for hydrogen evolution: A first-principles investigation.

Single-atom catalysis offers an effective way to reduce the amount of used noble metals and maximizes their catalytic activity. We systematically explore electrocatalytic performances of Pt doped Mo2TiC2O2 monolayer by the first principles calculations. Our results show that the presence of donor defects in Mo2TiC2O2 can always increase the reaction free energy of hydrogen adsorption and further promotes the performance in hydrogen evolution reaction (HER). More interestingly, the substitution of Pt for O in the Mo2TiC2 can modify the free energy to an ideal value and is responsible for the significantly enhanced catalytic activity. Furthermore, the large value of diffusion barrier indicates that single Pt atoms can be stabilized onto the O vacancy sites, which can effectively prevent them to aggregate into nanoparticles. Our works are useful for understanding the recent experimental observations and pave the way for further experimental improvements of catalytic activity for the HER.

Interface Schottky barrier in Hf2NT2/MSSe (T = F, O, OH; M = Mo, W) heterostructures.

The Schottky barrier height (SBH) is a critical parameter that determines the carrier transfer at metal/semiconductor interfaces. In this work, the interfacial properties of Hf2NT2/MSSe (T = F, O, OH; M = Mo, W) heterostructures are systematically investigated using first-principles calculations. It is found that, for MoSSe and WSSe, the use of S or Se atomic layers in contact with Hf2NT2 can give significantly different SBHs. In addition, SB-free contact for electron injection can be realized for F-S interfaces in Hf2NF2/MoSSe and Hf2NF2/WSSe heterostructures. Furthermore, the SBHs of the heterostructures can be tuned by applying compressive strain and p-type ohmic contact can be obtained for O-Se interfaces in Hf2NO2/MoSSe and Hf2NO2/WSSe heterostructures. This work proposes a feasible strategy to regulate the SBHs of interfaces.