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It is key to develop novel economical and effective non-noble metal bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting cells. Herein, a series of novel two-dimensional (2D) ultrathin donor-acceptor Co-based metal organic framework nanoplates (U-DA-CoMOF-NPs) as bifunctional HER/OER catalysts have been designed and fabricated based on a donor-acceptor strategy. Density functional theory calculations demonstrate that the fabricated U-DA-CoMOF-NPs are fine donor-acceptor pairs having HOMO-LUMO localizations and a HOMO-LUMO gap of 2.60 eV and give the Gibbs free energy for a reasonable OER mechanism. Additionally, changes in anions can affect the physicochemical characterizations and HER/OER performance of the fabricated U-DA-CoMOF-NPs. As a result, the fabricated U-DA-CoMOF-NPs-1 using NO 3 − as an anion exhibits the optimal HER/OER performance in alkaline solution thanks to the thinnest nanoplate thickness, the largest surface area and hierarchical mesoporous structure. Moreover, a self-assembled overall water splitting cell with U-DA-CoMOF-NPs-1/NF as both cathode and anode achieves a low potential of 1.65 V and a high cycling stability at 10 mA cm−2 for at least 15 h. The present study offers an option to design and fabricate other cost-effective donor-acceptor MOF-based catalysts for water splitting cells. • A series of U-DA-CoMOF-NPs have been fabricated with a donor-acceptor strategy. • The HOMO positioning is on Tdc, LUMO localization is at Tpt and a gap is 2.6 eV. • Co–N has more positive catalytic ability for OER than pyridinic-N and thiophene-S. • The representative U-DA-CoMOF-NPs-1 exhibits the optimal HER/OER performance. • A U-DA-CoMOF-NPs-1/NF cell shows a low potential and high stability at 10 mA cm−2. [ABSTRACT FROM AUTHOR]

Effect of saturation magnetization (Ms) of the free layer (FL) on the switching current is analyzed for spin transfer torque (STT) magnetic random access memory (MRAM). For in-plane FL, critical switching current (Ic0) decreases as Ms decreases. However, reduction in Ms also results in a low thermal stability factor (Δ), which must be compensated through increasing shape anisotropy, thus limiting scalability. For perpendicular FL, Ic0 reduction by using low-Ms materials is actually at the expense of data retention. To save energy consumed by STT current, two electric field (EF) controlled switching methods are proposed. Our simulation results show that elliptical FL can be switched by an EF pulse with a suitable width. However, it is difficult to implement this type of switching in real MRAM devices due to the distribution of the required switching pulse widths. A reliable switching method is to use an Oersted field guided switching. Our simulation and experimental results show that the bi-directional magnetization switching could be realized by an EF with an external field as low as  ±5 Oe if the offset field could be removed. [ABSTRACT FROM AUTHOR]

Design and development of cost-efficient multifunctional three-dimensional (3D) metal organic frameworks (MOFs) towards oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are very significant for green energy devices. Herein, a scalable one-pot solvothermal method is developed to obtain a series of multifunctional 3D flower-like MOFs. In addition, systematic studies are also conducted on the effects of various metal cations and N-containing ligands on the structures, compositions, and multifunctional performance of the obtained MOFs. As a result, 3D flower-like Co-MOFs using Co2+ as a metal cation and 2,2':6′,2″-terpyridine as a N-containing ligand exhibit the highest multifunctional performance towards ORR, OER and HER. The scalable method provides a new prospect to design and develop other MOFs-based multifunctional catalysts. • F–Co-MOFs have been developed via a scalable one-pot solvothermal method. • The effect factors of the obtained MOFs are studied in detail. • F–Co-MOFs display high ORR, OER and HER performance in alkaline medium. • The 3D flower-like structure and MOFs ensure high multifunctional performance. [ABSTRACT FROM AUTHOR]