Hybrid Mg/Li-ions batteries (MLIBs), combining the fast kinetics of Li and the advantages of magnesium ion batteries (MIBs), are regarded as one of the most prospective electrochemical energy storage systems. Nevertheless, the electrochemical properties of batteries are generally limited by the diffusion kinetics of highly-polarized divalent Mg ions in the cathode materials. Herein, rutile-type molybdenum dioxide (R-MoO 2 ) was synthesized by the hydrothermal treatment and subsequent thermal treatment and used as the cathode materials in MIBs and MLIBs. The initial discharge capacities of R-MoO 2 cathodes in MIBs and MLIBs are 50 and 253 mAh·g − 1 at the current density of 50 mA·g − 1 , respectively. The specific capacities are 17 and 111 mAh·g − 1 after 100 cycles. The R-MoO 2 cathode possesses good Coulombic efficiency and rate capability in MLIBs. Compared with MIBs, the electrochemical performances of MLIBs were greatly enhanced. The energy storage mechanisms were investigated by the experiments results and density functional theory (DFT) calculations. Moreover, the discharge-charge mechanisms were also explored by ex-situ characterizations. The diffusion/migration of Mg 2+ and Mg storage abilities are improved by introducing the Li + , promoting electrochemical performances. The energy storage mechanisms are Mg 2+ intercalation in MIBs and Mg 2+ /Li + co-intercalation in MLIBs. This work further investigates the energy storage mechanism of MLIBs and provides the theoretical groundwork for the follow-up development of high-performance cathode materials.
Hydrogen production from solar water splitting, especially via photovoltaic-electrocatalysis, has been regarded as a promising approach for the conversion of abundant but intermittent solar energy into storable chemical fuels. Despite much progress, conventional combined photoelectrochemical devices usually suffer from severe instability issues, which largely inhibit them for practical applications and may also lead to the uncertain efficiency value for true overall water splitting. Here, we report an unassisted solar water splitting device with concurrent high efficiency and stability, which is constructed by spatial coupling of tandem III-V-based GaInP/GaAs/Ge light absorber and robust earth-abundant Ni foil-based MoNi 4 /MoO 2 bifunctional electrocatalysts . Remarkably, apart from the outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance, bifunctional MoNi 4 /MoO 2 electrocatalysts also largely avoid electrode contamination issues, while the robust Ni substrate protects III-Vs from conventional corrosion problems . Consequently, this integrated photovoltaic-electrolysis system device exhibits a high solar-to-hydrogen (STH) conversion efficiency of 17.6 % in alkaline electrolytes with long-term stability of up to 845 h. Further construction into a wireless unassisted monolithic device could lead to an artificial leaf with an STH efficiency of 4.28 %, holding great promise in future solar fuel production with concurrent high efficiency, good stability as well as low cost.
Daming Feng,Lixue Zhou,Chang Liu,Hui Li,Yusheng Zhang,Yali Yao,Tianyi Ma
Electrocatalytic nitrogen reduction reaction (NRR) for the synthesis of ammonia (NH 3 ) is one of the green and mild methods of artificial nitrogen fixation, promising as an alternative to replace the existing industrial process. Under the requirements of green chemistry and sustainable development, the design and development of highly active and stable electrocatalysts is very important for improved synthesis performance. Mimicking from the natural nitrogenase, Fe and Mo based catalysts have attracted much attention due to their superior catalytic performance for N 2 adsorption and activation. In this work, an interfacial engineering strategy has been used to prepare a Fe, Mo-bimetallic electrocatalyst for the electrosynthesis of NH 3 . In detail, the pre-pyrolyzed biochar-based Fe 2 O 3 composites were decorated with nano-flowered MoS 2 /MoO 2 hybrids by a solvothermal process (MoS 2 /MoO 2 @Fe 2 O 3 /BC). As confirmed by the extensive characterization, the further modification not only introduced functional counterparts into the electrocatalysts but also regulated the morphology of the nanostructure. The electrochemical tests showed that the highest NH 3 yield rate of MoS 2 /MoO 2 @Fe 2 O 3 /BC was 4.87 μg h − 1 cm −2 and highest FE was 16.5% in 0.1 M Na 2 SO 4 . The catalytic stability and durability were also presented in the longtime electrolysis and cycling experiments. The improved catalytic performance of decorated catalyst, as evidenced by the comparison with Fe 2 O 3 /BC, is attributed to the increased electrocatalytic active area, the moderated hydrophilicity, and the synergistic effect of Fe, Mo-bimetallic active sites. This study provides a new perspective for the design and development of low-cost transition metal complexes as electrocatalysts for nitrogen reduction reactions.
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