Jingwen Zhao,Weitao Yan,Shijia Li,Shiyu Li,Wei-Hua Wang,Ying Bai
The Na superionic conductor of (NASICON)-type Na 4 VMn(PO 4 ) 3 (NVMP) with a three-dimensional framework and high operating voltage has been extensively investigated for sodium-ion batteries (SIBs). However, unexpected Jahn-Teller effect and sluggish Na + diffusion kinetics inevitably lead to rapid capacity fade and unfavorable structural distortion. Herein, the double-pinning effect of Al/F co-doping was adopted for the NVMP system to enhance structural stability and facilitate Na + diffusion. The as-synthesized NVMP-Al&F presents a highly reversible capacity of 110 mAh g −1 at 0.1 C, accompanied with a long-term lifespan of 1000 cycles at 5 C (capacity retention of 86.1 %). Moreover, in situ X-ray diffraction affirms the reversible structural evolution and small volume variation (∼4.43 %) during the highly reversible sodiation/desodiation processes. Benefiting from the double-pinning effect, the lowered Na + migration barrier effectively facilitates Na + diffusion and increases to higher reversible capacity by combining theoretical calculation and kinetic analysis . The assembled NVMP-Al&F//hard carbon (HC) full cell manifests a high energy density of 353.9 Wh kg −1 and excellent cycling durability of 91.3 % at 1 C after 100 cycles. This work sheds light on the double-pinning as a novel strategy to boost the cycling stability of high-performance NASICON-type cathodes.
Ruthenium (Ru) is widely recognized as a low-cost alternative to iridium as anode electrocatalyst in proton-exchange membrane water electrolyzers (PEMWE). However, the reported Ru-based catalysts usually only operate within tens of hours in PEMWE because of their intrinsically high reactivity of lattice oxygen that leads to irrepressible Ru leaching and structural collapse. Herein, we report a design concept by employing large-sized and acid-resistant lattice lead (Pb) as a second element to induce a pinning effect for effectively narrowing the moving channels of oxygen atoms, thereby lowering the reactivity of lattice oxygen in Ru oxides. The Pb-RuO 2 catalyst presents a low overpotential of 188 ± 2 mV at 10 mA cm −2 and can sustain for over 1100 h in an acid medium with a negligible degradation rate of 19 μV h −1 . Particularly, the Pb-RuO 2 -based PEMWE can operate for more than 250 h at 500 mA cm −2 with a low degradation rate of only 17 μV h −1 . Experimental and theoretical calculation results reveal that Ru-O covalency is reduced due to the unique 6 s −2 p −4 d orbital hybridization, which increases the loss energy of lattice oxygen and suppresses the over-oxidation of Ru for improved long-term stability in PEMWE.
The applications of any two-dimensional (2D) semiconductor devices cannot bypass the control of metal-semiconductor interfaces, which can be severely affected by complex Fermi pinning effects and defect states. Here, we report a near-ideal rectifier in the all-2D Schottky junctions composed of the 2D metal 1 T′-MoTe 2 and the semiconducting monolayer MoS 2 . We show that the van der Waals integration of the two 2D materials can efficiently address the severe Fermi pinning effect generated by conventional metals, leading to increased Schottky barrier height. Furthermore, by healing original atom-vacancies and reducing the intrinsic defect doping in MoS 2 , the Schottky barrier width can be effectively enlarged by 59%. The 1 T′-MoTe 2 /healed-MoS 2 rectifier exhibits a near-unity ideality factor of ~1.6, a rectifying ratio of >5 × 10 5 , and high external quantum efficiency exceeding 20%. Finally, we generalize the barrier optimization strategy to other Schottky junctions, defining an alternative solution to enhance the performance of 2D-material-based electronic devices.
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