Ni/Mn-based layered oxides have been widely studied for sodium ion battery cathode because of high capacity and simple preparation. However, its application has been restricted owing to unstable structure and poor cycling performance. Herein, the multi-element doped hexagonal sheet Ni/Mn-based layered oxide with ZrO 2 surface modification O3-NaNi 0.3 Mn 0.5-x Fe 0.1 Cu 0.1 Zr x O 2 @ZrO 2 (NFMCZ-x) cathode materials have been successfully synthesize by high temperature calcination method accompanied by ball milling activation. XRD refinement results show Zr 4+ substitution of Mn 3+ can increase interlayer distance of sodium layer. Benefiting from the synergetic effect of multi-element doping and ZrO 2 surface modification, the optimized NFMCZ-0.03 sample exhibits a higher discharge capacity of 178 mAh/g at 0.1C and good capacity retention (77 % after 50 cycles at 2C). Furthermore, NFMCZ-0.03 has an excellent air stability with a capacity retention rate of 86 % during 50 cycles at 1C after being exposed in the air for 20 days. The ex-situ XRD results of NMFC at different charge/discharge voltages show Zr 4+ doping can suppress O3 + P3′'–O3′-O3 + P3′' phase transition during charge/discharge process. These results confirm that synergistic effect of multi-doping combined with surface modification can improve electrochemical performance of layered oxides cathodes, which provides a research idea for development of Ni/Mn-based layered oxides cathodes for sodium-ion batteries.
It is highly desirable to enhance the charge separation and introduce catalytic functions for efficient water splitting into hydrogen on g-C 3 N 4 . Herein, heterojunctions of PCN-222(M)/g-C 3 N 4 -AA were successfully synthesized through the in-situ hydrothermal method, where metallic ions (M) were strategically incorporated into porphyrinic metal-organic framework (MOF) ligands. This heterojunction design strategy is considered to establish directional charge transfer channels for photogenerated electron-hole (e − -h + ) pairs and thereby enhance its separation efficiency. Remarkably, the 1 % PCN-222(Pd)/g-C 3 N 4 -AA composite demonstrated superior photocatalytic hydrogen evolution performance, achieving a rate of 2338.17 μmol·g −1 ·h −1 . This rate was 3.23 times higher than that of pure g-C 3 N 4 and 2.79 times higher than that of g-C 3 N 4 -AA. The composite morphology was characterized by a series of physicochemical properties. Bandgap analysis via Tauc plot revealed that metal ion doping in the porphyrin center effectively modulates the HOMO-LUMO levels at the composite interface. First-principles calculations coupled with hydrogen adsorption free energy analysis elucidated how interfacial engineering between PCN-222(M) and g-C 3 N 4 -AA governs heterostructure formation and charge transfer pathways. This work systematically deciphers the synergistic effects of bimetallic MOF integration and provides insights into the underlying photocatalytic reaction mechanism.
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