Surface reconstruction is the key to improving the intrinsic activity of non-precious metal-based catalysts for the urea oxidation reaction (UOR). In this work, Cerium doped Nickel phosphide (Ce-Ni 5 P 4 ) porous nanosheets were synthesized by conventional hydrothermal and phosphorylation methods. It is found that the introduction of Ce 4f induces the electron transfer from P and Ni to Ce, increasing the chemical state of Ni, boosting the reconstruction of Ni 5 P 4 toward active substances of NiOOH with higher UOR activity and improves the UOR intermediates adsorption behavior on the (210) crystal plane for efficient electrochemical reaction. The results show that Ce-doped Ni 5 P 4 improves the UOR performance of only 1.33 V at 500 mA cm −2 , and exhibits exceptional stability over 120 h. Meanwhile, the AEMWE assembly by Ce-doped Ni 5 P 4 || MoNi foam possess a lower voltage of 2.37 V than RuO 2 ||MoNi foam at 1 A cm −2 , demonstrating an excellent performance in industrial applications. The in-situ Raman confirms the enhanced electrochemical reconstruction process caused by the introduction of Ce, which promotes the large current density UOR process. The theoretical calculations show that the stable (210) crystal plane without reconstruction is activated by the Ce doping, and the modulated electron distribution around the Ni sites weakens the binding energy of the Ni N bond, reducing the energy barrier of the rate-determining step for more efficient reaction kinetics. This work provides a hierarchical reconstruction strategy to promote the coupling of activated structures and stable bulks, improving the catalytic UOR activity at large current density and providing new insights for the development of catalysts for industrial applications.
Yi Lu,Jiang-Ping Tu,Qin-Qin Xiong,Jia-Yuan Xiang,Yong-Jin Mai,Jun Zhang,Yan-Qiang Qiao,Xiu-Li Wang,Chang-Dong Gu,Scott X. Mao
A monophase nickel phosphide/carbon (Ni 5 P 4 /C) composite with a thin carbon shell is controllably synthesized via the two-step strategy of a wet-chemistry reaction and a solid-state reaction. In this fabrication, the further diffusion of phosphorus atoms in the carbon shell during the solid-state reaction can be responsible for a chemical transformation from a binary phase of Ni 5 P 4 -Ni 2 P to monophase Ni 5 P 4 . Galvanostatic charge-discharge measurements indicate that the Ni 5 P 4 /C composite exhibits a superior, high rate capacibility and good cycling stability. About 76.6% of the second capacity (644.1 mA h g −1 ) can be retained after 50 cycles at a 0.1 C rate. At a high rate of 3 C, the specific capacity of Ni 5 P 4 /C is still as high as 357.1 mA h g −1 . Importantly, the amorphous carbon shell can enhance the conductivity of the composite and suppress the aggregation of the active particles, leading to their structure stability and reversibility during cycling. As is confirmed from X-ray-diffraction analysis, no evident microstructural changes occur upon cycling. These results reveal that highly crystalline Ni 5 P 4 /C is one of the most promising anode materials for lithium-ion batteries.
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