Qingnan Wu,Ming Wen,Weixi Yan,Qingsheng Wu,Hezhong Wang,Yongqing Fu
A functionalized carbon nanotube (FCNT)/Ni(HCO3)2-Ni nanostructures were synthesized by decorating nanoflaky and mesoporous Ni(HCO3)2 onto FCNT along with in situ formed reduced metallic Ni for the purpose of constructing an energy-storage system with both high specific capacity and cycling stability. Such flaky nanostructures can significantly increase the contact surface areas between the mesoporous and nanoflaky Ni(HCO3)2-Ni and electrolyte, thus immensely reducing the electrolyte-ion diffusion paths and accelerating the electron-transport rates through the use of a FCNT. The in situ reduced metallic Ni atoms are directly contacted with the electrolytes and quickly converted into NiOOH in the alkaline environment. For this reason, the capacity retention of battery-type electrochemical materials can be significantly enhanced, especially at the beginning of cycles. The obtained flaky FCNT/Ni(HCO3)2-Ni nanomaterials exhibit excellent electrochemical performances with a high specific capacity of 203 mAh·g–1 at 3 A·g–1 current density for supercapacitor energy-storage systems. An aqueous asymmetric supercapacitor made of FCNT/Ni(HCO3)2-Ni//graphene oxide achieves a 132 Wh·kg–1 energy density at 2880 W·kg–1 power density and an excellent cycling stability with 84% after 6000 cycles.
Electrified synthesis of high-value organonitrogen chemicals from low-cost carbon- and nitrogen-based feedstocks offers an economically and environmentally appealing alternative to traditional thermocatalytic methods. However, the intricate electrochemical reactions at electrode surfaces pose significant challenges in controlling selectivity and activity, especially for producing complex substances such as N,N-dimethylformamide (DMF). Herein, we tackle this challenge by developing relay catalysis for efficient DMF production using a composite WO2–NiOOH/Ni catalyst with two distinctive active sites. Specifically, WO2 selectively promotes dimethylamine (DMA) electrooxidation to produce strongly surface-bound (CH3)2N*, while nearby NiOOH facilitates methanol electrooxidation to yield more weakly bound *CHO. The disparity in binding energetics of the key C- and N-intermediates expedites C–N coupling at the WO2–NiOOH interface. In situ infrared spectroscopy with isotope-labeling experiments, quasi-in situ electron paramagnetic resonance trapping experiments, and electrochemical operating experiments revealed the C–N coupling mechanism and enhanced DMF-synthesis selectivity and activity. In situ X-ray absorption spectroscopy (XAS) and postreaction transmission electron microscopy (TEM) studies verified the stability of WO2–NiOOH/Ni during extended electrochemical operation. A Faradaic efficiency of ∼50% and a production rate of 438 μmol cm–2 h–1 were achieved at an industrially relevant current density of 100 mA cm–2 over an 80 h DMF production period. This study introduces a new paradigm for developing electrothermo relay catalysis for the sustainable and efficient synthesis of valuable organic chemicals with industrial potential.
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