The design of high-performance and low-cost oxygen evolution reaction (OER) electrocatalysts is crucial for environment friendly hydrogen production. Some transition metals have been proven to be good substitutes for noble metals due to their unique electronic structural characteristics and good electrocatalytic performances, with examples including nickel and cobalt, which are usually used to prepare OER electrocatalysts. In this work, we synthesized three-dimensional Ni-Co-Fe ternary layered double hydroxide nanosheet array electrocatalysts via hydrothermal process. Iron element was introduced into the Ni-Co based hydroxide. The ternary layered double hydroxide has a nanoarrays microstructure. Theoretical analysis confirms that by adjusting the ratio of Ni/Co/Fe, the microstructure of the catalyst changes significantly. Attributed to the special nanostructure, the catalysts show superior catalytic activities in oxygen evolution reaction (OER). The results show that a small overpotential of 222 mV at the current density of 20 mA·cm−2for the OER in 1.0 M KOH is acquired. A small Tafel slope of 61.22 mVdec−1and a maximum specific capacitance of 239 Fg−1are also obtained.Keywords:oxygen evolution reaction;nanoarrays;Ni-Co based;electrocatalyst
Rational design and constructing multifunctional electrocatalysts featuring with low cost and high efficiency is critical for promoting the implement of sustainable energy devices such as water splitting and zinc air batteries. Herein, we report a facile means to prepare a selenide/sulfide hetero-structured NiCo 2 Se 4 /NiCoS 4 catalyst for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), overall water splitting (OWS), and Zn-air batteries (ZABs). The NiCo 2 Se 4 /NiCoS 4 heterostructure showed excellent OER and HER performance, evidenced by the small overpotential of 248 mV and 180 mV @ 10 mA cm −2 for OER and HER, and superior long-term stability to the benchmark IrO 2 and Pt/C catalyst for OER and HER, respectively. It also exhibited a potential of 1.660 V @ 10 mA cm −2 in the practical OWS test, close to the Pt/C + IrO 2 catalyst. Furthermore, when employed as air-cathode catalyst for ZABs, the NiCo 2 Se 4 /NiCoS 4 modified battery exhibited the narrow charge-discharge voltage gap of 0.98 V @ 50 mA cm −2 and a maximal specific capacity of 693.17 mA h g −1 , outperforming the IrO 2 counterpart. Such excellent performance can be attributed to the advantageous structural merit of the NiCo 2 Se 4 nanoflowers, and especially the heterostructure interfaces created in NiCo 2 Se 4 /NiCoS 4 , which significantly boosted the catalytic synergistic effects. This study can offer a new avenue to design and prepare abundant-element-based cost effective, efficient and durable electrocatalysts with multifunctionalities that hold great promises to be applied in electrochemical devices.
In the present study, the catalyst modified with alkaline oxide can enhance the selectivity to primary amines. However, the addition of alkaline oxide inevitably reduces catalytic activity. In this study, NiCo-NC@BaO-MFC catalyst derived from zeolitic imidazolate framework-67, Ba(CH 3 COO) 2 , and melamine formaldehyde (MF) resin was prepared and used for the hydrogenation of adiponitrile (ADN) to hexamethylene diamine (HDMA). The carbon layer obtained from the MF resin effectively prevents the interaction between barium (Ba) and the active center, thus improving target product selectivity without decreasing catalytic activity. The results of the density functional theory (DFT) calculation and characterization indicated that the effect of synergy between nickel (Ni) and cobalt (Co) bimetals induces an electron density growth on the Ni surface, bringing the d-band center toward the Fermi surface. Meanwhile, the high electron density of the active center compensates for the electron-deficient state of the carbon atom in –C N, thus improving the catalytic activity. Furthermore, it was found that the introduction of Ba promotes the formation of nucleophilic hydrogen anions, which facilitates the hydrogenation of 6-aminohexylimine (AHIM) to HDMA and inhibits the intramolecular condensation of AHIM, hence improving the selectivity to HDMA. The NiCo-NC@BaO-MFC catalyst gives 98.6 % ADN conversion and 97.2 % selectivity to HDMA in an alkali-free system.
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