Yan Cheng,Juhui Gong,Bo Cao,Xuan Xu,Peng Jing,Baocang Liu,Rui Gao,Jun Zhang
In this paper, an ingenious strategy was developed to construct a well-aligned nitrogen-doped carbon nanotube (NCNT) array electrode integrated with multiple electrocatalytically active components of single cobalt atoms with CoN4 configuration (CoSAs), cobalt nanodots (Co), and molybdenum- or tungsten-carbide (WC or MoC) for hydrogen evolution reaction (HER). The well-aligned nitrogen doped carbon nanotube array is fabricated via an in situ NCNT growth process using a MO4 unit-exchanged lamellar cobalt hydroxide–nitrate MO4–CoLHN (M = Mo or W) as both catalytic species and precursor and dicyandiamide as nitrogen/carbon source under a high-temperature carbonization process. The electrocatalytic performance with low overpotentials of 23 and 47 mV at 10 mA cm–2 in acidic electrolyte can be achieved in WC-Co@CoSAs-NCNTs/CC and MoC-Co@CoSAs-NCNTs/CC electrodes, respectively. Moreover, these electrodes also show good stability, which could maintain 30 h of stable performance. Coupling various characterizations with density functional theory calculations, it is disclosed that the synergistic coupling interactions exist among NCNTs, CoSAs, Co, and MC as well as N-dopants, facilitating effective regulations on exposed active sites, d-band center, vectorial electron transfer from Co and MC to NCNTs, and enhanced electrical conductivity derived from NCNTs array, which may account for the significant promotion of HER performance.
Designing stable and efficient electrocatalysts for both oxygen reduction and evolution reactions (ORR/OER) at low-cost is challenging. Here, a carbon-based bifunctional catalyst of magnetic catalytic nanocages that can direct enhance the oxygen catalytic activity by simply applying a moderate (350 mT) magnetic field is reported. The catalysts, with high porosity of 90% and conductivity of 905 S m −1 , are created by in situ doping metallic cobalt nanodots (≈10 nm) into macroporous carbon nanofibers with a facile electrospinning method. An external magnetic field makes the cobalt magnetized into nanomagnets with high spin polarization, which promote the adsorption of oxygen-intermediates and electron transfer, significantly improving the catalytic efficiency. Impressively, the half wave-potential is increased by 20 mV for ORR, and the overpotential at 10 mA cm −2 is decreased by 15 mV for OER. Compared with the commercial Pt/C+IrO 2 catalysts, the magnetic catalyzed Zn–air batteries deliver 2.5-fold of capacities and exhibit much longer durability over 155 h. The findings point out a very promising strategy of using electromagnetic induction to boost oxygen catalytic activity.
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