Fabrication Of Carbon Nanofibers/Pt-based Alloy Electrocatalytic Materials For Water Splitting And Their Performance

The ever increasing demand for energy and environmental pollution has stimulated a considerable interest in exploring new clean energy and efficient energy conversion. Hydrogen is proposed as an ideal clean energy. Electrocatalytic water splitting has been widely investigated as a highly promising method for hydrogen generation. To date, noble matels such as Pt have hitherto been the state-of-the-art electrocatalyst materials for water electrolysis. However, the consequently high cost and scarcity of these precious metals directly impede their large-scale application in the field of engineering. Therefore, methods based on decreasing the noble metals usage, while improving the electrocatalytic activity are important problems in water electrolysis. Two phases or multi-phase catalysts would lead to remarkably improved catalytic activity due to the electronic interaction between the interface regions of them. Recently, two phases or multi-phase catalysts have been widely foucused and researched. Electrospinning is the most ef?cient technique for the generation of one-dimentional nanomaterials, and the obtained carbon nanofibers(CNFs) possess large surface area, high porosity, excellent chemical stability and high electron transfer characteristic. Based on the above, CNFs were prepared by graphitizated the electrospun PAN nanofibers. In order to improve the utilization rate of the precious metal nanoparticles, stability and catalytic activity, CNFs were selected as catalysts carrier for noble nanoparticles(NPs) to fabricate the CNFs/Pt-based alloy electrocatalytic materials. In addition, we systematically studied the electrocatalytic hydrogen evolution or oxygen evolution activity of catalysts. The main points are summarized as follows:(1) The polyacrylonitrile/Pt nanofibers(Pt/PANFs) were synthesized using an electronspinning process, and then the as-spun Pt/PANFs were subjected a high temperature graphitization treatment to prepare CNFs supported Pt NPs(Pt/CNFs, the loading of Pt is ca. 7 wt%). In addition, the structure and morphology of the Pt/CNFs hybrid materials were determined by field-emission scanning electron microscope(FESEM), transmission electron microscope(TEM) and electrochemical measurements. The morphology results of the hybrid materials indicated that the average diameter of the nanofibers was ca. 440 nm, and Pt NPs were well-dispersed on CNFs. The electrocatalytic hydrogen results in acid solution showed that Pt/CNFs possessed high electrocatalytic activity and stability, and exhibited lower onset overpotential at-55 m V and the smallest Tafel slop of 50 mV decade-1. Research suggested that the high electrocatalytic activity and excellent stability mainly due to the high electron transfer, large surface area and good chemical stability. Moreover, the graphite carbon-wrapped and good dispersion of Pt NPs on CNFs also can improve the electrocatalytic activity and stability.(2) To further decrease the usage of Pt, we synthesized Pt alloy with Co. We fabricated the CNFs supported PtCo alloy NPs(PtCo/CNFs) by the same strategy. In addition, the structure and morphology of PtCo/CNFs hybrid materials were studied and as an electrocatalytic materials for water splitting to inveatigate the electrocatalytic activity for hydrogen evolution reaction(HER). The results showed that the PtCo alloy NPs were evenly dispersed in/on the CNFs. Notably, PtCo/CNFs(the Pt loading is about 5 wt%) exhibited extraordinary high electrocatalytic activity and durability for HER. Electrochemical measurement demonstrated that PtCo/CNFs afforded a current density of 10 mA cm-2 at the overpotential about-63 mV. In addition, the as-synthesized PtCo/CNFs exhibited an extraordinary low Tafel slope(28 mV decade-1), even identical with that of commercial Pt/C(ca. 20 wt% Pt). The strong electronic effect between the interfaces of PtCo alloy can provide more free and active Pt sites for electrocatalytic reactions due to a bifunctional mechanism, which significantly enhance the electrocatalytic activity.(3) Furthermore, the research also explored the influence of nitrogen-doped(N-droped) for the electrocatalytic performance of PtCo/CNFs. N-droped CNFs supported PtCo alloy NPs(PtCo/N-CNFs) were prepared by the precursor of PtCo/CNFs in NH3/Ar at medium temperature graphitization, and then subjected in high temperature graphitization. The amazing catalytic performance and durability of the PtCo/NCNFs for oxygen evolution reaction could be rationalized as follows: the structure performance of PtCo alloy and nitrogen-doped carbon materials can enable the electric transfer and act as a supplement of the active site, etc.