Small-Sized Tungsten Nitride Particles Strongly Anchored On Carbon Nanotubes And Electrochemical Applications

Energy and environment are two major themes in today’s world. Extensive use of fossil fuels has caused serious environmental pollution and global warming. So, it is important to develop a device that can meet our energy needs with environmentally-friend characteristics. The fuel cell is a new device for energy transformation that use clean energy （H2, CH₃OH, C₂H₅OH, etc.） as fuels. This process are high-efficient with little pollution to the environment. However, the high cost, low of catalytic activity, poor stability and CO-tolerant of the noble catalyst have restricted the practical application of fuel cell. Therefore, to study a low cost catalyst with excellent activity, high stability and improved anti-poisoning ability will be a top priority.The transition metal nitrides are the promising co-catalyst material for noble metal catalyst due to their unique characteristics. The anchoring of the small-sized WN （tungsten nitride） with good dispersion on carbon nanotubes （CNTs） are effective way to give promising materials in the electrocatalysis. In this paper, a effective way based on the "grinding" treatment followed by nitridation process is proposed to realize the goal. In the synthesis, the solution containing H₄[SiO₄（W₃O₉）₄] (SiW₁₂) and CNTs modified with polyethylenimine （PEI-CNTs） are grinded until the dry. The small-sized, well dispersed WN NPs are anchored onto CNTs after the calcination under NH₃. In the case of the hydrothermal assembly （absence of "grinding"）, the WN particles with larger size and poor dispersion are obtained, demonstrating the important role of "grinding" process. By using NaBH₄ reduction methods, the Pt nanoparticles was loaded on the WN/CNTs to give Pt-WN/CNTs-G-70 composites （the G represents the "grinding" treatment,70 is loading amount% of WN in WN/CNTs）. The catalysts have showed high activity about 817 mA mg^-1 Pt, better that those of commercial Pt/C (340 mA mg^-1Pt), and Pt/CNTs (162 mA mg^-1Pt). The Pt-WN/CNTs-G has also displayed good CO tolerance and stability. In contrast, the Pt-WN/CNTs prepared without grinding process only gives the activity of 344 mA mg^-1Pt, verifying the key role of "grinding" treatment in the preparation of WN/CNTs with good cocatalytic effect.The phosphorus molybdic acid (H₃PO₄·₁₂MoO3) was selected to substitute （or partially substitute） with SiW₁₂, giving MoN/CNTs-G and （WN-MoN）/CNTs-G-70. We found that the Pd-MoN/CNTs-G-type catalyst showed lower catalytic activity, stability and resistance to CO poisoning, while Pt-（WN-MoN）/CNTs-G-70 catalyst showed higher catalytic performance compared to Pt-WN/CNTs-G-70 catalyst.