Research On Electrocatalysis Properties Of Platinum Nanoparticles Loading On Titanium Nitride Substrate Prepared By New Type Method

Direct methanol fuel cell（DMFC）has attracted considerable interests as a new and clean energy source.In DMFC,Pt/C plays an important role in catalyzing the electro-oxidation of methanol and determining the energy transformation efficiency.However,the Pt/C catalyst suffers from the corrosion of carbon at high potentials.The TiN ceramic is well known for good electrochemical stability,high hardness and low electrical resistivity,and thus is regarded as an ideal candidate for Pt supports.In this work,novel Pt@TiN catalysts were fabricated through two steps:forming TiN on Ti substrate by plasma immersion N ion implantation and depositing Pt on TiN by magnetron sputtering.The preparation technique has the advantage of tuning the defects of TiN in a wide range when compared with the hydrothermal methods.The effects of implanting ions and parameters as well as the sputtering parameters on the morphologies,structures and electrochemical properties of Pt@TiN catalysts were investigated.Firstly,the effects of Pt loading on the catalytic performances of Pt@TiN were studied.By tuning the deposition time,Pt nanoparticles with different sizes and loading amounts were deposited on TiN.The results showed that the increase of deposition time resulted in the increase in both Pt size and loading.Moreover,the contact area between Pt and TiN gradually increases as the growth of the Pt particles.When the Pt deposition time reached 20 s,the resultant Pt@TiN with a Pt loading of 1.4μg/cm² displayed the best catalytic performances.Secondly,the influences of implantation voltage,implantation time,implantation pressure,partial pressure of nitrogen and NH₃ flow rate on the catalytic performances of Pt@TiN were studied.It was found that the catalytic activity increased with the increase of implantation voltage,implantation time and partial pressure of nitrogen.The origin of the improvement in catalytic performances could be attributed to the increase of N vacancies near the surface of TiN.However,the further increase of the implantation pressure and NH₃ flow resulted in the dramatical inelastic collision between N ions and gaseous molecules and decreased the implantation energy of N plasma.Consequently,the catalytic activity of Pt@TiN decreased.The optimized implanting parameters were:implantation voltage 24 k V;implantation time 1.5 h;N₂flow 30 sccm（chamber pressure 0.95 Pa）;NH₃ flow 30 sccm（chamber pressure 0.75Pa）.Finally,the effects of doping elements（Al and Mo）in TiN were studied.The increase of Al improved the oxidation kinetics of the TiN surface and decreased the overall activity of the Pt@TiN catalyst.In contrast,doping Mo with TiN improved the catalytic activity of the Pt@TiN,i.e.the onset potential of methanol reaction shifted negatively by 40 m V.