Fuel-cell Type CO Sensor Based On Pt/C/Nafion Sensing Electrode

In order to monitor very low traces of CO in the environment,a novel fuel-cell type CO sensor based on Pt/C/Nafion sensing electrode has been fabricated.It operated at the room temperature with low power consumption.The sensing signal for the fuel-cell type sensor was almost linear with the CO concentrations.Besides,the sensor had a high stability with no pollution for the environment.This sensor was mainly made up of the membrane electrode assembly(MEA),which was composed of the polymer membrane electrolyte,Pt/C sensing electrode and reference electrode.The MEA was fabricated using the hot-pressing and peeling-away method.The performance of CO sensor mostly depended on the sensing electrode materials in the MEA.When preparing high performance sensing electrode materials,there were two significant factors: One was the composition of the dispersants which would affect the diffusion of reaction gases and the transport of moisture.The other was the kind of the carbon-supporting materials for sensing electrode which had essential influences on the CO reaction rate and the conduction of protons and electrons in the MEA.Therefore,there were two major study contents in this paper as follows:1.Research on the effect of the dispersants on the performance of the fuel-cell type CO sensor.The MEA was fabricated using the wet.50% Pt/carbon blacks as the sensing electrode material and four kinds of organic solvents,tetraethyl orthosilicate(TEOS),ethylene glycol(EG),glycerol and EG/polytetrafluoro-ethylene(PTFE)as the dispersants.From the optical microscopy(OM)and scanning electron microscopy(SEM)measurements,it was observed that the MEA using EG as the dispersant had the best quality for the surface area.From the sensing performance testing,it was shown that the sensor using EG had the best sensitivity(0.088 ?A/ppm)toward CO,and the response and recovery times against 50 ppm CO were 22 and 24 s,respectively.Moreover,the sensor using EG dispersant also had a low detection limit(1 ppm),favourable selectivity and repeatability.2.Research on the influence of the carbon-supporting materials for sensing electrode in the fuel-cell type sensor.Three different carbon materials,carbon blacks(CBs),multiwalled carbon nanotubes(MWCNTs)and carbon fibers(CFs),were used as the support for the Pt nanoparticles(NPs)to prepare the Pt/C sensing materials with the weight ratio of 1:4 for Pt/carbon,respectively.It was observed from the SEM images that the Pt NPs were best-dispersed in the surface of CFs.From the BET measurement,the Pt/CFs with dispersant had the largest BET surface area(21.6 m2/g)and the smallest average pore diameter(28.5 nm).When making the MEA with Pt/CFs materials,the distortion of Nafion membrane found to be the minimum and the remaining sensing materials in the PTFE films were also found to be the minimum.It was measured by weighing method that both the sensing electrode and reference electrode of the MEA fabricated using Pt/CFs materials had the maximum of Pt loadings with the value of 0.63 and 0.54 mg/cm2,respectively.From the sensing test,the sensitivities of sensors toward CO with Pt/CBs,Pt/MWCNTs and Pt/CFs were 0.032,0.037 and 0.077 ?A/ppm,respectively.It had also been found that the sensor using Pt/CFs materials had rapid response and recovery times(28 and 32 s)with 5.03 ?A to 50 ppm CO.At the same time,this sensor had a very low detection limit(0.1 ppm),excellent selectivity and long stability.This paper mainly focused on the influences of the composition of dispersants and the kinds of carbon-supporting materials for sensing electrode on the sensing characters when fabricating the fuel-cell type CO sensor.It was exhibited that the EG was the best dispersant and the CFs was the optimal carbon-supporting material for Pt nanoparticles.In summary,the paper had fabricated a novel fuel-cell type CO sensor based on the Pt/C/Nafion sensing electrodes with high sensitivity,low detection limit,fast response/recovery time,good selectivity and excellent stability.This paper also laid the foundation for application of CO detection in the harsh environment.