Electrocatalytic Performance Of Bromine Doped Carbon Supported Pd Catalysts For Formic Acid Oxidation

Direct formic acid fuel cell?DFAFC?can be used as an energy device for mobile due to its high energy efficiency,less formic acid toxicity,safety and environmental protection,and convenient transportation.It has great potential in future scientific and technological applications.It has been reported that the catalytic oxidation activity of formic acid on Pd based catalyst is higher than that on Pt catalyst,but the stability of relative electrocatalytic oxidation is poor.Therefore,in order to improve the stability of Pd catalyst,this paper uses the form of non-metallic element doped carbon support to achieve this goal.In this paper,Br-doped and NP-doped carbon materials supported on palladium catalysts PWA and PMA modified carbon-supported PdNi catalysts have been prepared.The electrocatalytic oxidation of formic acid was studied by means of physical characterization and electrochemical measurement.The contents of the study are as follows:?1?A new kind of bromine contained carbon support?C-Br-X,X=700,800,900??was fabricated by calcining the mixture of the carbon and tetrabutylammonium bromide under nitrogen.The Pd/C-Br-X and Pd/C catalysts were synthesized by an improved liquid reduction method when the C-Br-X and C were used as supports.The catalysts were characterized by XRD,TEM,EDS,Raman spectroscopy and so on.The cyclic voltammetry curves show that the activity of Pd/C-Br-X catalyst is significantly higher than that of Pd/C catalyst.The catalytic activity of Pd/C-Br-800catalyst is the highest for formic acid oxidation.The peak current density of Pd/C-Br-800 catalyst for formic acid electrocatalytic oxidation is 18.39 A·m^-2and6.20 A·m^-2,and the former is 2.97 times as high as the latter.From the chronoelectric curve,it can be found that compared with Pd/C catalyst,Pd/C-Br-800 catalyst can significantly improve the stability of formic acid electrocatalysis.The ratio of oxidation current density of Pd/C-Br-800 catalyst to formic acid at 10 s is 22.25%and that of Pd/C catalyst to formic acid at 10 s is 1.86%.The longer the lifetime of the Pd/C-Br-800 catalyst is about 15 times longer than that of the Pd/C catalyst.The carbon monoxide dissolution curve showed that the peak potential of CO stripping oxidation of Pd/C-Br-800 catalyst moved 103 mV more negatively than that of Pd/C catalyst,which showed a better ability to resist CO poisoning.The impedance results show that the conductivity of Pd/C-Br-800 catalyst is higher than that of the other three catalysts.In conclusion,the addition of bromine can improve the activity and stability of Pd/C-Br-X catalyst for formic acid electrooxidation.?2?A new kind of nitrogen and phosphorus contained carbon support C-NP-800was fabricated by calcining the mixture of the carbon and HCCP under nitrogen.The Pd/C-NP-800 and Pd/C catalysts were synthesized by an improved liquid reduction method when the C-NP-800 and C were used as supports.The catalysts were characterized by XRD,TEM,EDS,Raman spectroscopy and so on.The results of cyclic voltammetry show that the activity of Pd/C-NP-800 catalyst is obviously higher than that of Pd/C catalyst.The peak current density of Pd/C-NP-800 for formic acid electrocatalytic oxidation is 10.19 A·m^-22 and Pd/C catalyst is 6.20 A·m^-2,the former is1.64 times as high as the latter.From the chronoelectric curve,it is found that compared with the Pd/C catalyst,the Pd/C-NP-800 catalyst has a significant increase in the electrocatalytic stability of the formic acid.The ratio of oxidation current density of Pd/C-NP-800 catalyst to formic acid at 10 s is 15.32%and that of Pd/C catalyst to formic acid at 10 s is 1.86%.obviously,the stability of the Pd/C-NP-800catalyst is about 8 times of that of the Pd/C catalyst.The carbon monoxide dissolution curve shows that the CO dissolution oxidation peak potential of the Pd/C-NP-800catalyst is more than 17 mV with the Pd/C catalyst,which shows a good resistance to the electrooxidation of formic acid in CO.The increase of sex and stability is mainly attributed to the introduction of nitrogen and phosphorus dual elements.?3?Activated carbon was modified with mixed phosphotungstic acid and phosphomolybdic acid by imregnation?control W:Mo=2:1,Pd:Ni=2:1?.CV measurements demonstrated that the activity of the corresponding catalyst Pd₂Ni₁/W₂M₁-C was higher than Pd/C.The formic aicd oxidative current of Pd₂Ni₁/W₂M₁-C and Pd/C catalyst was determined as 14.18 A m^-22 and 6.20 A m^-2,respectively.It is computed that the activity of Pd₂Ni₁/W₂M₁-C catalyst was enhanced as a factor of 2.29 than Pd/C catalysts.From the chronoelectric curve,it is found that the stability of the electrocatalytic oxidation of formic acid is significantly enhanced by the Pd₂Ni₁/W₂M₁-C catalyst compared with the Pd/C catalyst.At t=3600 s,the electrocatalytic oxidation current density of the Pd₂Ni₁/W₂M₁-C catalyst is 17.30%when the formic acid is 10 s.At t=3600 s,the electrocatalytic oxidation current density of the Pd/C catalyst is 1.86%when the formic acid is 10 s.The carbon monoxide dissolution curve shows that the CO dissolution peak potential of the Pd₂Ni₁/W₂M₁-C catalyst is less 65 mV than that of the Pd/C catalyst.Pd₂Ni₁/W₂M₁-C catalyst is mainly attributed to the synergism of the double heteropoly acid and the Ni promoter.