Study On The Performance Of Metal Oxide Suppotes For Anode Pd Catalysts In Direct Formic Acid Fuel Cells

The direct formic acid fuel cell（DFAFC）has been widely concerned due to its high theoretical electric potential and high power density at low temperatures.The core design in fuel cells is the anode catalyst,of which Pd and Pt catalysts are the most common,and for the electrooxidation of formic acid,Pd has superior performance than Pt catalysts.However,the activity and stability of Pd catalysts still need further improvement.Therefore,this work investigates the modification of carbon carriers and the effect of different metal oxide carriers on catalyst performance by exploring different carrier materials to solve the problems of low activity,high cost and poor durability of anode catalysts.The main research contents are as follows:In this work,the carbon powder treated with nitric acid and hydrogen peroxide was used as the carrier of Pd catalyst.The high activity Pd catalyst was prepared by microwave-assisted polyol method to study the catalytic oxidation performance of Pd/C catalyst for formic acid.The catalytic performance of Pd/C（a）prepared from treated carbon powder was improved compared to that of Pd/C（b）prepared from untreated carbon powder carrier.Pd/C（a）achieved an electrochemical active area（ECSA）of 57.83 m²g^-1,which was 1.69 times higher than that of Pd/C（b）.The current density of the oxidation peak of formic acid on the Pd/C（a）catalyst reached 51.98 mA cm^-2,which was 2.20 times higher than that of Pd/C（b）.Highly active Pd catalysts were prepared by introducing metal oxide WO₃ in the carrier,and the ratio of two carriers,WO₃ and CNTs,was optimized to study the performance of Pd-WO₃/CNTs catalysts for the catalytic oxidation of formic acid.The physical characterization results showed that there was a synergistic effect between the metal and the carrier between Pd and WO3 in the Pd-WO₃/CNTs catalyst and which lead to a more uniform dispersion of Pd nanoparticles on the carrier,and also reduced the particle size of the metal particles.The electrochemical test results showed that the best catalytic effect was achieved when the content of WO₃ was of carrier mass 10%.The electrochemically active surface area of Pd-WO₃/CNTs-10% was the largest at 71.90 m²g^-1,which was 2.24 times that of Pd/CNTs,and the current density of formic acid oxidation peak on Pd-WO₃/CNTs-10% was the largest at 59.92 mA cm^-2,which was 2.21 times that of Pd/CNTs.The carbon material modified with metal oxide CeO₂ modified carbon material was used as the Pd catalyst carrier,and the ratio of both CeO₂ and CNTs carriers was optimized to study the performance of Pd-CeO₂/CNTs catalyst for formic acid catalytic oxidation.Physical characterization showed that there was a strong metal-carrier interaction between Pd and CeO₂.And because the addition of CeO₂ facilitated the dispersion of Pd particles on the carrier and effectively reduced the particle size of Pd nanoparticles,the smallest Pd nanoparticle size was 3.23 nm in the Pd-CeO₂/CNTs-20% catalyst.Electrochemical test results showed that the electrochemical surface area of Pd-CeO₂/CNTs-20% was 105.71 m²g^-1and the catalytic activity of Pd-CeO₂/CNTs-20% was 3.29 times than that of the Pd/CNTs catalyst.The peak current density of formic acid oxidation on the Pd-CeO₂/CNTs-20% catalyst was 59.10 mA cm^-2,which was 2.18 times than that of the Pd/CNTs catalyst.The performance of the Pd-CeO₂-WO₃/CNTs catalyst for formic acid catalytic oxidation was investigated by adding a bimetallic oxide CeO₂/WO₃ composite to the carrier and optimizing the ratio of the two metal oxides of the CeO₂/WO₃ composite.Physical characterization showed strong metal-to-carrier interactions between Pd and CeO₂/WO₃.The Pd particles were reduced in size and uniformly dispersed,with the smallest Pd nanoparticle size in the Pd-CeO₂-WO₃/CNTs（1:1）catalyst.The electrochemical test results showed that the activity and stability of the catalysts were improved by adding CeO₂/WO₃ composites to the catalysts,and the best catalytic effect was achieved by adjusting the mass ratio of CeO₂ and WO₃ carriers to 1:1.The electrochemical surface area of Pd-CeO₂-WO₃/CNTs（1:1）reached 147.76 m²g^-1and Pd-CeO₂-WO₃/CNTs（1:1）catalysts on formic acid oxidation with a forward peak current density of 72.45 mA cm^-2.