Catalytic Properties Of Palladium-Gadolinium Catalysts Based On New Supports For Methanol Electrooxidation In Alkaline Media

Direct methanol fuel cell(DMFC)is a kind of fuel cell with anion exchange film and use methanol as the fuel directly.DMFCs have advantages of high energy conversion efficiency,safe and environmental friendliness,holding great promise in applications of the automobile and portable power sources.However,the low activity and stability of the commonly used anode catalyst Pd/C becomes one of the main obstacles restricting the commercialization of DMFCs.The catalyst for methanol electrooxidation is composed of the main catalyst and the carrier.The main catalyst is the catalytic center and the carrier can increase the active area of the main catalyst.Furthermore,the novel electronic structure of the carrier can influence the energy state of the main catalyst and improve the catalytic activity of the catalyst.Herein,high performance Pd catalyst with different main catalyst and different carrier are designed and prepared.The transmission electron microscopy(TEM)and X-ray diffraction(XRD)are operated to investigate the crystal structure and morphology of prepared catalysts.Meanwhile,electrochemical measurements including cyclic voltammetry(CV),Line scanning voltammetry(LSV)and chronoamperomerty(i-t)are also tested to analyze the catalytic behaviors.The Pd-Gd/C catalysts with different amounts of gadolinium were prepared,and the catalytic performance towards methanol electrooxidation in alkaline media was investigated.The current density of methanol oxidation on the 20%Pd-10%Gd/C catalyst is much higher than that on the 20%Pd/C catalyst.According to the CV,LSV and CA results,it is found that the 20%Pd-10%Gd/C catalyst has a lower apparent activation energy than the 20%Pd/C catalyst,as well as good durability,besides better catalytic activity.From CO stripping results,the addition of Gd can facilitate the oxidative removal of CO.Thus,the promoting effect of Gd can be explained by a bi-functional mechanism.The Pd-Gd catalysts with Ti407 as carrier were prepared and the catalytic performance for methanol electrooxidation in alkaline media was investigated by electrochemicalmeasurements.According to the CV,LSV and CA results,it is found that with Ti4O7 as carrier,the addition of Gd can increase the activity of the catalyst and facilitate the oxidative removal of CO for long cycle stability.However,the catalyst with Ti407 as carrier did not show a better performance than that with carbon as carrier.This result is not consistent with conclusion which is derived by the increase of the metallic Pd.According to the insight investigation,Ti407 is an ionic crystal,which can absorb the ion easily.So the catalyst with Ti407 as carrier could have a better performance than that with carbon as carrier in the solution with fuel dissociating.The methanol cannot dissociate in alkaline media.So the catalyst with Ti407 as carrier shows a worse performance in methanol electrooxidation in alkaline solution than Pd/C catalyst.Pd/C and Pd/Mg-Al-CO3 LDH catalysts were prepared and their catalytic performance for methanol electro-oxidation was compared.Cyclic voltammograms in the alkaline solution showed the much higher specific activity of Pd/LDH than that of Pd/C.The increase of the specific activity may be attributed to the OH-conductivity of Mg-Al-C03 LDH.According to CO stripping results,it is found that Mg-Al-C03 LDH facilitates the oxidative removal of adsorbed CO.The chronoamperograms indicated that Pd/LDH has a better stability.All the results imply that Pd/LDH is very promising for probable application in DMFC field.Furthermore,Mg-Al-CO3 LDH may act two important roles in the Pd/LDH catalyst:1)catalyst for Pd(?)reduction,2)hydroxide ion conductor for OH-concentrating.