Preparation Of Non-precious Metal Catalysts By Pulsed Laser Deposition And Their Catalytic Properties For Oxygen Reduction

In this paper,non-precious metal catalyst materials were deposited on the surface of conductive FTO glass by pulsed laser deposition technique to prepare different types of non-precious metal catalyst/carbon/FTO conductive glass composites.Composite materials with different stoichiometric ratios were prepared by changing deposition time,chamber pressure,laser frequency,laser beam energy and other factors,and optimal deposition conditions were explored and used to synthesize cathode oxygen reduction catalysts in fuel cells.The morphology and structure of the materials were characterized by SEM,EDS,AFM,XRD,XPS and Raman spectroscopy.Electrochemical properties were tested by electrochemical workstation,and catalytic mechanisms were analyzed and summarized.(1)Iron and graphite were employed as targets,conductive FTO glass was used as the substrate,and the target was ablated by Q-switched Nd:YAG laser.The laser wavelength was 532 nm,and the distance between the target and the substrate was 5 cm.Experimental results show that pulsed laser deposition technology can ablate the target under certain laser energy intensity and deposit Fe/C composite film on the FTO surface to prepare Fe/C/FTO composite.Elemental analysis shows that the content of Fe and C elements is proportional to deposition time;the Fe/C composite film deposited at nitrogen atmosphere is thinner,and the C layer is multi-layered with fewer defects.The prepared sample was used for oxygen reduction catalyst,and electrochemical tests show that Fe/C/FTO has a significant oxygen reduction peak in alkaline solution,but does not exhibit catalytic oxygen reduction performance in acidic solution.During the ablation process,when deposition time is 30 s and nitrogen pressure is 10 Pa,the sample has the best electrochemical performance with a starting voltage of oxygen reduction at-0.40 V,a reduction peak at-0.72 V and a peak current density of up to 1.30 mA/cm~2.(2)Nickel and graphite were used as the target,and FTO glass as the substrate.The target was ablated by a Q-switched Nd:YAG laser.Laser wavelength was 355 nm,and the distance between the target and the sample stage was 4.5 cm.Experimental results show that Ni/C composite film is deposited on the FTO surface by pulsed laser deposition.The film thickness is positively correlated with deposition time.The deposited Ni/C film has a large area,and the film is uniform,flat,and compact,wherein the C layer is a graphene layer.Electrochemical tests show that under vacuum,when the deposition time was 30 s and the laser frequency was 4 Hz,the prepared sample has the best electrocatalytic performance with a starting voltage of oxygen reduction at-0.30 V,an oxygen reduction peak at-0.75 V and a peak current density of up to 1.50 mA/cm~2.(3)Ni/Fe/C/FTO composites were prepared by using graphite target as carbon source,nickel-iron alloy target as nickel and iron sources,and FTO as substrate.The target was ablated using a Q-switched Nd:YAG laser with a laser wavelength of 355 nm and a fixed distance of 4.5 cm between the target and the sample stage.Ni/Fe/C composite film was successfully deposited on the FTO surface,and the film was large in area,uniform in thickness and good in appearance.The carbon layer is a graphene layer with many defects.When the deposition time is 45 s under vacuum,the Ni:Fe ratio of the nickel-iron alloy is 3:2,and the sample shows the most superior catalytic performance.The starting voltage of oxygen reduction is at-0.28 V,oxygen reduction peak at-0.75 V and the peak current density is up to 1.60 mA/cm~2.Comparing Fe/C/FTO,Ni/C/FTO and Ni/Fe/C/FTO composites,Ni/Fe/C/FTO composite exhibits the best catalytic performance,which will have broad applications as oxygen reduction catalysts in fuel cells.