| Spectro-electrochemistry is an inter-discipline with the application of spectroscopic techniques to in situ or ex situ study of electrochemical systems. Electrochemical infrared reflection absorption spectroscopy can provide the information of the orientation, arrangement, and coverage for adsorbates on electrode, and thus is regarded as a useful tool for probing electrochemical interfaces at molecular level.In particular, attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) has the advantages of simple surface selection rule, high surface sensitivity, and facile mass transport, facilitating the real-time monitoring of the dynamic electrode processes, including electrocatalytic reactions.As two important noble catalytic metals, Pt and Pd are widely used in fuel cells. However, pure Pt and Pd catalysts could not meet the performance needs. By means of alloying and surface modification with other metals, improved electrocatalysis with lower loading of Pt and Pd can be achieved owing to the synergy effect of alloys, the adjustment of surface electronic structure as well as the third-body effect. Not restricted to bimetallic alloy, ternary alloy was also usually designed to meet higher performance requirements.In addition, dealloying treatment could increase the surface area and adjust the surface electronic property, and it was also an effective approach to obtain better catalysts.Along this line, in this thesis work we not only investigated various platinum-based and platinum-based bimetallic or trimetallic films for formic acid and CO oxidation, and oxygen reduction, but also examined the dealloying effect on electrocatalytic properties for formic acid oxidation.Furthermore, in situ ATR-SEIRAS was applied to the study of the adsorption of CO or the oxidation of formic acid on Pd-Pt alloys and Au-modified Pt electrodes.The main contents and results of my research work are summarized as follows:1.Chemical deposition Pt, Pd and their alloys on silicon surface for SEIRASThe prerequisite of applying in situ ATR-SEIRAS to the electrocatalysis is to locate a facile process to deposit uniform and conductive Pt, Pd and their alloy films on the basal plane of a Si ATR element. To this end, we successfully developed a chemical plating method from simple acidic baths by using the hydrazine as the reductant. Compared to the deposition from complicated basic baths for plating Pt and Pd films in the literature, our new chemical deposition does not cause severe corrosion of Si, in addition, it is flexible and universal for fabricating Pt, Pd and their alloys of different compositions by changing the concentrations of precursor metal salts without the need of introducing organic complexing agents. XPS and ICP-AES analysis results indicated the enrichment of Pt on Pt-Pd alloys surface. ATR-SEIRAS measurements indicated that the as-deposited Pt and Pd nanofilms yield normally directed and enhanced infrared absorption for surface adsorbates. Increasing Pd component tunes the band shape, direction and intensity, which may be explained by effective medium theory (EMT).In addition, optimal electrocatalysis towards formic acid oxidations was pinpointed to the Pt9Pd91 alloy.2.Pd-Ni alloy for formic acid electro-oxidation and dealloy effectDealloyment could increase the reaction surface area and adjust the surface electronic properties, which is an important approach to obtain high-performance electrocatalytic materials.Here, we first adopted the potentiostatic method to deposit Pd-Ni thin film on Au electrode, then partly dealloyed Ni by repetitive potential scans and studied the dealloying effect on the formic acid electro-oxidation.FE-SEM, and CO stripping results showed that the roughness factor increased up to 16 with the above dealloying treatment. XPS and ICP-AES data indicated that the dealloyed Pd-Ni electrode had the Pd enrichment on its surface. The current density of the formic acid oxidation on the dealloyed electrode was found to be proportional with the square root of rotation speed, suggesting a mass-transport-controlled process.3. Au decorated Pt surfaces for formic acid electro-oxidationFor the sake of improving anti-CO poison ability and long-term stability of a Pt-based catalyst, we modified Au layer onto the platinum surface through initial Cu UPD on Pt followed by galvanic replacement of Au (and repeating the above process, the electrode thus obtained was denoted as Pt-Au2).In situ ATR-SEIRAS on the formic acid oxidation on Pt-Au2 electrode revealed that CO poisoning intermediate was significantly decreased compared to that on Pt electrode, attributable to the high efficiency and stability of Pt-Au2 towards formic acid oxidation. 4. Pt-Pd-Fe ternary alloy for oxygen reductionPt-Pd-Fe trimetallic alloys were prepared and examined for oxygen reduction. The trimetallic films on Au electrode were prepared by the potentiostatic deposition, and they showed significant electrocatalysis towards O2 reduction with a performance comparable to that of a Pt-Pd alloy film but better than that of a Pt film. |
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