Palladium, Nickel And Its Non-metallic Alloy Electrode Surface Infrared Spectroscopy And Application Of Research

The physicochemical properties of a metal such as its stability and reaction activity can be readily modified through its alloying with other metallic or metalloid elements, giving rise to the broad applicability of alloys. The fields of functional materials and catalysis have witnessed an increasing number of studies on the synthesis, activation, characterization and application of metal-metalloid alloys in the past decades. Nevertheless, less information has been provided regarding the changes in the surface geometric structure and electronic property of the metal caused by the introduction of a metalloid element. In electrocatalysis, fundamental studies concerning such modification effects are highly desired, which may be accessed by monitoring the surface adsorption and reaction at molecular level by means of in situ electrochemical surface vibrational spectroscopy.FTIR with the ATR configuration (ATR-FTIR) has the merits of high surface sensitivity, simple surface selection rule, high S/N ratio, and least obstruction of mass transport, thus facilitates the dynamic identification of surface adsorbates on an electrode. From the technical point of view, previous ATR-FTIR measurements were mainly focused on pure metal or metal-metal alloys. The spectroscopic study on metal-metalloid alloy electrodes is a new challenge for the extension of this analytical method.The adsorption and reaction on Ni, Pd and related metalloid alloy electrodes are the main systems studied in the present work. The effects of the alloying elememt P or B on surface adsorption and reaction at Ni or Pd alloy electrode has been probed by using in situ ATR-FTIR,. The geometric and electronic modifications are detected and discussed.The mechanistic study of the electrocatalytic oxidation of formic acid on Pd is the focus of this work in consideration of its great relevance to the fuandamental understanding the oxidation process of related small organic molecules and to the design of anode catalyts for direct formic acid fuel cell (DFAFC). By improving preparation of Pd film electrode and comparing various spectroscopic measurements, we are able to provide new reaction pathways for the CO formation and the role of formate on Pd surface in the processes of self-decomposition and oxidation of formic acid.The combination of spectroscopic studies and catalyst design provide a new approach for the development of high-performance electrocatalysts. Based on the results and conclusions from the spectroscopic studies, novel metal-metalloid electrocatalyst namely boron doped Pd was developed. The as-prepared Pd-B/C catalyst shows extraordinary activity and stability towards the electrooxidation of formic acid as compared to a commercially available pure Pd/C catalyst. The reason for the improvement in the performance was further confirmed by spectroscopic studies on Pd-B electrode.As an technical extension of forming metal or alloy films on Si surface, the controlled metal deposition was combined with surface self-assembly and printing technique to develop a non-photolithographic method for patterned metallization on various substrates.The main results and conclusions are summarized as follows:ATR-FTIR spectroscopy has been successfully applied for the first time to the study of electrosorption of CO and pyridine adsorptions at Ni-P alloy electrodes, with an emphasis on the alloying effect of P on their adsorption configurations on Ni sites. These results were further compared with those obtained on pure Ni electrode. Crystalline and amorphous Ni-P alloy film electrodes with 3 at.% and 13 at.% P, respectively, were prepared with initial seeding of a catalytic Pd layer on Si, followed by chemical deposition. P content was controlled by changing the concentration of the complexing agent, as well as the pH of electrolytes.Transition from bridge-bonded CO (COB) dominant to linearly bonded CO (COL) dominant adsorption was found with increasing P content, together with a blue-shift in the COL vibrational frequency and an attenuation of the Stark tuning rate of COL. The electronic effect, if any, with alloying P is probably not the main cause for the large frequency shift of the COL band. The structural effect due to the perturbed atomic arrangement of Ni with increasing P content was used to account for the change in adsorption behavior. The enhanced COL dipole-dipole coupling causes a blue-shift of the vibrational frequency and an attenuation of the Stark tuning rate for the COL adlayer at Ni-P surfaces. As for pyridine on Ni-P electrodes, essentially the N-end-on adsorption was revealed, in contrast to the edge-tilted adsorption on Ni electrode. Modification in the adsorption configuration as compared to that on Ni electrode is ascribed mainly to the site-blocking effect with alloying P, rather than to partial electron transfer between Ni and P. In previous mechanistic studies of the oxidation of formic acid on Pd, there are two important questions left:the first one is "Is COad formed and adsorbed on Pd as poisonous intermediates during the reaction? If any, what is its origin? The second one is what is the acting role of the surface adsorbed formate for formic acid oxidation on Pd electrode.The mechanism of the self-dissociation and electrooxidation of formic acid on Pd in perchloric acids was studied by means of in situ ATR-FTIR. By using improved preparation method of Pd electrode, a clean, pinhole-free and SEIRA-highly active Pd electrode can be readily obtained. In addition, the higher conductivity and better adhesion of the films is especially suited for the high and durable electrocatalytic currents involved. In situ ATR-FTIR spectra for Pd electrodes in different electrolytes (varying concentrations of formic acid or HClO4) have been comparatively studied. Some results that were not observed or different from the previous reports are summarized as follows.1) Nature of the poisoning species during the self-dissociation and electrooxidation of formic acid on Pd surfacesAdsorbed CO species (COad) were identified in the self-catalytic oxidation of formic acid under open-circuit conditions, as well as in the potential region below 0.4 V (vs. RHE) during the electro-catalytic oxidation of formic acid. The formation of COad was observed after the evolution of CO2 The rate and final coverage of the slow accumulation of COad on the surface was dependent on the concentration of H+ and oxidation potential applied. In a thin-layer flow cell experiment, by comparing the result to that obtained in the unrestricted cell, the formation rate and coverage of COad was found to be dependent on the amount of near-surface CO2 product in the same formic acid-containing electrolyte. Aiming to clarify the origin of COad, CO2 reduction reaction on Pd was on purpose studied in a CO2-saturated solution free from formic acid, and COad was proved to be slowly accumulated below 0.4 V. Thus the formation of COad can be mainly ascribed to the reduction of CO2 product, rather than the direct dehydration of formic acid.2) The role of adsorbed formate on Pd during the electro-oxidation of formic acidBy using Pd film electrode with improved adhesive and conductive properties, measurements in the electrolytes with higher concentrations of formic acid were enabled. The bridge-bonded formate band (1332 cm-1) was observed at ca.0.25 V (vs. RHE) in the electrolyte containing 0.1 and 0.5 mol·L-1 formic acid, while adsorbed formate was reported to show at ca.0.4 V (vs. RHE) on Pt electrode in the same eletrolyte. For the first time, the higher oxyphilic property of Pd was proved by spectroscopic results.In previous studies, formate was found to be a short-lived reactive intermediate during the formic acid oxidation. However, formate, at least on Pt, was suggested to be the spectator or promoter species of the reaction.In order to clarify the role of formate, in situ ATR-FTIR measurements of dynamic oxidation reaction were performed in the electrolytes with different concentrations of formic acid and perchloric acid. Adsorbed formate is quite stable upon the changes in the electrolytes. By introducing Cl" anions, significant supression was found in the oxidation current accompanied by minor decrease in the coverage (i.e., infrared band intensity) of formate. Thus, the role of formate is more close to be the spectator or promoter species of the reaction.In summary, under open-circuit condition and in the potential region below 0.4 V, during the self-dissociation and electrooxidation of formic acid on Pd, COad was detected as poisonous adsorbate. The formation of poisonous COad intermediates is proposed to be originated from the reduction of CO2, rather than the dehydration of formic acid. Adsorbed formate acts as spectator or promoter species, rather than a short lived active intermediate.In order to further improve the formic acid elecreooxidation performance of Pd catalyst, based on the results of the mechanistic studies, boron was introduced as the modifier for Pd, enabling the d-band center of Pd to be lowered, and the possible poisonous adsorption to be reduced, if any.Highly dispersed boron-doped palladium nanoparticles supported on carbon black (Pd B/C) with high Pd loading (ca.40 wt% Pd) are synthesized through an aqueous process using dimethylamine borane as the reducing agent. The doping of boron was confirmed by chemical composition analysis and structural characterization. The as-prepared Pd-B/C catalyst shows extraordinary activity toward formic acid electro-oxidation compared to that of a commercially available Pd/C catalyst and the one prepared by using NaBH4 as the reductant. Subsequent thermal treatment further enhances the durability of the electro-oxidation current on Pd B/C, enabling this new material to be a promising anode catalyst for direct formic acid fuel cells. The superior performance of our Pd B/C catalyst may arise from uniformly dispersed nanoparticles within optimal size ranges, the increase in surface-active sites, and the electronic modification effect of boron species.Two non-photolithographic approaches for patterned metallization on flexible and rigid substrates employing desktop printing are presented. The first comprises an initial self-assembly of aminosilane as the organic glue layer on the substrates followed by inkjet printing of Au colloids or Pd(Ⅱ) species as the catalyst template and finalized by selective chemical plating to form desired patterns of metals. The second starts with an inkjet/laser printing of a resist pattern on the copper clad boards, followed by the conventional selective etching. The minimum line width achieved in current work is 100-150μm. these approaches are low-cost and fast fabrication ways for metal pattern decoration, PCB circuits, parts of RFID, gas sensors and digital micro fluidic system.