Piezoelectric Electrochemical Studies On And Applications Of (Sub-)Nanostructured Noble Metal Modified Electrodes

Basic and applied researches of noble metal (sub-)nanomaterials have received wide attentions in diverse fields due to their unique structures and unique physicochemical properties. It is of significance to innovate the synthesis and analysis/characterization methods to stimulate the electrocatalysis and electroanalysis studies of noble metal (sub-)nanomaterials. In this dissertation, we briefly review the recent advances of quartz crystal microbalance (QCM) technology and the preparation and application of noble metal (sub-)nanomaterials, and then conduct electrocatalysis and electroanalysis studies of some noble metal (sub)nanomaterials and their modified electrodes. The main contents are summarized below.1. Underpotential deposition (UPD) of Cu on an Au electrode followed by galvanic replacement reaction (GRR) of CuUPD with a Pt source (H2PtCl6or K2PtCl4) yielded Au-supported Pt adlayers (for short, Pt(CuUPD-Pt4+)n/Au for H2PtCl6, or Pt(CuUPD-Pt2+)n/Au for K2PtCl4, where n denotes the number of UPD-replacement cycles). The electrochemical quartz crystal microbalance (EQCM) technique was used for the first time to quantitatively study the fabricated electrodes and estimate their mass-normalized specific activity (SECAm) for methanol oxidation in alkaline solution. In comparison with Pt(CuUPD-Pt2+)n/Au, Pt(CuUPD-Pt4+)n/Au exhibited a higher electrocatalytic activity, and the maximum SECAm was obtained to be as high as35.7mAμgpt-1at Pt(cuUPD-Pt4+)3/Au. The layer-by-layer architecture of Pt atoms on Au is briefly discussed based on the EQCM-revealed replacement efficiency, and the calculated distribution percentages of bare Au agree well with the experimental results deduced from the charge under the AuOx-reduction peaks.2. UPD of Cu on an Au electrode followed by GRR of CuUPD in the mixture of Pt source and Au source (H2PtCl6+HAuCl4) yielded Au-supported Pt-Au mixed atomic monolayer (PtxAuy(CuUPD-Pt4+)/Au, where x and y denote the ratio of molar concentration of H2PtCl6to HAuCl4in the mixture). The replacement efficiency between CuUPD atoms and Pt (or Au) atoms was calculated by QCM. By establishing the correlation between the electrochemical properties of Pt atom (determined by the electrochemistry) and the Pt loading (determined by QCM), a new method was proposed to calculate the Pt loading in the Pt-Au mixed atomic monolayer. Meanwhile, the Pt active area-normalized specific activity (SECAa) and the SECAm of Pt-Au mixed atomic monolayer toward the electrocatalytic oxidation of formic acid in acid solution were examined. In comparison with the performance of other Pt-M(M=Ir, Rh, Pd, Ru and Os) mixed atomic monolayer, the Pt-Au mixed atomic monolayer exhibited the best performance among the examined catalysts, with the highest SECAa (124mA·cmpt-2) and SECAm (102mA·μgPt-1) on the optimal electrode (Pt4Au1(CuUPD-Pt4+/Au) reported to date.3. GRR is the redox reaction betweem relatively active metal (reductant) and the salt of less active metal (oxidant), and UPD of metals refers to their (sub-)monolayer deposition at potentials more positive than the Nernstian potential for bulk deposition, both of which have attracted great academic and industrial interests in many areas. However, little is known about the possible occurrence and effect of UPD during GRR to date. As demonstration-of-concept examples here, we explore the co-occurrence of UPD of Cu or Pb on Pt during the corresponding GRR, mainly using a double cabin galvanic cell (DCGC) device, QCM, and relevent techniques. It is found that the UPD of either the ions of the template metals used in GRR or other added metal ions of appropriate electroactivities can spontaneously and universally occur during the GRR, and a simple, flexible (especially in the DCGC mode) and efficient protocol is thus recommended based on the integrated GRR-UPD concept for preparation of functional metal nanocomposites with improved electrocatalysis performance. The insights obtained here emphasize that the GRR involve the occurrence and effect of UPD, which should help the better understanding of various GRR for application explorations.4. The QCM and electrochemical noise (ECN) device technologies were employed to examine the UPD of Pb on Pd and the bulk stripping of Cu in the DCGC with a Cu anode and a Pd cathode. In addition, we used the concept of GRR-UPD to turn the GRR between Cu and Pt+Pd mixed salts (K2PtCl4+PdCl2) for synthesizing Pb-containing Pt-Pd nanoparticles on the cathode in a DCGC with a Cu anode, a multiwalled carbon nanotubes (MWCNTs) modified glassy electrode (GCE) cathode, a HC104anolyte, and a K2PtCl4+PdCl2+Pb(C104)2catholyte. The catalytic performance of the resultant Pb-containing Pt-Pd nanoparticles toward electrocatalytic oxidation of ethanol was examined in alkaline solution, and the Pb-containing Pt-Pd nanoparticles modified MWCNTs/GC electrode was used to construct an amperometric sensor for ethanol detection. The sensor exhibited a linear amperometric response to ethanol concentration from0.05to10mM with a sensitivity of138μAmM-1cm-2, a limit of detection (S/N=3) of6.6μM.5. The QCM and ECN technologies were employed to examine the UPD of Pb on Au and the bulk stripping of Cu in the DCGC with a Cu anode and a Au cathode. In addition, we used the concept of GRR-UPD to turn the GRR between Cu and Pt+Au mixed salts (H2PtCl6+HAuCl4) for synthesizing Pb-containing Pt-Au nanoparticles on the cathode in a DCGC with a Cu anode, a MWCNTs/GCE cathode, a HClO4anolyte, and a H2PtCl6+HAuCl4+Pb(C104)2catholyte. The catalytic performance of the resultant Pb-containing Pt-Au nanoparticles toward electrocatalytic oxidation of methanol was examined in alkaline solution.6. Here, we used the concept of GRR-UPD to turn the GRR between Cu and Pd+Au mixed salts (PdCl2+HAuCl4) for synthesizing Pb-containing Pd-Au nanoparticles on the cathode in a DCGC with a Cu anode, a MWCNTs/GCE cathode, a HClO4anolyte, and a PdCl2+HAuCl4+Pb(ClO4)2catholyte. The catalytic performance of the resultant Pb-containing PdAu nanoparticles toward electrocatalytic oxidation of formaldehyde was examined in alkaline solution, and the Pb-containing Pd-Au nanoparticles modified MWCNTs/GC electrode was used to construct an amperometric sesnor for formaldehyde detection. The sensor exhibited a linear amperometric response to formaldehyde concentration from0.01to5.0mM with a sensitivity of666μA mM-1cm-2, a limit of detection (S7N=3)of0.89μM.