Insights into the Electrooxidation of Formic Acid on Pt and Pd Shells on Au Core Surfaces via SERS at Dendritic Au Rod Electrodes

Abstract

Highly surface-enhanced Raman scattering (SERS)-active Pt and Pd layers were fabricated using dendritic Au rod (DAR) structures, prepared by simple electrodeposition, as core substrates. Electrochemical and SERS measurements using CO as a probe revealed that the SERS activity on DAR@Pt/Pd core–shell substrates originated exclusively from the Pt/Pd shell layers. The SERS enhancement factors obtained with DAR@Pt and DAR@Pd were 4.5 × 104 and 3.5 × 104, respectively. The unique structures of DAR with sharp edge sites and long-range enhancement caused by the underlying DAR cores contributed to the high activity of SERS. The well-defined and homogeneous surface morphology of DAR@Pt/Pd substrates resulted in good SERS reproducibility and stable electrochemical SERS behavior under potential excursions. The DAR@Pt and DAR@Pd substrates were used for the in-situ electrochemical SERS examination during the oxidation of formic acid (FA) at wavenumbers below 1000 cm–1, where the SERS provided unique spectral information regarding the oxidation/reduction of electrode surfaces. Based on the results of the electrochemical SERS examinations, the electrocatalytic activity of the DAR@Pt and DAR@Pd surfaces for FA oxidation was evaluated in a comparative way. The highly active and robust Pt/Pd SERS substrates could be used for the spectroelectrochemical investigation of other important electrode reactions.

Realization of the dehydrogenation pathway of formic acid oxidation by ultra-small core–shell Au–Pt nanoparticles with discrete Pt shells

“…Accordingly, they have strong adsorption to the CO species, which are the main intermediates produced from the indirect pathways (dehydration of formic acid) in FAOR, thus leading to which the loss of active sites on the surfaces. [5][6][7][8][9][10] Meanwhile, it is known that Au has good anti-poison ability to CO. [11][12][13] Therefore, continuous Pt atoms on the outersurfaces are well dispersed by a high fraction of Au atoms, which would bear an improved anti-poison ability to CO due to the decreasing density of Pt atoms and the presence of Au atoms. [14][15][16][17] In addition, the formation of atomically dispersed Pt atoms on the outer-surfaces of Au-Pt NPs would promote direct pathways (dehydrogenation of formic acid), and thus improving the catalytic performance towards FAOR.…”

Insights into the Electrooxidation Mechanism of Formic Acid on Pt Layers on Au Examined by Electrochemical SERS

“…The low wavenumber region corresponds to M–CO bonds, and the high wavenumber region corresponds to CO vibrations adsorbed on the surfaces. The detailed assignment of the five vibrational bands is presented in Table S1 based on previous results in the literature. ,,, On the DAR surfaces, no band was observed in the low wavenumber region (Figure S4); thus, bands 1 and 2 observed on the DAR@Pt­( n ) surfaces correspond to Pt–CO stretching modes.…”

“…The DAR surfaces were fabricated using electrodeposition from solutions containing 36 mM Au­(I) ions complexed with sulfite anions, as reported in our previous work. ,, A constant deposition potential of −0.83 V with a total deposition charge of 0.03 C (charge density of 0.45 C cm –2 , deposition time of ∼100 s) was applied for the formation of well-defined DAR structures (a typical SEM image of DAR is shown in Figure , inset). Ultrathin Pt layers were formed on the DAR surfaces using self-terminating electrochemical deposition techniques that were recently developed by Moffat and co-workers. − The electrodeposition of Pt layers was performed from solutions containing 3 mM K 2 PtCl 4 and 0.5 M NaCl (pH = 4) by stepping the potential between −0.75 V for 10 s and 0.4 V for 30 s. The potential stepping process was repeated for the desired number of times ( n ) to control the amount of Pt deposited on the DAR surfaces, which was denoted as DAR@Pt­( n ).…”

“… The indirect pathway involves adsorbed CO as a poisoning reaction intermediate (eq ). The electrooxidation of FA on Pt surfaces proceeds via the indirect reaction pathway, whereas direct pathways occur on Pd surfaces. − …”

Electrocatalytic activity of bimetallic Au–Pd nanoparticles in the presence of cobalt tetraaminophthalocyanine

“…Bimetallic nanoparticles have been used for various electrochemical reactions [1][2][3][4][5][6][7][8][9][10][11][12][13][14], including ethanol electro-oxidation [3,12,13], formic acid electro-oxidation [10,11,14], reduction of benzyl chloride [15] and hydrazine detection [16,17]. Bimetallic nanoparticles are based on two different metals and show improved catalytic activity compared to pristine metal nanoparticles, this has been attributed to the synergetic effect of the bimetallic nanoparticles.…”