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Scanning Tunneling Microscophy of Electrode Surfaces
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
The underpotential deposition (UPD) of hydrogen and metal adlayers is also important to understanding the role of surface structure at the electrode-electrolyte interface, because it is well known that UPD processes are extremely sensitive to the atomic structure of the electrode surface. Atomic resolution of individual adatoms in the UPD layers have been achieved in experiments using in situ STM and in situ AFM for Cu,16, 29–31 Ag,18,32 Pb,33 Hg,34 and Bi35 on Au(111), and Cu17 and Ag19 on Pt(111).
Synthesis and Characterization of Atomically Dispersed Metallic Materials
Published in Wei Yan, Xifei Li, Shuhui Sun, Xueliang Sun, Jiujun Zhang, Atomically Dispersed Metallic Materials for Electrochemical Energy Technologies, 2023
The electrodeposition has been systematically investigated for a series of single-metal moieties on the substrates.49 The deposited single atoms include Ir, Ru, Rh, Pd, Ag, Pt, Au, Fe, Co, Ni, Zn, V, Cr, Mn and Cu while the substrates such as Co(OH)2 nanosheets, N-doped carbon, MnO2 nanosheets, MoS2 nanosheets, and CoFeSe oxide nanosheets are alternated for the practical supports. For instance, in Ir1/CoFeSe oxide, during the cathodic electrodeposition process, the metallic ions (or positive complexes) migrate onto the substrate and reduced to metallic states (Figure 2.7a). Moreover, the active substrate with high conductivity and specific surface area is often used to induce an underpotential deposition (UPD) process, that is, a metal cation deposits on the active support at a potential more positive than its equilibrium potential (the potential at which it deposits onto itself).50 These possible metals are Cu, Sn, Pb, Bi, Rh, Pd, Pt, etc.50 For example, an S and N co-doped graphene oxide substrate enables Cu2+ to be reduced into single-atom state with an UPD process.51 Cu sites can be electrodeposited onto 2D TD2 (T=Mo, W; D=S, Se, and Sn) materials as an exfoliated support and then the precious metals of Pt, Pd and Rh are galvanically exchanged with Cu sites to achieve the precious metal based SAMs.50Notably, the depositing process was not always carried out under a potentiostatic process with a constant applied potential for a period. Since the ordinary coating technique will present a dense film or cluster of islands on the substrate but not the desired single-metal structure. The practical protocol is usually determined by a dynamic process, such as cyclic voltammetric (CV) scan in a redox window. The depositing and peeling-off processes take place consequently on the substrate to prevent the enlargement of the nuclei so as to achieve the single-atom structure.
Sustainable route of synthesis platinum nanoparticles using orange peel extract
Published in International Journal of Green Energy, 2019
N.A. Karim, N.J. Rubinsin, M.A.A. Burukan, S.K. Kamarudin
Figure 9 shows the typical CV scan in the 0.5 M H2SO4 and the electrochemical surface area (ECSA) is calculated using equation, ESCA = QH/(mass loading × qHPt) in which QH is the hydrogen underpotential deposition region and qHPt is the monolayer hydrogen charge of 210 µC/cm2. The ECSA for the synthesis Pt nanoparticle is 146 7 m2/g. Figure 9 is quite similar with the study of Taylor et al. (2016) at 20 wt.% of platinum as the authors found that the different platinum loading give different intensity shape in CV as well as lead to different value of ECSA. However, the low value ECSA in Taylor et al. (2016) is due to the larger platinum particle size which is 3.4 nm. Another study was done by Stevens and Dahn (2003) showed that low platinum loading and platinum particle size have high ECSA value and vice versa.
Structure, microstructure and electrodeposition behaviours of aluminium from AlCl3-EMIC and AlCl3-BMIC ionic liquid electrolytes – a comparative study
Published in Surface Engineering, 2020
B. Karthika, S. Mohan, Anuradha Bera, N. Rajasekaran
In AlCl3-EMIC electrolyte CV curve (Figure 1(a)), the onset potential is −55 mV versus Al for low scan rate (10 mV s−1) in cathodic direction and this value is shifted towards noble direction slowly from −55 to 79 mV versus Al for high scan rate (50 mV s−1). This indicates that the required overpotential is small for Al nucleation process and it is reduced further for the case of high scan rate. Further scanning towards the cathodic direction, two reduction peaks (C1 and C2) observed in all scan rates except 50 mV s−1 and these peaks are getting closer and overlap each other with respect to scan rate increment. In 50 mV s−1, we observed only one broad cathodic peak instead of two peaks. The C1 peak (peak potential range −300 mV for low scan rate to −500 mV for high scan rate) corresponds to underpotential deposition of aluminium and C2 (peak potential range −600 mV for low scan rate to −900 mV for high scan rate) peak corresponds to the aluminium deposition [36]. In some other reports, they have discussed these peaks were observed due to the different crystal growth mechanism, namely, C1 corresponds to nano-crystalline and C2 corresponds to microcrystalline growth [37]. The possibilities of these two different growth mechanisms are the cationic effect which is a chemical cause gives variations in several other physical properties of the liquid that could account for the observed differences in morphology. This will influence the diffusion of ions in the electrolytes and gives different crystal growth mechanisms. While sweeping towards the anodic side, we observed one peak A1 (peak potential range 100 mV for low scan rate to 300 mV for high scan rate) corresponds to the aluminium stripping process.
Thermochemical Evaluation of Standard Electrode Potential and Gibbs Energy of Formation of PuCl3 in LiCl-KCl Eutectic Melt
Published in Nuclear Technology, 2020
Suddhasattwa Ghosh, Gurudas Pakhui, S. Suganthi, S. Nedumaran, M. Kakkum Perumal, Manish Chandra, P. Venkatesh, Bandi Prabhakara Reddy
Cyclic voltammograms of LiCl-KCl-PuCl3 melt at 723 K recorded at tantalum as working electrode in the potential range −0.50 to −1.96 V and the scan rate range 25 to 125 mV/s are shown in Fig. 4. Similar CVs were recorded at 773 K as well. As seen from voltammograms, there is finite residual cathodic current density in the potential range −0.80 to −1.60 V varying from 6 mA·cm at 25 mV/s to 15 mA·cm at 125 mV/s. The cathodic peak, the onset of which varies from −1.716 to −1.698 V from 25 to 125 mV/s, corresponds to the PuPu couple, which is similar in nature to that described in literature.26,27,29,31,37 In the CVs reported by Shirai et al.,26 they observed two redox couples. The first redox couple for which the cathodic peak potential appeared in potential range −1.5 to −1.75 V and the corresponding anodic peak appearing in the potential range −1.0 to −1.2 V was explained on the basis of the underpotential deposition of plutonium due to alloy formation of Pu with the electrode material, phase transition in Pu during deposition, or formation of some other complexes of Pu. In the voltammograms shown in Fig. 4 there were no features of the underpotential deposition of Pu. In another paper by Shirai et al.,27 they reported the CV of PuCl3 in LiCl-KCl eutectic melt, where they observed a redox couple at slightly higher anodic potentials (cathodic and anodic peak at −1.6 and −1.0 V, respectively) that they attributed to the influence of crystallization overvoltage on Pu deposition leading to the formation of strongly adhered crystalline deposit at Mo working electrode, which dissolves at higher anodic potentials i.e., at −1.0 V.