Co-deposits of Pt and Bi on Au disk toward formic acid oxidation
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ORIGINAL PAPER
Co-deposits of Pt and Bi on Au disk toward formic acid oxidation Hyein Lee 1
&
Young Jun Kim 1
&
Youngku Sohn 1
&
Choong Kyun Rhee 1
Received: 23 June 2020 / Revised: 12 July 2020 / Accepted: 31 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Presented in this work is an investigation of co-deposits of Pt and Bi on Au disk (Pt-Bi/Au) toward formic acid oxidation (FAO) using voltammetry and X-ray photoelectron spectroscopy (XPS). The co-deposits of Pt and Bi on Au were prepared using an irreversible method in a mixed solution of Pt ion (1 mM) and Bi ion (5 mM), and the amount of co-deposits was controllable by the number of deposition cycles. The voltammetric studies revealed that the Pt-Bi/Au surfaces presented the characteristics of Pt, Bi, and Au depending on the number of deposition cycles. A detailed analysis of semi-quantitative results of XPS combined with hydrogen coverage on Pt and covered fraction of Au surface suggested two aspects of Pt-Bi co-deposits. One is that during coadsorption, Bi adsorbing with a low efficiency enhanced irreversible adsorption of Pt. The other is that the Pt-Bi co-deposits would be an alloy of Pt-Bi when the Pt amount was low or Pt deposits enriched with Bi in surface regions when the Pt amount was high. The best FAO catalytic efficiency among the investigated Pt-Bi/Au surfaces was ~ 14 mA/cm2, which was higher than that of plain Pt deposits on Au (~ 6 mA/cm2) and comparable to that of sequentially prepared Bi-modified Pt deposits on Au (Bi/ Pt/Au, ~ 20 mA/cm2). Because of a similarity in compositions and catalytic performances of the best Pt-Bi/Au and Bi/Pt/Au, the preparation procedure was concluded not to be critical so that the co-deposition method was more beneficial in terms of the number of deposition cycles in manufacturing electrocatalysts toward FAO. Keywords Pt . Bi . Au . Formic acid . Electro-oxidation . Irreversible adsorption
Introduction Direct formic acid fuel cell (DFAFC) has been highlighted as the technology converting CO2 to formic acid developed to reduce greenhouse gases [1–17]. DFAFC is a promising device to utilize the energy stored in formic acid during the conversion processes of CO2. Certainly, formic acid is one of the convenient energy storage liquids to transport and store compared with hydrogen, so that DFAFC can be employed as fixed power sources in remote sites and portable power sources for electronic devices or small-size vehicles. Formic acid oxidation (FAO) takes place along the dualpath mechanism [18–21]: dehydrogenation and dehydration. Dehydrogenation path is a route directly oxidizing to CO2 (HCOOH → CO2 + 2H+ + 2e) producing 2 electrons. On the other hand, dehydration path is a route indirectly oxidizing to CO 2 via poisonous CO (HCOOH → H 2O + CO; CO + * Choong Kyun Rhee [email protected] 1
Department of Chemistry, Chungnam National University, Daejeon 34134, Republic of Korea
H2O → CO2 + 2H+ + 2e). Because poisonous CO hampers dehydrogenation, the investigations searching for ef
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