Platinum Electrochemistry and Electrocatalysis: Unraveling the Origins of Its Unique Behavior　　

　

　Gregory Jerkiewicz, Professor

　　Department of Chemistry, Queen’s University, 90 Bader Lane, Kingston, ON. K7L3N6, Canada

　　

　　时间：2018年4月13日 下午3:00

　　地点：嘉定园区 A区 8 楼（1）会议室

　　联系人：王家成（69163661）

　　

　　Abstract：

　　In the emerging hydrogen economy involving electrochemical technologies, electrical energy is converted to chemical energy (H₂, a stable, reusable product) in water electrolysers and such generated H₂ is used to produce electrical energy in hydrogen fuel cells. It is a wonderful cycle, in which water is initially a reactant and eventually a product. The processes occurring in water electrolysers and hydrogen fuel cells, namely the hydrogen evolution (HER), the oxygen evolution (OER), the hydrogen oxidation (HOR) and the oxygen reduction (ORR) reactions, drive an interest in the hydrogen and oxygen electrochemistry and electrocatalysis. Platinum is the most effective electrocatalyst in these reactions, but the origin of its unique activity is poorly understood. However, it unique electrocatalytic activity needs to be explained in order for one to be able to develop guidelines for the design and fabrication of non-noble electrode materials possessing similar properties. The contribution focuses on two phenomena taking place at Pt electrodes: (i) the under-potential deposition of H (UPD H) and (ii) surface oxide growth and its dissolution.

　　Electrochemical, analytical and surface science research sheds new light on the unique interfacial behavior of Pt in aqueous electrolyte solutions. Temperature-dependent cyclic-voltammetry studies combined with theoretical data treatment facilitate the determination of thermodynamic state functions of the UPD H (D_ec-adsG°, D_ec-adsS°,D_ec-adsH°) and the Pt-H_UPD surface bond energy (E_Pt–Hupd). The data show that on a thermodynamic basis H_UPD is equivalent to H_chem, and suggest that H_chem and H_UPD occupy the same surface adsorption sites and are embedded in the Pt surface lattice. Electrochemical quartz-crystal nanobalance (EQCN) analysis of interfacial mass changes in the potential range of the UPD H and the HER reveals the existence of potential of minimum mass (E_pmm), the value of which coincides with the completion of a saturation layer of H_UPD and the onset of the HER. It is observed that the HER does not take place on bare Pt but on Pt modified with a layer of H_UPD, which modifies the electrode’s interfacial wetting ability making the surface hydrophobic-like. The discharge of H₃O⁺ in the HER or the dissociative adsorption of H₂(g) in the HOR proceed easily on Pt than on other metals because the species do not have to displace H₂O molecules or hydrated ions due to weak surface dipole–H₂O dipole and surface dipole–hydrated ion interactions. Effective and cheap non-Pt electrocatalysts for the HER and HOR should mimic the interfacial behavior of Pt; thus, they should: (i) be chemically and mechanically stable; (ii) adsorb H; (iii) dissociate H₂; and (iv) have weak interactions with H₂O molecules and hydrated ions. The electro-oxidation of Pt at well-defined conditions, i.e. polarization potential (E_p), polarization time (t_p), and temperature (T), leads to very thin oxide layers. Their surface chemical composition is analyzed using X-ray photoelectron spectroscopy (XPS) and reveals that PtO is the main species formed at E_p < 1.60 V. Application of higher potentials leads to slow growth of PtO₂ on top of the PtO layer. Treatment of the Pt oxide growth employing oxide-growth theories results in the evaluation of the reaction’s mechanism and kinetics. Formation of Pt surface oxides is accompanied by their slow but unavoidable dissolution. Stability of Pt oxides depends on the potential that they experience, exposure time, and electrolyte composition and concentration. Electrochemical and chemical Pt and Pt oxide dissolution pathways are discussed.

　　

　　BIOGRAPHY

　　Gregory JERKIEWICZ received his dual accreditation Master’s degree in Engineering Chemistry from Gdansk University of Technology, Poland, in 1984. He also studied solid state physics at the same university (1983-1985). In 1980 while being an undergraduate student in Poland, he became deeply involved in the Solidarno?? movement and was a co-founder of the Independent Student Association. In 1985, he immigrated to Canada. He completed his Ph.D. (1991) at the University of Ottawa under the supervision of the late Prof. Brian E. Conway (FRSC). He spent the summer of 1991 working in the Institute of Physics, the University of Fribourg, Switzerland. He joined the Department of Chemistry, University of Sherbrooke, as Research Associate in September 1991 and became Assistant Professor in June 1992. He was promoted to Associate Professorship with tenure in June 1997. In 1997, he won the Electrochemistry Award of the Société Fran?aise de Chimie, as the first recipient residing outside of France. In June 2002, he joined the Department of Chemistry, Queen's University, as tenured Associate Professor and was promoted to the rank of Professor in 2005. In 2004, he was awarded the W. A. E. McBryde Medal of the Canadian Society for Chemistry in recognition of his contributions to interfacial electrochemistry and of his advancement of the electrochemical quartz-crystal nanobalance (EQCN). In 2011, he was awarded the R. C. Jasobsen Award in recognition of his service to the Canada Section of the Electrochemical Society. He has authored ca. 140 publications that include peer-reviewed papers, peer-reviewed book chapters, papers in volumes of conference proceedings, and has co-edited one book and three volumes of conference proceedings. He has delivered ca. 160 invited keynote lectures, seminars, and conference presentations, and 240 contributed conference presentations. He has been an active member of the International Society for Electrochemistry, The Electrochemical Society and the Canadian Society for Chemistry by having served on several executive committees. He is the Editor-in-Chief of Electrocatalysis, a Springer journal. Throughout his career, he has trained sixty-two (62) highly qualified personnel, including graduate and undergraduate students, postdoctoral fellows and research associates, and has hosted eight (8) visiting faculty members. In 2012, the President of Poland, Mr. Bronis?aw Komorowski, conferred on him the Knight’s Cross of the Order of Polonia Restituta in recognition of his outstanding contributions to the Polish society in the 1980s (the Order of Polonia Restituta is equivalent to the Order of Canada).