Synthesis of Platinum Based Single-Atom Catalysts over Intermetallic Compounds for Hydrogen Evolution Reaction By Electrochemically Assisted Dissolution-Deposition

Abstract

Platinum metal is not inert as it undergoes irreversible surface oxidation1. Platinum oxide (PtO) formation and corresponding reduction brings irreversibility on the surface due to famous place-exchange phenomena. Rise of this irreversibility during PtO reduction results in Pt dissolution2. Pt dissolution has been investigated upto an appreciable extent, in rigorous fuel cell conditions, which gives immense opportunity to restrain it by controlling accessible electrochemical operational parameters3. Advantageousness of modulated electrochemical dissolution of Pt, deployed as sacrificial electrode (S.E), renders ultra-low amount of simultaneous Pt electrodeposition through electrolyte on an anchoring substrate electrode (A.S.E). Thereby isolated atoms and subnanometric clusters becomes achievable over suitable A.S.E, utilizing altered rates of dissolution and deposition, by a four-electrode assembly (FEA). Presently, field of electrochemical energy conversion is evolving with highly active and stable electrocatalysts for Hydrogen Evolution Reaction (HER). One such pinnacle group of electrocatalysts emerged as metal-based single-atom catalysts (SACs) are quite efficient as well as stable for HER4. Current research work is focussed on using Pt dissolution phenomena to prepare SACs over certain stable substrates by using four-electrode assembly (FEA).Electrochemically assisted Dissolution-Deposition (EADD) by using FEA is utilized in present work to prepare Pt SACs supported by Intermetallic compounds. EADD being a novel, controlled and efficient synthesis technique has helped to evaluate the insitu Pt dissolution-deposition mechanism by Alternating Current Voltammetry. Authors also demonstrates that typical three-electrode assembly (TEA) used for Pt dissolution from Pt counter electrode is an uncontrolled method for Pt deposition over working electrode. In TEA, Open Circuit Potential (OCP) measurements of counter electrode conducted during cyclic voltammetry (CV) has helped to evaluate the scan rates experienced by Pt counter electrode. Finally, scan rates has given the insights about Pt dissolution and redeposition kinetics demonstrating the problems associated with TEA in context of dissolution-deposition synthesis. While using FEA the challenges experienced in TEA has also overcome. Synthesized Pt SACs tested for HER showed onset potential (η0) of 0mV and over potential at 10mA/cm2 (η10) of 50mV with a quite stable performance for 20h. Ultimately, EADD is summarized as a general, unique and effective surface synthesis technique in the domain of single atom catalysis availing immense opportunities for various other catalytic applications too.(1) H. ANGERSTEIN-KOZLOWSKA; B. E. CONWAY and W. B. A. SHARP. Faraday Trans. I, 1973. Langmuir 1973, 43, 9–36.(2) Gómez-Marín, A. M.; Clavilier, J.; Feliu, J. M. Sequential Pt(1 1 1) Oxide Formation in Perchloric Acid: An Electrochemical Study of Surface Species Inter-Conversion. J. Electroanal. Chem. 2013, 688, 360–370. https://doi.org/10.1016/j.jelechem.2012.07.016.(3) Topalov, A. A.; Cherevko, S.; Zeradjanin, A. R.; Meier, J. C.; Katsounaros, I.; Mayrhofer, K. J. J. Towards a Comprehensive Understanding of Platinum Dissolution in Acidic Media. Chem. Sci. 2014, 5 (2), 631–638. https://doi.org/10.1039/c3sc52411f.(4) Ji, S.; Chen, Y.; Wang, X.; Zhang, Z.; Wang, D.; Li, Y. Chemical Synthesis of Single Atomic Site Catalysts. Chem. Rev. 2020. https://doi.org/10.1021/acs.chemrev.9b00818. Figure 1