(Invited) Fundamental and Practical Aspects of Catalyst Monolayer Synthesis Using SLRR of UPD and/or e-Less MLs

Abstract

Catalyst MLs on different substrates have been extensively studied.1–8 Their overall behavior is well described by the position of the d-band center energy level (ed ).9 For substrates with weak electronic effect, ed is mainly affected by the coherent strain (ecoh) caused by the lattice mismatch between the catalyst overlayer and the substrate.10 When substrates are strong ligands, the electronic and strain effects are coupled and ed is a function of both.9,11 An ideal ML catalysts are difficult to synthesize and they often exhibit defects that may contribute to their catalytic activity.12 The most common example is Pt which is very difficult to deposit in a true continuous ML configuration.13A functional Pt ML catalysts have a morphology consisting of compact 2D nanoclusters with certain size distribution and coverage of the substrate.14–17 Due to finite size effects,18,19 each 2D Pt nanocluster experiences a size-dependent compressive stress.20 Consequentially, the local strain in Pt nanoclusters (el) is a combination of the coherent strain and the strain caused by the finite size effects. Turning the finite size effect knob in desired direction by varying nanocluster sizes requires a better understanding of the conditions during ML catalyst synthesis which are responsible for nanocluster size control.Recent studies show that finite size effects dominate the Pt ML catalyst activity for both type of substrates i.e. strong ligand (Pd) and weak ligand (Au) 21,22,23. In the first part of the talk we will review several examples of the finite size effects on activity of ML catalyst as a prelude to the discussion about how to control catalyst ML morphology. The special emphasis is on identifying effective approach to control and manipulate conditions during ML catalyst synthesis via SLRR of UPD or e-less ML which result in desired nanocluster size, nucleation density and overall ML morphology. The analytical model describing the fundamental link between the nucleation kinetics and reaction kinetics of SLRR is discussed. Further on, the relation between the SLRR process parameters such as choice of UPD or e-less ML, concentration of metal ions, temperature, mixing and concentration of supporting electrolyte in solution for SLRR will be discussed within the frame work of the models describing the SLRR reaction kinetics and its link to the resulting catalyst ML morphology. References (1) Chem. Rev. 2012, 112, 5780.(2) Nat. Mater. 2004, 3, 810.(3) Nat. Mater. 2008, 7, 333.(4) J. Am. Chem. Soc. 2007, 129, 6485.(5) J. Am. Chem. Soc. 2004, 126, 4717.(6) Energy Environ. Sci. 2012, 5, 8335.(7) Phys. Chem. Chem. Phys. 2014, 16, 18866.(8) ACS Catal. 2014, 4, 1859.(9) J. Mol. Catal. A Chem. 1997, 115, 421.(10) Phys. Rev. Lett. 1998, 81, 2819.(11) Electrochim. Acta 2007, 52, 5512.(12) Catal. Today 2006, 111, 52.(13) Electrochim. Acta 2002, 47, 1461.(14) Electrochem. Solid-State Lett. 2001, 4, A217.(15) Adžić, R. Surf. Sci. 2001, 474, L173.(16) J. Am. Chem. Soc. 2002, 124, 2428.(17) Science 2012, 338, 1327.(18) J. Phys. Chem. Lett. 2013, 4, 222.(19) Quantum Phenomena in Clusters and Nanostructures; Khana, S. N.; Castleman, A. W., Eds.; Springer: New York, 2003.(20) Surf. Sci. 1997, 392, 103.(21) Surf. Sci. 2015, 640, 50.(22) Electrocatalysis 2012, 3, 203.(23) Angew. Chemie-International Ed. 2005, 44, 2132.(24) J. Am. Chem. Soc. 139, 13676 (2017)