Department of Physics

Indian Institute Of Technology Madras , Chennai

Effect of Mechanical Strain on Electrochemical Catalysis at Surfaces

Speaker : Tuhin Adit Maark (PDF applicant), DST Unit of Nanoscience, Department of Chemistry, IIT Madras

2015-04-15

Abstract :

The use of strain to affect the activity of heterogeneous catalysts has attracted attention for its ability to tailor the reactivity of catalytic surfaces. A popular strategy in this regard is the formation of a pseudomorphic overlayer in which atoms of the catalytically active element (e.g., Pd) are present in a thin layer on a substrate with a differing lattice constant (e.g., Ir). In such systems the catalytically active metal is subjected to strain effects arising from lattice mismatch as well as ligand effect due to interaction with the underlying substrate. Electronic structure calculations have shown that as a consequence a shift in the position of the central moment of the d-band (the d-band center, εd) occurs. This shift affects the interaction strength between the metal d states and the molecular orbitals of the adsorbates and thereby, the chemisorption energies. Often electrocatalytic activity trends can be described in terms of binding energies of key intermediates of the associated reaction mechanism. Therefore, new experimental techniques are identifying means to induce strain in catalytic materials in a manner that ligand effects are negligible. Thus, in order to understand optimal use of such newly available systems, knowledge of the differing magnitudes of the strain and ligand effects individually is paramount. Herein density functional calculations for hydrogen (H) adsorption at different coverages (θH) between 0.25 and 1.0 ML on ±5% biaxially strained Pd(111) are carried out to illustrate its differing catalytic behavior for the hydrogen evolution reaction (HER) in comparison to selected pseudomorphic Pd overlayers over metal M = Rh, Ir, Pt, Au and Pt-Ru 50:50 alloy (111) surfaces. The separation of the ligand and strain effects present in Pd/M pseudomorphs and the consequent modification of the binding strengths caused by them individually is estimated. In the compressed Pd/M systems the ligand effect dominates and adds to the weakening of H adsorption caused by the strain effect. In the absence of ligand effect, a broad volcano peak in the HER activity plot versus strain is predicted. Applicability of the above strategy will also be discussed in the context of electrochemical reduction of CO2 to methane. This is to be carried out at the Department of Physics as part of the research proposal.

Key Speaker Tuhin Adit Maark (PDF applicant), DST Unit of Nanoscience, Department of Chemistry, IIT Madras
Guests None
Place Conference Room
Start Time 11:00 AM
Finish Time 12:00 PM
External Link None