Seminar - On the interaction between mechanics and chemistry: two case studies by Prof. Pradeep R. Guduru
Date: 23 July 2015 (Thursday)
Time: 11:00 am – 12:00 pm
Venue: EF305, The Hong Kong Polytechnic University
Mechanics and chemistry are generally considered to be separate disciplines with little overlap. However, our experience in materials science in problems such as stress corrosion cracking and hydrogen embrittlement suggest that they mechanics and chemistry interact in important ways with important practical implications. In this talk, we will expand upon this idea and examine the chemo-mechanical coupling in solids in two examples: (i) heterogeneous catalysis on metal films and (ii) energy storage materials. In the former, we examine how elastic strain (i.e. stress) influences the catalytic reaction rate on metal films in the context of two important electrochemical reactions (hydrogen evolution reaction HER and oxygen reduction reaction ORR). Thin metal films supported on elastic substrates are uniaxially loaded in compression and tension while they participate in the HER. We show that elastic strain tunes the catalytic activity in a controlled and predictable way. Three metals that span the volcano plot were chosen: Ni (left of the volcano peak), Pt (near the volcano peak) and Cu (right of the volcano peak). The experimental results show that Pt and Ni films have increased HER activity under compressive strain; while Cu's HER activity is retarded by compressive strain. The opposite was observed under tensile strain. Experimental observations are understood and interpreted by density functional theory calculations on strained Pt, Ni, and Cu(111) surfaces.In the latter, we examine silicon, a promising anode material for lithium ion batteries. It is first shown that lithiated silicon undergoes substantial plastic deformation during lithiation and delithiation and that the energy dissipation due to plasticity is a substantial fraction of the total energy dissipation. These observations lead to conclude that the stress and potential must be coupled in silicon and this coupling is examined in terms of solution thermodynamics. It is shown that stress and potential of all electrode materials that undergo volume expansion during cycling are coupled through solution thermodynamics. We present an experimental investigation that demonstrates this effect, although the magnitude of the coupling is not satisfactorily explained by the existing theories.
Prof. Guduru’s research interests lie primarily in experimental mechanics. His research encompasses mechanics of fracture, friction, adhesion, energy storage materials, catalysis and dynamic failure of heterogeneous materials. Pradeep R. Guduru received Bachelor's degree in Mechanical Engineering from Sri Venkateswara University (India) and Master's degree in Aerospace Engineering from Indian Institute of Science. He received his PhD in Aeronautics from California Institute of Technology in 2001. Subsequently he joined the Division of Engineering at Brown University as a postdoctoral research associate and was appointed as an assistant professor of Engineering in 2002. He is currently the James R. Rice professor of engineering in Solid Mechanics at Brown University. Professor Guduru was the recipient of PECASE - Presidential Early Career Award for Scientists and Engineers – in 2007; and the National Science Foundation CAREER award in 2006. He received the William F. Ballhaus prize for outstanding doctoral dissertation in Aeronautics (Caltech, 2001), the Ernest E. Sechler Memorial Award for the most significant contributions to teaching and research in Aeronautics (Caltech, 1998).