Generalizing the Design Principles of Pt-Based Alloy Catalysts with Improved ORR Performance and Durability

Since the discovery of Pt skin type Pt₃Ni catalysts with superior performance towards oxygen reduction reaction,[1] there has been a blossoming of Pt-based alloy catalysts for ORR and various other applications.[2,3] In last couple years, the focus has slowly shifted from catalysts with monolayer skins to those with thicker Pt overlayers for the sake of improving the stability.[4-6] But the decrease in the activity has been observed with increasing overlayer thickness. Thus, how to increase the stability of catalysts, with no harm on the activity, or even simultaneously increase activity, have been the focus of the current catalyst development, but few systematic design principles have been established to guide these efforts. It is worsened by a lacking of atomic-scale understanding of water/electrode interface and consequently the bonding nature of ORR intermediates. For example, it is still in the debate regarding whether hydrated OH or non-hydrated OH is the plausible ORR intermediate.

In the present talk, we will start by determining the atomic-scale structure of oxygenated species at water/electrode interfaces under electrochemical ORR conditions, by combining a careful calibration of Density Functional Theory (DFT)-determined energetics, the liquid water/Pt interfaces generated from ab-initio molecular dynamics (AIMD) simulations and a detailed simulation of X-ray Photoelectron Spectroscopy (XPS) signatures.[7] In the second part, we will investigate the structure and the stability of Pt overlayers with various thickness. We will further analyze their activity based on a scheme established through above calibration. Then, general design principles will be proposed for searching for ORR catalysts with improved stability and activity. We will close by comparing the predicted stability and activity of various catalysts with those available in the literature and from our collaborators.

[1] V.R. Stamenkovic, B. Fowler, B.S. Mun, G.F. Wang, P.N. Ross, C.A. Lucas, N.M. Markovic, Science 315 (2007) 493.

[2] J. Greeley, I.E.L. Stephens, A.S. Bondarenko, T.P. Johansson, H.A. Hansen, T.F. Jaramillo, J. Rossmeisl, I. Chorkendorff, J.K. Nørskov, Nat. Chem. 1 (2009) 552.

[3] P. Strasser, S. Koh, T. Anniyev, J. Greeley, K. More, C. Yu, Z. Liu, S. Kaya, D. Nordlund, H. Ogasawara, M.F. Toney, A. Nilsson, Nat Chem 2 (2010) 454.

[4] M. Escudero-Escribano, P. Malacrida, M.H. Hansen, U.G. Vej-Hansen, A. Velázquez-Palenzuela, V. Tripkovic, J. Schiøtz, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff, Science 352 (2016) 73.

[5] N. Todoroki, H. Watanabe, T. Kondo, S. Kaneko, T. Wadayama, Electrochim. Acta 222 (2016) 1616.

[6] M. Asano, R. Kawamura, R. Sasakawa, N. Todoroki, T. Wadayama, ACS Catal. 6 (2016) 5285.

[7] Z. Zeng, J. Greeley, Nano Energy 29 (2016) 369.