Electrocatalysis and Catalyst Screening from Density Functional Theory Calculations - Fuel Cell Catalysis: A Surface Science Approach - page 77

and properties from known catalysts, however, a different type of search strategy must be
developed. For this purpose, we propose a computational, combinatorial search strategy.
Combinatorial screening of catalysts using experimental techniques is a well-
established technique in the catalysis industry [Corma et al., 2005; Hagemeyer et al.,
2001; Liu et al., 2003; Saalfrank and Maier, 2004; Yaccato et al., 2004]. To date, how-
ever, only limited efforts have been made to use computational techniques to screen for
improved catalysts [Andersson et al., 2006; Besenbacher et al., 1998; Faglioni and
Goddard, 2005; Gong et al., 2003; Greeley and Mavrikakis, 2004, 2005; Greeley
et al., 2002; Hammer et al., 1996; Jacobsen et al., 2001; Kitchin et al., 2004; Linic
et al., 2004; Muller et al., 2003; Pallassana and Neurock, 2000], and no successful com-
putational, combinatorial searches have been performed to find improved electrocata-
lysts. Given the expense associated with experimental combinatorial electrocatalyst
searches, it would seem to be well worth the effort to develop corresponding compu-
tational techniques; these techniques could be used to identify a limited number of
highly promising candidate electrocatalysts that could, in turn, be tested experimentally.
By reducing the number of electrocatalysts to be experimentally tested, considerable
speedup of catalyst discovery could be realized. In addition, by pointing to particular
catalyst structures that might not be intuitively obvious, computational screening tech-
niques might identify novel structures for known catalysts; these new structures, in
turn, could exhibit improved catalytic properties.
3.6.1 The Hydrogen Evolution Reaction
To illustrate the power and flexibility of computational, combinatorial electrocatalyst
searches, we first present a general search paradigm, and we apply this paradigm to the
hydrogen evolution reaction (HER). The HER is an attractive electrochemical reaction
with which to illustrate the power of computational search. There is significant techno-
logical interest in the reaction, because of the important role that it plays in electrodeposi-
tion and corrosion of metals in acids, in storage of energy via H 2 production, and as the
microscopic reverse of the hydrogen oxidation reaction in low temperature fuel cells
[Hamann et al., 1998; Jacobson et al., 2005]. These applications have motivated a
significant amount of research on the HER, from the development of fundamental reac-
tivity theories to the investigation of biomimetic catalysts for the reaction [Bockris et al.,
1998; Conway and Bockris, 1957; Gerischer, 1958; Harinipriya and Sangaranarayanan,
2002; Hinnemann et al., 2005; Krishtalik, 1966; Medvedev, 2004; Parsons, 1958; Tard
et al., 2005; Trasatti, 1972, 1977, 1995]. An additional benefit of choosing the HER to
illustrate the potential of theoretical search techniques is that the reaction is quite tractable
from a computational point of view; indeed, it has recently been shown that a single
adsorption energy can accurately predict trends in HER activity [Greeley et al., 2006b;
Nørskov et al., 2005] (see also the discussion below).
3.6.2 General Computational Screening Procedure
Although there are many procedures that could, in principle, be used to apply compu-
tational techniques to catalyst discovery processes, we have found that the following