Electrocatalyst electrochemical screening

Guerin S, Hayden BE, Lee CE, Mormiche C, Owen JR, Russell AE, Theobald B, Thompsett D. 2004. Combinatorial electrochemical screening of fuel cell electrocatalysts. J Comb Chem 6 149-158. 

Schematic of a 64-electrode cell for electrochemical screening of electrocatalysts. (Reprinted with permission from Journal of Combinatorial Chemistry, 6,149 (2004). Copyright 2004 American Chemical Society.)...

Two general techniques have been described for the high-throughput screening of electrocatalyst libraries optical screening and electrochemical screening. 

High-Throughput Electrochemical Screening of Electrocatalyst Libraries... 

Fig. 11.8 Schematic of the automated primary high-throughput electrochemical workflow employed at Symyx Technologies for the combinatorial development of new fuel cell catalysts. Individual steps of the workflow include choice of catalyst concept, design of appropriate materials library using Library Studio [31], synthesis of electrocatalyst library on electrode array wafer, XRD and EDX characterization of individual electrocatalysts before screening, high-throughput parallel electrochemical screening of library, XRD and EDX characterization of catalysts after screening, data processing and evaluation.

Structural and compositional characterization of high surface-area catalysts is crucial for evaluating whether the secondary synthesis of a particular electrocatalyst was successful. Similar to the primary screening workflow, XRD is used for the structural characterization of catalyst powders, while SEM/EDX is employed for the compositional characterization of electrocatalyst powders before and after electrochemical screening. 

Once we have developed our basic model and shown how it may be used to estab-hsh trends in electrochemical reactivity, we will take the further step of applying it to the identification of new bimetallic electrocatalysts. We will introduce simple procedures to rapidly screen bimetallic alloys for promising electrocatalytic properties, and we will demonstrate the importance of including estimates of the alloys stabihty in the screening procedure. Finally, we will give examples of successful apphcation of this method to specific problems in the area of electrocatalyst development. 

The experimental results are in complete agreement with the predictions of our computational screening approach the annealed BiPt sample shows enhanced HER activity compared with pure Pt. As mentioned above, this result is rather counterintuitive, given that Bi itself is a notoriously poor electrocatalyst for the HER [Trasatti, 1972]. Hence, it appears that our computational, combinatorial screening procedure is capable of identifying improved catalysts for electrochemical reactions that are not immediately apparent from simple intuitive arguments. 

The above results demonstrate that computational screening is promising technique for use in electrocatalyst searches. The screening procedure can be viewed as a general, systematic, DFT-based method of incorporating both activity and stability criteria into the search for new metal alloy electrocatalysts. By suggesting plausible candidates for further experimental study, the method can, ultimately, result in faster and less expensive discovery of new catalysts for electrochemical processes. 

Fernandez JL, White JM, Sun YM, Tang WJ, Henkelman G, Bard AJ. 2006. Characterization and theory of electrocatalysts based on scanning electrochemical microscopy screening methods. Langmuir 22 10426-10431. 

This chapter presents the design and application of a two-stage combinatorial and high-throughput screening electrochemical workflow for the development of new fuel cell electrocatalysts. First, a brief description of combinatorial methodologies in electrocatalysis is presented. Then, the primary and secondary electrochemical workflows are described in detail. Finally, a case study on ternary methanol oxidation catalysts for DMFC anodes illustrates the application of the workflow to fuel cell research. 

A third screening method for arrays of electrocatalysts was recently introduced by Hillier and coworkers [15, 29, 30]. Using a scanning electrochemical microscope (SECM), a microelectrode tip is moved over an electrocatalyst array. The resulting electrochemical feedback currents are measured and used to generate an activity map of the electrocatalyst library. This method does not require individual electronic addressability for each electrocatalyst... 

Fernandez et al. used a combined high throughput electrocatalyst study and DFT study to examine Pd-Co electrocatalysts for oxygen reduction. They screened an array of electrocatalysts using a scanning electrochemical microscope to assess the activity of each element. The DFT study was performed to help identify the role of Co in the system. They examined oxygen molecule adsorption, dissociation and... 

Also, a group of researchers at University of Texas at Austin used inkjet for rapid screening of non-platinum electrocatalysts such as Pd-Ti and Pd-Co-Au which show electrochemical performance similar to that found with commercial platinum catalysts [35]. 

Walsh, D.A., Fernandez, J.L., and Bard, A.). (2006) Rapid screening of bimetallic electrocatalysts for oxygen reduction in acidic media by scanning electrochemical microscopy. J. Electrochem. Soc., 153, E99-E103. 

Particle size effects of highly dispersed supported catalysts (Pt) on the hydrogen oxidation reaction were evaluated by the same authors using this technique (97). Moreover, electrocatalysts for oxidation of methanol were screened using a technique called scanning differential electrochemical mass spectrometry (98, 99). This method uses a capillary probe scanned over the array that allows the intake and detection by mass spectrometry of products generated locally on each electrode. 

The activity and performance of fuel cell electrocatalysts need to be evaluated in terms of electrochemieal parameters, including current density and electrode potential. Electrochemieal sereening methods have been identified as ideal direct approaches for combinatorial studies of fuel cell catalysts. Two types of electrochemical measurement systems have been developed for combinatorial screening of fuel cell catalysts the array half-cell system and the array single-cell system. 

Figure 12.9. Schematic drawing of an assembled electrochemical cell for combinatorial screening catalyst libraries prepared by sputter deposition [22], (Reprinted from Joiunal of Power Sources, 163(1), Cooper JS, McGinn PJ. Combinatorial screening of thin film electrocatalysts for a direct methanol fuel cell anode, 330-8, 32006, with permission from Elsevier.)...

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