Catalyst Screening Using SECM

Fast screening of materials for their catalytic activity has gained popularity in the area of polymer electrolyte fuel cells. The method involves preparing a combinatorial library of various candidate catalysts of different composition and a quick evaluation of a key electrochemical parameter such as open-circuit potential or high-frequency impedance. This enables a quick screening of an array of materials to identify 

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The SECM capacity for rapid screening of an array of catalyst spots makes it a valuable tool for studies of electrocatalysts. This technique was used to screen the arrays of bimetallic or trimetallic catalyst spots with different compositions on a GC support in search of inexpensive and efficient electrocatalytic materials for polymer electrolyte membrane fuel cells (PEMFC) [126]. Each spot contained some binary or ternary combination of Pd, Au, Ag, and Co deposited on a glassy carbon substrate. The electrocatalytic activity of these materials for the ORR in acidic media (0.5 M H2S04) was examined using SECM in a rapidimaging mode. The SECM tip was scanned in the x—y plane over the substrate surface while electrogenerating 02 from H20 at constant current. By scanning... 

Bard et al. are using SECM in G/C mode to screen the activity of binary and ternary metallic arrays for electro-reduction of oxygen (54, 1(X), 101). They used the TG/SC described in Section 12.4.3.1 to image the activity of both multi-metaUic and wired enzyme catalyst spots deposited on single glassy carbon substrates (Figures 12.23 and 12.24). Different from the previous approach, the spots do not need to be individually connected... 

High-Throughput Screening of ORR Catalysts Using SECM... 

Smaller catalyst libraries have been investigated by several other research groups. For example, Chen et al. electrodeposited a small library of noble metals (Pt, Ru, Rh, and Au) by means of a capillary-based droplet cell onto carbon nanotubes predeposited on glassy carbon by electrophoretic accumulation, and screened their ORR activity in a 0.1 M phosphate solution using the oxygen competition mode (pH = 6.7) [68, 82]. Our group employed RC-SECM to map the ORR activity of Pt, and Pt-based alloy nanoparticles, including core-shell structures... 

Besides SECM, other speetroseopie mefliods, such as scanning differential electrochemical mass spectrometry (SDEMS) and IR thermography, were also used as combinatorial screening methods for fuel cell electrocatalysis. The principle of SDEMS is to use mass spectrometry to locally measure dissolved gases and volatile liquid species near flie surfaces of catalyst arrays. IR thermography is based on reaction heat mapping. The heat results from the fuel cell electrochemical reactions on the catalyst arrays. Both methods can obtain reaction... 

When the species to be studied cannot be conveniently generated at an electrode and no product of the electrode reaction can be detected, then SECM shielding (Figure 16.3d) can be used to screen an array. In shielding, the same reaction occurs at the tip and the substrate so that the current at the tip is decreased compared to what would be observed with an insulating substrate. " Thus the tip is shielded by and competes with the substrate for the same reactant A reactant in bulk solution can be studied by noting how well the substrate competes with the tip for consumption of the reactant This approach, also called redox competition (RC-SECM), was used to study the ORR on model Pt and An catalyst spots as an alternative to TG/SC. " ... 

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