Combinatorial electrochemistry: Discovery and characterization of new direct methanol fuel cell electrocatalysts

The strength of combinatorial chemistry lies in the idea that many different materials can be quickly and efficiently searched for a particular property. Presented here is a combinatorial method to search for new electrocatalysts using the example of anode and cathode materials for the direct methanol fuel cell (DMFC). Half cell reactions for the DMFC, like all fuel cells, involve an imbalance of ions. In the case of a DMFC, methanol oxidation generates protons at the surface of the anode, and oxygen reduction consumes protons at the cathode. In both cases, there is a significant pH change at the electrode surface under diffusion-controlled conditions. Therefore, a library of electrode arrays of different composition can be rapidly screened and ranked for activity using a solution-phase pH indicator which fluoresces brightly in one form, but does not fluoresce in another form. This technique allows for rapid identification of active catalysts from an array of several hundred electrodes, while allowing one to ignore the uninteresting majority of compositional phase space.; Upon discovering new “leads”, individual compounds were tested and characterized to investigate why the new materials were active. Using the combinatorial technique, we discovered new methanol electro-oxidation catalysts (quaternary Pt-Ru-Os-Ir alloys) that appear to have a different reaction order with respect to methanol than the previously known catalyst. We also discovered new methanol tolerant cathode materials using this technique. Although this study was strictly confined to fuel cell electrocatalysts, this technique could be used to discover new materials for other electrocatalytic processes, batteries, or organic electrosynthesis.