Use of porphyrin-graphene nanostructures as fuel cell cathode catalysts.

Meital Eliyahu, Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer Sheva, Israel
Eli Korin, Department Of Chemical Engineering, Ben-gurion University Of The Negev, Beer Sheva, Israel
Armand Bettelheim, Department Of Chemical Engineering, Ben-gurion University Of The Negev, Beer Sheva, Israel



Oxygen reduction reaction occurs on the cathode of fuel cells. This reaction is considered to be very sluggish and therefore it is a necessity to use catalysts to improve the kinetics. Electrocatalytic reduction of oxygen occurs in 2 main pathways: direct reduction of the oxygen to water by a four-electron pathway and indirect reduction of oxygen by a two-electron pathway, forming hydrogen peroxide as an intermediate.
Although catalysts for oxygen reduction reaction that exhibit a very good activity exist, most of them are based on noble metal catalysts, which are considered to be very expensive. Developing efficient non-noble metal catalysts for the oxygen reduction reaction is one of the main keys to the production of commercially durable fuel cell devices for future renewable energy applications. Porphyrins have been extensively studied and demonstrated a good catalytic activity for oxygen reduction reaction, but most of them show activity only for the two-electron pathway to yield H2O2. The present study deals with interactions, such as π-π stacking, occurring between metalloporphyrin and graphene derivatives and their effect on the activity of the systems towards O2 reduction.

Stable suspensions were obtained from 5,10,15,20-tetrakis(1-methyl-4-pyridinio) porphyrin (CoTMPyP) and graphene oxide (GO) in a wide range of pH. UV/Vis spectroscopy measurements for suspensions of CoTMPyP-GO at pH 7.2 showed a 9 nm red shift for the CoTMPyP Soret band observed around 433 nm, thus indicating π-π stacking. Cyclic voltammetry measurements for glassy carbon electrode coated with CoTMPyP-GO showed that the O2 catalytic reduction peak is shifted 200 mV anodically in comparison to that observed for CoTMPyP (-0.09 and -0.29 V vs. Ag/AgCl, respectively).