Graphene-Based Catalysts for the Reduction of Oxygen at Fuel Cell Cathodes

Meital Eliyahu, Department of Chemical Engineering, Ben-Gurion University, Beer-sheva, Israel
Eli Korin, Department Of Chemical Engineering, Ben-gurion University, Beer-sheva, Israel
Armand Bettelheim, Department Of Chemical Engineering, Ben-gurion University, Beer-sheva, Israel

Oxygen reduction reaction (ORR) 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 ORR 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 ORR 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 ORR, 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).


Graphene-Based Catalysts for the Reduction of Oxygen at Fuel Cell Cathodes Meital Eliyahu, Department of Chemical Engineering, Ben-Gurion University, Beer-sheva, Israel Eli Korin, Department Of Chemical Engineering, Ben-gurion University, Beer-sheva, Israel Armand Bettelheim, Department Of Chemical Engineering, Ben-gurion University, Beer-sheva, Israel Oxygen reduction reaction (ORR) 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 ORR 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 ORR 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 ORR, 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).

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