Effects of Pb on Electrocatalysis of Alcohol Oxidation Reaction on Pt/C Catalysts in Alkaline Media
Authors: Chen Rongrong , Guo Junsong 
Published: February 2020

Electrocatalysis of ethanol oxidation reactions (EORs)  and methanol oxidation reactions (MORs) in alkaline media has gained great research interests due to the development of alkaline anion exchange membranes.  The EOR and MORs kinetics are more facile in alkaline media than those in acid media. The most importantly, there are more choices of materials to be used as the electrocatalysts for the EOR or MOR since these materials are stable in the alkaline media, but not in the acid media. Although extensive research has been done worldwide related to electrocatalysis of EORs and MORs in both acid and alkaline media, the EOR or MOR mechanisms are still not well understood.  It still remains as a major challenge of reducing the overpotentials of EORs and MORs in low temperature fuel cells. In this work, we aim to study effects of Pb on electrocatalysis of EORs and MORs on Pt/C catalysts in alkaline media.

The commercial available Pt/C catalysts were performed electrochemical characterizations in a standard tri-electrode electrochemical cell with a graphite column serving as the counter electrode and a Hg/HgO/1.0 M OH- electrode (0.098 V vs. NHE) as the reference electrode in an argon-saturated or ethanol or methanol-contained 1 M NaOH solution without or with 1mM lead(II) acetate (Sigma-Aldrich) presented. The EOR or MOR activities of the catalysts were also characterized with a single direct alcohol fuel cell. The membrane electrode assemblies (MEA) with an active electrode area of 4.5 cm2 were comprised of a catalyst coated membrane (CCM), a Ni foam (Hohsen Corp.) as the anode backing layer and a TGP-H-090 carbon paper (Toray) as the cathode backing layer. The anode catalyst ink was prepared by mixing the catalyst with Nafion solution. The cathode catalyst ink was prepared by ultrasonicating 8mg MnO2 nanorod catalyst, 8 mg active carbon (BP2000, Cabot Corp. ) and the A4 ionomer (Tokuyama Co.). The catalyst/ionomer (Nafion or A4) weight ratio is kept at 80:20 in both anode and cathode. A fuel cell test system (Scribner Associates Model 850e) was used for controlling the cell temperature, cathode humidity, O2 flow rate. The temperature of the fuel cell was maintained with a tolerance of ± 0.2 °C. The anode solution flow rate was controlled ESI's MP2 micro peripump (elemental scientific Inc.)

CV curves were obtained with the Pt/C in Ar-saturated 1.0 M NaOH or 1.0 M ethanol (or methanol) and 1.0 M NaOH solution without or with 1mM Pb2+ presented.  From the CV curves obtained in the 1.0 M NaOH solutions, the Pb2+ presence in the solution was found to alter surface characteristics on Pt/C catalysts. The EOR and MOR activities were also affected accordingly.  Both CV and chronoamperometry (CA) measurements indicate that the presence of Pb2+ in the solution leads to the increase of EOR and MOR  kinetics on the Pt/C catalysts, agree with what have been reported.  Detailed fuel cell characterizations with the Pt/C anode catalysts using fuels without and with 1mM Pb2+ presence were performed. Combining the electrochemical measurements and fuel cell test results, effects of Pb on the electrocatalysis of EOR and MOR on the Pt/C catalyst in alkaline media will be presented.

Acknowledgements

We acknowledge financial supports from the National Science Foundation (NSF) (Contract 1402422).