The material presented here is based upon work supported by the National Science Foundation under Award No. EEC-0813570.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Introduction

Methods

Synthesis

1. Incipient wetness impregnation with Pt salt/Water/Ethanol

solution and a chosen carbon nanotube followed by air drying

2. Reduction of the catalysts in a tube furnace under hydrogen

at 200oC for 30min shown in figure 3

3. Catalyst dispersion in 0.5wt% nafion solution by sonication

4. Placement 100μL of catalyst on glassy carbon electrode

followed by air drying as shown in figure 4

Testing

1. A standard three electrode set up was constructed with a

Ag/AgCl reference electrode, Pt wire counter electrode, and

glassy carbon working electrode shown in figure 5

2. All experiments were conducted in 0.5M H2SO4

3. Pre-treatment run using voltages as shown in figure 6

4. CO stripping technique performed

5. Surface area integration determined

Determination of the Active Sites on Platinum/Carbon Electrocatalysts Shelly Vanyo, Summer 2013 RET Project

Project Advisors: John Matthiesen & Dr. Jean-Philippe Tessonier Center for Biorenewable Chemicals, Iowa State University, Ames, IA 50010

Abstract

As the global human population increases, so does our per capita energy demands. Yet, our society still relies heavily on petroleum-based chemical energy. One focus of Chemical Engineering is to design catalysts, which are materials that increase the rate of a reaction without being appreciably consumed.1

However, a limiting factor of identifying ideal catalysts is the ability to be highly active, stable, and selective towards their reaction.1 In the following study electrocatalysts were synthesized to improve the hydrogen evolution reaction and oxygen evolution reaction, shown in figure 1.

Figure 1: Hydrogen Evolution Reaction & Oxygen Evolution Reaction2

Acknowledgements

When comparing electrocatalysts, the quality of the material needs to be

referenced to a defined quantity of the catalyst. Electrocatalyts can be

referenced to the mass of the electrocatalysts, geometric surface area of

an electrode, geometric surface area of the electrocatalyst, or to the

electrochemical active surface area of the material. As a researcher

approaches the end of the previous list, the quality of comparing

electrocatalysts increases as well as the difficulty of obtaining the value.3

The electrochemical active surface area (ECSA) is determined utilizing

two different techniques. This first technique is an integration under the

hydrogen desorption region correcting for the double layer. The values

calculated are then referenced towards 210μC/cm2, the charge of

stripping a monolayer of hydrogen on platinum.4 Carbon Monoxide (CO)

stripping is then used as the second technique to corroborate the

surface area determined by the previous integration. The integration in

the CO oxidation region is compared to a value of 420μC/cm2, the

charge of stripping a monolayer of CO on platinum.4

The final objective of this project is to create active, stable

electrocatalysts for the hydrogen evolution reaction and the oxygen

evolution reaction. Platinum surface atomic concentrations for a series of

5, 10, 20wt% Platinum/Carbon (Pt/C) electrocatalysts were explored

using cyclic voltammetry. However, only the 20wt% Pt/C sample is

shown. Figure 2 shows a representative SEM image of Pt supported on

high temperature annealed carbon nanotubes (here 5 wt% Pt/C).

National Science Foundation, sponsored by award No. EEC-0813570

Iowa State University

Dr. Adah Leshem, Program Director

Figure 2

SEM of 5wt % Pt/C

Future Research Determination of the electrochemical surface area on other

high temperature annealed carbon supports

Results

Works Cited 1 Satterfield, C. N. Heterogeneous Catalysis in Industrial Practice. 2nd Ed. (McGraw-Hill, Inc., 1991). 2 Greeley, J. & Markovic, N. The road from animal electricity to green energy: combining experiment and

theory in electrocatalysis. Energy & environmental science 5, 9246-9256 (2012). 3 Jaramillo, T. Energy Tutorial: Electrocatalysis 101. (Stanford, 2012). 4 Chen, D. et al. Determining the Active Surface Area for Various Platinum Electrodes. Electrocatalysis 2,

207-219 (2011).

Pretreatment-H2SO4

1. CV: 200mV/s

2. CA: 5min @ -0.3V vs. Ref

3. CV: 200mV/s

4. CA: 5min @ -0.3V vs. Ref

5. CV: 200mV/s figure 7

CO Stripping-H2SO4

1. CA: 1 hr 25 min at -0.094 V vs. Ref

2. CV: 10mV/s figure 8

Figure 4: Glassy Carbon

electrode with catalyst

Figure 5: Electrochemical

setup

Figure 6: Pre-Treatment and CO

stripping parameters

UPD-H Area

Apt = 20.05cm2

CO-Oxidation Area

Apt = 18.26cm2

UPD-H Area

Apt = 19.13cm2

Figure 7: Cyclic Voltammetry curve of step five

in the catalyst pretreatment

Figure 8: Cyclic Voltammetry curve of

step 2 in CO stripping

Figure 3: Tube furnace

Stripping of the under potential deposition region of hydrogen

(UPD-H) occurs around 0.0V as shown in figures 7 and 8. This is

indicative of how much hydrogen was adsorbed. By comparing this

value to the charge of the formed monolayer, 210 C/cm2, the

surface area can be calculated.4 This change is affected by the

surface characteristics and is necessary to ensure an effective

monolayer.

CO is easily adsorbed to the electrode surface and displaces pre-

adsorbed hydrogen. During CO stripping, CO is desorbed from the

electrocatalyst surface. The value is then compared to desorption

value of a monolayer of CO, which is 420 C/cm2.4 It is important to

ensure oxygen has been removed during these measurements.