[Paper Review] Hydrogen Peroxide Formation Rates in a PEMFC Anode and Cathode: Effect of Humidity and Temperature

Vijay A. Sethuraman, John W. Weidner+3 more|Scholar Commons (University of South Carolina)|Feb 20, 2020

Fuel Cells and Related Materials42 references127 citations

TL;DR

The paper estimates H2O2 formation rates in PEMFCs at both anode and cathode under varying humidity, temperature, and O2 concentration using RRDE, linking H2O2 yield to water activity and O2 levels.

ABSTRACT

Hydrogen peroxide (H2O2) formation rates in a proton exchange membrane (PEM) fuel cell anode and cathode were estimated as a function of humidity and temperature by studying the oxygen reduction reaction (ORR) on a rotating ring disc electrode (RRDE). Fuel cell conditions were replicated by depositing a film of Pt/Vulcan XC-72 catalyst onto the disk and by varying the temperature, dissolved O2 concentration and the acidity levels in hydrochloric acid (HClO4). The HClO4 acidity was correlated to ionomer water activity and hence fuel cell humidity. The H2O2 formation rates showed a linear dependence on oxygen concentration and square dependence on water activity. The H2O2 selectivity in ORR was independent of oxygen concentration but increased with decrease in water activity (i.e., decreased humidity). Potential dependent activation energy for the H2O2 formation reaction was estimated from data obtained at different temperatures.

Motivation & Objective

• Understand how humidity (water activity) and temperature affect H2O2 formation rates in PEMFCs.
• Quantify the dependence of H2O2 formation on oxygen concentration and water activity.
• Assess the selectivity of the oxygen reduction reaction toward H2O2 under different operating conditions.
• Relate acidity (via HClO4) to ionomer water activity to emulate fuel cell humidity.
• Provide activation energy insights for H2O2 formation through temperature variation.

Proposed method

• Use rotating ring disc electrode (RRDE) to study ORR and H2O2 formation on a Pt/Vulcan XC-72 catalyst film.
• Replicate fuel cell conditions by controlling temperature, O2 concentration, and acidity via HClO4 to adjust water activity.
• Measure H2O2 formation rates and analyze their dependence on O2 concentration and water activity.
• Investigate potential dependence to estimate activation energy for H2O2 formation across temperatures.

Experimental results

Research questions

• RQ1 How do humidity (water activity) and temperature influence H2O2 formation rates during ORR on PEMFC electrodes?
• RQ2 What is the relationship between O2 concentration and H2O2 formation rate and selectivity?
• RQ3 How does H2O2 selectivity change with decreasing water activity (humidity)?
• RQ4 Can acidity (via HClO4) be used to emulate fuel cell humidity effects on H2O2 formation?
• RQ5 What is the activation energy for H2O2 formation as a function of temperature?

Key findings

• H2O2 formation rates increase linearly with oxygen concentration.
• H2O2 formation rates show a quadratic (square) dependence on water activity.
• H2O2 selectivity is independent of oxygen concentration but increases as water activity decreases.
• HClO4 acidity correlates with ionomer water activity, enabling humidity control in experiments.
• Activation energy for H2O2 formation can be estimated from data collected at different temperatures.