05Checking performance and reading data

Which condition each published figure belongs to

Half-cell values and cell values do not sit side by side

A three-electrode half-cell test measures the catalytic activity of a single electrode against a reference electrode. A cell voltage adds the counter electrode, the membrane and ionomer, contact resistance and electrolyte resistance on top. A half-cell Tafel slope or potential therefore cannot be compared directly with a cell voltage.

Use half-cell values

To compare catalysts: how different they are on the same substrate under the same conditions.

Use cell and stack values

To see what voltage it takes under the conditions you will use. The membrane and cell design are part of the result.

Comparing your measurement with the datasheet

The same electrode gives a different cell voltage under different conditions: at lower temperature or concentration, the voltage at the same current density rises. Match the following before you compare.

• Temperature: the temperature the cell actually reached, not the setpoint.
• Electrolyte concentration. It differs from chart to chart in the datasheets; check the table above.
• The area behind the current density. State which area you divided by; a different basis turns the same cell into a different curve.
• Whether iR correction was applied, and the measurement mode: galvanostatic or potentiostatic, and the scan rate.
• Settling: whether you measured after the voltage had settled at rated current.
• Electrode condition: fresh, or already run.