Evaluation of nitrided titanium separator plates for proton exchange membrane electrolyzer cells

• We assess performance of nitrided titanium flow plates in PEM electrolysis cells.
• Nitrided Ti increases performance by 3–13% compared to untreated Ti.
• Nitrided Ti is susceptible to oxidation under anodic PEM-EC operating conditions.
• Even though oxidized, the thermally nitrided Ti demonstrates higher performance.
• Unlike surface abrasion/Pt-plating, nitrided Ti does not incur H2 embrittlement.

Proton exchanges membrane (PEM) regenerative fuel cell electrolysis of water is of great recent interest as a hydrogen generation technology. Anode side titanium current collectors and separator plates used in these applications typically employ coatings of platinum group metals to achieve durability and performance requirements in the high voltage, oxidizing environment. The present work assessed the potential for lower cost surface modified titanium by both thermal (gas) nitridation and plasma nitridation approaches. The nitrided Ti was found to result in far less hydrogen uptake in coupon testing than did Pt-plated Ti. Short-term (48 h) single-cell performance at 25 °C was approximately 13% better (lower voltage) at 1.2 A cm−2 for thermal and plasma nitrided plates vs. untreated Ti. However, at 50 °C and 1.5 A cm−2, the thermally nitrided plate exhibited only on the order of 3% better behavior (lower voltage) compared to the untreated Ti and plasma nitrided Ti. Durability testing for 500 h resulted in only a minor degradation in cell performance, on the order of 1–2% voltage increase, with the best behavior exhibited by the thermally nitrided Ti plate. Despite their relatively stable cell performance, extensive local oxidation of the thermally nitrided and plasma nitrided flow field regions was observed.