Fabrication of superhydrophobic TiN-coated SS304 flow field plates via femtosecond laser processing for fuel cell applications

Abstract

Fuel cell systems are potential power sources for transportation applications due to their high energy efficiency, rapid start-up, and low emissions. The bipolar plates, which constitute the major volume of the fuel cell stack, are usually made of graphite. However, the brittle nature of graphite plates makes them unable to resist shock or vibration; as a result, metallic plates are considered as bipolar plates in fuel cell stacks due to their resistance to impact, strength, and cost-effective manufacturing. However, surface corrosion and hydrophobicity are significant challenges that need to be overcome in the fuel cell working environment. In this study, the resistance of SS304 plates to the electrochemical environment is enhanced by coating them with TiN, while the hydrophobic surface of the stainless steel is induced using femtosecond lasers and vacuum treatments. The effects of treatment conditions on surface morphology, contact angle, interfacial resistance, and fuel cell performance are investigated. Results show that linearly polarized lasers with scanning speeds of 20 mm s⁻¹ and 80 mm s⁻¹ are the optimum treatments for SS304 and TiN-coated SS304 plates, respectively. The TiN coating greatly improves the performance of SS304 flow field plates, with a maximum power density of 0.9 W cm⁻² compared to 0.44 W cm⁻² without the coating. Fuel cells consisting of laser-processed TiN-coated SS304 flow field plates can also operate durably with hydrogen and oxygen at the anode and cathode, respectively.