Abstract
Research on the conductivity and corrosion resistance of stainless steel bipolar plates in a proton exchange membrane fuel cell (PEMFC) is commonly performed in a normal-temperature environment (about 20 °C). However, these fuel cells must function in low-temperature environments (lower than 0 °C) in some conditions, such as in vehicle fuel cells and in portable power supplies that operate during the winter in northern China. Stainless steel bipolar plates have higher requirements in terms of their hydrophobic and anti-icing properties, in addition to needing high conductivity and corrosion resistance. In this study, carbon nanotubes (CNTs) are grown on the surface of 304 stainless steel (304 SS) without a catalyst coating by plasma-enhanced chemical vapor deposition (PECVD), which is a simple and cheap method that allows stainless steel to be used as bipolar plates in low-temperature environments. The Raman spectroscopy and scanning electron microscopy (SEM) results show that the CNTs grown on the surface of 304 SS have different morphologies. The stainless steel samples with different CNT morphologies are tested by hydrophobicity and in situ icing experiments to prove that vertical CNTs can achieve a superhydrophobic state and have good anti-icing properties. The interfacial contact resistance (ICR) of the bare 304 SS and the 304 SS with vertical CNTs is compared by voltammetry, and then the corrosion resistances of both types is compared in a simulated PEMFC environment via a three-electrode system. Consequently, the ICR of the 304 SS with vertical CNTs was lower than the bare 304 SS. The corrosion potential was positive, and the corrosion current density was greatly reduced for the stainless steel with vertical CNTs grown directly on its surface when compared with the bare 304 SS. The experimental results show that vertical CNTs have good application prospects as bipolar plates for PEMFCs in low-temperature environments.
Highlights
Proton exchange membrane fuel cells (PEMFCs) are widely used in transportation, residential power generation and portable power supplies due to their high reliability, high output power and environmental friendliness [1,2]
The results prove that the morphology of the vertical carbon nanotubes (CNTs) on the stainless steel surface can improve hydrophobicity and anti-icing performance
Sample A was not subjected to plasma treatment, and the hydrofluoric acid (HF)-etched stainless steel surface was divided into large islands and particles of different sizes
Summary
Proton exchange membrane fuel cells (PEMFCs) are widely used in transportation, residential power generation and portable power supplies due to their high reliability, high output power and environmental friendliness [1,2]. A stainless steel bipolar plate dissolves metal ions that may contaminate the membrane electrodes because the PEMFC works in weakly acidic environments [11] To solve these problems and improve the performance of stainless steel bipolar plates, it is necessary to modify the surface of the stainless steel or provide a coating protection. The corrosion resistance and conductivity of a modified stainless steel bipolar plate in a fuel cell operating at a normal temperature will be greatly improved in the future [23,24]. The traditional modification method of a stainless steel bipolar plate can effectively improve conductivity and corrosion resistance, but there have been few studies on the hydrophobic and anti-icing properties at low temperatures. The modification method of directly arranging vertically aligned CNTs on the surface of stainless steel can improve conductivity and corrosion resistance and provide better hydrophobicity and anti-icing performance. CNTs on 304 SS bipolar plate fuel cells in a low-temperature environment is feasible
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