Simulated Proton Exchange Membrane Fuel Cell Cathode Research Articles

Nanostructured multilayer Cr/CrN coatings on 316L stainless steel for proton exchange membrane fuel cell bipolar plates

Nowadays, hybrid surface modification approaches offer tailored solutions for improving the corrosion resistance and electrical conductivity of the bipolar plates (BPPs) in proton exchange membrane fuel cells (PEMFCs). In the present study, a combination of plasma nitriding and physical vapor deposition (PVD) processes was used to apply a nanometric Cr/CrN multilayer coating onto 316L stainless steel (SS316L) bipolar plates. The performance of the resulting plasma nitrided, PVD-coated, and combined plasma nitriding/PVD-coated SS316L BPPs was examined by phase and morphological characterizations, surface wettability measurements, interfacial contact resistance (ICR), and electrochemical investigations. Potentiodynamic and potentiostatic polarization evaluations, electrochemical impedance spectroscopy (EIS) and Mott-Schottky asessments were conducted on the coated samples in a simulated PEMFC cathode environment at temperatures of 25 °C and 75 °C. Results indicated that the Cr/CrN multilayer coating deposited on the plasma-nitrided 316L BPP exhibited a remarkable 100-fold improvement in corrosion resistance compared to the uncoated substrate. Also, the combination of nitriding and PVD resulted in a significant reduction of the ICR from 186 mΩ cm2 for the uncoated SS316L to 10.2 mΩ cm2 for the coated sample. Multilayer coatings based on the combination of plasma nitriding and PVD treatment can identified as promise candidates for BPP applications.

Effect of nitrogen pressure on the microstructure, conductivity, and corrosion resistance of ZrN-coated stainless steel as bipolar plate for proton exchange membrane fuel cell

Zirconium nitride (ZrN) coatings were deposited on the stainless steel using multi-arc ion plating under varying nitrogen partial pressures (PN) ranging from 0.5 to 3.5 Pa. The effect of phase composition, microstructure, and surface morphology on the corrosion resistance and conductivity of the ZrN-coated stainless steel in a simulated proton exchange membrane fuel cell (PEMFC) cathode environment was systematically explored. XRD and TEM revealed that the columnar-structured ZrN coating mainly comprised the fcc-ZrN phase. The Zr3N4 phase was discovered near the substrate during coatings prepared at low nitrogen partial pressures. Surface defects were reduced at nitrogen partial pressures exceeding 2.5 Pa. The ZrN coating exhibited enhanced corrosion resistance and conductivity (ZrN-3.5, Ecorr = 0.307 V, Icorr = 2.085 × 10−7 A/cm2, Rct = 1.125 × 105 Ω·cm2) compared to bare stainless steel in the simulated PEMFC cathode environment. The presence of surface defects influenced the corrosion resistance, while differences in conductivity were related to the phase composition and microstructure of the coating. Thus, the findings indicate that ZrN coatings prepared under optimal deposition conditions can have potential applications in PEMFC bipolar plates.

Corrosion Resistance and Conductivity of Ta-Nb-N-Coated 316L Stainless Steel as Bipolar Plates for Proton Exchange Membrane Fuel Cells

The large-scale application of stainless steel (SS) bipolar plates (BPs) in proton exchange membrane fuel cells (PEMFCs) is mainly limited by insufficient corrosion resistance and electrical conductivity. In this work, Ta-Nb-N coatings were prepared on 316L SS substrates by unbalanced magnetron sputtering to improve corrosion resistance and conductivity. The Ta-Nb-N coatings had a dense structure without obvious defects. In simulated PEMFC cathode environments consisting of 0.5 M H2SO4 + 2 ppm HF at 70 ± 0.5 °C, which is harsher than the U.S. Department of Energy specification, the corrosion current density of Ta-Nb-N-coated BPs was reduced to 2.2 × 10−2 μA·cm−2. Ta-Nb-N-coated samples showed better electrical conductivity than 316L SS, which had an excellent interfacial contact resistance of 9.2 mΩ·cm2. In addition, the Ta-Nb-N-coated samples had a water contact angle of 100.7°, showing good hydrophobicity for water management. These results indicate that Ta-Nb-N coatings could be a promising material for BPs.

Excellent anti-corrosion and conductivity of NbN coated on Ti bipolar plate by controlling N2 flow rates

The metal bipolar plates which play a crucial role in proton exchange membrane fuel cells (PEMFCs) are applied extensively due to their excellent property. However, the degraded corrosion resistance by corrosive ion and the increased interfacial contact resistance by passivation layer under acidic operating environment will affect the efficiency of PEMFCs. Metal nitride can solve that problem in some extent, however, the effect of nitrogen flow rates on the metal nitride formation during coating deposition is unclear. To solve these, NbN coatings with different N2 flow rates were applied to the bare Ti substrate via magnetron sputtering and thereafter studied. Compared with bare Ti substrate, outstanding anticorrosion performance is exhibited for the coated sample, whose corrosion current decreased three orders of magnitude (∼10−8 A/cm2) in simulated PEMFC cathode environment and the interfacial contact resistance decreased to tenth of that bare Ti substrate (∼5 mΩ cm2).

Enhanced corrosion resistance of Ni/Sn nano-electrodeposited metal foam for flow field application in simulated PEMFC cathode environment

Metal foam, with large specific surface area, suffers serious corrosion problems, as flow field in proton exchange membrane fuel cell (PEMFC). Ni/Sn nanoparticles are deposited onto the surface at galvanostatic and gradient current, respectively. The morphology of coated foams is examined by scanning electron microscopy (SEM), coupled with x-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The effect of deposited current on its corrosion resistance in simulated PEMFC cathode environment is evaluated by Tafel polarization test, constant potential test and electrochemical impedance spectra. The results show that the coating effectively improved the stability of metal foam in acid environment. A uniform and dense protective film is formed by Ni/Sn electrodeposition at a gradient current density from 0 to 40 mA cm−2. Its corrosion current at 25, 50 and 80 °C, accounts around 38.0%, 47.3% and 46.7%, respectively, of the value of uncoated metal foam. The most positive corrosion current is obtained, −0.12 mA, which is explained to higher coating resistance (Rcoat). No obvious pitting is depicted in the surface morphology after 8 h, which further proves its high corrosion resistance.

Effect of Magnetic Field on Corrosion Behaviors of Gold-Coated Titanium as Cathode Plates for Proton Exchange Membrane Fuel Cells

Effects of the self-induced magnetic fields generated by the operating current of proton exchange membrane fuel cells (PEMFCs) on metal bipolar plates (BPPs) have hardly been noticed while cannot be ignored. Therefore, corrosion behaviors and surface conductivity of gold-coated titanium (Ti/Au) and bare titanium in simulated PEMFC cathode environment under magnetic fields were evaluated by electrochemical tests and interfacial contact resistance measurements. The results indicated a considerable decrease in corrosion current and interfacial contact resistance of as-received Ti/Au, reaching 1/16 and 1/10 of those of bare titanium, respectively. The applied magnetic field also led to a sharp decline in corrosion current of bare titanium but slight increase for Ti/Au. Electrochemical impedance spectroscopy and scanning electron microscopy results suggested that magnetic field significantly facilitated the corrosion durability of titanium and ameliorating the induced pitting due to coating defects on Ti/Au. Compared to results obtained without MF, interfacial contact resistance of titanium after 24 h potentiostatic polarization under MF further increased by 24%, while a decrease by 8% was recorded for Ti/Au. In sum, effects of self-induced magnetic fields on the corrosion of metal BPPs is significant and these results revised for taking magnetic fields effects in account could be more accurate and realistic.

Investigation of corrosion properties with Ni–P/TiNO coating on aluminum alloy bipolar plates in proton exchange membrane fuel cell

Aluminum alloy bipolar plates have unique application potential in proton exchange membrane fuel cell (PEMFC) due to the characteristics of lightweight and low cost. However, extreme susceptibility to corrosion in PEMFC operation condition limits the application. To promote the corrosion resistance of aluminum alloy bipolar plates, a Ni–P/TiNO coating was prepared by electroless plating and closed field unbalanced magnetron sputter ion plating (CFUMSIP) technology on the 6061 Al substrate. The research results show that Ni–P interlayer improves the deposition effect of TiNO outer layer and increase the content of TiN and TiOxNy phases. Compared to Ni–P and TiNO single-layer coatings, the Ni–P/TiNO coating samples exhibited the lowest current density value of (1.10 ± 0.02) × 10−6 A·cm−2 in simulated PEMFC cathode environment. Additionally, potential cyclic polarization measurements were carried out aiming to evaluate the durability of the aluminum alloy bipolar plate during the PEMFC start-up/shut-up process. The results illustrate that the Ni–P/TiNO coating samples exhibit excellent stability and corrosion resistance.

Investigation of acidity on corrosion behavior and surface properties of SS304 in simulated PEMFC cathode environments

This study presents the influence of acidity on the corrosion performance and surface properties of AISI 304 stainless steel (SS304) in the simulated cathode condition of proton exchange membrane fuel cells (PEMFC) with various concentrations of H2SO4. The electrochemical tests indicate that the corrosion resistance of SS304 samples decreases gradually with the solution acidity ascending, but the stable current densities (0.043–0.547 μA cm−2) in the simulated solutions after polarization (0.6 V, 5 h) are all lower than that of the relevant DOE 2025 target (icorr < 1 μA cm−2). Obvious pitting corrosion occur in the solutions with H2SO4 concentration higher than 10−3 M. The surface wettability and interfacial contact resistance (ICR) of the potentiostatically polarized SS304 show an upward trend with the solution acidity increasing, and whether the SS304 samples are polarized or not, their ICR (0.274–1.232 Ω cm2) is far higher than the latest DOE 2025 technical target (<0.01 Ω cm2). The results reveal that surface modification is indispensable for SS304 as bipolar plates, and more attention should be paid to possessing high and stable pitting resistance, hydrophobicity, and interfacial conductivity in an acid environment.

Study on Corrosion Resistance and Conductivity of TiMoN Coatings with Different Mo Contents under Simulated PEMFC Cathode Environment.

TiMoN coatings with different Mo contents on a SS316L substrate are deposited by using closed field unbalanced magnetron sputtering ion plating (CFUMSIP) technology to enhance the corrosion resistance and durability of stainless steel (SS) bipolar plates (BPs) in proton exchange membrane fuel cell (PEMFC) during the start-up/shut-down process. The electrochemical test results illustrate that TiMoN-4A coating has extremely good corrosion resistance compared to other coatings. The potentiostat polarization (+0.6 VSCE) tests indicate that the corrosion current density (Icorr) of TiMoN-4A coating is 5.22 × 10−7A cm−2, which meets the department of energy 2020 targets (DOE, ≤1 × 10−6 A cm−2). Otherwise, TiMoN-4A coating also exhibits the best corrosion resistance and stability in potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and high potential (+1.2VSCE) polarization tests. The interfacial contact resistance (ICR) measurement results show that TiMoN-4A coating has the minimum ICR of 9.19 mΩ·cm2, which meets the DOE 2020 targets (≤10 mΩ·cm2).

Performance of SS304 Modified by Silver Micro/Nano-Dendrite Coating with Hot-Water Super-Repellency in Simulated PEMFC Cathode Environment.

In this study, an silver (Ag) plating with micro/nano-dendrite structures is prepared on the 304 stainless steel (SS304) surface by potentiostatic deposition (Ag/SS304). After being modified by n-dodecyl mercaptan (NDM) with the low surface energy, the obtained sample (NDM@Ag/SS304) exhibits stable superhydrophobicity and excellent hot-water repellency. The surface morphology and composition of NDM@Ag/SS304 are analyzed by scanning electron microscope (SEM), X-ray spectrometer (EDS), X-ray diffractometer (XRD), and X-ray photoelectron spectrometer (XPS) characterization. The electrochemical measurements, tests of water contact angle (WCA), and interfacial contact resistance (ICR) are employed to systematically study the performance of the NDM@Ag/SS304 in the simulated cathode environment of proton exchange membrane fuel cell (PEMFC). The results show that the NDM@Ag/SS304 has high corrosion potential (~0.25 V) and low corrosion current density (~4.04 μA/cm2); after potentiostatic polarization (0.6 V, 5 h), the NDM@Ag/SS304 also shows high superhydrophobic stability.

Nb–Cr–C coated titanium as bipolar plates for proton exchange membrane fuel cells

Herein, a ternary Nb–Cr–C film is successfully prepared by arc ion plating for surface modification of titanium using as proton exchange membrane fuel cell (PEMFC) bipolar plates. Film morphology, composition as well as corrosion behavior, conductivity and performance of single cell are investigated. As results revealed, the Nb–Cr–C film is about 500 nm thick without obvious defects. Compared with the bare titanium, the corrosion current density of Nb–Cr–C coated titanium lowered to 0.022 μA/cm 2 and -0.051 μA/cm 2 in simulated PEMFC cathode and anode environments, respectively, accompanied with the interfacial contact resistance lowered to 1.15 mΩ cm 2 , indicating outstanding anti-corrosion and conductivity performance. The single cell with Nb–Cr–C coated titanium bipolar plates reaches its peak power density 1.167 W/cm 2 at 2.2 A/cm 2 , which is comparable with that of graphite bipolar plates and apparently better than that of bare titanium bipolar plates. The remarkable improvements in both ex-situ tests and single cell tests suggest that the Nb–Cr–C coated titanium might be a proper material for PEMFC bipolar plates. • A novel Nb–Cr–C film is designed to modify titanium for PEMFC bipolar plates. • Corrosion current density at 0.6 V in cathode is 0.022 μA/cm 2 . • ICR with carbon paper at 1.5 MPa is 1.15 mΩ cm 2 .

Influence of temperature on corrosion behavior, wettability, and surface conductivity of 304 stainless steel in simulated cathode environment of proton exchange membrane fuel cells

The effects of temperature on corrosion behavior, wettability, and surface conductivity of 304 stainless steel (SS304) in simulated cathode environment of proton exchange membrane fuel cells (PEMFC) are investigated systematically using electrochemical tests and surface analyses. The results indicate that although the corrosion resistance of SS304 is decreased with the rising of solution temperature, the current density of SS304 at the working potential in the simulated PEMFC cathode environment can still meet the 2025 U.S. Department of Energy (DOE) technical target (icorr < 1 μA cm−2). Meanwhile, the surface wettability and ICR of SS304 samples after potentiostatic polarization show a continuous increase with the rise of the simulated solution temperature. The surface conductivity of SS304 both before and after polarization cannot reach the 2025 DOE technical target (<0.01 Ω cm2) and needs to be improved by surface modification.

Development and evaluation of nitride coated titanium bipolar plates for PEM fuel cells

In order to improve the conductivity of titanium bipolar plate under the premise of ensuring its corrosion resistance for the proton exchange membrane fuel cell (PEMFC), the nitride coatings are deposited on the surface of titanium bipolar plate via a powder immersion reaction assisted coating (PIRAC) method. Both the scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) show that the dense titanium nitride coatings with the thickness around 1.5–2.5 μm are successfully prepared. Furthermore, the X-ray photoelectron spectroscopy (XPS) results confirm the presence of TiN, TiNxOy and TiO2 phases on the surface of nitride coatings, and the content of these phases is tunable by adjusting the prepared temperatures. Both the microstructure, the thickness and the composition of the nitride coatings could be associated with the corrosion resistance and the interfacial contact resistance of the nitrided samples. We find that the nitrided samples prepared at 1000 °C could be the ideal mixed coating materials with the proper combination of the corrosion resistance and the interfacial contact resistance, which also show the best long-term stability in simulated PEMFC cathode environment.

Preparation and performance of nanometric Ti/TiN multi-layer physical vapor deposited coating on 316L stainless steel as bipolar plate for proton exchange membrane fuel cells

The current research mainly focuses on surface properties, corrosion resistance and interfacial contact resistance (ICR) of nanometric titanium/titanium nitride (Ti/TiN) multi-layer coating deposited on 316L stainless steel via physical vapor deposition (PVD) technique for using in proton exchange membrane fuel cell (PEMFC) bipolar plate (BPP) application. The phase and microstructure of the coated BPPs is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and contact angle examinations. The performance of the BPPs is investigated by electrochemical corrosion tests including electrochemical impedance spectroscopy (EIS), potentiodynamic and potentiostatic polarization tests at two conditions including at ambient temperature and in the simulated PEMFC cathode environment. Electrochemical test results reveal that the Ti/TiN coating increases the polarization resistance of 316L stainless steel by 26 orders of magnitude at ambient temperature and by 1000 orders of magnitude in the simulated PEMFC cathode environment. The corresponding ICR of the BPPs is measured ex-situ in a PEMFC set-up. It is observed that the coated BPP has ICR value of 11 and 18 mΩ cm2 before and after potentiostatic polarization, respectively. Hence, the Ti/TiN coating studied in this work has promising properties as BPP material and is potentially suitable alternative to replace the graphite BPP in PEMFC.

Investigation of diffusion alloying time on electrochemical behavior and conductivity of Nb-modified AISI 430 SS as PEMFC bipolar plate

Purpose The purpose of this paper is to improve the surface electrical conductivity and corrosion resistance of AISI 430 stainless steel (430 SS) as bipolar plates for proton exchange membrane fuel cells (PEMFCs), a protective Nb-modified layer is formed onto stainless steel via the plasma surface diffusion alloying method. The effect of diffusion alloying time on electrochemical behavior and surface conductivity is evaluated. Design/methodology/approach In this work, the surface electrical conductivity and corrosion resistance of modified specimen are evaluated by the potentiodynamic and potentionstatic polarization tests. Moreover, the hydrophobicity is also investigated by contact angle measurement. Findings The Nb-modified 430 SS treated by 1.5 h (1.5Nb) presented a lower passivation current density, lower interfacial contact resistance and a higher hydrophobicity than other modified specimens. Moreover, the 1.5 Nb specimen presents a smoother surface than other modified specimens after potentionstatic polarization tests. Originality/value The effect of diffusion alloying time on electrochemical behavior, surface conductivity and hydrophobicity of modified specimen is evaluated. The probable anti-corrosion mechanism of Nb-modified specimen in simulated acid PEMFC cathode environment is presented.

Surface distortion as a unifying concept and descriptor in oxygen reduction reaction electrocatalysis

Tuning the surface structure at the atomic level is of primary importance to simultaneously meet the electrocatalytic performance and stability criteria required for the development of low-temperature proton-exchange membrane fuel cells (PEMFCs). However, transposing the knowledge acquired on extended, model surfaces to practical nanomaterials remains highly challenging. Here, we propose the ‘Surface Distortion’ as a novel structural descriptor, which is able to reconciliate and unify seemingly opposing notions and contradictory experimental observations in regards to the electrocatalytic oxygen reduction reaction (ORR) reactivity. Beyond its unifying character, we show that surface distortion is pivotal to rationalize the electrocatalytic properties of state-of-art of PtNi/C nanocatalysts with distinct atomic composition, size, shape and degree of surface defectiveness under simulated PEMFC cathode environment. Our study brings fundamental and practical insights into the role of surface defects in electrocatalysis and highlights strategies to design more durable ORR nanocatalysts.

The study of Ni-based nano-crystalline and amorphous alloy coatings on AISI 304 stainless steel for PEM fuel cell bipolar plate application

Bipolar plates are one of the most important parts of proton exchange membrane fuel cells (PEMFCs) which their performance has appreciable effect on cell operation. In this study, Ni–Mo and Ni–Mo–P alloy coatings were electrodeposited on AISI 304 stainless steel specimens as metallic bipolar plates in order to improve corrosion resistance, hydrophobicity and electrical conductivity of the specimens. Scanning electron microscopy (SEM) micrographs showed that the prepared coatings were uniform and compact. Moreover, X-ray diffraction (XRD) analysis indicated that the coatings were composed of a solid solution where Ni–Mo and Ni–Mo–P coatings had nanocrystalline and amorphous structures, respectively. The potentiodynamic and potentiostatic polarization tests in a simulated PEMFC cathode environment showed that corrosion resistance of the coated specimens was considerably improved compared to that of the bare one. Furthermore, interfacial contact resistance (ICR) before and after potentiostatic test was significantly decreased by applying Ni–Mo and Ni–Mo–P coatings, where ICR values of the as-deposited bipolar plates were reduced by approximately eight times in comparison to that of the bare 304 stainless steel at typical compaction force of 220 N/cm2. Therefore, the investigated Ni–Mo and Ni–Mo–P coatings would be potentially good candidates as metallic bipolar plates in PEMFC. Moreover, Ni–Mo and Ni–Mo–P alloy coatings showed higher surface hydrophobicity than the bare 304 stainless steel, which is advantageous for water management and also for corrosion resistance improvement.

Multilayered Zr–C/a-C film on stainless steel 316L as bipolar plates for proton exchange membrane fuel cells

A multilayered zirconium-carbon/amorphous carbon (Zr–C/a-C) coating is synthesized by magnetron sputtering in order to improve the corrosion resistance and interfacial conductivity of stainless steel 316L (SS316L) as bipolar plates for proton exchange membrane fuel cells (PEMFCs). Zr–C/a-C film contains an outmost pure amorphous carbon layer and a sub zirconium containing carbon layer. Interfacial contact resistance (ICR) between carbon paper and coated SS316L decreases to 3.63 mΩ cm2 at 1.4 MPa. Potentiodynamic polarization results reveal that the corrosion potential of Zr–C/a-C coated sample is more positive than pure a-C coated sample and the current density is only 0.49 μA cm−2 at the cathode applied potential 0.6 V. Electrochemical impendence spectroscopy also indicates that multilayered Zr–C/a-C film coated SS316L has much higher charge transfer resistance than the bare sample. After potentiostatic polarization, ICR values are 3.92 mΩ cm2 and 3.82 mΩ cm2 in the simulated PEMFCs cathode and anode environment, respectively. Moreover, XPS analysis of the coated samples before and after potential holding tests shows little difference, which disclose the chemical stability of multilayered Zr–C/a-C film. Therefore, the multilayered Zr–C/a-C coating exhibits excellent performance in various aspects and is preferred for the application of stainless steel bipolar plates.

Effects of Potential on Corrosion Behavior of Uncoated SS316L Bipolar Plate in Simulated PEM Fuel Cell Cathode Environment

AbstractThe effect of potential on the corrosion behavior of uncoated stainless steel SS316L as bipolar plate material in proton exchange membrane (PEM) fuel cell cathode environment is studied. Electrochemical methods, X‐ray photoelectron spectroscopy, scanning electron microscope are employed to characterize the corrosion behavior of SS316L at different polarization potentials in PEM fuel cell cathode environment. The results show that the corrosion current density of SS316L increases with the increase of polarization potential significantly. When the potential is higher than 0.7 V versus SCE, severe corrosion occurs on SS316L. The work also shed light on the corrosion mechanisms of SS316L at different potential in the PEM fuel cell cathode environment.

Characterization of Uncoated Stainless Steel as Proton Exchange Membrane Fuel Cell Bipolar Plates Material

AbstractThanks to their high conductivity, important gas tightness, good corrosion resistance, and low‐cost manufacturing pathways, stainless steels are considered as good candidates for proton exchange membrane fuel cell (PEMFC) bipolar plates materials. In this study, a proprietary alloy was identified as very promising: its initial electrical contact resistance (ECR) with the gas diffusion layer was low, while its corrosion resistance in simulated PEMFC environment was sufficient. Furthermore, the ECR did not increase dramatically during long‐term potentiostatic and potentiodynamic polarizations in simulated PEMFC cathode and anode environments. Finally, the stainless steel was successfully tested for 3,000 h in a commercial system using a 16‐cell stack, without detrimental cell voltage losses.