R Gnanamoorthy

In any proton-exchange membrane fuel cell, the bipolar plates grab attention because of the high production cost and heavyweight. Hence, the open-cell nickel foams are considered as an alternative to these grooved plates. The reliability of the metallic foams used as flow distributors and gas diffusion layers plays a vital role in the fuel cell's overall performance. Fretting wear damage of the metal foam at strut/strut interface and strut/supporting frame interface due to the vehicular vibrations and pressurized fuel flow is expected to affect the performance and is investigated. This paper discusses the fretting wear behaviour of nickel foam strut that constitutes open-cell nickel foam based on laboratory tests. The experiments are performed by using two different contact configurations: steel ball on wrought nickel flat and nickel strut on wrought nickel flat. The test results reveal the fretting friction coefficient's dependence on the normal load, surface roughness and contact geometry. Although the nickel strut versus nickel flat fretting wear tests showed a low coefficient of friction, severe damages were observed on the nickel struts’ worn surfaces compared to the wrought nickel flat. Scanning electron microscope images of worn scars on nickel foam struts indicate the presence of shallow grooves, craters, micro-cracks and delamination craters at higher loads.

The relative slippage between the open-cell metal foam flow fields and other parts in a fuel cell due to vehicular and flow-induced vibrations causes fretting. The material degradation due to fretting in nickel struts contaminate the stack and is investigated using simulated experiments. The as-formed strut surfaces are rough and increases the material loss during fretting. The total wear volume associated with a single contact in 22,000 cycles is 4.66 E−04 mm3. The contamination in the stack is estimated assuming a dodecahedron unit cell geometry and neglecting the fretting corrosion. About 47 g of debris is expected to be generated when an 8 ppi nickel foam flow fields used in a 50-cell stack for 8700 hours of operation. In addition, the generated flake shaped debris (<10 μm) can obstruct the flow of gases by clogging the gas diffusion layer. The proposed contamination estimation methodology will aid in performance prediction during service.