Laser Powder Bed Fusion of Multifunctional Bio-inspired Vertical Honeycomb Sandwich Structures: For the Application of Lightweight Bipolar Plates of Proton Exchange Membrane Fuel Cells

Abstract The bipolar plate (BPP) is a crucial component of proton exchange membrane fuel cells (PEMFC). However, the weight of BPPs can account for around 80% of a PEMFC stack, posing a hindrance to the commercialization of PEMFCs. Therefore, the lightweight design of BPPs should be considered as a priority. Honeycomb sandwich structures meet some requirements for bipolar plates, such as high mechanical strength and lightweight. Animals and plants in nature provide many excellent structures with characteristics such as low density and high energy absorption capacity. In this work, inspired by the microstructures of the Cybister elytra, a novel bio-inspired vertical honeycomb sandwich (BVHS) structure was designed and manufactured by laser powder bed fusion (LPBF) for the application of lightweight BPPs. Compared with the conventional vertical honeycomb sandwich (CVHS) structure formed by LPBF under the same process parameters setting, the introduction of fractal thin walls enabled self-supporting and thus improved LPBF formability. In addition, the BVHS structure exhibited superior energy absorption (EA) capability and bending properties. It is worth noting that, compared with the CVHS structure, the specific energy absorption (SEA) and specific bending strength of the BVHS structure increased by 56.99% and 46.91%, respectively. Finite element analysis (FEA) was employed to study stress distributions in structures during bending and analyze the influence mechanism of the fractal feature on the mechanical properties of BVHS structures. The electrical conductivity of structures were also studied in this work, the BVHS structures were slightly lower than the CVHS structure. FEA was also conducted to analyze the current flow direction and current density distribution of BVHS structures under a constant voltage, illustrating the influence mechanism of fractal angles on electrical conductivity properties. Finally, in order to solve the problem of trapped powder inside the enclosed unit cells, a droplet-shaped powder outlet was designed for LPBF-processed components. The number of powder outlets was optimized based on bending properties. Results of this work could provide guidelines for the design of lightweight BPPs with high mechanical strength and high electrical conductivity.