Experimental Study on the Electrochemical Performance of PEMFC under Different Assembly Forces

Proton exchange membrane fuel cell(PEMFC)is of paramount significance to the development of clean energy.The components of PEMFC are assembled using many pairs of nuts and bolts.The assembly champing bolt torque is critical to the electrochemical performance and mechanical stability of PEMFC.In this paper,a PEMFC with the threechannel serpentine flow field was used and studied.The different assembly clamping bolt torques were applied to the PEMFC in three uniform assembly bolt torque and six non-uniform assembly bolt torque conditions,respectively.And then,the electrochemical performance experiments were performed to study the effect of the assembly bolt torque on the electrochemical performance.The test results show that the assembly bolt torque significantly affected the electrochemical performance of the PEMFC.In uniform assembly bolt torque conditions,the maximal power density increased initially as the assembly bolt torque increased,and then decreased on further increasing the assembly torque.It existed the optimum assembly torque which was found to be 3.0 N·m in this work.In non-uniform assembly clamping bolt torque conditions,the optimum electrochemical performance appeared in the condition where the assembly torque of each bolt was closer to be 3.0 N·m.This could be due to the change of the contact resistance between the gas diffusion layer and bipolar plate and mass transport resistance for the hydrogen and oxygen towards the catalyst layers.This work could optimize the assembly force conditions and provide useful information for the practical PEMFC stack assembly.

Ground demonstration system based on in-orbit assembly oriented manipulator flexible force control

To eliminate the load weight limit of carrier rockets and reduce the burden on support structures,in-orbit assembly is a key technology to make design of scattering a large diameter telescope into submirror modules,which requires smooth operation of assembly robots,and flexible force control technology is necessary. A ground demonstration system is presented for in-orbit assembly focusing on flexible force control. A six-dimensional force/torque sensor and its data acquisition system are used to compensate for gravity. For translation and rotation,an algorithm for flexible control is proposed. A ground transportation demonstration verifies accuracy and smoothness of flexible force control,and the transportation and assembly task is completed automatically. The proposed system is suitable for the development of in-orbit assembly robots.

Effect of assembly pressure on the performance of proton exchange membrane fuel cell

The assembly force is a crucial factor in the process of proton exchange membrane fuel cell(PEMFC)stacking,and has significant effects on the fluid flow,mass transfer,and water and thermal management,which affect the fuel cell performance.In this study,from the most deformable component,the gas diffusion layer(GDL),combining with a finite-element analysis,and computational fluid dynamic method,the impact of the assembly force on a single-channel PEMFC is analyzed.A nonlinear stress-strain curve obtained from a microanalysis is creatively introduced into the two-dimensional compression model.The gas diffusion coefficient in the three-dimensional model is also obtained from the microscopic simulation.The simulated effective oxygen diffusion coefficient of the compressed GDL is approximately 0.86 times the Bruggemann estimated value.When the contact resistance is ignored,the output voltage at 2.5 MPa is decreased by approximately 15.4%at 1.7 A·cm^(−2)compared with that at 0.5 MPa.After the contact resistance is considered,the effects of the assembly pressure on the cell performance(V-I curve)are qualitatively different.The pressure drop of the 2.5 MPa case is 20%higher than that of the 1.4 MPa case at 1.7 A cm^(−2).O_(2)is hard to flow into the region under the rib where the porosity and permeability are lower.The results indicate that both liquid water and membrane water contents increase when the assembly force increases.The effect of the assembly force on the temperature is also analyzed.

The formation of fibers via complementary base pairing of DNA-conjugated bovine serum albumin

Assembled protein-based substances are emerging and promising classes of materials that provide unique properties for various applications in biotechnology and nanotechnolegy. Self-assembly is an effective way to immobilize protein. In this study, DNAs-conjugated bovine serum albumin （BSA） assembled into fibers via DNA hybridization is demonstrated. The morphology of fibers was observed by optical microscopy, scanning electron microscopy （SEM）, and atomic force microscopy （AFM）, and the assembly mechanism was then analysed and discussed. BSA molecules were first linked by DNA molecule and formed linear chains. These chains then were parallelly linked through additional DNA hybridization. Finally, several BSA chains further assembled into fibers by layering lamellae in a parallel manner. This work perhaps will provide a guide to the immobilization of enzyme, which could be applied to increase its catalytic efficiency in biomedicine and nanotechnology.