Well-Dispersed Nafion Array Prepared by the Freeze-Drying Method to Effectively Improve the Performance of Proton Exchange Membrane Fuel Cells

Abstract

The ordered membrane electrode assembly (MEA) is currently the frontier research field of proton exchange membrane fuel cells (PEMFCs). The ordered MEA is effective in increasing the utilization of the Pt catalyst and reducing the Pt catalyst loading and cost. Due to a larger specific surface area and faster rate of proton transfer, a Nafion array was used to prepare a high-performance MEA. In order to realize the ideal performance, the critical mission is to make a well-dispersed Nafion array. However, the pillars in the Nafion array are prone to form bundles induced by surface tension of water, resulting in a severe reduction in the specific surface area. In this work, we successfully prepared a well-dispersed Nafion array by the freeze-drying method, which greatly improved the performance of the ordered MEA of a PEMFC. The percentage of isolated pillars in the Nafion array is improved from about 0.8% after natural drying to about 90% after freeze-drying. The specific surface area of the Nafion array membrane after freeze-drying increases to 4.74, which is 2.1 times that after natural drying, and is close to the theoretical value of 4.99, indicating that the well-isolated array possesses a larger specific surface area to load a catalyst. Consequently, the electrochemical surface area of the catalyst layer reaches as high as 131.5 m2 gPt –1, which is 1.6 or 2.5 times that with the Nafion array after natural drying or without the Nafion array. For the ordered MEA, a long-term stability is vital for PEMFC operation. In this work, the lifetime of the ordered MEA with the Nafion array after freeze-drying is excellent compared to the Nafion array after natural drying and without the array. Besides, the scanning electron microscopy characterization clearly shows that the Nafion array remains a well-dispersed structure even after hot-pressing and plays a pivotal role in PEMFC operation. Therefore, this research proves that the freeze-drying method can effectively solve the aggregation of the Nafion array during drying and further proves that the well-dispersed Nafion array could show much higher performance. More importantly, this work provides an ideal basic material for the preparation of the ordered MEA.

Enhanced Triple-Phase Interface in PEMFC by Proton Conductor Absorption on the Pt Catalyst

“…On the one hand, it is the proton exchange membrane (PEM) that allows H + transfer from the anode side to the cathode side. On the other hand, it serves as a catalyst support carrier, such that the catalyst nanoparticles or inks are loaded in the membrane by knife coating, , sputtering, , spraying, , and electrodeposition. , In this work, the Nafion array membrane with a larger specific surface and higher proton conductivity was applied to play the above two roles to obtain a great PEMFC performance.…”

“…In recent years, with the continuous development of the economy and society, the problems of environmental pollution and resource shortage have aroused great concern. It is extremely urgent to develop clean energy with high energy density and environmental protection. − Compared with traditional energy sources, fuel cells have a wide range of application, such as aerospace, electric vehicles, mobile power, and so on. , Outstandingly, the proton exchange membrane fuel cell (PEMFC) possesses the advantages of a high conversion rate and yielding clean products, and it will play an epoch-making role in the sustainable development of the society. − …”

“…In this work, in order to reduce the catalyst loading and improve the catalyst utilization rate, a Nafion array membrane with a larger specific surface and higher proton conductivity was applied to make the ordered MEA and the Pt nanoparticles were filled into the Nafion array by sputtering . However, the agglomeration of Pt nanoparticles by sputtering reduced the transfer efficiency of H + from the Nafion array membrane to the catalyst surface .…”

“…The development of the third-generation ordered membrane electrodes is beneficial to reduce the catalyst loading and improve the fuel cell performance. The ordered MEAs are mainly divided into three categories, namely the ordered electronic conductor, 14,17 the ordered proton conductor, 7,8 and ordered catalyst layer. 15,25 The electronic conductivity is 100 S cm −126 and the proton conductivity is 0.15 S cm −1 , 27 which is much lower than the electronic conductivity.…”

Catalyst Degradation Mitigation and Fuel Utilization Enhancement of a Dead-Ended Anode and Cathode Proton Exchange Membrane Fuel Cell with Periodical Oxygen Supply

“…Proton exchange membrane fuel cells (PEMFCs) have gained a lot of attention as prospective clean energy conversion devices due to their environmental friendliness, high energy conversion efficiency, and quick start-up. − PEMFCs have a wide range of applications and huge potential markets in electric vehicles, stationary power stations, submarines, and space power supplies. , …”