The perfluorosulfonic acid (PFSA) proton exchange membrane (PEM) is the key component for hydrogen fuel cells (FCs). We used in situ synchrotron scattering to investigate the PEM morphology evolution and found a “stream-reservoir” morphology, which enables efficient proton transport. The short-side-chain (SSC) PFSA PEM is fabricated under the guidance of morphology optimization, which delivered a proton conductivity of 193 milliSiemens per centimeter [95% relativity humidity (RH)] and 40 milliSiemens per centimeter (40% RH) at 80°C. The improved glass transition temperature, water permeability, and mechanical strength enable high-temperature low-humidity FC applications. Performance improvement by 82.3% at 110°C and 25% RH is obtained for SSC-PFSA PEM FCs compared to Nafion polymer PEM devices. The insights in chain conformation, packing mechanism, crystallization, and phase separation of PFSAs build up the structure-property relationship. In addition, SSC-PFSA PEM is ideal for high-temperature low-humidity FCs that are needed urgently for high-power-density and heavy-duty applications.

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.

In a proton exchange membrane fuel cell (PEMFC), the membrane electrode assembly (MEA) is the core component and the region of the oxidation−reduction. In order to obtain a great performance, Pt with excellent catalyst efficiency is usually adopted in PEMFC as the catalyst. However, the high cost and poor durability remain the two major challenges in the application of PEMFC; thus, it is worth paying attention to enhance the utilization of the Pt catalyst and the stability of PEMFC. In this work, the Nafion array membrane with a larger specific surface and higher proton conductivity was applied to the cathode catalyst layer (CL) to prepare the ordered MEA. In order to improve the three-phase interface of the cathode CL, Nafion was adsorbed on the Pt particles as the proton conductor to expedite the proton transfer efficiency based on the principle that sulfonic acid is easily adsorbed on the Pt surface. In this case, the peak power density of PEMFC with Nafion absorption on the Pt surface is up to 843 mW cm −2 at the Pt loading of 61.4 μg cm −2 , which is much higher than that of the fuel cell without a proton conductor on the Pt catalyst in the cathode CL (710 mW cm −2 ). Besides, the durability tests show that PEMFCs with Nafion absorption on the Pt catalyst surface can work continuously for 100 h without obvious voltage attenuation, which is more stable than that of the bare Pt for 70 h. In conclusion, Nafion as the proton conductor was adsorbed on the Pt catalyst surface of the cathode CL to enhance the triple-phase interface in PEMFC, which is expected to be a universal method to prepare PEMFCs with high stability and peak power density at a low preparation cost.

The property of perfluorinated sulfonic acid (PFSA) membranes depends not only on the ion exchange capacity (IEC), but also on the chemical structure of the functional side-chain and the phase-separation morphology. Two PFSA membranes, the long side-chain (LSC) and the short side-chain (SSC), have been investigated to study the structure−property relationship, covering the ionic domain structure and the proton transport. The proton conductivity of the SSC PFSA membrane is 143 and 209 mS/cm at 30 °C and 80 °C in water, which is 30− 40% higher than that of the LSC PFSA membrane (103 and 161 mS/cm). The bound-to-free water ratio in the hydrated membranes was analyzed by differential scanning calorimetry and Raman spectroscopy, which show that a higher ratio accounts for the improved proton conductivity of the SSC PFSA membrane. The chain mobility was analyzed by solid-state nuclear magnetic resonance, which reveals that the side chain of the SSC membrane more readily self-assembles. This result was verified by the morphology from transmission electron microscopy. The small-angle X-ray scattering results show that the SSC PFSA membrane exhibits smaller domain spacing between the ionic clusters in dehydrated membranes. These observations, a larger ionic cluster and smaller domain spacing in the dehydrated SSC membrane, indicate a reduced size of the hydrophobic assembly feature domains, and the ionic channel connectivity is better in the SSC, which can be another key issue for its improved proton conductivity, in addition to the higher IEC and higher proton mobility.

In order to increase the applicability of wollastonite (Wo) in polycarbonate (PC) polymer, surface modification of Wo was carried out using different modifiers containing silane coupling agent KH570, stearic acid (SA), and sodium dodecylbenzene sulfonate. The physical, physic-chemical, and application properties of modified Wo were evaluated. Results showed that KH570 modified Wo had narrower particle size distribution, higher absolute zeta potential and were more evenly distributed. Scanning electron microscope study confirmed their changes in morphology and aspect ratio during the modification process. The tensile strength of Wo/PC composites, in which KH570-modified Wo was used were superior to those in which original Wo or other modifiers modified samples were used. The maximum tensile strength of 65 ± 1 MPa was obtained by adding 15 wt% KH570-modified Wo. Thermal analysis indicated that adding Wo to the polycarbonate increased the residue content but decreased the thermal decomposition temperature and glass transition temperature slightly, regardless of unmodified or modified Wo. These results indicated that the well-modified Wo mineral had the potential to replace expensive carbon and glass fibers as fillers in polycarbonate products.