Recently, a research article published in Science Bulletin by Prof. Junliang Zhang and Assoc. Prof. Xiaohui Yan from Shanghai Jiao Tong University has reported a molecular engineering strategy that synergically enhances the performance of proton exchange membrane fuel cells (PEMFCs) by tailoring the microenvironment of the ionomer (i.e., Nafion) within the cathode catalyst layer (CCL).
The work addresses two persistent challenges facing low-platinum PEMFCs. First, the CCL relies on costly platinum catalysts to drive the sluggish oxygen reduction reaction, yet lowering Pt loading greatly intensifies local oxygen transport resistance and constrains peak power output. Second, under practical operating conditions involving high temperatures above 90 °C and low humidity, the ionomer tends to dehydrate, leading to a marked decline in proton conductivity.
To overcome these limitations, the researchers introduced polyhydroxylated fullerenol, C 60 (OH) n , into the Nafion used in the cathode catalyst layer. The design exploits two defining features of the additive: its densely distributed hydroxyl groups and its rigid, quasi-spherical 0D scaffold.
These structural advantages translated into clear device-level gains for the membrane electrode assembly (MEA). Under H 2 /air conditions, the modified MEA reached a peak power density of 1.33 W cm − 2 , approximately 1.53 times that of the baseline system. Under H 2 /O 2 conditions, the peak power density reached about 2.79 W cm − 2 . The strategy also demonstrated broad applicability across multiple commercial catalysts and remained effective at reduced platinum loadings.
According to the study, the abundant hydroxyl groups form a robust hydrogen-bond network with the sulfonate groups of the Nafion side chains. This competitive interaction weakens the tendency of sulfonate adsorption on platinum, thereby freeing catalytically active sites. Simultaneously, the rigid fullerenol core acts as a nanoscale spacer that modifies the ionomer nanostructure and promotes microphase separation, creating more efficient pathways for oxygen transport.
Electrochemical and spectroscopic analyses confirmed that the modified ionomer effectively suppressed detrimental platinum-sulfonate interactions. The sulfonate coverage on platinum decreased by about 60% compared to the baseline system. Furthermore, this structural optimization decreased the pressure-independent oxygen transport resistance ( R np ) by over 45%, alongside an approximately 2.5-fold increase in the oxygen diffusion coefficient within the ionomer film.
The study further highlights that fullerenol improves local water retention in the ionomer, which is particularly important for operation under high-temperature and low-humidity conditions. Thermogravimetric measurements showed higher retained water content for the modified ionomer than for pure Nafion. In fuel cell tests, the modified electrodes maintained stronger performance under dry conditions and at temperatures up to 105 °C. Durability assessments further underscored the system’s operational stability. The modified MEA sustained a stable voltage during extended constant-current operation and met relevant durability targets in accelerated stress testing (AST).
The researchers conclude that the findings establish a versatile molecular engineering strategy for tuning the catalyst-ionomer interface and ionomer transport network at the same time. By simultaneously mitigating sulfonate poisoning, improving local oxygen transport, and strengthening water retention, the approach offers a promising route toward high-performance PEMFCs with low platinum loadings and improved tolerance to harsh operating conditions.
Science Bulletin
Experimental study