Missing-linker defects of Ce-UiO-66 for enhanced radical scavenging efficiency and proton conductivity in proton exchange membrane fuel cells

Ce-based scavengers are well known as free radical scavengers due to its fast Ce³⁺/Ce⁴⁺ conversion. However, the compatibility of redox capability and proton conductivity for long-life proton exchange membrane fuel cells (PEMFC) is a crucial consideration relevant to the rational development of Ce-based radical scavengers. In this study, the rational design of Ce-UiO-66 (d-UiO-66) with missing-linker defects was achieved by introducing acetic acid during the synthesis. The systematical investigation referring to redox capability and proton conductivity of d-UiO-66 demonstrated that, on one hand, the missing-linker defects in d-UiO-66 can reduce the energy barrier for the feasible Ce³⁺/Ce⁴⁺ conversion to enhance the free radical scavenging performance. On the other hand, it is also benefit for the delocalization of π-electron, which not only contributes to form hydrogen bonds formation with high density to establish effective pathways for proton hopping, but also gives rise to the enhanced mobility of π-electrons for the efficient proton transfer. Consequently, single-cell testing with missing-linker radical scavengers supports improved PEMFC performance with the highest voltage retention (94 %) and the lowest degradation of limiting powers around 12.2 % even after 100 h of open circuit voltage testing. The proof-of-concept demonstrates the potential of concurrent radical scavenging efficiency and proton conductivity for advancing PEMFC performance.