Improved performance of lanthanide-doped UIO-66/Nafion hybrid proton exchange membrane for water electrolyzer

Incorporating metal-organic frameworks (MOFs) especially the ones with protic functional groups into proton exchange membrane (PEM) can effectively improve its proton conductivity. Lanthanide MOFs (Ln-MOFs) have been recognized as more potential candidates exhibiting proton dissociation capability. However, the performance of PEM upon integrating Ln-MOFs in water electrolyzer has yet to be investigated. In this study, Nafion composites with different loadings of lanthanide Ce-UiO-66 were prepared, characterized and tested by comparing with the non-lanthanide Zr-UiO-66. It was revealed that the proton conductivity of Ce-UiO-66/Nafion composite membrane was higher than pristine Nafion and Zr-UiO-66/Nafion membrane, which was attributed to the fact that the Ce-UiO-66 doping contributed to the construction of the hydrogen-bonded network to enhance the proton conductivity. At 3 wt% Ce-UiO-66 doping, the proton conductivity of the composite membrane can reach 124.45 mS/cm, which is significantly improved by 17 % compared with Zr-UiO-66/Nafion. Such a trend is mainly contributed by the lower proton affinity and proton transfer capability of Ce atoms in Ce-UiO-66, and the higher number of water molecules around Ce atoms favors the reduced tortuosity of the proton conduction pathway in membranes. Single electrolytic cell tests demonstrated the enhancement of electrolysis efficiency upon Ce-UiO-66 doping was improved from 58.77 % to 65.37 % at a current density of 2 A cm−2.