Use of layered double hydroxides to improve the triple phase boundary in anion-exchange membrane fuel cells

We propose a novel approach that uses a positively charged inorganic compound, layered double hydroxide (LDH), as an anion conductor in anion-exchange membrane fuel cells to improve the triple phase boundary (TPB) of catalyst layers. Pt/C catalyst layers with hydrothermally prepared Mg–Al- and Ni–Al-based LDHs (MgAl-LDH and NiAl-LDH, respectively) were constructed, and their oxygen-reduction currents were evaluated under the same conditions as in anion-exchange membrane fuel cells. Scanning electron microscopy and a surface-area analysis revealed that the two LDHs had almost the same surface-area, size, and hexagonal cylinder structure. In contrast, electrochemical measurements showed that MgAl-LDH improved the current densities while NiAl-LDH showed the same current densities as the catalyst layer with no LDHs. These results suggest that MgAl-LDH introduced OH−-conducting paths within the catalyst layers and effectively increased the TPB region in anion-exchange membrane fuel cells.