Fig. 4: Chemical composition analyses after anodic cycling.

a, b EDS maps for the seven iridates particles are compared before and after 200 anodic cycles. No dissolution of Nb and Ta is identified, whereas Mn, Co, Ni, and In significantly dissolve, as expected from their Pourbaix diagrams. c Even after 800 cycles, Nb is observed to be stable without detectable dissolution. d As demonstrated in the EDS maps in (c), line-by-line EELS analyses consistently show a deficiency of alkaline-earth Ba in the surface region of Ba₄NbIr₃O₁₂. This dissolution accompanies amorphization, as shown in the HAADF image.