Dear Editor
In the recent paper by Gu et al. [1] the oxygen reduction reaction (ORR) mechanism of NdBaCo 2 O 5þd cathode (NBCO) for intermediate-temperature solid oxide fuel cells (SOFC) was investigated by the electrochemical impedance spectroscopy (EIS) under cathodic polarization using three-electrode configurations. Samaria-doped ceria, Ce 0.8 Sm 0.2 O 2Àd (SDC), was used as electrolyte material in the study.
To be honest, it was surprising to read that, on page 2417 of the Volume 34, No. 5 issue of the International Journal of Hydrogen Energy, the authors reported the following essential information to the readers: "The pattern of SCM was indexed on the basis of the orthorhombic lattice geometry of space group Pmmm." [1] Thus you can imagine my amazement, when I noticed that this orthorhombic "SCM" phase is not introduced in the cited paper [1], and there is no explanation of what the letters stand for or what the acronym is. At last, after the first unpleasant surprise, my attention has been attracted to other interesting manuscripts by the same authors in previous issues of International Journal of Hydrogen Energy [2] and Electrochimica Acta [3].