“…Common metal elements for solid catalysts included Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, La, Hf, Ta, W, Re, Os, Ir, Pt, and so forth. However, only a part of metal elements can be selected to form a single-phase HEO, where the atomic radius and crystal field coordination behavior play a major role. − According to the law of metal selection for HEOs, Fe and Zn were adjusted, while the introduction of other metal elements such as Cr, Mo, or Ti can cause impurity phases. The influence of changing Fe or Zn in HEOs was not significant on E ov ( E ov/(MnCuCo8NiFe) x O y = 2.36 eV, E ov/(MnCuCo8NiZn) x O y = 2.47 eV, E ov/(MnCuCo3NiZn) x O y = 2.54 eV, E ov/(MnCuCo3NiFe) x O y = 2.28 eV, and E ov/(MnCuCoNiFe) x O y = 2.41 eV), as shown in Scheme .…”