With the increasing demand for energy supply and awareness of climate crisis, green energy generation has attracted intensive and extensive research attention during the past decades. Hydrogen, as a high energy density non-carbon energy source, has been one of the spotlights and its green production has been one of the top research topics in scientific community. Among the many existing hydrogen generation processes, water splitting (H₂O → H₂ + 1/2O₂) driven by renewable energies is considered a dream everlasting process for hydrogen supply. Water splitting however is obstructed by one of the two reactions involved, the oxygen evolution reaction (OER, 4OH^- → O₂ + 2H₂O + 4e^- in alkaline solutions), because of its high over-potentials and sluggish kinetics caused by the four electron transfer process. Consequently, extensive efforts have been devoted to develop more efficient catalysts to lower the over-potential and thus energy consumption and to accelerate the kinetics of the OER. Mixed oxides or phosphides have been found to exhibit positive synergistic effects and achieve ultralow over-potentials for the OER. In this presentation, two recent examples are offered to illustrate this point, one involving mixed NiO/NiCo₂O₄ nanocrystals grown in situ from skeleton of 3D porous nickel network and the other concerning hollow nanocubes composed of well-dispersed mixed metal-rich phosphides, Ni₅P₄ and Fe₃P, in N-doped carbon.