Fig. 8 Calculated free-energy diagram of hydrogen evolution on (a) pure surface, (b) Pt@La and Pt@Ta, (c) Ru@La and Ru@Ta, and (d) Ni@La and Ni@Ta. Varied relaxed structures and the corresponding values of ΔG H are attached. Coloring scheme: green (La), light blue (Ta), red (O), blue (N), grey (Pt), purple (Ru), orange (Ni) and white (H).