For Rh, the most favorable sites for H adsorption are the hollow (4-fold) and the hollow (3-fold) fcc sites for Rh(100)  and Rh(111)  faces, respectively, corresponding to N4(8,8,8,8) (starting from m = 4) and N3fcc(9,9,9) (starting from m = 6) adsorption sites. DFT calculations over small sized Rh clusters (tetrahedron Rh4 and octahedron Rh6) indicated that bridge sites are the most stable , corresponding to N2(5,5), for a small cuboctahedron cluster (m = 2). When the cluster size increases, N2(5,7) (starting from m = 3) and N2edge(7,7) (starting from m = 4) equivalent adsorption sites are created, due to the additional appearance of edge atoms. As shown for Pd clusters, the N4(8,8,8,8) sites for (100) faces can lead to the creation of additional 4-fold sites (N4(5,5,5,5)+N4(5,7,7,8)+N4(7,7,8,8)) as the cluster size decreases. Finally, the number of H atoms that can be adsorbed on the Rh cuboctahedron surface (for a given m, denoted NH,Rh) can be calculated as follows (Equation (5)): (5)NH,Rh=N2(5,5)+N2(5,7)+N2edge(7,7)+N3fcc(9,9,9)+N4(5,5,5,5)+N4(5,7,7,8)+N4(7,7,8,8)+N4(8,8,8,8)