以下是文章对这个图的描述：
Following Pathway I, two major reaction steps，namely,
hydrogen activation and hydrogen transfer，are involved. In
the hydrogen activation step, first, the H2 molecule is weakly
adsorbed on the catalyst (Figure 2,IM1), with the adsorption
energy of −0.14 eV and the shortest distance between the
physisorbed H2 and B-doped phosphorene of 3.30 Å. The
physisorbed H2 molecule then dissociates heterolytically into
two separated H atoms，one atom (Ha) bound to B site and
the other (Hb) bound to P site, thus generating hydridic (Ha)
and protic (Hb) hydrogens. Note that there are three
nonequivalent B/P pairs in B-doped phosphorene, namely,
(i) B/P2, (ii) B/P4, and (iii) B/P5 sites, to accommodate the
two dissociated H atoms.