Bond energy, metal-oxygen discussion

As discussed earlier, such mechanisms involving two adsorbed H species with different bond energies and sites probably apply to all transition metals. It is likely that the sites for the HER adsorbed intermediate (OP HajJ are the weakly bonded on-top sites. But on oxidizable metals, H electroadsorption in the hollow strongly bonded sites followed by absorption is possible only at potentials below the limit of desorption of the oxygen species, calculated for Ni and Fe to be dose to 0V(rhed [28]. It is admitted that on iron and ferrous alloys the HER and the HAR share a common H ds intermediate and that the surface-bulk transfer step is in quasiequilibrium [8] (see Section 2.2.2.2.S). The mechanism of H absorption into the bulk of transition metals at cathodic overpotential must then involve a sequence of two consecutive adsorption steps ... 

A recent discussion concludes that high-valent transition metal ions such as iron(IV) are thermodynamically incompatible with the strongly electronegative 0x0 dianion, particularly when electron transfer results in unpaired valence electrons that can stabilize each other via covalent bond formation. Such stabilization of the two unpaired electrons of ground-state atomic oxygen attenuate its redox potential and it reactivity to an extent proportional to the energy of the metal-oxygen covalent bond. 

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