HER: [6] The active sites for HER and OER can be theoretically determined by estimating the adsorption energy of the corresponding intermediates, namely H* and OH* species, respectively. Generally, the electron-deficient site is more active for the adsorption of OH*, while the H* species tends to be adsorbed at the electron-rich site (Figure ). By employing the computational hydrogen electrode model proposed by Nørskov et al., the thermodynamics of HER and OER can be evaluated by estimating the ΔG of the two and four elementary steps of HER and OER processes, respectively. The standard hydrogen electrode (SHE) model is used as a reference and the potential for H + + e -→ 1/2 H2 is thus set to equilibrium with 0 V at pH = 0 vs. SHE.