To further unveil the OER/ORR catalytic performance of TMP4 systems, the change of free energy of every reaction pathway was analyzed. Typically, the OER process related to four steps, including the dissociation of H2O to form *OH, *OH converts to *O and H + , subsequently *O reacts with H2O molecule to product *OOH and H + , and following *OOH will dissociate into H + and O2, the detail reaction processes are described in Support Information. Figure and Figure exhibit the free energy diagrams of every OER reaction step over TMP4 systems, containing the Gibbs free energy at U=0 and 1.23 V. The applied external voltage will promote the energy of every reaction process shifts up and down, and the free energy of each step decreases or keeps unchanged with the direction of OER/ORR reactions sequentially indicating that the spontaneous catalytic reaction can be presented. Meanwhile, the ∆𝐺 was calculated to determine the potential-limited step. Results show that the free energy differences of first step for OER (∆𝐺 𝑂𝐻 * ) over the TMP4 systems (TM = Ti, V, Cr, Mn, Zr, Nb, Mo, Ru, Hf, Ta, W, Re, Os, Ir) are negative ranging from -2.15 to -0.12 eV, demonstrating the strong bonding interactions between TM and *OH intermediate. Therefore, the third or fourth proton-coupled electron transfer steps of *O converting to *OOH and *OOH converting to O2 fragment, respectively, and the desorption of O2 from the TMP4 surfaces become the overpotential-limiting steps. As embedded in Figure and Figure , the calculated overpotentials (η OER ) of TiP4 (2.0 V), VP4 (1.76 V), CrP4 (2.01 V), MnP4 (1.57 V), ZrP4 (1.99 V), NbP4 (1.88 V), MoP4 (2.03 V), RuP4 (0.97 V), HfP4 (2.39 V), TaP4 (2.25 V), WP4 (2.23 V), ReP4