Fig. 5: Thermodynamic properties of molecular catalysts.
From: Toward a mechanistic understanding of electrocatalytic nanocarbon
a The scaling relationships between the thermodynamic hydricity (ΔG) and the first reduction potential E1 of the metal-free (orange) and metal-based hydrides (blue). Adapted and reprinted with permission from ref. 89. b Two-electron redox potential (blue triangles) and pKa (red squares) contributions to ΔG (black circles) of metal hydrides plotted by their average redox potentials. Adapted and reprinted with permission from ref. 92. c Pourbaix diagram for Rh molecular catalysts (red triangles) and Rh attached to glassy carbon electrode (GCC-Rh, blue circles). The black solid line denotes the thermodynamic potential of HER. The orange region denotes the potential-pH region in which the model is catalytically active, while the blue region shows conditions where GCC-Rh catalyzes HER97. d Proposed interfacial free energy diagrams for GCC-Rh electrodes. The gray area represents the filled band states of the electrode, while beige denotes the unfilled band states. The dotted horizontal black line indicates the EF of the electrode. The electrical double layer, EDL, is labeled by a vertical dotted black line. The redox potential of the molecule (E1/2(RhIII/I)) and the potential for formation of a Rh−H species at the GCC site (E(Rh + H+/Rh−H)) are illustrated with dotted gray and blue lines, respectively. The electrostatic potential is shown with the dotted red line, and the potential of zero free charge (EPZFC), is indicated with a dotted gray line. Adapted and reprinted with permission from ref. 97, https://pubs.acs.org/doi/full/10.1021/jacs.9b04981. All future permission should be directed to the ACS.
