Fig. 3: Determination of RDS of FAD on Pd/C catalysts.
a Initial TOFs for FAD on Pd at different solution pHs. pH1 solution: 0.1 M HClO4 + 1.0 M HCOOH, pH3.7 solution: 0.2 M HCOOH + 0.2 M NaHCOO, pH~7 solution: 1.0 M NaHCOO, and pH13 solution: 0.1 M KOH + 1.0 M KHCOO. Labels C-H and C-D refer to the use of HCOOH/HCOO− and DCOOH/DCOO−, and O-H and O-D to the use of H2O and D2O in the measurements, respectively. Test condition: 298 K for pH1, 3.7 and ~7, and 333 K for pH13. b KIE factors of C-H/D and O-H/D for FAD at different pHs calculated from the data obtained in a. c Open circuit potentials (Eocp) measured at the catalyst surface during FAD (without deuteration) at different pHs at 298 K, the dotted lines are used for the guide of eyes. d Evans diagrams for KIE measurements of FAD in solutions of pH3.7. e Comparisons between measured FAD reaction rates (adapted from data in a) and predicted FAD reaction rates by the Evans diagram method (adapted from data in d). f Scheme of pH-dependent RDS for FAD as analyzed by the mixed potential theory. The chemical equilibrium among CO2, bicarbonate and carbonate in solutions is neglected in this scheme. φ0 refers to the potential when the second term on the right side of Eq. 1 or 2 is zero. Source data are provided as a Source Data file.
