Fig. 3: Mechanistic investigations.
a The linear sweep voltammetry (LSV) of PdO in 0.1 M TMAF, the scan rate is 10 mV/s. b The pulsed chronoamperometry (CA) measurement where PdO electrode was first kept in 0.05 M cyclohexene (for cyclohexene adsorption) and 0.1 M TMAF at 1.1–1.3 VRHE for 1 hr (highlighted by area of blue color), following by a switch of potential to 1.8 VRHE and to the electrolyte of 0.1 M tetrabutylammonium perchlorate (TBAP, for cyclohexene oxidation, highlighted by area of red color); the inset is Fourier transform infrared spectroscopy (FTIR) of PdO powder, which was immersed in 0.1 M cyclohexene for 1 hour. c Mass spectra of cyclohexene oxide for the electro-oxidation of cyclohexene in CH3CN-18O-labeled water, CH3CN–water, and standard theoretical isotopic distributions. d Systematic evaluation of possible active species (for a reaction time of 6 hours). TMABr and TMACl were reactive by forming Br·/Cl· radicals under standard electrochemical conditions. HClO, Br2, BrO−, and BrO3− were directly added as active chemical species, and free Br· radical was introduced by photochemical generation, error bars in (d) represent the standard deviation from multiple reactions (n = 3). e The EPR test of reactive free radical species. f The relationship between cyclohexene oxidation reaction performance and the onset potential values for oxidation of water, bromine ion, cyclohexene, bromine+cyclohexene, from different catalytic materials of α-MnO2, α-Ni(OH)2, amorphous-RuO2, commercial-RuO2, commercial-IrO2, NiFe-LDH, Pd/C, and PdO.
