Coupling ATR-FTIR spectroscopy, Scanning Electron Microscopy and Dynamic Light Scattering to understand the formation of 5-hydroxymethylfurfural (HMF) derived humins.

The electrochemical conversion of carbon dioxide (CO 2 ) into value-added chemicals is regarded as one of the promising routes to mitigate CO 2 emission. A nitrogen-doped carbon-supported palladium (Pd) single-atom catalyst that can catalyze CO 2 into CO with far higher mass activity than its Pd nanoparticle counterpart, for example, 373.0 and 28.5 mA mg −1 Pd , respectively, at −0.8 V versus reversible hydrogen electrode, is reported. A combination of in situ X-ray characterization and density functional theory (DFT) calculation reveals that the PdN 4 site is the most likely active center for CO production without the formation of palladium hydride (PdH), which is essential for typical Pd nanoparticle catalysts. Furthermore, the welldispersed PdN 4 single-atom site facilitates the stabilization of the adsorbed CO 2 intermediate, thereby enhancing electrocatalytic CO 2 reduction capability at low overpotentials. This work provides important insights into the structure-activity relationship for single-atom based electrocatalysts.