Electrochemical Valorization of Glycerol on Ni-Rich Bimetallic NiPd Nanoparticles: Insight into Product Selectivity Using in Situ Polarization Modulation Infrared-Reflection Absorption Spectroscopy

Glycerol partial electrooxidation was studied on NixPd1-x (x = 100, 95, 90, and 80 atom %) nanoparticles synthesized using a polyol method. The shape-controlled urchin-like monometallic Ni and spherical NixPd1-x catalysts were synthesized. The morphology, crystal structure, and composition of Ni-rich catalysts were characterized using a number of physicochemical techniques. Detailed electrochemical characterizations showed that Ni and NixPd1-x NPs are active for GEOR and that the reaction follows either the direct electron transfer mechanism at low glycerol concentrations or the indirect electron transfer mechanism at high concentration. Among all investigated electrocatalysts, Ni80Pd20 exhibited the highest current density at lower overpotentials due to both a synergetic effect of Ni and Pd and the smaller particle size of Ni80Pd20. In situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) at various anodic potentials allowed discriminating the reaction products and intermediates directly on the electrode surface and in the electrolyte solution. PM-IRRAS showed that the main reaction products on NixPd1-x are glyceraldehyde, carbonyl groups for mesoxalate and tartronate ions, carboxylate ions, and traces of carbon dioxide. NixPd1-x catalysts are promising anode materials for glycerol oxidation to value added products and could be potentially combined with cathodic hydrogen production or CO2 electro-reduction processes in alkaline media.