Electrolysis of Glycerol by Non-Noble Metal Hydroxides and Oxides

A series of free-standing electrodes consisting of hydroxides (Ni(OH)2, Co(OH), NiFeLDH, and CoFeLDH) and oxides (NiO, Co3O4, NiFe2O4, and CoFe2O4) supported by carbon paper were fabricated via an in situ hydrothermal process and further examined for glycerol conversion. The morphology and structures of the samples were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The performance of the samples was studied by cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The products of glycerol oxidation were analyzed by high-performance liquid chromatography. Operando electrochemical Raman spectroscopy was employed to monitor the variations on the active sites and intermediates. Among the samples, the NiO exhibited superior activity with the largest current density of 0.8 mA cm–2 at 1.7 V and selectivity of 97% for formic acid. Furthermore, coupling the hydrogen evolution reaction with the glycerol electro-oxidation reaction (GOR), we explored the electrolysis of water and glycerol. The potential of the electrolysis process was negatively shifted from 1.68 to 1.28 V by replacing the oxygen evolution reaction with GOR. The strategy reported in this work could afford a sustainable approach to produce hydrogen and value-added chemicals with high energy efficiency.