Novel high stable electrocatalyst based on non-stoichiometric nanocrystalline niobium carbide toward effective hydrogen evolution

In this work, we have developed a method for the synthesis of non-stoichiometric nanocrystalline niobium carbide (NbC_y) using special heat treatment of niobium citrate in a vacuum. The powder synthesized was investigated by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), and low-temperature nitrogen sorption-desorption technique. The PXRD results showed that the synthesized niobium carbide nanocrystals had a cubic structure (space group Fm-3m), isometric morphology, and average crystallite size of about 12 nm. The Rietveld method was used to refine the unit cell parameters: a = b = c = 446.8 pm; R_wp = 5.48%. The specific surface area about 212 m²/g (BET) and the porosity about 0.02 cm³/g (BJH) of the sample were determined by adsorption-structural analysis; it was found that niobium carbide had a weakly pronounced microporous structure associated with the presence of interparticle porosity, which was also confirmed by the HRSEM results. The catalytic activity of non-stoichiometric niobium carbide in the process of electrolytic reforming of an aqueous ethanol solution was analyzed. The electrocatalyst has a low hydrogen overpotential value (?245 mV), a Taffel slope (90 mV/dec), and high operational stability: the absolute value of the overvoltage increases by 21 mV after 500 voltammetry cycles, and the current density decreases by 5% after 20 h of chronoamperometry. The results obtained make it possible to consider non-stoichiometric niobium carbide as a promising electrode base for electrocatalytic production of hydrogen from renewable aqueous-alcoholic solutions.