Synthesis and characterization of hybrid nickel/mesoporous TiO2 catalysts for hydrogen evolution reaction

E. A. FRANCESCHINI; G. I. LACCONI; M. J. GÓMEZ

Congreso; 20th Topical Meeting of International Society of Electrochemistry; 2017

Synthesis and characterization of hybrid nickel/mesoporous TiO2 catalysts for hydrogen evolution reaction.Melisa J. Gómez, Esteban A. Franceschini and Gabriela I. LacconiINFIQC-CONICET, Dto. de Fisicoquímica . Facultad de Ciencias Químicas, Universidad Nacional de Córdoba.Ciudad Universitaria, 5000, Córdoba,Argentina.Gabriela.lacconi1@gmail.comHydrogen has attracted recent attention as a clean energy vector, which can be used in fuel cells, or in replace of natural gas in the so-called hydrogen economy. Hydrogen production through water electrolysis is considered to be the cleanest production way for hydrogen economy in the near future.In this communication, a simple and reproducible method for the synthesis of hybrid nickel/TiO2 electrodes is presented. This method consists in a direct modification of a conventional nickel electrodeposition bath, making the synthesis industrially scalable. The synthesized catalyst was structural and electrochemically characterized, and compared to the conventional electrodeposited nickel. The kinetics of hydrogen evolution reaction (HER) was studied on conventional nickel Watts (Ni-Watts), a nickel/TiO2 hybrid (Ni/TiO2) synthesized using commercial TiO2 particles and a nickel/TiO2 hybrid (Ni/mTiO2) synthesized using a mesoporous TiO2 aerosol synthesized in our laboratory.The catalysts were synthesized using a conventional Ni Watts electrodeposition bath prepared by dissolution of 25 g of boric acid in water at 50 ºC. 240 g of nickel sulfate and then 25 g of nickel chloride were added to the boric acid solution under constant stirring to obtain 1 L of solution. This Watts electrodeposition bath was used to synthesize a conventional electrodeposited nickel catalyst.Part of that Ni Watts bath was separated to prepare a modified Ni/TiO2 bath to electrodeposite the Ni/TiO2 and Ni/mTiO2 hybrid catalysts. For that, 0.2 g of the TiO2 powder was added to 65 mL of the Watts bath.The synthesis of both catalysts was carried out by electrodeposition on a commercial Ni electrode (RC S.A. 99.9 purity), with a circular area of 0.196 cm2, which is mounted on a rotating disk electrode (RDE) support (Pine Research Inst.; Raleigh, NC). The nickel electrodes were polished with 0.05 m alumina and cleaned with ethanol and consecutive immersion steps in KOH (1 M), and HCl (10 % w/w) solutions, during 1 minute, in order to clean the surface. Both syntheses of catalysts were carried out in a two electrodes electrochemical cell thermostatized at 50 ºC, using a massive nickel counter electrode with high area. During the process, to ensure the homogeneity of the electrodeposit, the working electrode was maintained with a rotation rate of 1600 rpm. Moreover, the working electrode rotation facilitates the species in the solution (both, Ni ions and TiO2 particles) reach the surface of the electrode.The electrodes were electrochemically characterized in 1 M KOH by cyclic voltammetry (between 0.1 and -1.5 V vs. SCE), 4 hs chronoamperometry at -1.5 V (vs SCE) and EIS at different potentials.Changes in the catalytic activity and the formation of superficial nickel hydrides were observed. The Ni/TiO2 catalyst presents a higher catalytic activity towards HER and the presence of TiO2 in the Ni matrix inhibits the nickel hidruration.It can be seen that the presence of TiO2 in the catalyst matrix significantly increases the catalytic activity of nickel, which is increased even more in the case of the mesoporous TiO2 particles. This may be due to a synergistic electronic effect, and an increase in the electrochemically accessible surface area of the nickel electrode. Figure 1: (left) SEM micrographs of Ni/mTiO2 hybrid catalyst, (center) SEM micrographs of Ni/TiO2 hybrid catalyst, (right) comparison of cyclic voltammograms of pure nickel, Ni/TiO2 and Ni/mTiO2.