Synthesis and properties of a hybrid nickel/nitrogenated-GO for hydrogen evolution reaction

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

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

ISE

Synthesis and properties of a hybrid nickel/nitrogenated-GO for hydrogen evolution reaction.Melisa J. Gómez, Luis A. Pérez, 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 is considered one of the most promising alternatives as an energy vector for the future. New methods for hydrogen production that do not generate greenhouse gases emission are of great interest, being the water electrolysis in alkaline medium, one of the most interesting. Since the hydrogen evolution reaction (HER) is an heterogeneous reaction, the electronic state of the electrode surface plays a dominant role in determining the reaction kinetics.Graphene oxide (GO) can be nitrogenated for different chemical methods that have been proposed in the last years [ ]. The obtained product (NGO) is a promising material for heterogeneous catalysis, particularly when the flakes are included in the nickel matrix.In this communication, hybrid nickel/nitrogenated-GO catalysts were synthesized via direct electrodeposition employing a modified nickel Watts bath. The synthesized catalyst was structural and electrochemically characterized, and compared to the conventionally electrodeposited nickel electrode.The catalytic activity for HER in alkaline solutions of modified nickel electrodes is analyzed using a rotating disk electrode. The catalysts were synthesized using a conventional Ni Watts 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 electrodeposition bath was used to obtain a conventional electrodeposited nickel catalyst on steel samples.Part of that Ni Watts bath was separated to prepare the modified Ni/Graphene bath in order to obtain the electrodeposited Ni-NGO hybrid catalyst. For that, a 0.08 g/L NGO aqueous dispersion was sonicated during 30 minutes in order to disperse the NGO flakes. Then, an aliquot of 10 mL of the NGO dispersion was added to 40 mL of the Watts bath. The catalysts obtained with the different electrodeposition baths have very different optical properties. While the Ni-Watts electrode is dull gray, the Ni-NGO electrode is black, suggesting the presence of NGO reduced in the matrix of the catalyst, which is homogeneously distributed.The Raman scattering spectra from the Ni-Watts electrode don?t show signals, indicating that nickel is in a metallic state and there is no evidence of nickel hydrides. However, bands at 3581 and 3660 cm-1 indicate the nickel hydrides presence in the composite catalyts. Furthermore, the Ni-NGO electrode spectra show the NGO characteristic bands, evidencing the intercalation of graphene in the structure of the nickel electrodeposits.The catalysts were electrochemically characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). The comparison of cyclic voltammograms without electrode rotation shows that Ni-Watts catalysts have the same values of HER onset potential (OP) and current density (at -1.5 V vs. SCE), before and after chronoamperometric ageing in alkaline solutions. On the other hand, the Ni-NGO catalysts after ageing maintain the OP values (100 mV lower than that observed with electrodeposited Ni-Watts), but there is a diminution of the current density.It was demonstrated that GO is electrochemically reduced during the catalyst synthesis, increasing the conductivity of flakes. As a consequence, the charge transfer resistance corresponding to pure nickel electrodeposits can be significantly decreased.It can be seen that both catalysts behave differently in terms of variations of the (dj/dV) slopes when they are characterized by CV (without electrode rotation), and linear sweep voltammetry (at 1600 rpm). These results are due to the catalysts show different dependencies on the diffusional control, indicating that the Ni-NGO catalyst possibly has better performance.