PtNi and PtMo nanoparticles towards HER using TEA-PS.BF4 ionic liquid as electrolyte

The hydrogen evolution reaction (HER) is one of the most studied electrochemical reactions, owing to the high interest in the use of alternative energy resources. Recent research and development efforts have been focused in electrodes with higher electrocatalytic activity for HER. One alternative for these electrocatalystics are metallic nanoparticles (NPs) on black carbon support. This study investigated the HER using bimetallic NPs on black carbon support (PtNi/C e PtMo/C) in presence of TEA-PS.BF4 IL1 aqueous solution. The efficiency of electrocatalystics was through Tafel analysis and electrochemical impedance spectroscopy (EIS). The Tafel cathodic coefficient values (b) are 39, 43 and 47 mVdec-1 obtained for Pt/C, PtMo/C, and PtNi/C respectively and are very closed one to each other suggesting that all cathodes present the Volmer-Heyrovsky kinetic mechanism2. The effective exchange current density (jo) for HER is bigger to Pt/C (1.4 x 10-5 A cm-2) and PtMo/C (2.7 x 10-5 A cm-2) in compared to PtNi/C (6.4 x 10-6 A cm-2), confirming the correlation between the electrode composition. The Nyquist plots show three depressed semicircles for all cathodes, each related to atime constant, Ϯ(Ϯ = R x C). At high frequencies, the process is related to hydrogen adsorption on the electrode surface followed by charge transfer kinetics and associated at the first time constant (Ϯ1), where R1 is the resistance related to the charge transfer of NP-Hads on the active sites and C1 is the pseudocapacitance of a charge arrangement at the electrode/electrolyte interface (fast step or Volmer step). The second time constant (Ϯ2) is due to the hydrogen desorption process, where R2 is the second charge transfer resistance and C2 is the pseudocapacitance associated to modifications of the electrical double layer due to the reduction of H+ and their desorption, leading to H2 formation (slow step or Heyrovsky step). At low frequencies, the third time constant (Ϯ3) is in the same range for all studied cathodes and can be related to the electrode surface porosity response and it is related with R3 and C3. The R3 is the resistance and C3 the pseudocapacitance associated to gas occlusion in the porous structure of the cathodes. All results of electrochemical measurements present in this paper (current density, apparent activation energy, Tafel parameters and impedance data) prove that the carbon-supported bimetallic NPs, PtNi/C and PtMo/C are responsible for the catalytic effect observed when these materials are used as cathodes in the HER conducted with the in TEA-PS.BF4 aqueous solution.