Hydrogen evolution in acid solution at Pd electrodeposited onto Ti2AlC
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abstract
2016 Elsevier Ltd The hydrogen evolution reaction (HER) was studied in 0.5M H2SO4 at 25C on Pd electrodeposited onto Ti2AlC substrate, as an excellent substrate due to its high conductivity and high stability in concentrated sulfuric acid. Pd was electrodeposited onto Ti2AlC by pulse technique from the solutions containing different concentrations of PdCl2 in 1M NH4Cl. It was shown that in all investigated solutions Pd electrodeposition occurs by the diffusion-controlled 3D nucleation and growth. Two types of Pd electrodeposits were submitted to the study of the HER by the polarization measurements and the electrochemical impedance spectroscopy (EIS). The surface of Pd samples was characterized by scanning electron microscopy (SEM), by energy dispersive X-ray spectroscopy (EDS) and by atomic force microscopy (AFM). High catalytic activity for the HER was observed for all investigated samples. The Tafel slope of 64mVdec1 was recorded for the Pd layer electrodeposited at 20mV vs. saturated calomel electrode (SCE) for 5s, mainly composed of isolated hemispherical 3D Pd centers and dendrites (sample (2)), while for Pd electrodeposit with the theoretical thickness of 1000nm (sample (1)) Tafel slope of 143mVdec1 was detected. All Tafel slopes recorded for the investigated samples could be explained by the Volmer-Tafel mechanism for the HER assuming Temkin adsorption isotherm, with either of the steps (Volmer or Tafel step) being the rate-determining one. By the analysis of the EIS results similar slopes for the E vs. log (RF)1 dependences were observed for all investigated samples respectively, while the electrochemically active surface area (EASA), obtained by the integration of the charge for Pd-oxide reduction was found to be the highest for the sample (1). The exchange current densities corrected for the EASA were presented for all samples.
