In this investigation a kinetic study of the HER was carried out employing a steel rotating disk with different aqueous solutions containing Phosphoric Acid (H3PO4) with or without metallic manganese (Mn) and Nitric Acid (HNO3). Furthermore, the HER was evaluated on iron and manganese phosphate coatings. Analyses of Tafel plots and the charge transfer coefficients, revealed one electrical potential zone where the monoatomic hydrogen can be recombined electrochemically to H2 as the rate determining step, with charge transfer coefficients similar to an activationless process (α→0). On the other hand, an increase in the concentration of H3PO4 promotes a higher exchange current for the HER. The Mn in the aqueous solutions has a catalytic effect on the hydrogen generation rate at room temperature. However, the precipitation of Mn3(PO4)2 on steel decreases the HER kinetics at high temperatures. These observations are also supported with SEM (Scanning Electron Microscopy) characterizations.
Polarization, Tafel, monoatomic hydrogen, HER.
Gabriela Alvarado Macías is grateful to CONACyT (México) for the postgraduate scholarship received. Also, the collaboration of Felipe Márquez, Socorro García and Teodoro Caballero in this investigation is duly recognized.
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