The hydrogen evolution reaction (HER) has been studied extensively due to the potential application of molecular hydrogen H2as a green fuel. Recently this particular reaction attracted the attention of several electrometallurgical researchers because of another promising application, in which the monoatomic hydrogen species H· (intermediate product of HER) is employed as a reducing agent for copper-sulfide minerals. Consequently, knowledge about the kinetics, mechanisms and rate determining step (rds) of HER in sulfuric acid solutions employing aluminum, copper, Inconel® or glassy carbon(GC) cathodes is necessary to determine the under and overpotential domains where H2 and H· can be generated in a selective manner. Analyses of Tafel plots and the charge transfer coefficients, revealed two electrical potential zones for copper, Inconel and GC, where the monoatomic hydrogen can be recombined chemically or electrochemically to H2 as the rds. On the other hand, with aluminum, only the electrochemical recombination to H2 occurs as the rds. A catalytic effect on the hydrogen recombination reaction was also found when ferrous ion is contained in the solution. Finally, it was determined that aluminum is the most efficient electrocatalyst for producing H· and H2, followed by inconel, copper and GC.
polarization, tafel, monoatomic hydrogen, HER
The authors would like to thank Bryan Leyda of Energy Re-search and Generation, Inc. and Professor Fiona M. Doyle of Uni-versity of California-Berkeley for the continued support and helpful discussions regarding the nature of monoatomic hydrogen. Juan Carlos Fuentes-Aceituno is grateful to his wife Rosy and newborn son Carlitos for the inspiration transmitted and to CONACyT (México) for the postgraduate scholarship received.
 G. Jerkiewicz, Electrocatalysis, 1, 179 (2010).
 M. Sustersic, T. Zanón, S. Albano y A. Menguershausen, Información Tecnológica, 19, 49 (2008).
 M.C. Tavares, S.A.S. Machado and L.H. Mazo, Electrochimica Acta, 46, 4359 (2001).
 T. Sasaki and A. Matsuda, J. Res. Inst. Catalysis, Hokkaido Univ., 29, 113 (1981).
 N. Pentland, J.O’M. Bockris and E. Sheldon, Journal of the Electrochemical Society, 104, 182 (1957).
 L.I. Krishtalik, in “Charge Transfer Reactions in Electrochemical and Chemical Processes”, 1st Edition, Consultants Bureau New York, Ed., U.S.A., 1986, pp. 26-67.
 R. Greef, R. Peat, L.M. Peter, D. Pletcher and J. Robinson, in “Instrumental Methods in Electrochemistry”, 3rd Edition. Ellis Horwood Ed., Great Britain, 1993, p. 233.
 J.C. Fuentes-Aceituno, G.T. Lapidus and F.M. Doyle, Hydrometallurgy, 92, 26 (2008).
 G.T. Lapidus and F.M. Doyle, in “Electrochemistry in Mineral and Metal Processing VII”, Eds. F.M. Doyle, G.H. Kesall and R. Woods, ECS Transactions, U.S.A., 2006, 2(3), p. 189.
 A.K. Vijh and A. Belanger. International Journal of Hydrogen Energy, 11, 147 (1986).
 M.H. Elhamid, B.G. Ateya, K.G. Weil and H.W. Pickering, Journal of the Electrochemical Society, 147, 2148 (2000).
 L.L. Shreir, in “Corrosion, Volume I: Metal/Environmental Reactions”, 2nd Edition. Newnes-Butterworths, Shreir, L.L. (Ed), London, 1976, p9.