Enhancement of uncoupled nonlinear equations method for determining kinetic parameters in case of hydrogen evolution reaction after dropping two assumptions

Hydrogen evolution reaction involves three reaction steps, i.e., Volmer, Heyrovsky and Tafel. Out of six kinetic parameters, only four are independent. Tafel polarization and alternating current admittance data at various frequencies and at various overpotentials can be utilized for obtaining values of independent kinetic parameters. In the previous work [Bhardwaj M, Balasubramaniam R. Uncoupled nonlinear equations method for determining kinetic parameters in case of hydrogen evolution reaction following Volmer–Heyrovsky–Tafel mechanism and Volmer–Heyrovsky mechanism. Int J Hydrogen Energy 2008;33:2178–88], uncoupled nonlinear equations methods for determining kinetic parameters in case of systems following Volmer–Heyrovsky–Tafel mechanism and Volmer–Heyrovsky mechanism were developed. In that work, Heyrovsky and Tafel backward reaction rates were neglected and Volmer and Heyrovsky symmetry factors were assumed equal to half for obtaining the values of kinetic parameters. In the present work, both of these assumptions have been dropped and uncoupled nonlinear equations have been re-derived. The equations have been validated using literature data.