Investigation of hydrogen evolution kinetics of metal-doped MoS2 electrocatalysts by exploring the charge transfer coefficients

Abstract

Charge transfer coefficient (α) is an intrinsic activity parameter of hydrogen evolution reaction (HER), as it deals with the fraction of supplied energy used to increase the HER kinetics. This article investigated the HER kinetics of MoS₂, aluminium (Al-MoS₂) and tin (Sn-MoS₂) doped MoS₂ nanostructures by estimating the exact values of α. This article proposes a simple method of the least square curve fitting of the Butler-Volmer equation on the experimentally produced polarization curve of HER to derive α. Since the charge transfer coefficient depends on the current density, in curve fitting, values of α are determined at three different current density regions. The correctness of the estimated α was verified by comparing it with the same derived from Tafel plots of experimental values. Overpotential, Tafel slope, Turnover frequency (TOF), double layer capacitance, electrochemically active surface area (ECSA) and exchange current densities were estimated to confirm the reliability of obtained α values. All electrocatalytic parameters show that Al-MoS₂ has excellent HER activity with overpotential: 249 mV at 10 mA/cm², Tafel slope: 67 mV/Dc, TOF: 0.32 s⁻¹, double layer capacitance: 17 mF/cm², ECSA: 425/cm² and Exchange current density: 1.38 mA/cm². The estimated value of α for Al-MoS₂ is 0.89 at the current density region −5 mA/cm² and − 15 mA/cm² which exhibit the excellent electrocatalytic activity of the catalyst. Estimation of the exact value of α will help to understand the exact electrocatalytic mechanism of the catalyst.