Mechanism, Kinetics and Simulation of Electrocatalytic Oxidation of Dimethylamine Borane (DMAB) on Electroless Gold

Abstract

Dimethylamine borane ((CH3)2NHBH3) or DMAB, is broadly used as a reducing agent in electroless autocatalytic platings like gold and nickel-boron, hydrogen storage, and reductive amination. However, the mechanism of its DMAB oxidation procedure remains unclear. This project is based on the hypothesis that a multi-step electron transfer mechanism exists for oxidizing the reducing agent DMAB on gold in alkaline media. According to this mechanism, the active species produced when DMAB is used at high hydroxide content is the BH3OH-. This species is created through a series of irreversible electrochemical oxidation producing the following intermediates BH2(OH)2-, BH(OH)3- and B(OH)4-, which is the final product. Multiple electrochemical methods have been used to uncover the properties of DMAB oxidation progress and verify above-mentioned hypothesis. Electrochemical Impedance Spectroscopy (EIS) was used to test the uncompensated resistance between the working electrode and reference electrode and calibrated in the following experiments: Cyclic voltammetry (CV) showed that DMAB in hydroxide electrolytes have three half-wave potentials with E_(1/2) of -0.778, -0.174 and 0.248 V. Kinetic current values obtained from the Koutecky-Levich plot decreased with temperature with -4.065, -3.62 and -1.45 mA/cm2 at 25°C, 41°C and 52°C, respectively. Rotating Disk Electrode (RDE) and Chronoamperometry (CA) were used to determine the Diffusion Coefficient of BH3(OH)-; BH2(OH)2- and BH(OH)3- 1.38E-05, 3.31E-05 and 1.01E-04, respectively. Tafel analysis was used in obtaining the transfer coefficient, whereas Klingler and Kochi’s method evaluated the constant. These kinetic parameters were used in KISSA-1D software to simulate the CVs. Gas Chromatography with Mass Spectrometry (GC/MS) was used to verify the existence of B(OH)4- and a peak at m/z 78.8 was recorded. All of this provided evidence that the three intermediates are involved in the proposed mechanism. In the future, simulated and experimental approaches will be investigated for other amine boranes compounds such as Sodium cyanoborohydride (NaBH3CN), Sodium triacetoxyborohydride (NaBH(O2CCH3)3), and Sodium borohydride (NaBH4). This work will have far-reaching consequences in enhancing the practical applications of gold and nickel in microelectronics and fuel cells.