Aromatic amines as proton carriers for catalytic enhancement of hydrogen evolution reaction on copper in acid solutions

The catalytic effect of some aromatic amines towards hydrogen evolution reaction on copper in diluted sulfuric acid solution has been studied. Since amines facilitate the transport of protons from the solution bulk to the interface in the cathodic hydrogen evolution reaction, they are known as proton carriers. The catalytic effect of aniline, N-methylaniline, N-ethylaniline, N,N-dimethylaniline, N,N-diethylaniline, o-toluidine, m-toluidine and p-toluidine has been highlighted by linear sweep voltammetry. The kinetic parameters for the hydrogen evolution reaction (cathodic transfer coefficient 1-α and exchange current density io) in the presence of the studied aromatic amines were derived from the Tafel plots. It has been found that the catalytic effect of amines is active even at low concentration. Thus, in 0.5 mol L−1 H2SO4 solution the exchange current density increases by two orders of magnitude, from 2.01⋅10−5 A m−2 in the absence of aniline to 2.85⋅10−3 A m−2 in the presence of 10−4 mol L−1 aniline. The influence of amines concentration on the catalytic effect is described in detail for the case of m-toluidine. The results obtained by voltammetry have been compared with electrochemical impedance spectroscopy data. Furthermore, the kinetic parameters for the hydrogen evolution reaction have been determined as a function of temperature and amines concentration.

► Catalytic effect of some aromatic amines for HER on copper in H2SO4 solution.
► Exchange current density increase of two orders of magnitude for 10−4 M aniline.
► There is a strong dependence between amine structure and catalytic effect.
► Rct decreases in the order: blank > MA > EA > DMA > pT > DEA > oT > mT > A.
► A catalytic mechanism for HER has been proposed involving amine adsorption.