Fundamental investigation of the HER on a Pt(111) surface at temperatures down to 120K

The hydrogen evolution reaction (HER) is of fundamental importance in electrochemistry, and despite the large number of theoretical and experimental investigations, it is still far from being completely understood. In the present work, the HER is studied on a Pt(111) surface in a wide range of temperatures down to 120 K. The overall reaction and the first reaction step, the Volmer reaction, were evaluated separately using potentiostatic pulses in order to obtain a detailed understanding of the different reaction steps. At room temperature, the Volmer reaction exhibits a Tafel slope of 120mV/dec, which is the expected value for a single electron transfer. For the overall reaction a change in Tafel slope at -η ≈ 50 mV is found. While the Tafel slope is ≈ 30 mV/dec for small overpotentials, it is 120mV/dec for larger overpotentials. For both the overall reaction and the Volmer reaction, a strong dependence of the apparent transfer coefficient on temperature is found. This temperature dependence cannot be explained using classical electron transfer theory.