Non-noble electrocatalysts such as NiMo have been shown to be highly active outperforming Ni activity in alkaline hydrogen evolution reaction (HER). However, the fundamental understanding of this effect is still missing despite numerous studies address the intrinsic NiMo activity. This work aims to combine the evaluation of catalyst activity with a comprehensive structural investigation. We will examine material properties, including surface and crystal structures, compositions and changes thereof. The use of identical location transmission electron microscopy (TEM) will allow us to focus on a reaction site and monitor the effect of HER on the catalyst, following the ultimate aim to elucidate the reasons for enhanced NiMo catalyst activity.

NiMo thin film cathodes with low roughness of varying Mo content (0-100 at%) were magnetron sputter deposited. Catalytic activities were examined via cyclic voltammetry studies using an electrochemical three electrode measurement setup to obtain HER polarization curves in the region between 0.3 and -0.35 V vs. RHE. Comparative studies revealed the nano-crystalline NiMo thin film containing 10 at% of Mo developed the most promising results in terms of catalytic activity towards HER. It should be mentioned that NiMo thin films in our studies are mainly amorphous, thus impending catalytical activity compared to crystalline samples. Employing a combination of characterization techniques including laser confocal microscopy (LEXT), atomic force microscopy (AFM) and TEM, the original state of the thin film electrodes and changes thereof during the HER are analyzed. The direct combination of identical location TEM, selected area diffraction (SAED) and energy dispersive X-ray analysis (EDX) with electrochemical measurements allows the detailed visualization of changes in the thin film structure and composition during HER.

The current experiments cannot confirm the leaching of Mo to be relevant in the observed time and current density ranges, as reported in literature for higher Mo content alloys. Therefore, further experiments will include long-term identical location studies on amorphous as well as crystalline NiMo thin films in order to elucidate the effects of HER on the material.