Probing the activity and stability of MoO2 surface nanorod arrays for hydrogen evolution in an anion exchange membrane multi-cell water electrolysis stack

he development of sustainable electrocatalysts is essential for promoting anion exchange membrane water electrolysis (AEMWE) technology. Ni-Mo and MoO2 materials have enhanced alkaline hydrogen evolution reaction (HER) activity. This study investigates an active HER catalyst synthesized from MoNiO4 nano-rod arrays on nickel foam using high-temperature reductive annealing. Complete characterization of the nanostructure by SEM, HR-TEM and XPS indicates that during synthesis the crystalline MoNiO4 structure of individual rods segregates a surface enriched polycrystalline MoO2 layer rather than a Ni4Mo alloy as reported previously. Mo and Ni electrochemical dissolution was studied by the scanning flow cell technique coupled with inductively coupled plasma mass spectrometry (SFC-ICP-MS). It was found that only Mo undergoes detectable dissolution phenomena, with the MoO2/Ni cathode prepared at 600 °C being the most stable. Tests in an AEMWE with a Ni foam anode demonstrate a current density of 0.55 A cm-2 (2 V) at 60 °C and H2 production was stable for more than 300 h (0.5 A cm-2). The synthesis procedure was scaled up to prepare electrodes with an area of 78.5 cm2 that were employed and evaluated in a three-cell AEM electrolyser stack.