In this study, we report the synthesis and characterization of non-precious bimetallic ironmolybdenum sulfide bioinspired electrocatalysts for the hydrogen evolution reaction (HER).Iron-molybdenum sulfide materials were obtained through three distinct scalable synthetic approaches using microwave irradiation or heat treatment in furnace under inert and reductive atmospheres. These electrocatalysts were combined with carbon nanotubes (CNTs) and their activity for the hydrogen evolution reaction (HER) was studied in acidic environment. The most efficient composite material of the series was obtained by microwave synthesis and displays a current density per geometric area of 10 mAcm -2 at an overpotential of 140 mV with unity faradaic efficiency for hydrogen evolution. This composite cathode catalyst was implemented into a proton exchange membrane (PEM) electrolyzer single cell with iridium black as anode catalyst and could be operated at 0.5 Acm -2 requiring less than 300 mV additional voltage compared to Pt, and with remarkable stability during accelerated stress testing.PEM-compatible oxygen evolution reaction (OER) catalysts based on Earth-abundant elements. [99][100] ASSOCIATED CONTENT Supporting Information. Supporting Information. Additional experimental details, PEM electrolyzer setup, SEM images, Raman spectra, XPS spectra, electrochemical results (PDF).

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Cobalt-promoted molybdenum sulfide (CoMoS) is known as a promising catalyst for H2 evolution reaction and hydrogen desulfurization reaction. This material exhibits superior catalytic activity as compared to its pristine molybdenum sulfide counterpart. However, revealing the actual structure of cobalt-promoted molybdenum sulfide as well as the plausible contribution of a cobalt promoter is still challenging, especially when the material has an amorphous nature. Herein, we report, for the first time, on the use of positron annihilation spectroscopy (PAS), being a nondestructive nuclear radiation-based method, to visualize the position of a Co promoter within the structure of MoS at the atomic scale, which is inaccessible by conventional characterization tools. It is found that at low concentrations, a Co atom occupies preferably the Mo-vacancies, thus generating the ternary phase CoMoS whose structure is composed of a Co-S-Mo building block. Increasing the Co concentration, e.g., a Co/Mo molar ratio of higher than 1.12/1, leads to the occupation of both Mo-vacancies and S-vacancies by Co. In this case, secondary phases such as MoS and CoS are also produced together with the CoMoS one. Combining the PAS and electrochemical analyses, we highlight the important contribution of a Co promoter to enhancing the catalytic H2 evolution activity. Having more Co promoter in the Mo-vacancies promotes the H2 evolution rate, whereas having Co in the S-vacancies causes a drop in H2 evolution ability. Furthermore, the occupation of Co to the S-vacancies leads also to the destabilization of the CoMoS catalyst, resulting in a rapid degradation of catalytic activity.