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• Understanding catalysts structural/electronic properties under operating conditions. • Elucidating Fe doping's role in iron-molybdenum sulfide electrocatalysts. • Identification of active species in HER molybdenum sulfides. • Understanding HER activity promoted by iron-doped and non-doped MoS x. • X-ray absorption spectroscopy investigation of amorphous molybdenum sulfides. The comprehensive characterization of the structure-electrocatalytic activity relationships is of great interest to support the development of efficient catalysts for hydrogen evolution reaction (HER) in proton-exchange membrane (PEM) electrolyzers. The successful implementation of a bimetallic iron-molybdenum sulfide electrocatalyst for HER into a PEM electrolyzer has been reported. However, the precise nature of their active sites is still elusive. In this study, we employed X-ray absorption spectroscopy (XAS) to study iron-molybdenum and molybdenum sulfides obtained by a microwave irradiation synthetic approach. Operando XAS measurements in an acidic environment revealed sulfur-defective amorphous MoS x and FeS phases. Although the amount of dopant Fe is 10 times lower than that of Mo, the synergy between the two phases promotes the HER performance of iron-molybdenum sulfides. [ABSTRACT FROM AUTHOR]

To reduce the platinum group metal (PGM) loading in anion exchange membrane fuel cells (AEMFCs), it is important to transition to catalysts with very low PGM content, and eventually to catalysts that are completely PGM-free. In this work, four supported low-PGM Pt and PtRu catalysts were prepared using a new, simple, scalable technique: Controlled Surface Tension (CST) method. CST allows for a high density of very small multi-atom clusters. Catalysts were physically characterized using a wide array of techniques and tested for their ORR and HOR activity both ex-situ and integrated into operating AEMFCs. The PGM loading was reduced by a factor of 14 while achieving comparable performance to commercial catalysts. AEMFCs were also assembled with ultralow PGM loading (0.05 mgPGM cm-2), where PtRu anodes were paired with Fe–N–C cathodes to achieve a specific power of 25 W/mg PGM (40 W/mg Pt). [Display omitted] • Simple synthesis of multi-atom clusters of supported Pt and PtRu. • Quantified the ex-situ and in-situ activity of the catalysts. • AEMFCs with record-high specific peak power density. • Demonstrated very high performance with only 0.05mgPGM/cm2 loading. • Exceeded DOE 2022 target for initial AEMFC performance. [ABSTRACT FROM AUTHOR]