Role of water structure in alkaline water electrolysis

Efficient Alkaline Freshwater/Seawater Hydrogen Production via Heterogeneous N-Doped FeMoO4/Mo2N Rod-Shaped Electrocatalysts

Durable and efficient Fe-based electrocatalysts in alkaline freshwater/seawater electrolysis is highly desirable but persists a significant challenge. Herein, we report a durable and robust heterogenous nitrogen-doped FeMoO4/Mo2N rod-shaped catalyst on nickel foam (denoted NF@FMO/MN) affording hydrogen evolution reaction (HER) low overpotentials of 23/29 mV@10 mA cm-2 and 112/159 mV@100 mA cm-2 in both alkaline freshwater/seawater electrolytes, respectively. These results are significantly superior to the pristine FeMoO4 catalyst. Theoretical calculations consistently reveals that the combination of N-FeMoO4 and Mo2N effectively reduces water activation energy barrier, modulates the sluggish water-dissociation kinetics and accelerates the hydrogen adsorption process for efficient HER. The enhanced HER performance of the as-designed NF@FMO/MN catalyst is attributed to the in situ hetero-interfacial engineering between N-doped FeMoO4 and Mo2N. This present work nurtures the progress of FeMo-based electrocatalysts in alkaline freshwater/seawater electrolysis.

Coherent anti-Stokes Raman scattering spectroscopy system for observation of water molecules in anion exchange membrane

Anion exchange membrane fuel cells (AEMFCs) provide one of the most feasible remedies to fuel cells' dependency on the dwindling Pt group catalysts. Nevertheless, AEMFCs still suffer reduced durability, which requires an in-depth understanding of their membranes. The low thermal endurance of the anion exchange membranes (AEMs) usually limits the direct application of powerful techniques, such as Raman spectroscopy. We sought to establish a system for coherent anti-Stokes Raman scattering (CARS) spectroscopy capable of taking measurements inside an AEM rapidly and accurately without photodamage. A 785 nm CARS system was newly developed to study the water species in an AEM (QPAF-4) located vertically in a fuel cell. From the results of water measurement in a QPAF-4 membrane, the OH-related region was deconvoluted into nine Gaussian peaks: Five H-bonded OH peaks, non-H-bonded OH, OH-, and two CH peaks. The H-bonded species increased with increasing relative humidity, but the other species remained constant. These results open unlimited possibilities for studying and comparing different AEMFCs, enabling more rapid technology optimization.

Computational screening of layered metal chalcogenide materials for HER electrocatalysts, and its synergy with experiments

Layered materials have emerged as attractive candidates in our search for abundant, inexpensive and efficient hydrogen evolution reaction (HER) catalysts, due to larger specific area these offer. Among these, transition metal dichalcogenides have been studied extensively, while ternary transition metal tri-chalcogenides have emerged as promising candidates recently. Computational screening has emerged as a powerful tool to identify the promising materials out of an initial set for specific applications, and has been employed for identifying HER catalysts also. This article presents a comprehensive review of how computational screening studies based on density functional calculations have successfully identified the promising materials among the layered transition metal di- and tri-chalcogenides. Synergy of these computational studies with experiments is also reviewed. It is argued that experimental verification of the materials, predicted to be efficient catalysts but not yet tested, will enlarge the list of materials that hold promise to replace expensive platinum, and will help ushering in the much awaited hydrogen economy.