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Researchers at the University of Arkansas, with colleagues from Brookhaven National Lab and Argonne National Lab, have found that nanoparticles composed of nickel and iron are more effective and efficient than other more costly materials when used as catalysts in the production of hydrogen fuel through water electrolysis.

A paper on their work is published in the journal Nanoscale.

Researchers at the U of A have designed nanoparticles that act as catalysts, making the process of water electrolysis more efficient. Credit: Jingyi Chen, Lauren Greenlee and Ryan Manso.

Controlling the 3-D morphology of nanocatalysts is one of the underexplored but important approaches for improving the sluggish kinetics of the oxygen evolution reaction (OER) in water electrolysis. This work reports a scalable, oil-based method based on thermal decomposition of organometallic complexes to yield highly uniform Ni–Fe-based nanocatalysts with a well-defined morphology (i.e. Ni–Fe core–shell, Ni/Fe alloy, and Fe–Ni core–shell). Transmission electron microscopy reveals their morphology and composition to be NiO_x–FeO/NiO_x core-mixed shell, NiO_x/FeO_x alloy, and FeO_x–NiO_x core–shell.

… The Ni diffusion from the amorphous Ni-based core to the iron oxide shell makes the NiO_x–NiO_x/FeO_x core-mixed shell structure the most active and the most stable nanocatalyst, which outperforms the comparison NiO_x/FeO_x alloy nanoparticles expected to be active for the OER.

This study suggests that the chemical environment of the mixed NiO_x/FeO_x alloy composition is important to achieve high electrocatalytic activity for the OER and that the 3-D morphology plays a key role in the optimization of the electrocatalytic activity and stability of the nanocatalyst for the OER.

—Manso et al.

University of Arkansas researchers Jingyi Chen, associate professor of physical chemistry, Lauren Greenlee, assistant professor of chemical engineering and colleagues discovered that when nanoparticles composed of an iron and nickel shell around a nickel core are applied to the process, they interact with the hydrogen and oxygen atoms to weaken the bonds, increasing the efficiency of the reaction by allowing the generation of oxygen more easily. Nickel and iron are also less expensive than other catalysts, which are made from scarce materials.

… we developed a scalable, oil-based synthesis based on the thermal decomposition of organometallic complexes that could manipulate both the morphology and crystalline phase of the Ni–Fe-based nanocatalysts. Highly uniform Ni–Fe-based nanostructures with different morphologies (i.e. Ni–Fe core–shell, Ni/Fe alloy, and Fe–Ni core–shell) were synthesized via either sequential or simultaneous injection.

… the amorphous, disordered nature of the NiO_x core, which appears to be most similar to α-Ni(OH)₂, allowed the diffusion of Ni into the FeO_x for the NiO_x–NiO_x/FeO_x core-mixed shell nanoparticles. The resultant mixed metal hydroxide/oxide shell provided the most active and stable nanocatalyst, which outperformed the comparison NiO_x/FeO_x alloy nanoparticles with a 1 : 1 composition expected to be active for the OER. These findings highlight that not only the crystallinity, but also the 3-D morphology, phase, and chemical environment of both metal species, disorder, and composition can significantly affect the electrocatalytic activity and stability of nanocatalysts for the alkaline OER.

—Manso et al.

Resources

• Ryan H. Manso, Prashant Acharya, Shiqing Deng, Cameron C. Crane, Benjamin Reinhart, Sungsik Lee, Xiao Tong, Dmytro Nykypanchuk, Jing Zhu, Yimei Zhu, Lauren F. Greenlee* and Jingyi Chen (2019) “Controlling the 3-D morphology of Ni–Fe-based nanocatalysts for the oxygen evolution reaction” Nanoscale doi: 10.1039/C8NR10138H