The oxygen evolution reaction is highly crucial in producing molecules and energy carriers that use electrons. Multiple technologies producing alternative fuels for transportation are based on an electrochemical mechanism that splits water molecules to produce oxygen. However, a catalyst is required to enable this reaction, and current versions require the usage of rare and expensive materials like iridium, limiting the potential of such fuel production.
Fig 1: Schematic representation of the Ni and Fe nanoparticles and the Ni-Fe Janus nanoparticles synthesis through the oleate-assisted micelle formation and the illustration on the HER across the Ni-γ-Fe2O3 interface in alkaline medium. b STEM-HAADF image of a single Ni–Fe NP nanoparticle and its corresponding EDS line-scan spectrum (scale bar: 1 nm). c High-resolution EDS mapping on STEM-HAADF images of the nanoparticles for Ni and Fe selected area electron diffraction inset (image scale bars: 20 nm; SAED scale bar: 2 nm−1).
The MIT researchers discovered that by substituting the metal oxide in such materials with particular metal hydroxides, they could develop precisely tunable materials that were also stable enough to be useful as catalysts.
Combining enzyme systems' inherent tunability with well-known oxide-based catalysts can result in the breakthrough potential for high activity and stability.
A new type of catalyst called the metal hydroxide-organic framework (MHOF) synthesized by transforming layered hydroxides into two-dimensional sheets crosslinked using aromatic carboxylate linkers is inexpensive and has abundant components.
Fig 2: Structural design and stability optimization of MHOFs
MHOFs serve as a customizable catalytic platform for the oxygen evolution reaction, with stability dictated by the π–π interactions between adjacent stacking linkers and catalytic activity modulated by the nature of transition metals in the hydroxides. The oxygen evolution reaction activity is increased by nearly three orders of magnitude per metal site when Ni-based MHOFs are substituted with acidic cations or electron-withdrawing linkers, with Fe substitution yielding a mass activity of 80 A gcatalyst1 at 0.3 V overpotential for 20 hours. The improved oxygen evolution reaction activity is linked to the MHOF-based manipulation of Ni redox and the optimal binding of oxygenated intermediates, according to density functional theory calculations.
Reference: Yuan, S., Peng, J., Cai, B. et al. Tunable metal hydroxide–organic frameworks for catalyzing oxygen evolution. Nat. Mater. (2022). DOI: 10.1038/s41563-022-01199-0
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