Isolating the Electrocatalytic Activity of a Confined NiFe Motif within Zirconium Phosphate

Abstract

Unique classes of active‐site motifs are needed for improved electrocatalysis. Herein, the activity of a new catalyst motif is engineered and isolated for the oxygen evolution reaction (OER) created by nickel–iron transition metal electrocatalysts confined within a layered zirconium phosphate matrix. It is found that with optimal intercalation, confined NiFe catalysts have an order of magnitude improved mass activity compared to more conventional surface‐adsorbed systems in 0.1 m KOH. Interestingly, the confined environments within the layered structure also stabilize Fe‐rich compositions (90%) with exceptional mass activity compared to known Fe‐rich OER catalysts. Through controls and by grafting inert molecules to the outer surface, it is evidenced that the intercalated Ni/Fe species stay within the interlayer during catalysis and serve as the active site. After determining a possible structure (wycherproofite), density functional theory is shown to correlate with the observed experimental compositional trends. It is further demonstrated that the improved activity of this motif is correlated to the Fe and water content/composition within the confined space. This work highlights the catalytic enhancement possibilities available through zirconium phosphate and isolates the activity from the intercalated species versus surface/edge ones, thus opening new avenues to develop and understand catalysts within unique nanoscale chemical environments.

Single-Source Deposition of Mixed-Metal Oxide Films Containing Zirconium and 3d Transition Metals for (Photo)electrocatalytic Water Oxidation

“… 52 These methods for the fabrication of Zr-based mixed-metal films usually require annealing at high temperatures for the solid-state reaction of the precursors 51 , 53 or multistep synthetic routes for the incorporation of the dopant. 50 , 54 Moreover, MOFs containing a variety of transition metals acting as active sites have also been employed in electrocatalysts. 55 , 56 However, these usually present their own challenges, such as poor conductivity and stability, and are difficult to scale up.…”

New Applications of Zirconium Phosphate Nanomaterials

“…Nonetheless, in a recent joint study with close collaborators, a mixed metal (NiFe) active motif inside the interlayer of ZrP was isolated. 56 A different joint study with other close collaborators also shows signs that if a molecular Co-porphyrin catalyst is intercalated into ZrP, activity coming from the interlayer can be observed. 57 Meanwhile, our efforts were focused on improving the ZrP surface adsorbed catalysts.…”

“…Intercalated metals are possibly not electrochemically accessible to perform OER due to a variety of reasons, including mass transport limitations in which water is unable to access the active species in the interlayer, and or conductivity issues. Nonetheless, in a recent joint study with close collaborators, a mixed metal (NiFe) active motif inside the interlayer of ZrP was isolated . A different joint study with other close collaborators also shows signs that if a molecular Co-porphyrin catalyst is intercalated into ZrP, activity coming from the interlayer can be observed …”

“…This work highlights that the activity of this catalyst stems from the interlayer and isolates the active motif from surface or edge species. 56…”

“…In the electrocatalysis work, it is encouraging that a NiFe mixed metal OER catalytic system gives it best results at a Fe/(Fe+Ni) ratio of 90%, unique in this field, which suggest that the chemical microenvironment in ZrP could provide new efficient catalytic motifs based on earth-abundant catalysts. 56 Further studies, including operando measurements while obtaining XAS data in synchrotron facilities will allow us to gain insights into the nature of the active catalytic species. Mixed metal systems will be further studied, as well as bifunctional catalyst systems.…”