Low Iridium Content Confined inside a Co₃O₄ Hollow Sphere for Superior Acidic Water Oxidation

Abstract

Noble-metal-oxide support catalysts have been demonstrated to be unique for electrocatalytic water oxidation in acidic media. Highly porous three-dimensional oxide supported can serve as an ideal platform to confine ultrasmall metal catalysts on specific sites and modulate their reactivity, resulting in the reduction of noble metal content in the catalyst by boosting the mass activity. However, due to poor control over the support morphology, geometricdriven shifts in mass activity of metal-oxide support catalysts for the oxygen evolution reaction in acidic media have not been realized. Herein, a nanoscale Kirkendall effect is exploited to produce and control a structural evolution yielding an oxygen-evolving catalyst that is highly efficient and robust in acidic medium. By selective reaction−diffusion under oxidizing conditions, the starting solid CoIr NC is directly transformed into an unprecedented Ir−Co 3 O 4 @Co 3 O 4 porous-core@shell hollow nanospheres (ICO PCSHS), in which an ultrasmall Ir catalyst is spatially isolated within a porous Co 3 O 4 -backbone core, encapsulated by a hollow Co 3 O 4 outer shell. With a low Ir content of 14 wt %, the iridium mass activity exhibited by ICO PCSHS-400 catalyst is 24 times higher than that of benchmark RuO 2 , substantially exceeding the known oxide-supported metal catalysts. More importantly, the electrocatalyst shows high stability during 8 h of continuous testing in acidic medium.

Two‐Dimensional Metal‐Organic Framework Nanosheet Supported Noble Metal Nanocrystals for High‐Efficiency Water Oxidation

“…Notably, the existence of Ir-O bonds indicated a high oxidation state of Ir (e.g., Ir (III) or Ir (IV)) on the surface of the nanocrystals, implying a charge migration via oxygen-containing functional groups. [5,36] In the Ir 4f spectrum of Ir-Ni-NS, Ir (IV) 4f 7/2 and Ir (IV) 4f 5/2 peaks at 62.0 and 64.8 eV, respectively, further verified the above results (Figure 3d and S7, Supporting Information). [37,38] Moreover, compared with Ni-NS, the Ni 2p spectra of Ir-Ni-NS exhibited a red shift of 0.7 eV (Figure 3c), indicating a charge migration from O to Ni (II) ions.…”

Recent Development of Oxygen Evolution Electrocatalysts in Acidic Environment

“…[85] For example, Figure 5c displays a highly active and robust hexagonal ruthenium oxide NSs evolved from layered NaRuO 2 . [73] Third, a class of catalysts with 3D structures, such as 3D Ir superstructure, [86] core-shell IrO 2 @RuO 2 , [42] 3D nanoporous Ir 25 Os 75 alloy, [87] Cudoped RuO 2 hollow porous polyhedral, [74] and so on, [88,89] have been synthesized as OER catalysts in acid. These 3D structures are believed to offer more active sites for better efficiency.…”

Understanding Surface Modulation to Improve the Photo/Electrocatalysts for Water Oxidation/Reduction

“…Electrocatalytic reactions typically involve multiple, successive steps occurring on the interface of a solid electrocatalyst and the electrolytes [108][109][110][111][112][113]. It is generally known that the adsorption of reactants is considered the initial step, followed by the reaction, and finally desorption for any kind of heterogeneous catalytic processes.…”