Hollow‐Structured Metal Oxides as Oxygen‐Related Catalysts

Abstract

high overpotential and sluggish kinetics. Generally, Pt, IrO 2 , and RuO 2 noble metal catalysts have improved kinetics. But, the high cost and unsatisfactory long-term durability of noble-metal-based catalysts are the main limitations for large-scale commercial applications. Supplying flexible electronic structures, transition metal oxides are the optimal oxygen-related catalysts in which the adsorbents binding to metal cations (M) are neither too strong nor too weak. [9] With overall understanding of crystal structure for common transition metal oxides, it has been demonstrated that [MO 6 ] octahedral configuration effectively accelerates the charge transfer process during a redox reaction. [10] In the octahedral field, the transition metal 3d orbit will be split into e g and t 2g . The e g orbital directed toward an O 2 molecule overlaps the O-2p δ orbital more strongly than the overlap between the t 2g and O-2p π orbitals. It thereof determines the energy gained by both the adsorption/desorption of oxygen on transition metal ions. Furthermore, the hollow structure promotes their reaction kinetics and durability. [11,12] Here, we will focus on the hollow structures (spinels, perovskites, and rutiles) and their oxygenrelated catalysis properties. And general design strategies and precise fabrication of hollow-structured transition metal oxides for oxygen-related catalysis will be summarized. To simplify, the hollow structure discussed here is a system with independent inner voids and can be monodisperse. Advantage and Synthesis of Hollow Structures Importance of Hollow Structures in Oxygen-Related CatalysisA large surface area is critical for hollow structure in oxygenrelated catalysis. It can significantly increase the active sites and reduce the mass density of an energy conversion device. In some special systems, the consumption of co-catalysts (especially noble metal) could also be saved. [13] Meanwhile, large void size is another key feature for hollow structure. It will mitigate the effects of volume change, provide structural stability and enhance the metal-air battery cyclic performance. The interconnected channels will promote the mass transfer performance and enhance the rate capability. [14] In addition, the encapsulation ability of hollow structure can avoid catalyst poisoning and increase chemical and thermal stabilities. [15] With precise control of the geometric parameter (length, diameter, and shell thickness), a shortened charge transfer path is Metal oxide hollow structures with large surface area, low density, and high loading capacity have received great attention for energy-related applications. Acting as oxygen-related catalysts, hollow-structured transition metal oxides offer low overpotential, fast reaction rate, and excellent stability. Herein, recent progress in the oxygen-related catalysis (e.g., oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and metal-air batteries) of hollow-structured transition metal oxides is discussed. Through a comprehensive outline of hollo...

Designed Formation of Double‐Shelled Ni–Fe Layered‐Double‐Hydroxide Nanocages for Efficient Oxygen Evolution Reaction

“…Hollow nanostructures have exhibited desirable advantages as OER catalysts owing to their architectural features, such as large surface area, low density, multiple interfaces, and reduced diffusion lengths for mass transport. [ 25–27 ] Compared with single‐shelled hollow structures, hollow catalysts with the multi‐shelled feature exhibit apparent superiorities for electrocatalysis. [ 28–30 ] To be more specific, multi‐shells provide larger surface area and better utilization of the inner space.…”

Hollow cobalt-nickel phosphide nanocages for efficient electrochemical overall water splitting

“…In particular, transition metal phosphides, especially bimetallic transition metal phosphides have attracted significant attentions as bi-functional electrocatalysts for water-splitting owing to their remarkably enhanced catalytic activities [32,33]. To maximize the electrochemical performance of the catalysts, endowing the electrocatalysts with hollow nanostructures is regarded as an effective approach, which can significantly increase their specific surface areas and expose more reactive sites [34][35][36][37]. Moreover, the ion diffusion length and transport resistance for water splitting can be effectively reduced by their large void spaces, which has been fully demonstrated by previous studies [38][39][40].…”

Structure-induced hollow Co3O4 nanoparticles with rich oxygen vacancies for efficient CO oxidation

“…Besides, it has been reported that the surface atomic configuration of Co 3 O 4 was strongly influenced by its morphology [12]. Specially, metal oxides with hollow structures were demonstrated to possess more defect sites on their surfaces than the solid counterparts [13][14][15][16][17][18]. Therefore, we could reasonably speculate that fabrication of Co 3 O 4 with hollow structure may maximize the oxygen vacancies on its surface to achieve high catalytic efficiency in CO oxidation.…”