Boosting OER performance of IrO2 in acid via urchin-like hierarchical-structure design

ZIFs-Derived Hollow Nanostructures via a Strong/Weak Coetching Strategy for Long-Life Rechargeable Zn-Air Batteries

Recently, zeolitic imidazolate frameworks (ZIFs) composites have emerged as promising precursors for synthesizing hollow-structured N-doped carbon-based noble-metal materials with diverse structures and compositions. Here, a strong/weak competitive coordination strategy is presented for synthesizing high-performance electrocatalysts with hollow features. During the competitive coordination process, the cubic zeolitic-imidazole framework-8 (Cube-8)@ZIF-67 with core-shell structures are transformed into Cube-8@ZIF-67@PF/POM with yolk-shell nanostructures employing phosphomolybdic acid (POM) and potassium ferricyanide (PF) as the strong chelator and the weak chelator, respectively. After calcination, the hollow Mo/Fe/Co@NC catalyst exhibits superior performance in both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Interestingly, the Mo/Fe/Co@NC catalyst exhibits efficient electrocatalytic performance for Zn-air batteries (ZABs), with a high power density (≈150 mW cm-2) and superior cycling life (≈500 h) compared to commercial platinum/carbon (Pt/C) and ruthenium dioxide (RuO2) mixture benchmarks catalysts. In addition, the density functional theory further proves that after the introduction of Mo and Fe atoms, the adsorption energy with the adsorption intermediates is weakened by adjusting the d-band center, thus weakening the reaction barrier and promoting the reaction kinetics of OER. Undoubtedly, this study presents novel insights into the fabrication of ZIFs-derived hollow structure bifunctional oxygen electrocatalysts for clean-energy diverse applications.

Modulated Electronic Structure of Co3O4 by Single Atoms for Efficient Anodic Oxygen Evolution in Acid

The challenge of the practical application of a water electrolyzer system lies in the development of low-manufacturing cost, highly active, and stable electrocatalysts to replace the noble metal ones, in order to enable environmentally friendly hydrogen production on a large scale. Herein, a facile method is proposed for boosting the performance of Co3O4 through the incorporation of large-sized single atoms. Due to the larger ionic radius of rare earth metals than that of Co, the incorporation elongates the bond length of Co─O, resulting in the narrowed d-p band centers and the high spin configuration, which is favorable for the interaction and charge transfer with absorbent (*OH). As a result, the Ce-incorporated Co3O4 with the longest Co─O bond length exhibits the best oxygen evolution reaction (OER) performance, specifically, the turnover frequency is over 17 times higher than that of pristine Co3O4 nanosheet under an overpotential of 400 mV. Powered by a commercial Si solar cell, a two-electrode solar water-splitting device combining Ce-incorporated Co3O4 and Pt delivers a solar-to-hydrogen conversion efficiency of 13.53%. The strategy could provide a new insight for improving the performance of OER electrocatalysts in acid toward practical applications.

Ce Single-Atom Incorporation Enhances the Oxygen Evolution Reaction of Co3O4 in Acid

Oxygen evolution reaction (OER) plays an important role in energy conversion processes such as water electrolysis and metal-air batteries. At present, finding a high-performance and low-cost catalyst for the OER in acidic media remains a great challenge. It is therefore important to develop efficient, robust, and inexpensive electrocatalysts by replacing noble metal-based catalysts with transition-metal electrocatalysts. Herein, we propose a facile method for incorporating Ce-metal single atoms into Co3O4 nanosheets to boost their OER activity and stability. Owing to the enhanced charge transfer and improved electronic structure resulting from Ce incorporation, the obtained Ce single-atom-doped Co3O4 nanosheet exhibits greatly enhanced OER performance. It achieves a 10 mA cm-2 current density under a low overpotential of 348 mV in a 0.5 M H2SO4 solution with excellent stability, outperforming the state-of-the-art non-noble electrocatalysts recently reported in acid.

Strain-Induced Electronic Structure Modulation on MnO2 Nanosheet by Ir Incorporation for Efficient Water Oxidation in Acid

Oxygen electrochemistry plays a key role in renewable energy technologies, such as fuel cells and electrolyzers, but its slow kinetics limits the performance and the commercialization of such devices. Here, a strained MnO2 nanosheet induced by Ir incorporation is developed with optimized electronic structure by a simple hydrothermal method. With the incorporation of Ir, the strain induces elongated Mn─O bond length, and thereby tuning the electronic structure to favor the oxygen evolution reaction (OER) performance. The obtained catalyst exhibits an excellent mass activity of 5681 A g-1 at an overpotential of 300 mV in 0.5 m H2 SO4 , and reaches 50 and 100 mA cm-2 at overpotentials of only 240 and 277 mV, respectively. The catalyst is also stable even at 300 mA cm-2 in 0.5 m H2 SO4 . Using the nanosheet as the OER catalyst and the Pt/C as the hydrogen evolution reaction catalyst, a two-electrode electrolyzer achieves 10 mA cm-2 with only a cell voltage of 1.453 V for overall water splitting in 0.5 m H2 SO4 . This strategy enables the material with high feasibility for practical applications on hydrogen production.

Nanostructured Iridium Oxide: State of the Art

Iridium Oxide (IrO2) is a metal oxide with a rutile crystalline structure, analogous to the TiO2 rutile polymorph. Unlike other oxides of transition metals, IrO2 shows a metallic type conductivity and displays a low surface work function. IrO2 is also characterized by a high chemical stability. These highly desirable properties make IrO2 a rightful candidate for specific applications. Furthermore, IrO2 can be synthesized in the form of a wide variety of nanostructures ranging from nanopowder, nanosheets, nanotubes, nanorods, nanowires, and nanoporous thin films. IrO2 nanostructuration, which allows its attractive intrinsic properties to be enhanced, can therefore be exploited according to the pursued application. Indeed, IrO2 nanostructures have shown utility in fields that span from electrocatalysis, electrochromic devices, sensors, fuel cell and supercapacitors. After a brief description of the IrO2 structure and properties, the present review will describe the main employed synthetic methodologies that are followed to prepare selectively the various types of nanostructures, highlighting in each case the advantages brought by the nanostructuration illustrating their performances and applications.

CoTe2–NiTe2 heterojunction directly grown on CoNi alloy foam for efficient oxygen evolution reaction

One-step fabrication of a self-supported CoTe2–NiTe2 heterojunction electrocatalyst directly grown on CoNi foam for efficient and durable oxygen evolution reactions.

Ultra-small RuO2/NHC nanocrystal electrocatalysts with efficient water oxidation activities in acidic media

RuO2/NHC3 with ultra-small and abundant electrochemically active sites requires a low overpotential of 186 mV at 10 mA cm−2 for acidic OER and maintains wonderful long-term stability within 27 h in 0.5 M H2SO4.