Mixed bimetallic oxides offer great opportunities for a systematic tuning of electrocatalytic activity and stability. Here, we demonstrate the power of this strategy using well-defined thermally prepared Ir–Ni mixed oxide thin film catalysts for the electrochemical oxygen evolution reaction (OER) under highly corrosive conditions such as in acidic proton exchange membrane (PEM) electrolyzers and photoelectrochemical cells (PEC). Variation of the Ir to Ni ratio resulted in a volcano type OER activity curve with an unprecedented 20-fold improvement in Ir mass-based activity over pure Ir oxide. In situ spectroscopic probing of metal dissolution indicated that, against common views, activity and stability are not directly anticorrelated. To uncover activity and stability controlling parameters, the Ir–Ni mixed thin oxide film catalysts were characterized by a wide array of spectroscopic, microscopic, scattering, and electrochemical techniques in conjunction with DFT theoretical computations. By means of an in...

Molecular insight in structure and activity of highly efficient, low-Ir Ir-Ni oxide catalysts for electrochemical water splitting (OER)

The influence of particle size on the oxygen reduction reaction (ORR) activity of Pt was examined in three different electrolytes: two acidic solutions, with varying anionic adsorption strength (HClO(4) < H(2)SO(4)); and an alkaline solution (KOH). The experiments show that the absolute ORR rate is dependent on the supporting electrolyte; however, the relationship between activity and particle size is rather independent of the supporting electrolyte. The specific activity (SA) toward the ORR rapidly decreases in the order of polycrystalline Pt > unsupported Pt black particles (~30 nm) > high surface area (HSA) carbon supported Pt nanoparticle catalysts (of various size between 1 and 5 nm). In contrast to previous work, it is highlighted that the difference in SA between the individual HSA carbon supported catalysts (1 to 5 nm) is rather trivial and that the main challenge is to understand the significant differences in SA between the polycrystalline Pt, unsupported Pt particles, and HSA carbon supported Pt catalysts. Finally, a comparison between measured and modeled activities (based on the distribution of surface planes and their SAs) for different particle sizes indicates that such simple models do not capture all aspects of the behavior of HSA carbon supported catalysts.

http://ma.ecsdl.org/content/MA2012-02/13/1520.full.pdf

The Particle Size Effect on the Oxygen Reduction Reaction Activity of Pt Catalysts: Influence of Electrolyte and Relation to Single Crystal Models

Single‐Atom Catalysts for Electrocatalytic Applications

Recent advances in palladium-based electrocatalysts for fuel cell reactions and hydrogen evolution reaction

Understanding the structure-performance relationship of active sites at atomic scale

Nitrogen-coordinated metal single atoms in carbon have aroused extensive interest recently and have been growing as an active research frontier in a wide range of key renewable energy reactions and devices Herein, a step-by-step self-assembly strategy is developed to allocate nickel (Ni) and iron (Fe) single atoms respectively on the inner and outer walls of graphene hollow nanospheres (GHSs), realizing separate-sided different single-atom functionalization of hollow graphene The Ni or Fe single atom is demonstrated to be coordinated with four N atoms via the formation of a Ni-N4 or Fe-N4 planar configuration The developed Ni-N4 /GHSs/Fe-N4 Janus material exhibits excellent bifunctional electrocatalytic performance, in which the outer Fe-N4 clusters dominantly contribute to high activity toward the oxygen reduction reaction (ORR), while the inner Ni-N4 clusters are responsible for excellent activity toward the oxygen evolution reaction (OER) Density functional theory calculations demonstrate the structures and reactivities of Fe-N4 and Ni-N4 for the ORR and OER The Ni-N4 /GHSs/Fe-N4 endows a rechargeable Zn-air battery with excellent energy efficiency and cycling stability as an air-cathode, outperforming that of the benchmark Pt/C+RuO2 air-cathode The current work paves a new avenue for precise control of single-atom sites on carbon surface for the high-performance and selective electrocatalysts

Dual Single-Atomic Ni-N4 and Fe-N4 Sites Constructing Janus Hollow Graphene for Selective Oxygen Electrocatalysis

Freestanding ultrathin 2D noble metal nanosheets have drawn enormous attention due to their potential applications in various fields. However, the synthesis of 2D noble metal nanosheets still remains a great challenge due to the lack of an intrinsic driving force for anisotropic growth of 2D structures. Here, a facile one-pot synthesis of ultrathin freestanding porous Pd nanosheets (≈2.5 µm in lateral size and 10 nm in thickness) flexibly knitted by interweaved ultrathin nanowires with the assistance of poly(diallyldimethylammonium chloride) is presented. Nanoparticles attachment and subsequent self-assembly in the synthetic process are responsible for the formation of such intriguing nanostructures. Moreover, finely controlling the pH value of the precursor solution leads to yield different Pd nanostructures with tunable dimensionalities, including 3D nanoflowers, 2D nanosheets, and 1D nanochains. Owing to the unique structural features, the obtained freestanding porous Pd nanosheets exhibit excellent electrocatalytic activity and stability towards formic acid oxidation compared to those of other dimensional counterparts and commercial Pd black.

One‐Pot Synthesis of Freestanding Porous Palladium Nanosheets as Highly Efficient Electrocatalysts for Formic Acid Oxidation

The rational design of economical and high-performance nanocatalysts to substitute Pt for the oxygen reduction reaction (ORR) is extremely desirable for the advancement of sustainable energy-conversion devices. Isolated single atom (ISA) catalysts have sparked tremendous interests in electrocatalysis due to their maximized atom utilization efficiency. Nevertheless, the fabrication of ISA catalysts remains a grand challenge. Here, a template-assisted approach is demonstrated to synthesize isolated Fe single atomic sites anchoring on graphene hollow nanospheres (denoted as Fe ISAs/GHSs) by using Fe phthalocyanine (FePc) as Fe precursor. The rigid planar macrocycle structure of FePc molecules and the steric-hindrance effect of graphene nanospheres are responsible for the dispersion of Fe-N x species at an atomic level. The combination of atomically dispersed Fe active sites and highly steady hollow substrate affords the Fe ISAs/GHSs outstanding ORR performance with enhanced activity, long-term stability, and better tolerance to methanol, SO2, and NO x in alkaline medium, outperforming the state-of-the-art commercial Pt/C catalyst. This work highlights the great promises of cost-effective Fe-based ISA catalysts in electrocatalysis and provides a versatile strategy for the synthesis of other single metal atom catalysts with superior performance for diverse applications.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201801103

Isolated Fe Single Atomic Sites Anchored on Highly Steady Hollow Graphene Nanospheres as an Efficient Electrocatalyst for the Oxygen Reduction Reaction.

One-dimensional (1D) Au nanowires with narrow diameters and high aspect ratios have attracted increasing attention because of their distinctive physicochemical properties and extensive applications. Despite significant advancements in the synthesis of 1D Au nanowires, many of the early reported synthetic strategies usually involve complicated procedures and commonly produce Au nanowires with large diameters, low aspect ratios and low yields. Herein, we report a feasible α-naphthol-assisted preparation of ultrathin Au nanowires with an extremely rapid reaction rate (completed in ∼1 min) under moderate conditions. The resultant Au nanowires possess a Boerdijk–Coxeter helix-structured morphology dominated by (111) facets. The rapid coordination-induced formation of Au nanowire-arrayed microspheres and their gradual dissociation account for the formation of ultrathin Au nanowires. Due to the 1D anisotropy, plentiful surface atoms and abundant structural defects, these ultrathin Au nanowires exhibit outstanding electrocatalytic performance toward the oxygen reduction reaction (ORR) with boosted activity, durability and alcohol resistance compared to Au nanowire-arrayed microspheres, Au nanoparticles and a commercial Pt black catalyst. The present work provides a novel perspective for synthesis of ultrathin Au nanowires with various promising applications.

Highly simple and rapid synthesis of ultrathin gold nanowires with (111)-dominant facets and enhanced electrocatalytic properties

A universal sacrificial template-based synthesis strategy was reported to prepare three dimensional (3D) reduced oxide graphene supported PtM (M=Fe, Co, Ni) hollow nanospheres (PtM/RGO HNSs). The inner 3D wrinkle-free graphene skeleton can promote electron and ion kinetics, resulting in enhancement for the permeation of small organic molecule in fuel cells. As inspired by this, the 3D PtM (M=Fe, Co, Ni)/RGO HNSs exhibit clearly enhanced electrocatalytic activity and durability towards the methanol oxidation reaction (MOR) in acidic medium compared with a commercial Pt/C catalyst. This study provides a versatile approach of realizing controlled synthesis of 3D graphene-metal hybrid nanostructures irrespective of the components of the metal domains, and will pave the way for the design of hetero-nanostructures with optimized morphologies and functions.

A General Strategy for the Synthesis of PtM (M=Fe, Co, Ni) Decorated Three-Dimensional Hollow Graphene Nanospheres for Efficient Methanol Electrooxidation

Xiaoyu Qiu

Papers

Dual Single-Atomic Ni-N4 and Fe-N4 Sites Constructing Janus Hollow Graphene for Selective Oxygen Electrocatalysis

One‐Pot Synthesis of Freestanding Porous Palladium Nanosheets as Highly Efficient Electrocatalysts for Formic Acid Oxidation

Isolated Fe Single Atomic Sites Anchored on Highly Steady Hollow Graphene Nanospheres as an Efficient Electrocatalyst for the Oxygen Reduction Reaction.

Highly simple and rapid synthesis of ultrathin gold nanowires with (111)-dominant facets and enhanced electrocatalytic properties

A General Strategy for the Synthesis of PtM (M=Fe, Co, Ni) Decorated Three-Dimensional Hollow Graphene Nanospheres for Efficient Methanol Electrooxidation