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When two metal precursors are reduced to form alloy nanoparticles (NPs), the final size usually varies by the composition because the reduction rate is different for each precursor. In this study, we report that the composition of IrPt alloy NPs can be easily controlled without affecting the size using an antisolvent crystallization-based method owing to the separation of the particle growth and precursor reduction steps. The synthesized IrPt alloy NPs displayed low overpotentials in both hydrogen evolution reaction (65 mV with a Tafel slope of 32.2 mV dec–1) and oxygen evolution reaction (240 mV with a Tafel slope of 77.9 mV dec–1) to deliver a current density of 10 mA cm–2 in H2SO4 (0.5 M), showing their enhanced electrocatalytic activities compared with the pure Pt and Ir catalysts. [ABSTRACT FROM AUTHOR]

Tantalum cobalt nitride photocatalysts were preparedusing a simpledrop coating method on a Ta foil substrate followed by thermal ammoniatreatment, and their photoelectrochemical (PEC) properties for wateroxidation under visible light were studied. The resulting Ta0.9Co0.1Nxfilms showed a photocurrentof ca. 1.5 mA/cm2(12 times higher than that of Ta3N5) under 100 mW/cm2visible light irradiationat 0.7 V vs Ag/AgCl in a 0.1 M Na2SO4aqueoussolution (pH 11). The good PEC performance was attributed to the introductionof cobalt and the formation of cobalt nitride, which efficiently facilitateselectron transfer and suppresses the recombination of photogeneratedelectron–hole pairs. Some cobalt nitride could further be oxidizedto generate cobalt oxide, which serves as an efficient electrocatalystfor water oxidation. The enhanced visible light activity and filmstability under light irradiation make tantalum cobalt nitride a promisingsemiconductor for PEC water oxidation. [ABSTRACT FROM AUTHOR]

Oxygen-based electrocatalysis is an integral aspect of a clean and sustainable energy conversion/storage system. The development of economic bifunctional electrocatalysts with high activity and durability during reversible reactions remains a great challenge. The tailored porous structure and separately presented active sites for oxygen reduction and oxygen evolution reactions (ORR and OER) without mutual interference are most crucial for achieving desired bifunctional catalysts. Here, we report a hybrid composed of sheath-core cobalt oxynitride (CoO x @CoN y ) nanorods grown perpendicularly on N-doped carbon nanofiber (NCNF). The brush-like CoO x @CoN y nanorods, composed of metallic Co 4 N cores and oxidized surfaces, exhibit excellent OER activity ( E = 1.69 V at 10 mA cm -2 ) in an alkaline medium. Although pristine NCNF or CoO x @CoN y alone had poor catalytic activity in the ORR, the hybrid showed dramatically enhanced ORR performance ( E = 0.78 V at -3 mA cm -2 ). The experimental results coupled with a density functional theory (DFT) simulation confirmed that the broad surface area of the CoO x @CoN y nanorods with an oxidized skin layer boosts the catalytic OER, while the facile adsorption of ORR intermediates and a rapid interfacial charge transfer occur at the interface between the CoO x @CoN y nanorods and the electrically conductive NCNF. Furthermore, it was found that the independent catalytic active sites in the CoO x @CoN y /NCNF catalyst are continuously regenerated and sustained without mutual interference during the round-trip ORR/OER, affording stable operation of Zn-air batteries.

A simple wet-chemical route for the preparation of core-shell-structured catalysts was developed to achieve high oxygen reduction reaction (ORR) activity with a low Pt loading amount. Nickel nitride (Ni 3 N) nanoparticles were used as earth-abundant metal-based cores to support thin Pt layers. To realize the site-selective formation of Pt layers on the Ni 3 N core, hydrogen molecules (H 2 ) were used as a mild reducing agent. As H 2 oxidation is catalyzed by the surface of Ni 3 N, the redox reaction between H 2 and Pt(IV) in solution was facilitated on the Ni 3 N surface, which resulted in the selective deposition of Pt on Ni 3 N. The controlled Pt formation led to a subnanometer (0.5-1 nm)-thick Pt shell on the Ni 3 N core. By adopting the core-shell structure, higher ORR activity than the commercial Pt/C was achieved. Electrochemical measurements showed that the thin Pt layer on Ni 3 N nanoparticle exhibits 5 times higher mass activity and specific activity than that of commercial Pt/C. Furthermore, it is expected that the proposed simple wet-chemical method can be utilized to prepare various transition-metal-based core-shell nanocatalysts for a wide range of energy conversion reactions.

We studied the electrochemical synthesis of NH 3 on Fe-CuS/C catalysts in an alkaline aqueous solution under ambient conditions. The metal chalcogenide catalyst is active in the nitrogen reduction reaction (NRR) for approximately 45 min with an NH 3 production yield of 16 μg h -1 cm -2 at -0.4 V RHE , while it decomposes to CuO. The rapid degradation of the catalyst hinders the precise investigation of the NH 3 production activity in longer time measurements. Herein, the electrochemical NH 3 production rate is enhanced with increased overpotentials when the degradation effect is mitigated in the measurement, which was difficult to observe in the NRR reports. In the Tafel analysis, the exchange current density, heterogeneous rate constant, and transfer coefficient of the Fe-CuS/C catalyst on the NRR were estimated. When the electrode degradation is mitigated, one of the best NH 3 production activities among the reported metal sulfide electrochemical NRR catalysts is obtained, which is 42 μg h -1 cm -2 at -0.6 V RHE .

Multilevel data storage using resistive random access memory (RRAM) has attracted significant attention for addressing the challenges associated with the rapid advances in information technologies. However, it is still difficult to secure reliable multilevel resistive switching of RRAM due to the stochastic and multiple formation of conductive filaments (CFs). Herein, we demonstrate that a single CF, derived from selective oxidation by a structured Cu active electrode, can solve the reliability issue. High-quality pyramidal Cu electrodes with a sharp tip are prepared via the template-stripping method. Morphology-dependent surface energy facilitates the oxidation of Cu atoms at the tip rather than in other regions, and the tip-enhanced electric fields can accelerate the transport of the generated Cu ions. As a result, CF growth occurs mainly at the tip of the pyramidal electrode, which is confirmed by high-resolution electron microscopy and elemental analysis. The RRAM exhibits highly uniform and low forming voltages (the average forming voltage and its standard deviation for 20 pyramid-based RRAMs are 0.645 and 0.072 V, respectively). Moreover, all multilevel resistance states for the RRAMs are clearly distinguished and show narrow distributions within 1 order of magnitude, leading to reliable cell-to-cell performance for MLC operation.