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Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of oxygen evolution electrocatalysts in acid. Herein we report iridium‐containing strontium titanates (Ir‐STO) as active and stable, low‐iridium perovskite electrocatalysts for the oxygen evolution reaction (OER) in acid. The Ir‐STO contains 57 wt % less iridium relative to the benchmark catalyst IrO2, but it exhibits more than 10 times higher catalytic activity for OER. It is shown to be among the most efficient iridium‐based oxide electrocatalysts for OER in acid. Theoretical results reveal that the incorporation of iridium dopants in the STO matrix activates the intrinsically inert titanium sites, strengthening the surface oxygen adsorption on titanium sites and thereby giving nonprecious titanium catalytic sites that have activities close to or even better than iridium sites. [ABSTRACT FROM AUTHOR]

The overall water splitting into hydrogen and oxygen is one of the most promising ways to store intermittent solar and wind energy in the form of chemical fuels. However, this process is quite thermodynamically uphill, and thus needs to be mediated simultaneously by efficient hydrogen evolving and oxygen evolving catalysts to get any feasible output from it. Herein, we report the synthesis of such a catalyst comprising ultrasmall Ni x Co 3−x S 4 -decorated Ni 3 S 2 nanosheet arrays supported on nickel foam (NF) via a partial cation exchange reaction between NF-supported Ni 3 S 2 nanosheet arrays and cobalt(II) ions. We show that the as-prepared material, denoted as Ni x Co 3−x S 4 /Ni 3 S 2 /NF, can serve as a self-standing, noble metal-free, highly active and stable, bifunctional electrocatalyst for the two half reactions involved in the overall water splitting: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Furthermore, we demonstrate that a high-performance electrolyzer for the overall water splitting reaction can be assembled by using Ni x Co 3−x S 4 /Ni 3 S 2 /NF as the electrocatalyst at both the cathode and the anode sides of the electrolyzer. This electrolyzer delivers water-splitting current densities of 10 and 100 mA/cm 2 at applied potentials of 1.53 and 1.80 V, respectively, with remarkable stability for >200 h in both cases. The electrolyzer's performance is much better than the performances of electrolyzers assembled from many types of other bifunctional electrocatalysts as catalyst couple. Moreover, the overall performance of the electrolyzer is comparable with the performances of electrolyzers containing two different, benchmark, monofunctional HER and OER electrocatalyst couple ( i.e. , Pt/C-IrO 2 ). [ABSTRACT FROM AUTHOR]

Making highly efficient catalysts for an overall water splitting reaction is vitally important to bring solar/electrical-to-hydrogen energy conversion processes into reality. Herein, the synthesis of ultrathin nanosheet-based, hollow MoO x/Ni3S2 composite microsphere catalysts on nickel foam, using ammonium molybdate as a precursor and the triblock copolymer pluronic P123 as a structure-directing agent is reported. It is also shown that the resulting materials can serve as bifunctional, non-noble metal electrocatalysts with high activity and stability for the hydrogen evolution reaction (HER) as well as the oxygen evolution reaction (OER). Thanks to their unique structural features, the materials give an impressive water-splitting current density of 10 mA cm−2 at ≈1.45 V with remarkable durability for >100 h when used as catalysts both at the cathode and the anode sides of an alkaline electrolyzer. This performance for an overall water splitting reaction is better than even those obtained with an electrolyzer consisting of noble metal-based Pt/C and IrO x/C catalytic couple-the benchmark catalysts for HER and OER, respectively. [ABSTRACT FROM AUTHOR]

The development of earth-abundant water oxidation electrocatalysts with high activity and durability is very important for many renewable energy conversion/storage processes. Herein, we report a facile synthetic method for the preparation of amorphous nickel-iron oxide/carbon composite nanofibers with high electrocatalytic activity and stability for the oxygen evolution reaction (OER). This method involves two main steps: (i) the electrospinning synthesis of Ni- and Fe-embedded polyvinylpyrrolidone (PVP) polymer nanofibers as the precursor and (ii) the thermal conversion of this precursor in air at 250 °C into nickel-iron oxide/carbon composite nanofibers. Moreover, we show that the as-obtained composite material exhibits a comparable catalytic activity and a superior catalytic stability to IrO x/C and RuO x, which are state-of-the-art noble-metal-based water oxidation electrocatalysts. In particular, the obtained amorphous nickel-iron oxide/carbon composite nanofibers with an optimal Ni/Fe molar ratio of 1:2 afford a small overpotential of 310 mV at a current density of 10 mA cm−2, show high catalytic stability for >15 h, and give >90 % Faradaic yield toward the OER. The efficient catalytic activity of the material can be attributed to its overall conducive structural features for the OER, mainly including the amorphous phase structure of nickel-iron oxide, tunable Ni/Fe atomic ratio, and strongly coupled interaction between nickel-iron oxide and nanocarbon. [ABSTRACT FROM AUTHOR]

In our efforts to obtain electrocatalysts with improved activity for water splitting, meticulous design and synthesis of the active sites of the electrocatalysts and deciphering how exactly they catalyze the reaction are vitally necessary. Herein, we report a one-step facile synthesis of a novel precious-metal-free hydrogen-evolution nanoelectrocatalyst, dubbed Mo2C@NC that is composed of ultrasmall molybdenum carbide (Mo2C) nanoparticles embedded within nitrogen-rich carbon (NC) nanolayers. The Mo2C@NC hybrid nanoelectrocatalyst shows remarkable catalytic activity, has great durability, and gives about 100 % Faradaic yield toward the hydrogen-evolution reaction (HER) over a wide pH range (pH 0-14). Theoretical calculations show that the Mo2C and N dopants in the material synergistically co-activate adjacent C atoms on the carbon nanolayers, creating superactive nonmetallic catalytic sites for HER that are more active than those in the constituents. [ABSTRACT FROM AUTHOR]

Layered double hydroxide has been used in a variety of areas, including but not limited to catalysis, energy storage, drug or gene delivery, water treatment, etc. Herein, we report a new simple hydrothermal method to prepare a high surface area flower-like Ni–Fe layered double hydroxide (LDH) assembled by nanosheets by using nickel alkoxide and FeSO4 as the only starting materials. It is free of alkaline solution and other additives for directing or supporting in the synthesis procedure. The formation mechanism of this flower-like LDH formed by ultrathin nanosheets is also discussed. Moreover, the as-obtained LDH material shows increased electrocatalytic activity and stability toward WOR in alkaline media compared with the materials prepared without a Ni alkoxide precursor or Fe precursor, namely α-Fe2O3 and Ni(OH)2, respectively. In addition, the electrocatalytic activity is demonstrated to be related to the molar ratio of Fe and Ni in the final Ni–Fe material, and the best activity is achieved when the ratio reaches 0.52 : 1. The phase compositions of the resulting Ni–Fex are discussed. Furthermore, the Ni–Fe LDH material reported herein might be employed as a promising noble-metal-free water oxidation catalyst to replace the IrOx material―the state-of-the-art water oxidation catalyst. [ABSTRACT FROM AUTHOR]

2D layered materials with atomic thickness have attracted extensive research interest due to their unique physicochemical and electronic properties, which are usually very different from those of their bulk counterparts. Heterojunctions or heterostructures based on ultrathin 2D materials have attracted increasing attention due to the integrated merits of 2D ultrathin components and the heterojunction effect on the separation and transfer of charges, resulting in important potential values for catalytic applications. Furthermore, 2D/2D heterostructures with face‐to‐face contact are believed to be a preferable dimensionality design due to their large interface area, which would contribute to enhanced heterojunction effect. Here, the cutting‐edge research progress in 2D/2D heterojunctions and heterostructures is highlighted with a specific emphasis on synthetic strategies, reaction mechanism, and applications in catalysis (photocatalysis, electrocatalysis, and organic synthesis). Finally, the key issues and development perspectives in the applications of 2D/2D layered heterojunctions and heterostructures in catalysis are also discussed. This work highlights the general strategies and recent progress in the synthesis and catalytic applications (involving photocatalysis, electrocatalysis, and organic synthesis) of 2D/2D heterojunctions, which are excellent candidates for the rational design of interfacial contacts to modify textural and electronic structures and thus the final catalytic performance. [ABSTRACT FROM AUTHOR]

T. Asefa, X. Zou, and co‐workers present a nickel foam‐supported, ultrathin nanosheet‐based, hollow Ni3S2‐based electrocatalyst for overall water splitting on page 4839. By using this material as electrocatalyst both at the cathode and the anode sides of an electrolyzer, a water‐splitting efficiency is achieved that outperforms even noble‐metal‐based Pt/C and IrOx/C benchmark electrolyzers. This result represents an important step toward efficient, non‐noble metal electrocatalyst‐based overall water splitting. [ABSTRACT FROM AUTHOR]

More active sites and high conductivity are two effective ways to improve the activity of non-noble metal electrocatalysts. Herein, we present a facile electrostatic spinning technique to synthesize highly dispersed CoSe 2 nanoparticles on three-dimensional nano-netlike carbon fibers through simple thermal treatment of polyacrylonitrile fibers containing Co ions (Co 2+ -PANF) and subsequent in-situ selenization. Moreover, we show that the resulting material (denoted as CoSe 2 -CFN) can serve as highly active, efficient and stable non-precious metal electrocatalyst for HER in acidic media. This material achieves a current density of 10 mA/cm 2 at an overpotential of 133 mV with a loading amount of the active material CoSe 2 about 0.128 mg/cm 2 , which is lower than that of the reported CoSe 2 -based materials. Meanwhile, CoSe 2 -CFN exhibits excellent catalytic stability for at least 20 h and gives nearly 100% Faradaic yield. The excellent hydrogen evolution reaction performance is due to the highly dispersed CoSe 2 nanoparticles providing more active sites as well as the high electrical conductivity of the carbon fibers. [ABSTRACT FROM AUTHOR]

The development of efficient and inexpensive water splitting electrocatalysts is essential for the large-scale production of hydrogen. Herein, we show that a novel nanohybrid with CoS nanosheets vertically grown on carbon cloth (CoS/CC) can be used as an efficient self-supported hydrogen-evolving cathode for water splitting over a wide pH range. This material affords a current density of 10 mA/cm 2 at a small overpotential of 192 mV and 212 mV in basic and acidic media, respectively, along with a long-term stability for over 50 h. The unique 3D structure constructed by the vertically arranged nanosheets and the intimate contact between the CoS nanosheets and the underlying conductive carbon are believed to be responsible for the excellent catalytic performance. [ABSTRACT FROM AUTHOR]

Elaborate design and synthesis of efficient and stable non-Pt electrocatalysts for some renewable energy-related conversion/storage processes is one of the major goals of sustainable chemistry. Herein, we report a facile, general, one-step synthetic method that leads to a family of non-noble metal hydrogen-evolving electrocatalysts that composed of metal phosphide nanoparticles embedded within nitrogen-doped carbon matrix. The synthesis of the materials is achieved via a facile one-step thermal treatment in inert atmosphere of homogeneously mixed urea, diammonium hydrogen phosphate and metal salts ( e.g. , ammonium molybdate for the synthesis of MoP). The use of inexpensive urea is crucial in the synthesis as it helps the deoxygenation-reduction of some metal salts and phosphor source ( i.e. , diammonium hydrogen phosphate) and undergoes in situ carbonization, leading to the formation of a composite material containing metal phosphide nanoparticles and nitrogen-doped carbon (NC) in one pot. Furthermore, we show that the resulting composite nanomaterials can serve as highly active, stable, noble metal-free electrocatalysts towards the hydrogen evolution reaction (HER). In particular, the MoP@NC material exhibits the best electrocatalytic activity in our study. This material affords a current density of 10 mA/cm 2 at a low overpotential of 135 mV, exhibits excellent catalytic stability as long as 20 h, and gives nearly 100% Faradaic yield towards HER. [ABSTRACT FROM AUTHOR]

Developing efficient nonprecious electrocatalysts to accelerate the hydrogen evolution reaction (HER) is of importance for the hydrogen energy technology. Herein, we report the in situ growth of single-crystalline γ -Cu 2 S nanoplates on copper foam (CF) in a hydrothermal system, with the assistance of a small amount of cobalt(II) acetate. The presence of cobalt(II) acetate in the synthesis system has been proven to have multiple roles: (i) inhibiting the formation of copper(I) oxide (Cu 2 O); (ii) directing the fromation of the crystal phase of γ - Cu 2 S; and (iii) controlling the morphology of the as-formed γ - Cu 2 S. Furthermore, we show that the resulting γ - Cu 2 S/CF material can serve as an efficient integrated 3D electrode toward HER at neutral pH. The γ - Cu 2 S/CF delivers a current density of 10 mA/cm 2 at a small overpotential of 190 mV, gives 100% Faradaic yield during HER, and maintains its electrocatalytic activity for >10 hours. To the best of our knowledge, this is the first time that a copper(I) sulfide-based material is demonstrated to electrocatalyze the HER efficiently. Identifying copper(I) sulfide as the active phase for HER and constructing advantageous 3D γ -Cu 2 S nanostructure via an ion-induced method might open a door for the further investigation of Cu-based hydrogen-evolution electrocatalysts. [ABSTRACT FROM AUTHOR]