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Developing low‐cost and high‐activity pH‐universal hydrogen evolution reaction (HER) catalysts is very crucial to the industrialization of water electrolysis. However, the high price, low yield, and poor stability of current HER catalysts make them difficult to meet practical requirements. Herein, a plasma spraying technique is employed to prepare self‐supported Cu catalysts with tensile strain for the first time. The tensile strain upshifts the d‐band of Cu, improves the water dissociation and H* adsorption, eventually improves the intrinsic HER catalytic activity. As such, Cu electrode achieves overpotentials of 182 mV in 0.5 m H2SO4, 261 mV in 1 M PBS, and 121 mV in 1 M KOH at 10 mA cm–2. In addition, Cu electrode also performs well at high current densities, the overpotentials at 1 A cm–2 are much lower than those of Pt foil in acid, neutral, and alkaline solutions. [ABSTRACT FROM AUTHOR]

A self-supported silver electrode was prepared by plasma spraying and used for catalysing the hydrogen evolution reaction. Thanks to the non-equilibrium synthetic conditions, the silver catalyst exposes high-energy (200) crystal planes, which enhance the adsorption of hydrogen and improve the intrinsic catalytic activity. As a result, the silver catalyst delivers an overpotential of 349 mV at 10 mA cm−2, which was much lower than those of Ag foil (742 mV) and commercial Ag powder (657 mV). This work provides a new idea of preparing active electrocatalysts by traditional processes. [ABSTRACT FROM AUTHOR]

Metallic catalysts with nanopores are advantageous on improving both activity and selectivity, while the reason behind that remains unclear all along. In this work, porous Zn nanoparticles (P‐Zn) were adopted as a model catalyst to investigate the catalytic behavior of metallic nanopores. In situ X‐ray absorption spectroscopy, in situ Fourier transform infrared spectroscopy, and density functional theory (DFT) analyses reveal that the concave surface of nanopores works like a pincer to capture and clamp CO2 and H2O precursors simultaneously, thus lowering the energy barriers of CO2 electroreduction. Resultantly, the pincer mechanism endows P‐Zn with a high Faradic efficiency (98.1 %) towards CO production at the potential of −0.95 V vs. RHE. Moreover, DFT calculation demonstrates that Co and Cu nanopores exhibit the pincer behavior as well, suggesting that this mechanism is universal for metallic nanopores. [ABSTRACT FROM AUTHOR]

Elemental doping has been proved to be an efficient approach to adjust the performance of NiFe layered double hydroxides (NiFe LDHs) for water oxidation. However, the mechanism by which elemental doping affects catalytic activity remains unclear. Herein, we doped NiFe LDH with the Mn element and investigated the effect of elemental doping on the electronic structure of NiFe LDH and oxygen evolution reaction (OER) performance. Operando X-ray absorption spectroscopy analysis indicates that Mn doping promotes the formation of Ni(IV) ions. Density functional theory calculations reveal that Mn doping causes hybridization between Ni 3d and O 2p orbitals which facilitates the oxidation of Ni(II) ions. Resultantly, more active Ni(IV) sites could be generated at a lower applied voltage, which is beneficial for the OER performance. [ABSTRACT FROM AUTHOR]

Catalyst support with good conductivity and stability is an eternal pursuit in the search for a high‐performance electrocatalyst. Here, an unusual catalyst support, laser‐modified boron nitride with C, O dopants (L‐BN), for the oxygen evolution reaction is reported. L‐BN exhibits unique advantages for electrocatalysis, namely, high corrosion resistance under oxidizing conditions, enhanced electrical conductivity arising from interlayer B–B dipolar interaction, and strong interaction with IrOx catalyst caused by NCN bonds. As an excellent substrate, L‐BN helps to achieve higher activity and stability than its carbon black counterpart. [ABSTRACT FROM AUTHOR]

Developing highly efficient and low‐cost photocatalysts for overall water splitting has long been a pursuit for converting solar power into clean hydrogen energy. Herein, we demonstrate that a nonstoichiometric nickel–cobalt double hydroxide can achieve overall water splitting by itself upon solar light irradiation, avoiding the consumption of noble‐metal co‐catalysts. We employed an intensive laser to ablate a NiCo alloy target immersed in alkaline solution, and produced so‐called L‐NiCo nanosheets with a nonstoichiometric composition and O2−/Co3+ ions exposed on the surface. The nonstoichiometric composition broadens the band gap, while O2− and Co3+ ions boost hydrogen and oxygen evolution, respectively. As such, the photocatalyst achieves a H2 evolution rate of 1.7 μmol h−1 under AM 1.5G sunlight irradiation and an apparent quantum yield (AQE) of 1.38 % at 380 nm. [ABSTRACT FROM AUTHOR]

Ultrathin nanosheets attract considerable attention with regard to both fundamental research and potential applications. Nevertheless, non-layer structured materials are hard to make into nanosheets due to their isotropous bonds in three dimensions. Herein, ultrathin Cd4S5 nanosheets were synthesized via chemical vapor deposition followed by chemical etching. These nanosheets show the thinnest thickness (1 nm) and largest lateral size (10 μm) among those reported for CdS materials so far. As a catalyst for photocatalytic hydrogen production, ultrathin Cd4S5 nanosheets achieve a high apparent quantum efficiency of 4.15% under 420 nm light irradiation. The superior photocatalytic performance is ascribed to the unique structure (surface S− anions and a reconstructed surface structure), and the ultrathin structure endows 1 nm NSs with long-term durability. This work opens a new avenue for producing two-dimensional nanostructures of non-layered compounds and improving their photocatalytic properties. [ABSTRACT FROM AUTHOR]

FeCo2O4 nanoparticles with abundant oxygen vacancies were produced by laser fragmentation. The oxygen vacancies can lower the thermodynamic energy barriers as well as accelerate the electron transfer, eventually promoting oxygen evolution and reduction reactions simultaneously. [ABSTRACT FROM AUTHOR]

Abstract: The spin state, specifically antibonding orbital (e g) occupancy, of transition‐metal ions is recognized as a descriptor for oxygen electrocatalysts with perovskite or spinel structures, and can be facilely adjusted by varying the valence states of transition metals. However, both perovskites and spinels show unsatisfactory performance even at the optimal spin states. In comparison, some oxides with a rock salt structure (e.g., NiIICoIIO2) exhibit higher activity than perovskites and spinels, nevertheless, the rock salt structure excludes valence changes of the transition metals, obstructing further e g optimization and performance enhancement. Herein, an innovative strategy is demonstrated to regulate the spin states of CoII in NiCoO2 via crystallinity manipulation, thus providing a new strategy for eg optimization. Remarkably, the catalyst (CNO‐8) with a moderate eg occupancy (≈1.2) achieves the best electrocatalytic activity, which is among the highest achieved by the state‐of‐the‐art electrocatalysts, namely, an overpotential of ≈269 mV at 10 mA cm−2 for oxygen evolution reaction and an onset potential of 935 mV for oxygen reduction reaction. As an efficient bifunctional catalyst for rechargeable Zn‐air batteries, CNO‐8 even outperforms the noble metal catalyst (Pt/C + RuO2), demonstrating high potential for practical applications in electrochemical energy conversion. [ABSTRACT FROM AUTHOR]

Zinc oxide is a cost-efficient and eco-friendly material for solar-to-chemical energy conversion. However, the relatively wide band gap and poor stability restrict its practical applications. Herein, we report on the modification of ZnO nanosheets with a porous atomically thin ZnS overlayer. The as-prepared ZnS/ZnO/ZnS sandwich nanosheets exhibit a reduced band gap (2.72 eV) and yet a slightly elevated conduction band minimum, which remarkably broadens the wavelength range for light absorption and generates electrons with enough reducing capability. At the same time, the newly-prepared sandwich nanosheets possess alternatively exposed ZnS and ZnO surface patches, which attract and accommodate photo-generated holes and electrons, respectively. In addition, the ZnS overlayer catalyzes and accelerates hole-consumption reactions, thus preserving electrons for efficient water splitting. As a result, the ZnS/ZnO/ZnS sandwich nanosheets demonstrate intensive light absorption, fast charge separation, long electron lifetime, and eventually the highest hydrogen production rate reported for oxide catalysts so far. This work proves that passivation with an ultrathin layer is a potent approach for energy-band engineering, and semiconductor sandwich nanostructures are promising for highly efficient water splitting under sunlight. [ABSTRACT FROM AUTHOR]

CdSe nanowires (NWs) were grown in solution under microwave irradiation with the catalysis of solid gold nanoparticles, following a solution–solid–solid (SSS) mechanism. The monocrystal CdSe nanowires distributed evenly on fluorine doped tin oxide (FTO) glass, exhibited intensive light absorption and degraded methyl blue efficiently. [ABSTRACT FROM AUTHOR]

Introduction of lattice strain into catalysts is a facile way to modify catalytic behaviour. Here, we report the synthesis of Pd nanoparticles with compressive strain by pulsed laser ablation of a Pd target immersed in an aqueous solution. The intensive quenching effect induces obvious compressive strain which improves the ORR performance of the Pd nanoparticles significantly. [ABSTRACT FROM AUTHOR]

Mesocrystals are known to be unusual materials derived from the self-assembly of nanoparticles. However, their advantages arising from their unique structure have not been fully exploited to date owing to hindrance by a secondary phase. Herein, we employ a pulsed laser to synthesize mesocrystalline cupric oxide (CuO) with pure phase and clean surface. A gas sensor based on a CuO mesocrystal exhibits the highest sensitivity, the fastest response, and the best selectivity ever reported towards ethanol. Our study elucidates the inherent characteristics of mesocrystals and clears doubts regarding their practicability. [ABSTRACT FROM AUTHOR]

Cadmium chalcogenide nanocrystals (CCNCs) are regarded as promising materials for photoelectrochemical (PEC) water splitting. However, the relatively low PEC response and poor stability restrict their practical applications. In the present work, we demonstrate that a well-designed inverse opal structure (IOS) composed of CCNCs can achieve an unprecedentedly high photocurrent and hydrogen production rate. In particular, the IOS electrode remains stable during 3 h of continuous illumination, which is even superior to those photoanodes with surface passivation and/or co-catalysts. Quantitative investigation reveals that the IOS possesses high charge-separation efficiency and light-absorption capacity, which eventually result in excellent PEC performance. [ABSTRACT FROM AUTHOR]

GLO:OKZ/10mar20:adfm202000364-fig-0002.jpg PHOTO (COLOR): S2 a) Low-resolution transmission electron microscopy image of C-CO nanoparticles. The inset is size distribution pattern with an average particle size ~2.0 ± 0.5 nm. b) High-resolution transmission electron microscopy image of C-CO nanoparticles. gl. [Extracted from the article]

Engineering surface structure of catalysts is an efficient way towards high catalytic performance. Here, we report on the synthesis of regular iridium nanospheres (Ir NSs), with abundant atomic steps prepared by a laser ablation technique. Atomic steps, consisting of one-atom level covering the surface of such Ir NSs, were observed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The prepared Ir NSs exhibited remarkably enhanced activity both for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic medium. As a bifunctional catalyst for overall water splitting, they achieved a cell voltage of 1.535 V @ 10 mA/cm2, which is much lower than that of Pt/C-Ir/C couple (1.630 V @ 10 mA/cm2). [ABSTRACT FROM AUTHOR]

Ultrasmall size and abundant defects are two crucial factors for improving the performance of catalysts. However, it is a big challenge to introduce defects into ultrafine catalysts because of the surface tension and self‐purification effect of the nanoparticles. In the present work, physical laser fragmentation with chemical oxidization reaction is combined to synthesize Co3O4 nanoparticles (L‐CO) with ultrasmall size (≈2.1 nm) as well as abundant oxygen vacancies, thus providing an effective solution to the long‐standing contradiction between the size reduction and defect generation. The ultrasmall particle size allows more catalytic sites to be exposed. The surficial oxygen vacancies enhance the intrinsic activity, while the internal oxygen vacancies improve the electron transfer, and all of these benefits make L‐CO an active and durable bifunctional catalyst for oxygen reduction/evolutions. As the air cathode of zinc–air battery, L‐CO displays excellent rechargeable performance with a power density of ≈337 mW cm−2, outperforming the commercial noble metal couple (Pt/C+RuO2). [ABSTRACT FROM AUTHOR]

Highly efficient and stable catalysts for the hydrogen evolution reaction, especially in alkaline conditions are crucial for the practical demands of electrochemical water splitting. Here, the synthesis of a novel RuAu single‐atom alloy (SAA) by laser ablation in liquid is reported. The SAA exhibits a high stability and a low overpotential, 24 mV@10 mA cm−2, which is much lower than that of a Pt/C catalyst (46 mV) in alkaline media. Moreover, the turnover frequency of RuAu SAA is three times that of Pt/C catalyst. Density functional theory computation indicates the excellent catalytic activity of RuAu SAAs originates from the relay catalysis of Ru and Au active sites. This work opens a new avenue toward high‐performance SAAs via fast quenching of immiscible metals. [ABSTRACT FROM AUTHOR]

As a cheap and earth-abundant metal, copper is known highly conductive but inactive for catalyzing hydrogen evolution reaction (HER) due to its fully filled d orbital and weak adsorption for hydrogen intermediate. Herein, we adopt a mechanical stirring process to introduce a large number of dislocations into copper plate, and retain the dislocations by the quenching effect of dry ice. Theoretical computation indicates that dislocation can cause uneven distribution of charge density, and the electron-deficient area remarkably enhances the hydrogen adsorption, turning inactive copper into active HER catalyst. The product achieves high turnover frequency, low overpotential and long-term durability. Our work bridges mechanical process and functional materials, and exploits a powerful technology on producing self-supported catalysts in a rapid way : [Display omitted] [ABSTRACT FROM AUTHOR]

Metallic materials with unique surface structure have attracted much attention due to their unique physical and chemical properties. However, it is hard to prepare bulk metallic materials with special crystal faces, especially at the nanoscale. Herein, we report an efficient method to adjust the surface structure of a Cu plate which combines ion implantation technology with the oxidation-etching process. The large number of vacancies generated by ion implantation induced the electrochemical oxidation of several atomic layers in depth; after chemical etching, the Cu(100) planes were exposed on the surface of the Cu plate. As a catalyst for acid hydrogen evolution reaction, the Cu plate with (100) planes merely needs 273 mV to deliver a current density of 10 mA/cm 2 because the high-energy (100) surface has moderate hydrogen adsorption and desorption capability. This work provides an appealing strategy to engineer the surface structure of bulk metallic materials and improve their catalytic properties.

As a metal-free photocatalyst, graphitic carbon nitride (g-CN) shows great potential for photocatalytic water splitting, although its performance is significantly limited by structural defects due to incomplete polymerization. In the present work, we successfully synthesize highly conjugated g-CN nanofoam through an iodide substitution technique. The product possesses a high polymerization degree, low defect density, and large specific surface area; as a result, it achieves a hydrogen evolution rate of 9.06 mmol h -1 g -1 under visible light irradiation, with an apparent quantum efficiency (AQE) of 18.9% at 420 nm. Experimental analysis and theoretical calculations demonstrate that the recombination of photogenerated carriers at C-NH x defects was effectively depressed in the nanofoam, giving rise to the high photocatalytic activity.

The surface of an electrocatalyst undergoes dynamic chemical and structural transformations under electrochemical operating conditions. There is a dynamic exchange of metal cations between the electrocatalyst and electrolyte. Understanding how iron in the electrolyte gets incorporated in the nickel hydroxide electrocatalyst is critical for pinpointing the roles of Fe during water oxidation. Here, we report that iron incorporation and oxygen evolution reaction (OER) are highly coupled, especially at high working potentials. The iron incorporation rate is much higher at OER potentials than that at the OER dormant state (low potentials). At OER potentials, iron incorporation favors electrochemically more reactive edge sites, as visualized by synchrotron X-ray fluorescence microscopy. Using X-ray absorption spectroscopy and density functional theory calculations, we show that Fe incorporation can suppress the oxidation of Ni and enhance the Ni reducibility, leading to improved OER catalytic activity. Our findings provide a holistic approach to understanding and tailoring Fe incorporation dynamics across the electrocatalyst-electrolyte interface, thus controlling catalytic processes.

Engineering high-performance electrocatalysts is of great importance for energy conversion and storage. As an efficient strategy, element doping has long been adopted to improve catalytic activity, however, it has not been clarified how the valence state of dopant affects the catalytic mechanism and properties. Herein, it is reported that the valence state of a doping element plays a crucial role in improving catalytic performance. Specifically, in the case of iridium doped nickel-iron layer double hydroxide (NiFe-LDH), trivalent iridium ions (Ir 3+ ) can boost hydrogen evolution reaction (HER) more efficiently than tetravalent iridium (Ir 4+ ) ions. Ir 3+ -doped NiFe-LDH delivers an ultralow overpotential (19 mV @ 10 mA cm -2 ) for HER, which is superior to Ir 4+ doped NiFe-LDH (44 mV@10 mA cm -2 ) and even commercial Pt/C catalyst (40 mV@ 10 mA cm -2 ), and reaches the highest level ever reported for NiFe-LDH-based catalysts. Theoretical and experimental analyses reveal that Ir 3+ ions donate more electrons to their neighboring O atoms than Ir 4+ ions, which facilitates the water dissociation and hydrogen desorption, eventually boosting HER. The same valence-state effect is found for Ru and Pt dopants in NiFe-LDH, implying that chemical valence state should be considered as a common factor in modulating catalytic performance., (© 2021 Wiley-VCH GmbH.)

Metallic catalysts with nanopores are advantageous on improving both activity and selectivity, while the reason behind that remains unclear all along. In this work, porous Zn nanoparticles (P-Zn) were adopted as a model catalyst to investigate the catalytic behavior of metallic nanopores. In situ X-ray absorption spectroscopy, in situ Fourier transform infrared spectroscopy, and density functional theory (DFT) analyses reveal that the concave surface of nanopores works like a pincer to capture and clamp CO 2 and H 2 O precursors simultaneously, thus lowering the energy barriers of CO 2 electroreduction. Resultantly, the pincer mechanism endows P-Zn with a high Faradic efficiency (98.1 %) towards CO production at the potential of -0.95 V vs. RHE. Moreover, DFT calculation demonstrates that Co and Cu nanopores exhibit the pincer behavior as well, suggesting that this mechanism is universal for metallic nanopores., (© 2020 Wiley-VCH GmbH.)

Developing highly efficient and low-cost photocatalysts for overall water splitting has long been a pursuit for converting solar power into clean hydrogen energy. Herein, we demonstrate that a nonstoichiometric nickel-cobalt double hydroxide can achieve overall water splitting by itself upon solar light irradiation, avoiding the consumption of noble-metal co-catalysts. We employed an intensive laser to ablate a NiCo alloy target immersed in alkaline solution, and produced so-called L-NiCo nanosheets with a nonstoichiometric composition and O 2- /Co 3+ ions exposed on the surface. The nonstoichiometric composition broadens the band gap, while O 2- and Co 3+ ions boost hydrogen and oxygen evolution, respectively. As such, the photocatalyst achieves a H 2 evolution rate of 1.7 μmol h -1 under AM 1.5G sunlight irradiation and an apparent quantum yield (AQE) of 1.38 % at 380 nm., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

FeCo2O4 nanoparticles with abundant oxygen vacancies were produced by laser fragmentation. The oxygen vacancies can lower the thermodynamic energy barriers as well as accelerate the electron transfer, eventually promoting oxygen evolution and reduction reactions simultaneously.