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The complexes of metal center and nitrogen ligands are the most representative systems for catalyzing hydrogenation reactions in small molecule conversion. Developing heterogeneous catalysts with similar active metal‐nitrogen functional centers, nevertheless, still remains challenging. In this work, we demonstrate that the metal‐nitrogen coupling in anti‐perovskite Co4N can be effective modulated by Cu doping to form Co3CuN, leading to strongly promoted hydrogenation process during electrochemical reduction of nitrate (NO3−RR) to ammonia. The combination of advanced spectroscopic techniques and density functional theory calculations reveal that Cu dopants strengthen the Co−N bond and upshifted the metal d‐band towards the Fermi level, promoting the adsorption of NO3− and *H and facilitating the transition from *NO2/*NO to *NO2H/*NOH. Consequently, the Co3CuN delivers noticeably better NO3−RR activity than the pristine Co4N, with optimal Faradaic efficiency of 97 % and ammonia yield of 455.3 mmol h−1 cm−2 at −0.3 V vs. RHE. This work provides an effective strategy for developing high‐performance heterogeneous catalyst for electrochemical synthesis. [ABSTRACT FROM AUTHOR]

Developing high‐performance oxygen evolution reaction (OER) catalysts are critical for the practical application of many electrochemical energy devices. In this study, taking layered perovskite oxide thin films as the model system, it is demonstrated that the OER pathway can be effectively shifted by activating lattice oxygen, leading to strongly enhanced intrinsic activity. The OER performance of Ruddlesden‐Popper (RP)‐phase cobaltite is significantly enhanced as Sr doping at the A site increases, which is attributed to the shift of the reaction pathway from adsorbate evolution mechanism (AEM) to lattice oxygen‐mediated mechanism (LOM). Advanced spectroscopic techniques and density functional theory calculations reveal that the Sr dopant effectively facilitates oxygen ligand hole formation, charge transfer from the oxygen sites, and the formation and migration of oxygen vacancy, hence promoting lattice oxygen to participate in surface reactions. The results provide critical insight into the role of oxygen activity and offer a potential way for constructing highly active electrocatalysts. [ABSTRACT FROM AUTHOR]

Combining the characteristics of hybrid perovskites and layered materials, 2D Ruddlesden–Popper perovskites exhibit unique properties, some of which still require to be deeply understood. In this study, the vibrational signatures of such materials are analyzed by collecting experimental Raman spectra of four distinct compounds. Supported by density functional theory simulations, the role of the phenyl spacer single fluorination on the phonon modes of two similar yet different compounds, i.e., phenethylammonium lead iodide (PEAI) and 4‐fluorophenethylammonium lead iodide (PEAI‐F), is explained. In addition, this work analyzes some so‐far unreported experimental Raman peaks in the 600–1100 cm−1 range and discusses their origin in this class of 2D compounds. This work paves the way for a better design of novel compounds as well as for their exploitation in (opto)electronic applications. [ABSTRACT FROM AUTHOR]

Although ionic conjugated passivation systems, such as ionic liquids (ILs), have been used to passivate perovskite in carbon‐based printable mesoscopic perovskite solar cells (FP‐PSCs), their tautomerism process and synergistic effect of multifunctional groups have not yet caused enough attention. In this work, a series of novel ILs including 1‐allyl‐3‐methylimidazole tetrafluoroborate ([AMIm]BF4) and 1‐benzyl‐3‐methylimidazole tetrafluoroborate ([BzMIm]BF4) used as passivants for FP‐PSCs are reported. Combining Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculation, it is found that one of its tautomers (positive ion at the near end N atom of conjugated side chain) plays a key role on dual‐site simultaneous passivation. As the conjugation degree of side chain increases from allyl to benzyl, it not only effectively inhibits the non‐radiative charge recombination, but also reduces the passivation adsorption energy and increases the charge transfer rate. A high efficiency of 16.87% has been achieved with a high FF (>0.7), a Jsc of 23.88 mA cm–2 value and Voc value up to 1.0 V, by using the "tautomeric dual‐site passivation" strategy. [ABSTRACT FROM AUTHOR]

Single‐phase white luminescence phosphors are emerging for potential phosphor‐converted white light‐emitting diodes (pc‐WLEDs) and alternatives to trichromatic phosphor blends. In this work, Ba2ZnWO6:Bi3+ phosphors are prepared by a high‐temperature solid‐state reaction method and the luminescent properties are investigated. The broadband excitation from 250 to 400 nm is perfectly matched with the emission of nearly ultraviolet (n‐UV) InGaN chip, which ultrabroadband emission band (full width at half maximum = 217 nm) can cover a wider luminescence region. Li+/Na+/K+ codoping is more desirable for the ultrabroadband emission of Ba2ZnWO6:0.006Bi3+ due to the charge compensation and rationally designed lattice distortion while improving the thermal stability of the phosphor. Furthermore, tunable emissions can be achieved either by changing the content of doped ions or the excitation wavelength due to the different occupation of Ba2+ and Zn2+ sites by Bi3+ ions. Finally, single‐phase warm WLED ((x, y) = (0.4170, 0.4035)) devices with a correlated color temperature of 3329 K and color rendering index of Ra = 75.3 are successfully prepared using Ba2ZnWO6:0.006Bi3+, 0.03Na+ phosphor, and 365 nm InGaN chips. These results indicate that Ba2ZnWO6:Bi3+ has excellent potential as phosphor for n‐UV pc‐WLEDs and provides new ideas for the application of ultrabroadband emitting phosphors in WLEDs. [ABSTRACT FROM AUTHOR]

Doping perovskite oxide with different cations is used to improve its electro‐catalytic performance for various energy and environment devices. In this work, an activated lattice oxygen activity in Pr0.4Sr0.6CoxFe0.9−xNb0.1O3−δ (PSCxFN, x = 0, 0.2, 0.7) thin film model system by B‐site cation doping is reported. As Co doping level increases, PSCxFN thin films exhibit higher concentration of oxygen vacancies (Vo••) as revealed by X‐ray diffraction and synchrotron‐based X‐ray photoelectron spectroscopy. Density functional theory calculation results suggest that Co doping leads to more distortion in FeO octahedra and weaker metaloxygen bonds caused by the increase of antibonding state, thereby lowering Vo•• formation energy. As a consequence, PSCxFN thin film with higher Co‐doping level presents larger amount of exsolved particles on the surface. Both the facilitated Vo•• formation and B‐site cation exsolution lead to the enhanced hydrogen oxidation reaction (HOR) activity. Excessive Co doping until 70%, nevertheless, results in partial decomposition of thin film and degrades the stability. Pr0.4Sr0.6(Co0.2Fe0.7Nb0.1)O3 with moderate Co doping level displays both good HOR activity and stability. This work clarifies the critical role of B‐site cation doping in determining the Vo•• formation process, the surface activity, and structure stability of perovskite oxides. [ABSTRACT FROM AUTHOR]

Toward pursuing high‐performance photodetectors based on 2D transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2), it is desirable to reduce the high dark current and sluggish response time. Here, in multilayer MoS2‐based photodetectors, a 2D halide perovskite, (C6H5C2H4NH3)2PbI4 ((PEA)2PbI4), is introduced as a bifunctional material: both as electron reservoir to reduce free carriers and passivation agent to passivate defects. Surprisingly, dark current is suppressed by six orders of magnitude after coating a (PEA)2PbI4 thin layer onto pristine MoS2 photodetector, with the dark current decreased to 10−11 A. This huge reduction of dark current suggests an efficient interlayer charge transfer from MoS2 to (PEA)2PbI4, which is further verified by photoluminescence quenching phenomenon. It indicates that (PEA)2PbI4 serves as electron reservoir to reduce carrier density of MoS2, resulting in ultrahigh detectivity (1.06 × 1013 Jones). Moreover, the response speed is also accelerated by more than 100‐fold due to passivation by 2D perovskite. In addition, it is found that this type of photodetectors can further work at self‐power mode (with the bias of 0 V). Therefore, the strategy of applying 2D perovskite on the surface of TMDs provides a novel way to fabricate high‐performance photodetectors. [ABSTRACT FROM AUTHOR]

Halide perovskite materials feature strong optical absorption, light carrier masses and, as a consequence, high charge‐carrier mobility, making them one of the candidates for next‐generation optoelectronic devices. This interesting class of materials exhibits unconventional properties that cannot be readily rationalized by traditional concepts. In this regard, single‐crystals of halide perovskites represent an ideal test bench to better understand the intrinsic properties of the material, building the foundation for further investigations of polycrystalline films and related nanoarchitectures. In this Minireview, we analyze charge carrier transport in organic halide perovskite single crystals, summarizing the current literature insights on this matter from theoretical and experimental perspectives. Halide perovskite materials exhibit unconventional properties that cannot be readily rationalized by traditional concepts. In this regard, single crystals of halide perovskites represent an ideal test bench to better understand the intrinsic properties of the material, building the foundation for further investigations in polycrystalline films and related nano‐ and meso‐architectures. In this Minireview, we analyze charge carrier transport in halide perovskite single crystals, summarizing the current literature insights from an experimental and theoretical perspective. [ABSTRACT FROM AUTHOR]

An intriguing reversible band gap narrowing behavior of the lead‐free hybrid perovskite single crystal DMASnI3 (DMA=CH3NH2CH3+) from yellow to black is observed without phase transformation. We discuss the transformation mechanism in detail. More interestingly, the transformed samples in black can rapidly self‐heal into yellow ones when exposed to deionized water (DI water). Contrary to other hybrid perovskites, DMASnI3 crystals exhibit excellent water phase stability. For example, DMASnI3 was immersed in DI water for 16 h and no decomposition was observed. Inspired by its excellent water phase stability, we demonstrate a potential eco‐friendly application of DMASnI3 in photo‐catalysis for H2 evolution in DI water. We present the first H2 evolution rate of 0.64 μmol h−1 with good recycling properties for pure DMASnI3 crystals. After the narrowing process, the optical band gap of DMASnI3 can be lowered from 2.48 eV to 1.32 eV. Systematical characterizations are applied to investigate their structures and optoelectronic properties. The reversible band gap narrowing behavior and outstanding electrical properties, such as higher carrier mobility and long carrier lifetime show that DMASnI3 has a great potential for optoelectronic applications. Reversible band gap narrowing behavior of Sn‐based hybrid perovskite single crystal was first revealed with excellent phase stability, narrow band gap, higher carrier mobility and longer carrier lifetime. This is encouraging for the optoelectronic application. [ABSTRACT FROM AUTHOR]

Abstract: Composite cathodes of solid oxide fuel cells (SOFCs) are normally fabricated by mechanical mixing of electronic‐ and ionic‐conducting phases. Here, a dual‐phase SOFC cathode, composed of perovskite PrNi0.5Mn0.5O3 (PNM) and exsoluted fluorite PrOx particles, produced in situ through a glycine–nitrate solution combustion process, is reported. When applied as the cathode for a BaZr0.1Ce0.7Y0.1Yb0.1O3‐based protonic ceramic fuel cell, the hybrid cathode displays excellent electrocatalytic activity (area‐specific resistance of 0.052 Ω cm2 at 700 °C) and remarkable long‐term stability when operated at a cell voltage of 0.7 V for ≈500 h using H2 as fuel and ambient air as oxidant. The excellent performance is attributed to the proton‐conducting BaPrO3‐based coating and high‐concentration oxygen vacancies of a Ba‐doped PNM surface coating, produced by the reaction between the cathode and Ba from the electrolyte (via evaporation or diffusion), as confirmed by detailed X‐ray photoelectron spectroscopy, Raman spectroscopy, and density functional theory‐based calculations. [ABSTRACT FROM AUTHOR]

Highlights from the article: Oxygen Defect Engineering: Improving the Activity for Oxygen Evolution Reaction by Tailoring Oxygen Defects in Double Perovskite Oxides (Adv. Funct. However, oxygen vacancies also increase the energy band gap and lower the O 2 I p i band center of PBSCF. Electronic structure, thin film, surface reaction, oxygen defect, double perovskite oxide.

Developing cost effective electrocatalysts with high oxygen evolution reaction (OER) activity is essential for large‐scale application of many electrochemical energy systems. Although the impacts of either lattice strain or oxygen defects on the OER performance of oxide catalysts have been extensively investigated, the effects of both factors are normally treated separately. In this work, the coupled effects of both strain and oxygen deficiency on the electrocatalytic activity of La0.7Sr0.3CoO3−δ (LSC) thin films grown on single crystal substrates (LaAlO3 (LAO) and SrTiO3 (STO)) are investigated. Electrochemical tests show that the OER activities of LSC films are higher under compression than under tension, and are diminished as oxygen vacancies are introduced by vacuum annealing. Both experimental and computational results indicate that the LSC films under tension (e.g., LSC/STO) have larger oxygen deficiency than the films under compression (e.g., LSC/LAO), which attribute to smaller oxygen vacancy formation energy. Such strain‐induced excessive oxygen vacancies in the LSC/STO increases the eg state occupancy and enlarges the energy gap between the O 2p and Co 3d band, resulting in lower OER activity. Understanding the critical role of strain–defect coupling is important for achieving the rational design of highly active and durable catalysts for energy devices. The coupled effects of lattice strain and oxygen deficiency on the oxygen evolution raction (OER) activity of La0.7Sr0.3CoO3−δ (LSC) thin films grown on single crystal LaAlO3 (LAO) and SrTiO3 (STO) are investigated. The LSC/LAO with compressive strain exhibits considerably higher OER activity than the LSC/STO with tensile strain, which are attributed to the strain‐induced excessive oxygen vacancy in the LSC/STO. [ABSTRACT FROM AUTHOR]