Combining transition metal oxide catalysts with conductive carbonaceous material is a feasible way to improve the conductivity. However, the electrocatalytic performance is usually not distinctly ...improved because the interfacial resistance between metal oxides and carbon is still large and thereby hinders the charge transport in catalysis. Herein, the conductive interface between poorly conductive NiO nanoparticles and semi‐conductive carbon nitride (CN) is constructed. The NiO/CN exhibits much‐enhanced oxygen evolution reaction (OER) performance than corresponding NiO and CN in electrolytes of KOH solution and phosphate buffer saline, which is also remarkably superior over NiO/C, commercial RuO2, and mostly reported NiO‐based catalysts. X‐ray photoelectron spectroscopy and extended X‐ray absorption fine structure spectrum reveal that a metallic Ni–N bond is formed between NiO and CN. Density functional theory calculations suggest that NiO and CN linked by a Ni–N bond possess a low Gibbs energy for OER intermediate adsorptions, which not only improves the transfer of charge but also promotes the transmission of mass in OER. The metal–nitrogen bonded conductive and highly active interface pervasively exists between CN and other transition metal oxides including Co3O4, CuO, and Fe2O3, making it promising as an inexpensive catalyst for efficient water splitting.
The conductive interface between nickel oxide nanocrystals and polymer carbon nitride is produced by a Ni–N bond, which exhibits highly efficient performance in electrocatalytic oxygen evolution reaction.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Designing efficient electrocatalysts for hydrogen evolution reaction is significant for renewable and sustainable energy conversion. Here, we report single-atom platinum decorated nanoporous Co
Se ...(Pt/np-Co
Se) as efficient electrocatalysts for hydrogen evolution. The achieved Pt/np-Co
Se shows high catalytic performance with a near-zero onset overpotential, a low Tafel slope of 35 mV dec
, and a high turnover frequency of 3.93 s
at -100 mV in neutral media, outperforming commercial Pt/C catalyst and other reported transition-metal-based compounds. Operando X-ray absorption spectroscopy studies combined with density functional theory calculations indicate that single-atom platinum in Pt/np-Co
Se not only can optimize surface states of Co
Se active centers under realistic working conditions, but also can significantly reduce energy barriers of water dissociation and improve adsorption/desorption behavior of hydrogen, which synergistically promote thermodynamics and kinetics. This work opens up further opportunities for local electronic structures tuning of electrocatalysts to effectively manipulate its catalytic properties by an atomic-level engineering strategy.
Passivation interlayers such as Al2O3 are required to improve the hole selectivity of dopant‐free passivating contact based on transition metal oxides. For the interlayer to provide low surface ...recombination as in conventional silicon heterojunctions (SHJs) or tunnel oxide passivated contact (TOPCon) technologies, “hydrogenation” strategies to effectively introduce hydrogen in passivation interlayers while being compatible with transition metal oxides (TMOs) are urgently sought after. In this work, an easy‐to‐implement strategy to successfully incorporate extra hydrogen in the Al2O3 passivation layer is developed. The chemical and field‐effect passivation mechanisms of the extra hydrogen are revealed via comprehensive experimental analyses and density functional theory calculations. By implementing H‐Al2O3 with Cu2O as the hole‐selective rear contact in p‐type crystalline silicon (c‐Si) solar cells, a remarkable efficiency of 20.35% is achieved (fill factor of 84.76%). The study highlights a promising approach to improve the passivation quality of dielectric interlayers and boost the performance of dopant‐free c‐Si solar cells to compete against mainstream c‐Si photovoltaics technologies.
In exploring p‐type semiconductor Cu2O as a dopant‐free hole‐selective contact for crystalline Si solar cells, an ultra‐thin H‐Al2O3 prepared by atomic layer deposition utilizing a H2/N2 mixture as the carrier gas is adopted to improve the passivation quality. Finally, the device with a structure of p‐Si/H‐Al2O3/Cu2O/Pt/Ag dilivers a photoconversion efficiency of 20.35%.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The sluggish kinetics of air electrodes largely limits the practical applications of metal–air batteries. At present, preparing single-atom catalysts confined in ultrathin N-doped porous carbon (NPC) ...with a high surface area remains a challenge. Herein, a facile strategy by complexation of biomass and metal ions combined with the gas-foaming method was used to synthesize substantial Co–N 4 active sites on ultrathin NPC with a super-high specific surface area of 1977.9 m 2 g −1 . The catalyst owns brilliant oxygen reduction reaction properties with higher half-wave potential of 0.863 V and faster kinetics process (68.3 mV dec −1 ) than those of Pt/C (0.856 V and 80.46 mV dec −1 , respectively). Remarkably, it exhibits distinguished reversibility with a high initial cycle efficiency of 60.8% and satisfactory stability when used in Zn–air batteries. Moreover, the assembled Al–air battery displays preeminent discharge performance with ultrahigh power density (494 mW cm −2 ) and energy density (2387 W h kg −1 ) at 200 mA cm −2 . This study opens a new avenue to fully utilize biomass for constructing Co single-atom catalysts for metal–air batteries.
Tuning and optimizing luminescent properties of oxonitridosilicates phosphors are important for white light-emitting diode (WLED) applications. To improve the color rendering index, correlated color ...temperature and thermal stability of layer-structured MSi2O2N2:Eu (M = Sr, Ba) phosphors, cation substitutions have been used to adjust their luminescent properties. However, the underlying mechanisms are still unclear. In this research, a series of (Sr1–x Ba x )Si2O2N2:Eu (0 ≤ x ≤ 1) compounds were prepared by solid-state reaction, after which systematic emission variations were investigated. The crystal structures of (Sr1–x Ba x )Si2O2N2:Eu (0 ≤ x ≤ 1) are nominally divided into three sections, namely, Phase 1 (0 ≤ x ≤ 0.65), Phase 2 (0.65 < x < 0.80), and Phase 3 (0.80 ≤ x ≤ 1) based on the X-ray diffraction measurements. These experimental results are further confirmed by optimizing the crystal structure data with first-principle calculations. Continuous luminescence adjustments from green to yellow are observed in Phase 1 with gradual replacement of Sr2+ with Ba2+, and the abnormal redshift is clarified through extended X-ray absorption fine structure analysis. Sr(Eu)–O/N bond length shrinkage in local structure causes the redshift emission, and the corresponding luminescence mechanism is proposed. Controllable luminescence in Phase 2 (from blue to white) and Phase 3 (from cyan to yellowish green) are observed. Based on the high-resolution transmission electron microscopy and selected area electron diffraction analysis, the two kinds of luminescence tuning are attributed to phase segregation. This study serves as a guide in developing oxonitride luminescent materials with controllable optical properties based on variations in local coordination environments through cation substitutions.
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Direct synthesis of hydrogen peroxide (H2O2) through electrochemical oxygen reduction has gained close attention yet remains a great challenge due to the slow kinetics. Herein, combining with the ...virtues of the native high energy state and fascinating surface environment of metastable materials and doping strategy, an efficient phosphorus‐optimized metastable hexagonal‐close‐packed phase nickel catalyst (P‐hcp Ni), belonging to the space group (P63/mmc, 194), with P doping is demonstrated. Significantly, it achieves high selectivity of 97% and a high intrinsic turnover frequency of 2.34 s−1, much better than those of the stable face‐centered‐cubic Ni catalyst. It also displays high stability with remaining in the metastable phase after the stability test. More importantly, P‐hcp Ni also achieves a productivity of 4917.2 mmol gNi−1 h−1 and an accumulated concentration of (H2O2) of 2.38 mol L−1 after 130 h stability test in pure water with a solid electrolyte. Further investigation reveals that the P doping not only greatly enhances the stability of metastable phase, but also weakens the *OOH adsorption on the active site, promoting the high production of H2O2 in the neutral media.
An efficient phosphorus‐optimized metastable hexagonal‐close‐packed phase nickel catalyst is first synthesized for 2e− oxygen reduction reaction under neutral conditions, where P doping can not only effectively stabilize the metastable hcp phase, but also attract electrons from the surrounding Ni to weaken the *OOH adsorption.
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A self-standing NiFe-LDH@CoSx/NF electrocatalyst is developed by electrodepositing amorphous CoSx onto NiFe-LDH nanosheet arrays, which shows highly efficient performance towards ...overall water splitting.
•A novel self-standing 3D NiFe-LDH@CoSx/NF bifunctional electrocatalyst is fabricated.•Integration of HER-active CoSx and OER-effective NiFe-LDH endows dual-function activity.•The NiFe-LDH@CoSx/NF assembly requires ultralow overpotentials for both HER and OER.•Interface interactions and synergistic effect favor the both HER and OER activity.
Electrocatalytical water splitting to produce hydrogen energy is a promising green technology to solve energy crisis and environmental issues. The development of highly efficient and low-cost electrocatalysts is crucial for mass hydrogen production from water splitting. We newly assemble the self-standing 3D NiFe-LDH@CoSx/NF bifunctional electrocatalysts, via the electrodeposition of amorphous CoSx on two-dimensional (2D) NiFe-LDH nanosheets which are supported by porous nickel foam (NF). The integration of HER-active electrocatalyst of CoSx with outstanding OER catalyst of NiFe-LDH guarantees the bifunctional electrocatalytic activity. Furthermore, the formation of the constructed interfaces between amorphous CoSx and NiFe-LDH nanosheets synergistically favors the electron transfer. Therefore, this novel NiFe-LDH@CoSx/NF hierarchical assembly needs ultralow overpotentials of 136 mV (for HER) and 206 mV (for OER) to afford the 10 mA cm−2 current density in alkaline medium (1 M KOH). An electrolyzer based on the NiFe-LDH@CoSx/NF produces an extremely low cell voltage (1.537 V) and good durability. This study offers a promising strategy for facile fabrication of low-cost electrocatalysts which boost the electrocatalytic performance for overall water splitting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The lack of model single-atom catalysts (SACs) and atomic-resolution operando spectroscopic techniques greatly limits our comprehension of the nature of catalysis. Herein, based on the designed model ...single-Fe-atom catalysts with well-controlled microenvironments, we have explored the exact structure of catalytic centers and provided insights into a spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, and the developed operando57Fe Mössbauer spectroscopy. In combination with theoretical studies, the N-FeN4C10 moiety is evidenced as a more active site for ORR. Moreover, the potential-relevant dynamic cycles of both geometric structure and electronic configuration of reactive single-Fe-atom moieties are evidenced via capturing the peroxido (∗O2−) and hydroxyl (∗OH−) intermediates under in situ ORR conditions. We anticipate that the integration of operando techniques and SACs in this work shall shed some light on the electronic-level insight into the catalytic centers and underlying reaction mechanism.
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•Single-Fe-atom material with controlled microenvironment as efficient ORR catalyst•Operando57Fe Mössbauer spectroscopy developed for the characterization of SACs in ORR•Evidence for electronic and structural dynamics of single-Fe-atom moieties in ORR
Single-atom catalysts (SACs) build a conceptual bridge between homo- and heterogeneous catalysis. However, the lack of model SACs and atomic-resolution operando spectroscopic techniques greatly limits our comprehension of the nature of catalysis. Herein, based on the newly designed model single-Fe-atom catalysts, we explored the exact structure of catalytic centers and provided a spin-crossover-involved mechanism for oxygen reduction reaction (ORR) using operando Raman, X-ray absorption spectroscopies, and the newly developed operando57Fe Mössbauer spectroscopy. The potential-relevant electronic and structural dynamic cycles of active single-Fe-atom moieties were evidenced via capturing the ∗O2− and ∗OH− intermediates and further supported by theoretical calculations. These results provide a proof of concept for the integration of operando techniques and SACs, which may direct the way toward the electronic-level insight into the catalytic centers and reaction mechanism.
Operando Mössbauer spectroscopy was developed for in situ monitoring the evolution of catalytic centers in single-Fe-atom catalyst under practical oxygen reduction reaction conditions. Combining with operando Raman and X-ray absorption spectroscopies, the potential-relevant electronic and structural dynamic cycles of active single-Fe-atom moieties were evidenced via capturing the ∗O2− and ∗OH− intermediates and further supported by theoretical calculations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Li‐rich layered oxides (LRLO) exhibit significant potential for use in all‐solid‐state lithium batteries (ASSLBs) owing to their high capacities and wide range of operating voltages. However, the ...practical application of LRLO in ASSLBs is hindered by the severe failure of carrier transport at the solid–solid interface, which subsequently limits the electrochemical activity of these batteries. Here, the spatially asynchronous activation mechanism of the LRLO in ASSLBs is presented. A spectroscopic study extending from the surface into the bulk interior of LRLO indicates that the activation kinetics of anionic oxygen prefers hysteretic delivery over uniform delivery and fast transition metals (TMs) activation. This spatial hetero activation is dominated by the failure of carrier transport at the interface, which is induced by microstructural defects in the composite cathode. This study is expected to facilitate the microstructural design of high‐performance LRLO‐based ASSLBs.
The carrier transport failure at solid–solid interface induced by the microstructure defects within composite cathode causes the spatial asynchronous activation of Li‐rich cathode in ASSLBs: a sluggish activation of O from the surface to the bulk region throughout the long‐term cycles over a fast and uniform activation of transition metals predominantly occurs in the initial cycle.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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•The locally distorted CoN4 active sites in single atom Co catalyst were synthesized via coordination-intercalation assisted strategy.•It exhibits eminent ORR property with high E1/2 ...of 0.89 V and Jk of 15.4 mA cm−2 at 0.85 V.•It can offer high ORR performance by decreasing reaction energy barrier of the rate-determining step.•The fabricated Al-air battery shows brilliant energy density of 2466.7 Wh kgAl−1 and power density of 453.8 mW cm−2.
Adjusting the coordination environment of active sites for oxygen reduction reaction (ORR) is a desired method to realize efficient energy conversion. Herein, we synthesized a single atom Co catalyst (Co-SA/NC) with CoN4 active sites in locally distorted carbon configuration via a coordination-intercalation assisted strategy. The distinctive existing form of CoN4 structure has been confirmed according to X-ray absorption fine spectroscopy. The Co-SA/NC displays satisfactory ORR performance with higher half-wave potential of 0.89 V and kinetic current density (Jk) of 15.4 mA cm−2 at 0.85 V in alkaline solution, than those of Pt/C (0.87 V and 8.7 mA cm−2). Density functional theory calculations demonstrate that locally distorted CoN4 sites are instrumental in adsorption/desorption of oxygen species, promoting the reaction kinetics of ORR. Furthermore, the fast ORR kinetics is proved by small Tafel slope of 57.9 mV/dec. Applying Co-SA/NC as air electrode in Al-air battery, it presents high specific capacity (1992.7 mAh gAl−1) and energy density (2466.7 Wh kgAl−1) at 200 mA cm−2. The electrocatalyst with unique coordination configuration for M-N4 active sites at atomic level will have wide applications in regulating its intrinsic activity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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