It is vitally essential to design highly efficient and cost-effective bifunctional electrocatalysts toward water splitting. Herein, we report the development of P-doped Co3O4 nanowire array on nickel ...foam (P-Co3O4/NF) from Co3O4 nanowire array through low-temperature annealing, using NaH2PO2 as the P source. As a 3D catalyst, such P-Co3O4/NF demonstrates superior performance for oxygen evolution reaction with a low overpotential (260 mV at 20 mA cm–2), a small Tafel slope (60 mV dec–1), and a satisfying durability in 1.0 M KOH. Density functional theory calculations indicate that P-Co3O4 has a reaction free-energy value that is much smaller than that of pristine Co3O4 for the potential determining step of the oxygen evolution reaction. Such P-Co3O4/NF also performs efficiently for hydrogen evolution reaction, and a two-electrode alkaline electrolyzer assembled by P8.6-Co3O4/NF as both anode and cathode needs only 1.63 V to reach a water-splitting current of 10 mA cm–2.
Abstract
Currently, NH
3
production primarily depends on the Haber–Bosch process, which operates at elevated temperatures and pressures and leads to serious CO
2
emissions. Electrocatalytic N
2
...reduction offers an environmentally benign approach for the sustainable synthesis of NH
3
under ambient conditions. This work reports the development of biomass‐derived amorphous oxygen‐doped carbon nanosheet (O−CN) using tannin as the precursor. As a metal‐free electrocatalyst for N
2
‐to‐NH
3
conversion, such O−CN shows high catalytic performances, achieving a large NH
3
yield of 20.15 μg h
−1
mg
−1
cat.
and a high Faradic efficiency of 4.97 % at −0.6 V vs. reversible hydrogen electrode (RHE) in 0.1
m
HCl at ambient conditions. Remarkably, it also exhibits high electrochemical selectivity and durability.
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•3D snowflake graphene was prepared by “Microwave expansion assisted Hummers method”.•Appropriate graphene doping improves the catalyst morphology and pore structure.•4 %rGO@α-MnO2 ...has excellent low-temperature catalytic activity and stability.•Graphene doping can build electronic bridges thereby promoting electron transfer.•Graphene can induce the transformation of facet, promoting the formation of Oads.
Manganese oxide is a promising catalyst for volatile organic compounds oxidation with merits of low cost, abundant valence states, diverse crystal forms and morphology, however, its catalytic activity at low temperature (<200 °C) is limited due to the poor dispersion and inferior electron transfer. To solve these problems, a novel 3D snowflake graphene is doped into α-MnO2 to fabricate rGO@α-MnO2 catalyst to enhance the catalytic activity at low temperature. Compared with α-MnO2, the rGO@α-MnO2 catalysts present larger specific surface area and pore volume, which facilitates the adequate contact reaction between active component and VOCs. The unique graphene electronic bridge promotes the electron transfer on rGO@α-MnO2, which results in higher concentration of surface defects and more surface adsorbed oxygen to the catalyst. The performance tests show that the catalyst doped with 4% 3D snowflake graphene has the best activity, which can achieve 90% toluene conversion at 155 °C, and even 100% toluene conversion with 80% CO2 selectivity at 200 °C. In particular, 4%rGO@α-MnO2 demonstrates excellent catalytic stability and moisture resistance, presenting similar catalytic performance after 5 cycles for both the dry and high relative humidity (RH = 85%) conditions. The excellent activity of 4%rGO@α-MnO2 can be attributed to the enhancement of toluene adsorption energy after graphene doping and the defect induced by the interface effect between graphene and (211) facet. In general, 3D snowflake graphene doping provides a convenient and cost-effective method to enhance the low-temperature activity of the α-MnO2 catalyst, presenting great application potential.
Fabricating highly efficient and long‐life redox bifunctional electrocatalysts is vital for oxygen‐related renewable energy devices. To boost the bifunctional catalytic activity of Fe‐N‐C single‐atom ...catalysts, it is imperative to fine‐tune the coordination microenvironment of the Fe sites to optimize the adsorption/desorption energies of intermediates during oxygen reduction/evolution reactions (ORR/OER) and simultaneously avoid the aggregation of atomically dispersed metal sites. Herein, a strategy is developed for fabricating a free‐standing electrocatalyst with atomically dispersed Fe sites (≈0.89 wt.%) supported on N, F, and S ternary‐doped hollow carbon nanofibers (FeN4‐NFS‐CNF). Both experimental and theoretical findings suggest that the incorporation of ternary heteroatoms modifies the charge distribution of Fe active centers and enhances defect density, thereby optimizing the bifunctional catalytic activities. The efficient regulation isolated Fe centers come from the dual confinement of zeolitic imidazole framework‐8 (ZIF‐8) and polymerized ionic liquid (PIL), while the precise formation of distinct hierarchical three‐dimensional porous structure maximizes the exposure of low‐doping Fe active sites and enriched heteroatoms. FeN4‐NFS‐CNF achieves remarkable electrocatalytic activity with a high ORR half‐wave potential (0.90 V) and a low OER overpotential (270 mV) in alkaline electrolyte, revealing the benefit of optimizing the microenvironment of low‐doping iron single atoms in directing bifunctional catalytic activity.
A strategy of combining PIL and Fe‐modified zeolitic imidazole framework‐8 (ZIF‐8) as co‐precursors is developed for fabricating Fe single‐atom bifunctional electrocatalysts. The efficient regulation of isolated Fe centers comes from the dual confinement of ZIF and PIL. The coordination microenvironment engineering of low‐doping Fe sites induced by ternary heteroatomic doping and hierarchical porous structures contributes to high‐efficient ORR/OER electrocatalysis.
Modulating the electronic configuration of the substrate to achieve the optimal chemisorption toward polysulfides (LiPSs) for boosting polysulfide conversion is a promising way to the efficient Li–S ...batteries but filled with challenges. Herein, a Co/CoS2 heterostructure is elaborately built to tuning d‐orbital electronic structure of CoS2 for a high‐performance electrocatalyst. Theoretical simulations first evidence that Co metal as the electron donator can form a built‐in electric field with CoS2 and downshift the d‐band center, leading to the well‐optimized adsorption strength for lithium polysulfides on CoS2, thus contributing a favorable way for expediting the redox reaction kinetics of LiPSs. As verification of prediction, a Co/CoS2 heterostructure implanted in porous hollow N, S co‐doped carbon nanocage (Co/CoS2@NSC) is designed to realize the electronic configuration regulation and promote the electrochemical performance. Consequently, the batteries assembled with Co/CoS2@NSC cathode display an outstanding specific capacity and an admirable cycling property as well as a salient property of 8.25 mAh cm−2 under 8.18 mg cm−2. The DFT calculation also reveals the synergistic effect of N, S co‐doping for enhancing polysulfide adsorption as well as the detriment of excessive sulfur doping.
A hollow porous nanocage with Mott–Schottky heterostructure, nitrogen‐sulfur co‐doped carbon is presented. Theoretical modelings unveil that built‐in electric field in the heterojunction is constructed by the electron donor effect of the metal. The introduction of the heterogeneous component can modulate the electronic structure, provide reasonable adsorption to LiPSs, and delightful electrocatalytic ability for the high‐performance of Li–S batteries.
Three-dimensional porous MoS2/nitrogen-doped graphene aerogels (MoS2/NGA) with different MoS2 loading masses were synthesized by a simple hydrothermal method. The unique structure can provide more ...Na+ (K+) transport channels and the three-dimensional porous morphology could greatly absorb the volume expansion of MoS2 during charging and discharging process. As the anode of sodium-ion batteries (SIBs), this material provides a specific capacity of 673 mAh g−1 at a current density of 100 mA g−1 with long cycle stability. In addition, the composite shows a specific capacity of 305 mAh g−1 at 2000 mA g−1 and exhibits excellent capacity reversibility after rate performance test, indicating that it is a promising anode choice for SIB. As the anode material of potassium-ion batteries (KIBs), it provides a reversible specific capacity of 349 mAh g−1 at a current density of 100 mA g−1. It has a specific capacity of 72 mAhg−1 at 5000 mAg−1 and exhibits excellent capacity reversibility after rate performance test as well. Therefore, this work provides some insights into the fabrication of MoS2/graphene composites and is helpful for the design of high-performance anode materials of metal ion batteries.
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•A facile hydrothermal method was used to prepare MoS2/N-graphene aerogel (MoS2/NGA).•MoS2/NGA composite could inhibit dissolution of cations and reduce dissolution of electrolytes, simultaneously.•The interface between active materials and electrolytes could increase stability of the electrode structure.•Synergistic effects of interface storage and alloying/dealloying reaction improve electrochemical performance significantly.
In this study, we investigate the structural and photoluminescence (PL) properties of rare-earth-doped GdCa4O(BO3)3 (GdCOB) phosphors, specifically focusing on the spectral behaviour induced by ...doping with Eu³⁺ and Tb³⁺ ions. The powder X-ray diffraction (XRD) spectra confirm the formation of a monoclinic phase. The XRD data were also refined by a Rietveld refinement method. The existence of B, O, Ca, Gd, Tb, Eu and K elements was verified by EDS spectra. We introduce a detailed examination of the charge compensation process using Kröger-Vink notation to clarify the mechanisms essential for tailoring the optical properties of the phosphors. The PL excitation spectrum of GdCOB:Eu3+, monitored at 611 nm, reveals sharp excitation peaks at 319, 361, 380, and 392 nm, corresponding to 7F0→5H3, 7F0→5D4, 7F0→7F0, and 7F0→5L6 transitions, respectively. The PL spectrum under excitation of 392 nm exhibits that phosphors doped with Eu3+ a significant red emission at 611 nm, which is attributed to the 5D₀→7F₂ transition. This emission intensity is particularly enhanced at non-centrosymmetric sites of the Eu³⁺ ions. Similarly, the PL excitation spectrum of GdCOB:Tb3+, monitored at 552 nm, displays distinct excitation peaks at 316, 341, 353, and 379 nm, which correspond to the transitions 7F₆→5D₀, 7 F₆→5L₇, 7F₆→5D₂, and 7F₆→5D₃, respectively. Tb³⁺-doped phosphors display a bright green emission, with a dominant peak at 552 nm, resulting from the 5D₄→7F₅ transition. Additionally, the introduction of K⁺ ions as co-dopants results in modifications to the local environments of Eu³⁺ and Tb³⁺ ions. These changes allow for fine-tuning of the emission peaks, significantly enhancing the luminescent output of the phosphors. Optimal doping concentrations of 5 mol% for Eu³⁺ and 1 mol% for Tb³⁺ enhance luminescent intensity and prevent concentration quenching. This phenomenon, often resulting in reduced PL intensity at higher dopant levels, is primarily due to dipole-dipole interactions, consistent with Dexter's theory of energy transfer. Strategic modulation of doping concentrations, coupled with a deep understanding of energy transfer mechanisms are critical for the development of advanced luminescent materials Our analysis of the Commission de l′Eclairage (CIE) chromaticity coordinates reveals enhanced energy transfer dynamics in rare-earth-doped borates, facilitating the tuning of luminescent properties. These results not only deepen our understanding of the fundamental physics governing such phosphors but also open pathways for the development of optoelectronic applications requiring consistent color output, such as LED technologies and solid-state lighting.
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•Eu and Tb doped GdCa4O(BO3)3 phosphors synthesized via sol-gel microwave combustion.•K+ co-doping further enhances Eu and Tb-doped GdCa4O(BO3)3 luminescence.•Optimal Eu3+ and Tb3+ levels identified for peak emission.•Concentration quenching observed beyond optimal doping.•CIE analysis confirms consistent color output for tech applications.
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•This work discoveries that plasma can reconstitute ZIF-67 into 2D Co(OH)2 nanosheets.•Mo and N doping of Co(OH)2 is achieved by a one-step synthesis improve MOR performance.•Mo, N ...co-doped Co(OH)2 shows significant impedance reduction in methanol.•DFT calculation and in-situ electrochemical IR spectra reveals the key effect of Mo, N co-doping.
The development of low-cost electrocatalysts to selectively oxidize methanol to formate to replace the oxygen evolution reaction (OER) will be beneficial to reduce the overpotential of electrocatalytic water splitting. Herein, we propose a one-step low-temperature strategy for anion and cation co-doping to reconstruct ZIF-67 into two-dimensional Mo, N co-doped Co(OH)2 N-CoMo(OH)x. The N-CoMo(OH)x only needs 1.36 V to achieve 10 mA cm−2 for methanol oxidation reaction (MOR). Meanwhile, N-CoMo(OH)x exhibits good stability at 100 mA cm−2 with Faraday efficiency of 98.1 %. The Mo6+ and N co-doping synergistically enhance the conductivity and dehydrogenation energy barrier of OCH2 intermediate species, leading to good catalytic performance. This work thus provides a strategy for designing anion and cation co-doped catalysts for methanol upgrading.
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•Ti/SrxLa1-xMnyCo1-yO3-δ anode is prepared by doping Sr and Mn into LaCoO3 matrix.•Sr and Mn are doped into LaCoO3 to form oxygen vacancies and improve conductivity.•Oxygen vacancies ...can inhibit the recombination of e−-h+ pairs to produce more OH.•Ammonia nitrogen and organics can be degraded effectively under optimum condition.•The anode shows attractive reusability and stability with low energy consumption.
To obtain a kind of highly active, robust, inexpensive anode for electrocatalytic oxidizing wastewater, perovskites SrxLa1-xMnyCo1-yO3-δ (SLMCOxy) were prepared by doping Mn at B-Site and Sr at A-Site into the LaCoO3 matrix to form oxygen vacancies, inducing more production of reactive oxidized substance. Then the perovskites mixed with binder and conductive agent were coated on titanium plate as alternative anodes Ti/SLMCOxy, which were applied for cleaning simulated wastewater composed of 200 mg L−1 ammonium nitrogen (AN) and 20 mg L−1 methyl orange (MO) to confirm the optimum doping amount of Sr and Mn and operation conditions like temperature, current density, pH and the concentration of chloride. The highest removal ratio up to 98.23% for AN, 99.61% for MO, 88.16% for COD and current efficiency up to 86.47% were achieved respectively with the contribution of OH, O2− and active chlorine, and the removal ratio of AN and MO can keep above 95% after 5-time’s reusing the anode. Moreover, the anode performed good degradation effect for landfill leachate with 96.12% of AN and 85.43% of COD removed at energy consumption of 26.88 kWh (Kg COD)−1. Therefore, this original anode Ti/SLMCOxy would be a promising candidate for effective organic wastewater treatment.
Here, we have thoroughly studied the effect of chemistry of graphene derivatives on the composition of N-species after N-doping with the help of core-level spectroscopy techniques. The modulation of ...the N-species by tailoring the functionalization and atomic structure of graphene derivatives prior to chemical N-doping is experimentally demonstrated for the first time. The large extent of non-terminated or phenol-functionalized graphene edges is found to facilitate the formation of pyridinic nitrogen with its relative content exceeding 72%. In turn, the predominant decoration by the pyrazolic moieties is shown for the perforated and carboxyl-derived graphene layers. The thermal annealing at moderate temperatures of ca.345 °C is shown to equally readjust the composition of N-species in graphene derivatives regardless of their chemistry, nanostructure, and the initial distribution of the N-species. Further examination of N K-edge X-ray absorption spectra (XAS) pointed out that the oxidation of the graphene layer governs the manifestation of the π∗ resonances and configuration of the σ∗ resonance. As a result, a set of facile methods to synthesize graphene derivatives with the desired type of the embedded nitrogen species for the optoelectronic and catalytic applications are proposed and crucial features of their identification using core-level spectroscopy techniques are emphasized.
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•Extent and functionalization of graphene edges regulates the form of embedded nitrogen.•Hydrazine treatment of carboxylated graphene leads to a predominant formation of pyrazoles.•Graphene oxidation governs the manifestation of π∗ resonances in the NK XAS spectra.•Thermal annealing equalizes the relative content of embedded nitrogen species.
