Induced Charge Redistribution Research Articles

Molten-Salt Electrochemical-Assisted Synthesis of the CeO2-OV@GC Composite-Supported Pt Clusters with a Pt-O-Ce Structure for the Oxygen Reduction Reaction.

Highly active and robust Pt-based electrocatalysts for an oxygen reduction reaction (ORR) are of crucial significance for the development of proton exchange membrane fuel cells (PEMFCs). Herein, the high-loading and well-dispersive Pt clusters on graphitic carbon-supported CeO2 with abundant oxygen vacancies (PtAC/CeO2-OV@GC) were successfully fabricated by a molten-salt electrochemical-assisted method. The bonding of Pt with the highly electronegative O induces charge redistribution through the Pt-O-Ce structure, thus reducing the adsorption energies of oxygen-containing species. Such a PtAC/CeO2-OV@GC electrocatalyst exhibits a greatly enhanced ORR performance with a mass activity of 0.41 ± 0.02 A·mg-1Pt at 0.9 V versus a reversible hydrogen electrode, which is 2.7 times the value of a commercial Pt/C catalyst and shows negligible activity decay after 20000 cycles of accelerated degradation tests. It is anticipated that this work will provide enlightening guidance on the controllable synthesis and rational design of high-performance Pt-based electrocatalysts for PEMFCs.

Strategically designing and fabricating nitrogen and sulfur Co-doped g-C3N4 for accelerating photocatalytic H2 evolution

Doping engineering is an effective strategy for graphitic carbon nitride (g-C3N4) to improve its photocatalytic hydrogen evolution reaction (HER) performance. In this work, a novel nitrogen and sulfur co-doped g-C3N4 (N, S-g-C3N4) is elaborately designed on the basis of theoretical predictions of first-principle density functional theory (DFT). The calculated Gibbs free energy of adsorbed hydrogen (ΔGH*) for N, S-g-C3N4 at the N-doping active sites is extremely close to zero (0.01 eV). Inspired by the theoretical predictions, the N, S-g-C3N4 is successfully fabricated through ammonia-rich pyrolysis synthesis strategy, in which ammonia is in-situ obtained by pyrolyzing melamine. Subsequent characterizations indicate that the N, S-g-C3N4 possesses high specific surface area, outstanding light utilization, good hydrophilicity, and efficient carrier transfer efficiency. Consequently, the N, S-g-C3N4 displays an extremely high H2 evolution rate of 8269.9 µmol g−1 h−1, achieves an apparent quantum efficiency (AQE) of 3.24%, and also possesses outsatnding durability. Theoretical calculations further demonstrate that N and S dopants can not only introduce doping energy level to reduce the band gap, but also induce charge redistribution to facilitate hydrogen adsorption, thus promoting the photocatalytic HER process. Moreover, femtosecond transient absorption (fs-TA) spectroscopy further corroborates the efficient photogenerated carrier transport of N, S-g-C3N4. This research highlights a promising and reliable strategy to achieve superior photocatalytic activity, and exhibits significant guidance for precise designing high-efficiency photocatalysts.

Controling surface reconstruction of transition metal-hydroxide organic framework to enhance the stability of oxygen evolution reaction

The surface reconstruction of the electrocatalysts often occurs in the oxygen evolution reaction (OER), which inevitably leads to the deterioration of stability. Hence, Ce-doped transition metal-hydroxide organic frameworks (Ce-TMHOF) with varying molar ratios of Ce were synthesized using a simple one-step hydrothermal method. The 21% Ce-TMHOF exhibited overpotentials of 200 and 240 mV to achieve current densities of 10 and 100 mA cm-2, respectively. Moreover, it maintained a remarkable efficiency of 98.3% after 110 hours of stability testing during the OER process. When incorporated into an anion exchange membrane (AEM) electrolyzer alongside commercial Pt/C electrocatalysts, the 21% Ce-TMHOF maintained an efficiency of 98.8% even after 500 hours of testing. Our findings suggest that 4f orbital electron of Ce induce charge redistribution through electronic coupling with Ni and Fe, thereby mitigating surface reconstruction and improving the activity and stability of the electrocatalyst. This study sets a foundation for developing more stable and efficient electrocatalysts for energy storage and conversion applications.

Ultrathin graphitic carbon nitride interface layer regulated nickel-iron oxyhydroxide stabilized on nickel foam for efficient oxygen evolution reaction

Regulating interfacial properties of electrocatalysts to enhance the performance of oxygen evolution reaction (OER) possesses practical significance for water splitting. Herein, we report a novel strategy to form a graphitic carbon nitride (g-C3N4) interface layer on nickel foam (NF), followed by the growth of nickel-iron (oxy)hydroxides (NiFe-OH). The NiFe-OH nanosheets are tightly anchored on the g-C3N4 layer, exhibiting enhanced surface and structural characteristics. Therefore, the as-prepared NF/g-C3N4/NiFe-OH demonstrates superior OER activity with low overpotentials of 272, 342, and 476 mV at the current densities of 50, 100, and 200 mA cm−2, respectively. The reduced Tafel slope and raised TOF values of the electrode compared to NF/NiFe-OH reveal the promoting roles of g-C3N4, which provides more active sites, induces charge redistribution, and facilitates electron transfer. Furthermore, the electrode presents reliable stability and durability without observable morphological damage, alteration in the surface chemical state, and significant depletion of active components.

Electronic properties of c-BN/diamond heterostructures for high-frequency high-power applications

Using first principles calculations, this work investigates the suitability of diamond/c-BN heterojunctions for high frequency, high power device applications. The key quantities of band offsets and interface charge polarization are examined for different crystallographic orientations [(110), (111), or (100)], bond terminations (CB or CN), and substrates (diamond or c-BN). The results indicate that both the (111) and (100) structures with polar interfaces are likely to be a type-I alignment with the diamond conduction and valence band extrema nested within the c-BN bandgap, whereas the non-polar (110) counterpart may form type II as the valence band of c-BN is shifted down substantially lower. The valence band offsets are estimated to be around 0.2–0.55 eV and 1.2–1.3 eV for types I and II, respectively, with only a modest dependence on the order of layer stacking and bond termination. The (111) and (100) structures also show net charge polarization in a narrow region at the interface. The electron-deficient and electron-rich nature of the CB and CN bonding are found to induce charge redistribution leading to an essentially 2D sheet of negative and positive polarization, respectively, with a density on the order of 1012−1013q/cm2 (q=1.6×10−19 C). With the predicted band alignments suitable for carrier confinement as well as the possibility of the modulation and polarization doping, the diamond/c-BN heterostructures are a promising candidate for high-performance electronic devices with a highly conductive 2D channel. Both p-type and n-type devices appear possible with a judicious choice of the heterojunction configuration.

Synergistic Electronic Interaction of Nitrogen Coordinated Fe-Sn Double-Atom Sites: An Efficient Electrocatalyst for Oxygen Reduction Reaction.

Double-atom site catalysts (DASs) have emerged as a recent trend in the oxygen reduction reaction (ORR), thereby modifying the intermediate adsorption energies and increasing the activity. However, the lack of an efficient dual atom site to improve activity and durability has limited these catalysts from widespread application. Herein, the nitrogen-coordinated iron and tin-based DASs (Fe-Sn-N/C) catalyst are synthesized for ORR. This catalyst has a high activity with ORR half-wave potentials (E1/2 ) of 0.92V in alkaline, which is higher than those of the state-of-the-art Pt/C (E1/2 =0.83V), Fe-N/C (E1/2 =0.83V), and Sn-N/C (E1/2 =0.77V). Scanning electron transmission microscopy analysis confirmed the atomically distributed Fe and Sn sites on the N-doped carbon network. X-ray absorption spectroscopy analysis revealed the charge transfer between Fe and Sn. Both experimental and theoretical results indicate that the Sn with Fe-NC (Fe-Sn-N/C) induces charge redistribution, weakening the binding strength of oxygenated intermediates and leading to improved ORR activity. This study provides the synergistic effects of DASs catalysts and addresses the impacts of P-block elements on d-block transition metals in ORR.

Structural Engineering of Co-Metal-Organic Frameworks via Ce Incorporation for Improved Oxygen Evolution.

The rational design of metal-organic framework (MOF)-basedelectrocatalysts plays a key role in achieving high-efficiency oxygen evolution reaction (OER). Herein, a synergetic morphology and electronic structure engineering strategy are proposed to design a Co-MOF nanoflower grown on carbon paper via rare-earth cerium doping (CoCe-MOF/CP). Compared with Co-MOF/CP, the developed CoCe-MOF/CP exhibited superior OER performance with a low overpotential of 267mV at 10mA cm-2 and outstanding long-term stability over 100h. Theoretical calculations show that the unique 4f valence electron structure of Ce induced charge redistribution of the Co-MOF surface through the strong Co 3d-O 2p-Ce 4f orbital electronic coupling below the Fermi level. Ce-doped plays a key role in the engineering of the electronic states of the Co sites to endow them with the optimal free energy landscape for enhanced OER catalytic activity. This work provides new insights into comprehending the RE-enhanced mechanism of electrocatalysis and provides an effective strategy for the design of MOF-based electrocatalysts.

Ab Initio Molecular Dynamics Study of Electron Excitation Effects on UO2 and U3Si.

In this study, an ab initio molecular dynamics method is employed to investigate how the microstructures of UO2 and U3Si evolve under electron excitation. It is found that the U3Si is more resistant to electron excitation than UO2 at room temperature. UO2 undergoes a crystalline-to-amorphous structural transition with an electronic excitation concentration of 3.6%, whereas U3Si maintains a crystalline structure until an electronic excitation concentration reaches up to 6%. Such discrepancy is mainly due to their different electronic structures. For insulator UO2, once valence U 5f electrons receive enough energy, they are excited to the conduction bands, which induces charge redistribution. Anion disordering is then driven by cation disordering, eventually resulting in structural amorphization. As for metallic U3Si, the U 5f electrons are relatively more difficult to excite, and the electron excitation leads to cation disordering, which eventually drives the crystalline-to-amorphous phase transition. This study reveals that U3Si is more resistant to electron excitation than UO2 under an irradiation environment, which may advance the understanding of related experimental and theoretical investigations to design radiation-resistant nuclear fuel uranium materials.

Metal-free 2D/2D VdW heterojunction fabricated by amorphous covalent triazine frameworks with nitrogen-defect on polymeric carbon nitride towards enhanced photocatalytic performance

The structural design of Van der Waals (VdW) heterojunction photocatalysts has still been a challenging issue, because it usually plays a decisive role in improving photocatalytic performance. Herein, a unique metal-free 2D/2D VdW heterojunction is fabricated by decoration of amorphous covalent triazine frameworks with nitrogen defect (VN-CTFs) on the surface of polymeric carbon nitride (PCN) via a simple acid stripping, self-assembly and heat-treatment process, which demonstrates high-efficiency and stable photocatalytic performance for hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR). The results of experiments reveal that the synergy produced by strong electron-withdrawing effect from cyano groups in VN-CTFs induces charge redistribution at the interface with PCN through π-π interaction of 2D/2D VdW heterojunction, resulting in the formation of built-in electric field, which effectively drives the transfer and separation of photogenerated carriers to enhance the photocatalytic performance. The optimal PCN/VN-CTFs-10 sample exhibits that the average HER rate reaches up to 75.1 and 3.7 times higher than that of onefold VN-CTFs and PCN, respectively, as well as achieves apparent quantum yield (AQY) of 21.5 % at 420 nm and stable operation of 10 cycles totaling 40 h. Meanwhile, CO yields of 28.3 and 2.5 times as high as that of pristine VN-CTFs and PCN, respectively, are also obtained over the optimal PCN/VN-CTFs-10 sample for CO2RR. This work exploits a new structural unit design strategy for developing the metal-free PCN-based VdW heterojunction photocatalysts to boost the photocatalytic performance.

The effect of dopant P[dbnd]O functional group and OH, O, H2O adsorption on the structural, electronic, and optical properties of triangular g-C3N4 quantum dots by first-principles study

The effect of dopant PO functional group and OH, O, H2O adsorption on the structural, electronic, and optical properties of triangular g-C3N4 QDs has been studied by first-principle calculations. Negative formation energies indicate that the formation processes of these systems are exothermic. PO doping can enhance the stability of C3N4–H QD and weaken the stability of C3N4–F QD. O–C3N4–H QD presents a chemisorption process, whereas the adsorption of OH group or H2O molecule on the C3N4–H QD is proposed to be a physisorption process. The substitutional PO group significantly deforms the geometric structure of the tri-s-triazine unit and induces charge redistribution in the PO-C3N4–H and PO-C3N4–F QDs. For C3N4–H QD, PO-C3N4–H QD, C3N4–F QD, and PO-C3N4–F QD, the calculated HOMO-LUMO gaps are 3.248, 1.583, 2.821 and 1.478 eV, respectively. The charge transfer between the O radical and the C3N4–H QD is +0.522 e, indicating a strong chemical bonding interaction. The tiny charge transfers of +0.107 e and +0.003 e indicate weak interaction between OH or H2O and C3N4–H QD. The study will provide an effective theoretical foundation for the development of new g-C3N4 QDs sensors or catalysis systems.

Interface Interaction Enhanced Piezo‐Catalytic Hydrogen Peroxide Generation via One‐Electron Water Oxidation

AbstractPiezo‐catalysis, which is possible to utilize natural mechanical energy, is an ideal technology for synthesizing hydrogen peroxide (H2O2) but is still challenging. Herein, C‐layer coated ZnO (C‐ZnO) with modulated electronic structure is constructed for piezo‐catalytic H2O2 generation. The C‐layer not only provides more active sites but also induces higher piezo‐response to mechanical stimuli. As a result, the optimized C‐ZnO exhibits ultrahigh piezocatalytic activity for H2O2 yield with a rate of 294 µM h−1 in pure water. Theoretical calculation demonstrates that the interaction at the interface induces charge redistribution, leading to the hole accumulation on the surface, thus promoting one‐electron water oxidation. In addition, the C‐ZnO exhibits excellent piezo‐catalytic performance for the degradation of different pollutants. This study not only provides a promising way (utilization of mechanical energy) for efficient H2O2 production in pure water but also opens a new avenue for designing highly active piezo‐catalytic systems for pollutants degradation.

Activating the PdN4 single-atom sites for 4 electron oxygen reduction reaction via axial oxygen ligand modification

The absence of Pd ensemble sites and weak affinity for O-intermediates in tetracoordinate planar PdN4 sites inhibit O-O bond dissociation and restrict 4e- oxygen reduction reaction (ORR) pathway. Optimizing the adsorption energy between O-intermediates and PdN4 sites is a rational approach for selectively promoting 4e- ORR electrocatalysis. Herein, we propose a molten-salt strategy for introducing axial oxygen ligand into the PdN4 sites to manipulate the electronic structure and create catalytic O-PdN4 sites (one subsurface axial Pd-O configuration on PdN4 plane) on N-doped graphene nanosheets (O-PdN4-NGS). Density functional theory calculations revealed that the axial Pd-O coordination can induce charge redistribution, downshift the d-band center of Pd and enhance the adsorption affinity of PdN4 site for O-intermediates, thereby leading to superior electrocatalysis activity and selectivity for 4e- ORR process compared to conventional PdN4 sites in 0.1 M KOH (with a positive half-wave potential E1/2 of 0.90 V vs RHE). Moreover, zinc-air battery featuring with O-PdN4 sites delivers a peak power density of 178 mW cm−2 at 227.5 mA cm−2 and stable long-term cycling performance, effectively showcasing the advantages of the axial O ligand modification in practical application. This work provides a constructive strategy to activate the reaction activity and specificity of PdN4 single-atom sites by precisely-tuning the local coordination environment of Pd.

Interface charge distribution modulation of Au@NiO Core-Shell nanoparticles for efficient oxygen evolution reaction

Developing non-precious metal catalysts with efficient catalytic activity and excellent durability of the oxygen evolution reaction (OER) is of prime importance. As a consequence, we effectively achieved significant OER improvement by constructing Au@NiO core–shell octahedral nanoparticles with optimized charge distribution. Density functional theory (DFT) calculations expounded that the existence of Au species, which serves as an electron acceptor, can effectively induce charge redistribution and modulate of binding strength between intermediates and catalysts, resulting in noticeable improvement in catalytic performance for alkaline OER, compared with pristine NiO electrode. Our proposed strategy for implementing interface charge distribution by constructing a core–shell structure may be applicable to other Ni-based OER electrocatalysts.

Interfacial Electron Transfer and Synergistic Effects on NiCo(CA)@M Microbars That Boost the Alkaline Oxygen Evolution Reaction

The development of oxygen evolution reaction electrocatalysts with a low cost, high activity, and strong stability is of great significance to the breakthrough of energy conversion technology. Herein, a composite material (NiCo(CA)@M) was obtained by growing nickel-cobalt nanoparticles on MIL-88A in situ by a simple two-step solvent thermal method. The results show that NiCo(CA)@M composite has rich active sites, and the formation of the composite induces charge redistribution between NiCo(CA) and MIL-88A, effectively reducing the reaction energy barrier, while growth in situ was conducive to the improvement of material stability. Impressively, the NiCo(CA)@M catalyst achieved a current density of 10 mA cm−2 in alkaline electrolyte required an overpotential of only 270 mV and the Tafel slope was 69 mV dec−1. At the same time, the NiCo(CA)@M catalyst had excellent stability at a current density of 10 mA cm−2, and after the 16 h i-t test, the catalyst still had 91.1% current density retention. The electrocatalytic activity did not decay significantly after 2000 CV cycles.

Elucidating the promotion mechanism of the ternary cooperative heterostructure toward industrial-level urea oxidation catalysis

From the perspective of electronic structure modulation, it is highly desirable to rationally design the active urea oxidation reaction (UOR) catalysts through interface engineering. The binary cooperative heterostructure systems have been shown significant enhancement for catalyzing UOR, but their performance still remains unsatisfactory for industrialization because of the unfavorable intermediate adsorption/desorption and deficient electron transfer channels. In response, taking the ternary cooperative Ni5P4/NiSe2/Ni3Se4 heterostructure as the proof-of-concept paradigm, a catalytic model is rationally put forward to elucidate the UOR promotion mechanism at the molecular level. The rod-like Ni5P4/NiSe2/Ni3Se4 nanoarrays with three-phase heterojunction are experimentally fabricated on Ni foam (named as Ni5P4/NiSe2/Ni3Se4/NF) via simple two-step processes. The density functional theory (DFT) calculations disclose that construction of Ni5P4/NiSe2/Ni3Se4 heterostructure model not only induce charge redistribution at the interfacial region for creating innumerable electron transfer channels, but also endow it with a moderate d-band center that could help to build a balance between adsorption and desorption of diverse UOR intermediates. Benefiting from the unique rod-like nanoarrays with large specific surface area and the optimized electronic structure, the well-designed Ni5P4/NiSe2/Ni3Se4/NF could act as a robust catalyst for driving UOR at industrial-level current densities under tough environments, offering great potential for commercial applications.

Polydopamine bridging strategy enables pseudomorphic transformation of multi-component MOFs into ultrasmall NiSe/WSe2@NC heterojunctions for enhanced alkaline hydrogen evolution

Heterojunction catalysts can synergistically promote the kinetics of energy-related reactions, but a significant challenge remains in fully exposing and engineering interfacial active sites. Herein, we developed a polydopamine (PDA) bridging strategy to construct multi-component metal-organic frameworks (MOFs) precursors to form ultrasmall NiSe/WSe2 @NC heterojunctions. Due to the ambiphilic binding of PDA to both NiMg-MOF and polyoxometalate (POM = H3PW12O40), subsequent selenization and MgO removal yield highly dispersed NiSe/WSe2 @NC with intimate heterointerfaces. By adjusting Mg2+ and POM loadings in PDA⊂NiMg-MOF-POM, the Ni:W:C ratios in NiSe/WSe2 @NC were fine-tuned, resulting in an optimized catalyst with low overpotential and high stability (21 mV at 10 mA·cm−2 for 60 h in 1.0 M KOH), rivaling the commercial 20% Pt/C (30 mV). X-ray absorption spectroscopy and density-functional theory calculations unveil that such “PDA bridging” strategy ensures highly exposed dual active centers and induced charge redistribution on heterointerface, resulting in accelerated water adsorption/dissociation and H2 evolution kinetics.

Interfacial Defect Engineering Triggered by Single Atom Doping for Highly Efficient Electrocatalytic Nitrate Reduction to Ammonia

Electrochemical reduction of nitrate (NO3RR), a widespread water pollutant, to high-valued ammonia is encouraging for sustainable artificial nutrient recycling and environmental-friendly pollution management. However, the limited available catalytic active sites and competitive hydrogen evolution make the catalytic performance still unsatisfactory. In this work, interfacial defect engineering via single atom doping was conducted to achieve highly efficient electrocatalytic NO3RR. Upon introduction of isolated Fe atoms, abundant oxygen vacancies are generated over atomic interface of TiO2, and the induced charge redistribution triggers the formation of considerable active sites for nitrate reduction, which plays a crucial role in inhibiting the proton reduction and promoting the adsorption and activation of nitrate. As expected, single atom Fe modified TiO2 exhibits a maximum ammonia yield rate of 137.3 mg h–1 mgcat.–1 and a Faradaic efficiency of 92.3% at −1.4 V (vs RHE), which are among the best of all the reported values yet. This work provides valuable insights into the exploration of highly efficient electrocatalysts toward nitrate reduction through the heteroatom doping and defect engineering over atomic interface.

BN-Doped Carbon Nanotubes and Nanoribbons as Nonlinear-Optical Functional Materials for Application in Second-Order Nonlinear Optics

Pure carbon-based nanomaterials with good π conjugation and thermal stability, e.g., nanotubes and nanoribbons, have long served as promising conjugated materials for application in second-order nonlinear-optical (NLO) devices but suffer from two inherent structural problems: weak polarity (or even nonpolarity) and high chemical reactivity ascribed to zigzag edge states. In the present work, boron nitride (BN) chains are used to divide carbon nanotubes and nanoribbons, forming a functional block to tune the electronic structure, and thus induce charge redistribution or modify the molecular energy gap for second-order NLO materials or integrated electronic materials. A balance between the electronic kinetic stability and second-order NLO properties is established by structural manipulation. The strong second-order NLO responses in the visible and near-infrared regions make these hybridized carbon-based molecules potential NLO materials for applications in biological nonlinear optics. The application of BN to tune the electronic structure of carbon nanomaterials paves a path for fabricating nanoelectronic and nano-NLO devices.

Anomalous metastable hcp Ni nanocatalyst induced by non-metal N doping enables promoted ammonia borane dehydrogenation

Developing high-performing non-noble transition metal catalysts for H2 evolution from chemical hydrogen storage materials is of great significance for the hydrogen economy system, yet challenging. Herein, we present for the first time that anomalous metastable hexagonal close-packed Ni nanoparticles induced by heteroatom N doping encapsulated in carbon (N-hcp-Ni/C) can exhibit admirable catalytic performance for ammonia borane (AB) dehydrogenation, prominently outperforming conventional fcc Ni counterpart with similar morphology and favorably presenting the state-of-the-art level. Comprehensive experimental and theoretical studies unravel that unusual hcp phase engineering of Ni together with N doping could induce charge redistribution and modulate electronic structure, thereby facilitating H2O adsorption and expediting H2O dissociation (rate-determining step). As a result, AB dehydrogenation can be substantially boosted with the assistance of N-hcp-Ni/C. Our proposed strategy highlights that unconventional crystal phase engineering coupled with non-metal heteroatom doping is a promising avenue to construct advanced transition metal catalysts for future renewable energy technologies.

Heteroatom Doping Synergistic Iron Nitride Induced Charge Redistribution of Carbon based Electrocatalyst with Boosted Oxygen Reduction Reaction

AbstractOxygen reduction reaction (ORR) is Achilles’ heel of zinc‐air battery. The ideal electrocatalyst for ORR should combine both high activity and high stability. In order to achieve this goal, a new N, S co‐doped carbon coated Fe3N nanoparticles electrocatalyst with redistributed charge was designed and synthesized. The doping of S elements destroyed the ordered structure of carbon matrix, which cooperated with Fe3N nanoparticles to cause charge redistribution of carbon atoms. Furthermore, the carbon shell protected Fe3N from corrosion during the electrocatalytic process. Fe3N/NSC electrocatalyst showed excellent ORR property with E1/2=0.86 V, and the zinc‐air battery assembled based on it could run stably for more than 650 hours. This work provides a strategy to regulate the redistributed charge of carbon atoms to boost its electrocatalytic activity and stability together.