Accelerated Charge Transfer Research Articles

Synergy of phosphorus vacancies and build-in electric field into NiCo/NiCoP Mott-Schottky integrated electrode for enhanced water splitting performance

Vacancy engineering and Mott-Schottky heterostructure can accelerate charge transfer, regulate adsorption energy of reaction intermediates, and provide additional active sites, which are regarded as valid means for improving catalytic activity. However, the underlying mechanism of synergistic regulation of interfacial charge transfer and optimization of electrocatalytic activity by combining vacancy and Mott-Schottky junction remains unclear. Herein, the growth of a bifunctional NiCo/NiCoP Mott-Schottky electrode with abundant phosphorus vacancies on foam nickel (NF) has been synthesized through continuous phosphating and reduction processes. The obtained NiCo/NiCoP heterojunctions show remarkable OER and HER activities, and the overpotentials for OER and HER are as low as 117 and 60 mV at 10 mA/cm2 in 1 mol/L KOH, respectively. Moreover, as both the cathode and anode of overall water splitting, the voltage of the bifunctional NiCo/NiCoP electrocatalyst is 1.44 V at 10 mA/cm2, which are far exceeding the benchmark commercial electrodes. DFT theoretical calculation results confirm that the phosphorus vacancies and build-in electric field can effectively accelerate ion and electron transfer between NiCo alloy and NiCoP semiconductor, tailor the electronic structure of the metal centers and lower the Gibbs free energy of the intermediates. Furthermore, the unique self-supported integrated structure is beneficial to facilitate the exposure of the active site, avoid catalyst shedding, thus improving the activity and structural stability of NiCo/NiCoP. This study provides an avenue for the controllable synthesis and performance optimization of Mott-Schottky electrocatalysts.

Pt nanoparticles mediated Bi12O17Cl2 nanosheets for enhanced organic pollutants photodegradation: Boosting kinetics and molecular oxygen activation

With the increasing serious environmental pollution caused by urbanization and industrialization, it is urgent to develop photocatalysts with broad spectral response and high photogenerated carriers’ separation efficiency. In this work, the Pt nanoparticles (NPs)-loaded Bi12O17Cl2 nanosheets composites (Pt/Bi12O17Cl2) were synthesized by a facile photoreduction method. The Pt NPs can serve as electron capture trap, accelerating charge transfer and boosting molecular oxygen activation, enhancing the photodegradation performance of rhodamine B (RhB) and ciprofloxacin (CIP). The prepared Pt/Bi12O17Cl2-2 exhibits the optimized photocatalytic removal constants for RhB and CIP under visible light irradiation, which is 6.36 and 2.97 times compared with that of pristine Bi12O17Cl2, respectively. Furthermore, the intermediates and possible degradation pathways for RhB and CIP were deduced based on liquid chromatography-mass spectrometry (LC-MS) analysis. Finally, the photodegradation mechanism was proposed based on the active substance capture experiments. This study affords a promising approach for enhancing the molecular oxygen activation of photocatalysts.

High‐efficiency sodium storage of Co0.85Se/WSe2 encapsulated in N‐doped carbon polyhedron via vacancy and heterojunction engineering

AbstractWith the advantage of fast charge transfer, heterojunction engineering is identified as a viable method to reinforce the anodes' sodium storage performance. Also, vacancies can effectively strengthen the Na+ adsorption ability and provide extra active sites for Na+ adsorption. However, their synchronous engineering is rarely reported. Herein, a hybrid of Co0.85Se/WSe2 heterostructure with Se vacancies and N‐doped carbon polyhedron (CoWSe/NCP) has been fabricated for the first time via a hydrothermal and subsequent selenization strategy. Spherical aberration‐corrected transmission electron microscopy confirms the phase interface of the Co0.85Se/WSe2 heterostructure and the existence of Se vacancies. Density functional theory simulations reveal the accelerated charge transfer and enhanced Na+ adsorption ability, which are contributed by the Co0.85Se/WSe2 heterostructure and Se vacancies, respectively. As expected, the CoWSe/NCP anode in sodium‐ion battery achieves outstanding rate capability (339.6 mAh g−1 at 20 A g−1), outperforming almost all Co/W‐based selenides.

Bimetallic PtNi alloy modified 2D g-C3N4 nanosheets as an efficient cocatalyst for enhancing photocatalytic hydrogen evolution

Platinum-based alloy materials as effective cocatalysts in improving the performance of photocatalytic H2 production have raised great interest. Herein, a facile strategy of chemical reduction is established to synthesize bimetallic PtNi nanoparticles on 2D g-C3N4 nanosheets with excellent photocatalytic activity. The addition of PtNi nanoparticles can provide new H+ reduction sites and increase more active sites of the material. The synergistic effect between PtNi alloy nanoparticles and 2D g-C3N4 nanosheets can regulate electronic structure, narrow the band, accelerate charge transfer efficiency and inhabit the recombination of photo-induced electron (e−) and hole pairs (h+), contributing to the improvement of hydrogen evolution activity. The optimal hydrogen evolution rate of Pt0.6Ni0.4/CN shows higher hydrogen evolution rate (9528 μmol·g−1·h−1), which is 13.1 times than that of pure g-C3N4 nanosheets. Besides, a possible mechanism of photocatalytic hydrogen generation has been brought up according to a series of physical and chemical characterization. This work also provides a potential idea of developing cocatalysts integrating metal alloys with 2D g-C3N4 nanosheets for promoting photocatalytic hydrogen evolution.

Significant enhancement of photocatalytic activity of g-C3N4/vermiculite composite by the introduction of nitrogen defects

Nitrogen-defect g-C3N4/vermiculite composites (gCVx, x = 0.1, 1, 3, 4) with high efficient photocatalytic performance were constructed by a wet chemical method cooperating with the calcination process, as well as using the pre-expanded vermiculite and the melamine pre-treated by hydrochloric acid solutions of 0.1, 1, 3, 4 mol/L, respectively. Micron-sized g-C3N4 sheets with nitrogen defects were synthesized and uniformly distributed in the gCVx composites. Photocatalytic performance was evaluated by degrading Rhodamine B (RhB) aqueous solution. The results indicated that photocatalytic activities of gCVx increased firstly and then dropped down gradually with the increase of HCl concentration. gCV3 achieved the maximum degradation rate of 97.90 % for RhB after photocatalysis for 20 min, whose degradation rate constant was 14.9 times than that of bulk g-C3N4. gCV3 also exhibited the highest photocatalytic activity toward degrading the tetracycline and phenol solutions. The excellent photocatalytic performance was ascribed to the enhanced amounts of active sites, increased specific surface area, improved visible light absorption ability, accelerated charge transfer and separation efficiency of photogenerated-carriers, which resulted from the synergistic effect between vermiculite and nitrogen defects in g-C3N4, as well as the mutual electrostatic repulsion between the negative-charged vermiculite and the photo-induced electron from the nitrogen-defect g-C3N4.

Ni3N@Ni juncture layer enabled performance enhanced electrocatalytic water oxidation

High-performance and cost-effective catalysts for water splitting are key components of hydrogen-based energy technologies. As a classical catalyst, NiFe-LDH is confirmed as the ideal answer to the dynamic slow oxygen release reactions (OER). While, how to take best advantage of the electrocatalyst came to a non-negligible challenge. Herein, NiFe-LDH/Ni3N@Ni/CP electrode was assembled with Ni3N@Ni as a juncture layer for optimized performance. An overpotential of only 233 mV was needed to drive a current density of 100 mA cm−2, with a very low Tafel slope of 25.8 mV dec-1 and excellent durability of 150 h. The superior performance was ascribed to the optimized conductivity, accelerated charge transfer kinetics and enlarged ECSA for the juncture layer of Ni3N@Ni. This work provides brand-new ideas for the rational design of electrodes for water splitting.

CuFeSe2/Cu2Se@C heterostructures as high-rate ultra-stable anodes for sodium ion half/full batteries

Transition metal selenides can be potentially implemented as a new generation of sodium storage anode owing to their abundance and high theoretical specific capacity. However, their practical applications are limited by large volume changes and slow kinetics. Therefore, the construction of transition metal selenide heterojunctions with long cycle stability and high capacity as anodes in sodium ion batteries remains challenging. In this study, carbon coated CuFeSe2/Cu2Se heterojunctions (CFS/CS@C) were successfully prepared via a simple aging and annealing strategy. The abundant heterojunction interfaces and carbon layers accelerated charge transfer, promoted the reaction kinetics, enhanced the electrical conductivity, and extended the cycle life. Consequently, the target material yielded ultra-long cycle stability (301.2 mAh/g at 10.0 A/g after 3000 cycles) and excellent rate performance (330.96 mAh/g at 20 A/g). The directly constructed full cell also exhibited remarkable cycling stability (138.6 mAh/g after 200 cycles at 0.5 A/g). Accordingly, this work demonstrated the construction of transition metal selenide composites as high-performance electrochemical energy storage electrodes.

Electrodeposited copper oxides with a suppressed interfacial amorphous phase using mixed-crystalline ITO and their enhanced photoelectrochemical performances

The effectiveness of photoelectrochemical (PEC) water splitting is significantly restricted by insufficient light harvesting, rapid charge recombination, and slow water reduction kinetics. Since the presence of amorphous phases in the interfaces hinders the overcome of these inherent limitations, a photoelectrode must be built strategically. Herein, we artificially controlled the crystallographic orientation of indium tin oxide (ITO) to determine the orientation with the smallest lattice mismatch at the Cu2O interface, thus significantly reducing the amorphous phase in the early stage of electrodeposition nucleation. The [222]/[400] mixed orientation ITO primarily exposed the {400} surface planes and accelerated charge transfer by forming an optimal interface with preferentially grown (111) oriented Cu2O and minimized amorphous region. In addition, the ITO surface energy was calculated using density functional theory to theoretically verify which plane is more active for growing the photoactivation layer. The rationally designed ITO/Cu2O/Al-dope ZnO/TiO2/Rh-P device, with each layer serving a specific purpose, achieved a photocurrent density of 8.23 mA cm−2 at 0 VRHE under AM 1.5 G illumination, providing a standard method for effective solar-to-hydrogen conversion photocathodes.

Minimized Energy Loss at the Buried Interface of p‐i‐n Perovskite Solar Cells via Accelerating Charge Transfer and Forming p–n Homojunction

AbstractThe energy loss (Eloss) aroused by inefficient charge transfer and large energy level offset at the buried interface of p‐i‐n perovskite solar cells (PVSCs) limits their development. In this work, a BF4− anion‐assisted molecular doping (AMD) strategy is first proposed to improve the charge transfer capability of hole transport layers (HTLs) and reduce the energy level offset at the buried interface of PVSCs. The AMD strategy improves the carrier mobility and density of poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) and poly[N,N′‐bis(4‐butilphenyl)‐N,N′‐bis(phenyl)‐benzidine] (Poly‐TPD) HTLs while lowering their Fermi levels. Meanwhile, BF4− anions regulate the crystallization and reduce donor‐type iodine vacancies, resulting in the energetics transformation from n‐type to p‐type on the bottom surface of perovskite film. The faster charge transfer and formed p–n homojunction reduce charge recombination and Eloss at the HTL/perovskite buried interface. The PVSCs utilizing AMD treated PTAA and Poly‐TPD as HTLs demonstrate a highest power conversion efficiency (PCE) of 24.26% and 22.65%, along with retaining 90.97% and 85.95% of the initial PCE after maximum power point tracking for 400 h. This work provides an effective way to minimize the Eloss at the buried interface of p‐i‐n PVSCs by accelerating charge transfer and forming p–n homojunctions.

Advanced Functional Carbon Nitride by Implanting Semi-Isolated VO2 Active Sites for Photocatalytic H2 Production and Organic Pollutant Degradation.

It is critical to facilitate surface interaction for liquid-solid two-phase photocatalytic reactions. This study demonstrates more advanced, efficient, and rich molecular-level active sites to extend the performance of carbon nitride (CN). To achieve this, semi-isolated vanadium dioxide is obtained by controlling the growth of non-crystalline VO2 anchored into sixfold cavities of the CN lattice. As a proof-of-concept, the experimental and computational results solidly corroborate that this atomic-level design has potentially taken full advantage of two worlds. The photocatalyst comprises the highest dispersion of catalytic sites with the lowest aggregation, like single-atom catalysts. It also demonstrates accelerated charge transfer with the boosted electron-hole pairs, mimicking heterojunction photocatalysts. Density functional theory calculations show that single-site VO2 anchored into the sixfold cavities significantly elevates the Fermi level, compared with the typical heterojunction. The unique features of semi-isolated sites result in a high visible-light photocatalytic H2 production of 645µmol h-1 g-1 with only 1wt% Pt. They also represent an excellent photocatalytic degradation for rhodamine B as well as tetracycline, surpassing the activities obtained from many conventional heterojunctions. This study presents exciting opportunities for the design of new heterogeneous metal oxide for a variety of reactions.

Engineering Cost-Efficient CoS-Based Electrocatalysts for Rechargeable Zn-Air Battery Application

The development of low-cost and efficient electrocatalysts toward the oxygen evolution reaction (OER) is crucial for clean energy devices such as metal-air batteries and fuel cells. Herein, a novel CoS@FeOOH electrocatalyst is synthesized by in-situ deposition of FeOOH nanoparticles on metallic organic frame (MOF) derived CoS hollow polyhedrons. Due to the coupling synergetic effect of FeOOH and CoS, CoS@FeOOH presents an excellent OER catalytic performance with both high electrocatalytic activity and durable cycling stability, far superior to the pristine CoS and commercial RuO2 electrocatalysts. The assembled rechargeable zinc-air battery (ZAB) using CoS@FeOOH as the OER electrocatalyst shows a maximum power density of 89.1 mW cm–2 and continuously runs 60 h without evident polarization increment, which is far better than the ZAB using the commercial RuO2 OER electrocatalyst. The robust catalytic performance of the CoS@FeOOH electrocatalyst is mainly attributed to the regulated electronic configurations accelerating charge transfer, abundant oxygen vacancies promoting catalytic activity, and an FeOOH protection layer inhibiting active Co dissolution.

Synergistic effect customized for cobalt pentlandite (Co,Ni,Fe)9S8 accelerated charge transfer toward highly efficient oxygen evolution reaction

The oxygen evolution reaction (OER) is one of the core reaction modules of important renewable energy technologies with applications in water splitting, metal-air (oxygen) cells and regenerative fuel cells. However, OER catalysts are forced to operate with a significant intrinsic overpotential and inefficient charge transfer due to the adsorption energy scaling balance between the reaction intermediates. It is critical to develop an understanding of structure-activity relationship of catalysts, determine the speed control steps and improve catalytic activity. In this work, cobalt pentlandite (Co,Ni,Fe)9S8 (CNFS) electrocatalysts were successfully prepared by combining the earth-abundant transition metal elements Co, Ni and Fe into a single structure. Benefiting from the structure, nanoflower morphology, and the synergistic effect among the three elements, the optimized sample requires an overpotential of only 335 mV to drive a current density of 50 mA cm–2 under alkaline conditions. The experimental results establish a composition-structure-function relationship, and the density functional theory results further indicate that the Fe sites bind more moderately to the intermediates and the electron synergistic effect occurs dynamically during the OER cycle reaction. This work not only provides a very promising catalyst candidate for efficient OER processes but also highlights the superiority of the cobalt pentlandite structure in the rational design of efficient OER electrocatalysts.

Zn vacancy-tailoring mediated ZnIn2S4 nanosheets with accelerated orderly charge flow for boosting photocatalytic hydrogen evolution

Defect engineering is one of the most effective ways to accelerate charge transfer, and thus to boost the H2 evolution of photocatalyst. However, this strategy remains a challenge for the precise control of defect structures to realize the orderly charge transfer in photocatalyst. Herein, ZnIn2S4 nanosheets with controlled Zn vacancies were designed, where the conduction band structure and localized charge density of ZnIn2S4 were optimized. The promoted conduction band property enables photoexcited charges to be captured in the defect centers, which leads to the orderly charge flow. The reconstituted surface microenvironment provides a powerful driving force for H2-evolution reaction. These favorable conditions contribute to an improved photocatalytic H2 evolution performance of 212.0 μmol through a four-hour test, which is 1.9 times that of pristine ZnIn2S4. This work clarifies the electronic structure characteristics of metal vacancy and affords valuable views for purposeful construction of photocatalytic nanomaterials with metal vacancies.

Charge Regulation on Hybrid Nanosheet Stereoassembly via Interfacial PO Coupling Enables Efficient Overall Water Splitting

AbstractPrecise regulation on interfacial electronic coupling is essential to achieve efficient catalysts with tailored electrocatalytic behaviors but remains challenging. Herein, a straightforward topochemical strategy is presented to realize Co‐based heterostructured nanofiber stereoassembled with PO coupled nanosheet (CoHF/PO). By constructing well‐defined metal oxide/phosphide interface, prominent electron redistribution can be established via interfacial PO coupling, which is strongly correlated with the catalytic activities. Density functional theory calculations indicate that the rational interface engineering renders accelerated charge transfer and more importantly, optimized surface adsorption/desorption behaviors, contributing to boosted kinetics for both hydrogen evolution reaction and oxygen evolution reaction. Particularly, CoHF/PO featuring promoted intrinsic activity and accessible active sites exhibits intriguing activity and stability at higher current densities in alkaline media, surpassing commercial Pt/C and Ir/C. This study is expected to demonstrate noteworthy promise of covalent coupling toward modulated electronic environment and interface chemistry for electrocatalytic applications and beyond.

External electric field-assisted electronic restructuring of transition metal oxides derived from spent lithium-ion batteries to enhance persulfate activation

Discarded lithium-ion batteries contain abundant transition metal oxides, which benefit to persulfate activation. Inspired by electrocatalysis and the structural properties of the ternary lithium-ion battery cathode, we investigate the effect of external electric field polarization on the electronic structure reorganization behavior of NCM and the catalytic performance of peroxymonosulfate (PMS). Firstly, external electric field polarization promotes the gathering of Co and Ni. Secondly, the electric field modified waste NCM (E-PD@NCM) has 1.61 times higher degradation rate of SMX than the non-electric field modified waste NCM (PD@NCM). Meanwhile, electric field polarization increased the oxygen vacancy content in the spent NCM, and the abundant oxygen vacancies effectively restructured the electronic structure of E-PDNCM, further accelerating charge transfer and significantly improving the PMS activation efficiency. The catalytic mechanism analysis indicates that SO4•− and 1O2 play a dominant role in the degradation of pollutants. This study demonstrates the high catalytic performance of TMO through reorganization of the electronic structure and provides a new strategy to guide the design of other metal oxide nano-catalysts.

Potassium-doped g-C3N4 enables efficient visible-light-driven dye degradation.

Element doping is recognized as an efficient method to boost the photocatalytic performance of photocatalysts. Here, a new potassium ion-doped precursor, potassium sorbate, was employed in melamine configuration during calcination process to prepare the potassium-doped g-C3N4 (KCN). By various characterization techniques and electrochemical measurements, the doping of K in g-C3N4 can efficiently modify the band structure to enhance the light absorption and greatly increase the conductivity to accelerate charge transfer and photogenerated carrier separation, ultimately achieving an excellent photodegradation of the organic pollutant (methylene blue, MB). These results have demonstrated that the approach of potassium incorporation in g-C3N4 has potential in fabricating high-performance photocatalysts for organic pollutant removal.

Boosting Charge Mediation in Ferroelectric BaTiO3−x‐Based Photoanode for Efficient and Stable Photoelectrochemical Water Oxidation

Oxygen evolution reaction (OER) is a bottleneck to photoelectrochemical (PEC) water splitting; however, there remains an impressive challenge for intrinsic charge transport for the development of integrated photoanodes. Herein, covalent triazine frameworks as conjugated molecules are grafted on the surfaces of ferroelectric BaTiO3−x (CTF/BTO) nanorod array, and then oxyhydroxide oxygen evolution cocatalyst (OEC) is constructed as an integrated photoanode. The OEC/CTF/BTO array not only achieves a high photocurrent density of 0.83 mA cm−2 at 1.23 V versus reversible hydrogen electrode (vs RHE) and low onset potential of ≈0.23 VRHE, but also optimizes outstanding stability. To disclose the origin, the enhanced PEC activity can be contributed to the integration of CTF and OEC, enhancing light‐harvesting capability, boosting charge carrier mediation, and promoting water oxidation kinetics through electrochemical analysis and density functional theory calculations. This study not only provides an alternative to accelerate charge transfer, but also paves the rational design and fabrication of integrated photoanodes for boosting PEC water splitting performance.

Indium oxide induced electron-deficient indium hollow nanotubes for stable electroreduction of CO2 at industrial current densities

Despite high selectivity for CO2 electroreduction to formate, the current density and stability over indium-based catalysts are far from the requirements of industrial applications. Herein, we report an aminated In-MOF-derived In/In2O3 hollow nanotube catalyst (In/In2O3 Ho-nt), which can maintain a stable In0/In3+ heterostructure during the CO2 electrocatalysis. The stable In0/In3+ species boosts the formate FE (Faradaic efficiency) to over 90% with a highest current density of ∼ 650 mA cm−2 in a wide potential range from −0.8 V to −1.2 V vs. RHE in flow cells. More impressively, In/In2O3 Ho-nt demonstrates a full-cell EE (energy efficiency) of 44.5% and a long-term stability of 70 h at a current density of 200 mA cm−2 in membrane electrode assembly (MEA) cells by controlling the hydrophobicity of the catalyst interface. DFT calculations reveal that the charge redistribution between In3+ and In0 sites endows In0 sites with an electron-deficient environment, which enhances the adsorption capacity of CO2* intermediate and accelerates charge transfer kinetics, thus improving the activity of CO2 electroreduction to formate.

Carbon and nitrogen co-doped In2O3 porous nanosheets with oxygen vacancies for remarkable photocatalytic CO2 conversion

Photocatalytic CO2 reduction to sustainable products by utilizing solar energy has great prospects for development. However, most of the conventional catalysts have the disadvantages of inefficient, low visible light absorption, and poor product selectivity. For this reason, in this study, carbon and nitrogen co-doped In2O3 (C,N-In2O3) porous nanosheets with oxygen vacancies have been successfully prepared by pyrolyzing the as-prepared carbon-rich InOOH (C-InOOH) nanosheets precursor in an ammonia-helium mixture gas. The derived C,N-In2O3 photocatalyst possesses a mesoporous structure, large surface area, accelerated charge transfer and separation, and high visible-light absorption ability. The carbon and nitrogen co-doping produced proper surface defects (oxygen vacancies), which can facilitate CO2 adsorption and inhibit photogenerated charge recombination. As expected, an efficient CO2 photoreduction is achieved over the C,N-In2O3 sample with a CO production rate of 152 μmol h−1 g−1 and 80% selectivity together with an excellent stability. This study provided an efficient C,N co-doping strategy for fabricating high-active and stable photocatalysts, which could be applied to the conversion and utilization of solar energy in the future.

Design of Ti-Pt Co-doped α-Fe2O3 photoanodes for enhanced performance of photoelectrochemical water splitting

This study demonstrates Ti and Pt co-doping can synergistically improve the PEC performance of the α-Fe2O3 photoanode. By varying the doping methods, the sample with in-situ Ti ex-situ Pt doping (Tii-Pte) exhibits the best performance. It demonstrates that Ti doping in bulk facilities charge separation and Pt doping on the surface further accelerates charge transfer. In contrast, Ti doping on the surface inhibits charge separation, and Pt doping in bulk hinders charge separation and transfer. HCl treatment is used to minimize the onset potential further, while it is favorable for the ex-situ doped α-Fe2O3, which is more efficient on Tie than the Pte-doped ones. On the ex-situ Ti-doped α-Fe2O3 after HCl treatment, anatase TiO2 is probed, suggesting that Ti-O bonds accumulate when Fe-O bonds are partly removed, which enhances the charge transfer in surface states. Unfortunately, HCl treatment also induces lattice defects that are adverse to charge transport, inhibiting the performance of in-situ doped α-Fe2O3 and excessively treated ex-situ doped ones. Coupled with methanol solvothermal treatment and NiOOH/FeOOH cocatalysts loading, the optimized Ti-Pt/Fe2O3 photoanode exhibits an impressive photocurrent density of 2.81 mA cm−2 at 1.23 V vs. RHE and a low onset potential of 0.60 V vs. RHE.