Promote Electron Transport Research Articles

Facile Surface Engineering of Composite Electron Transport Layer for Highly Efficient Perovskite Solar Cells with a Fill Factor Exceeding 81%

AbstractAfter perovskite became a star material, research on perovskite solar cells (PSCs) became a hot topic and developed rapidly. Electron transport layers (ETLs) with high mobility, low‐defect state, and suitable energy level arrangement dominate the development of planar heterojunction PSCs. In this work, the K+ and Cs+ doped composite SnO2 ETL (x mg KC‐SnO2) by a continuous spin‐coating of the x mg Cs+@KOH and SnO2 aqueous solution shows a substantial improvement in carries extraction, transport and collection properties, leading to the increased fill factor (FF) from 72.48% to 81.00% of the planar heterojunction PSCs, and finally the champion device average efficiency is 21.62%. Moreover, this work improves the interface contacts between ETL/Perovskite, as it reduces energy disorder and simultaneously promotes electron transport, charge extraction at the interface, improve energy level alignment and quasi‐Fermi level splitting, and decreased resistance for charge transfer in the device. In conclusion, this simple and effective method of improving the FF value provides a certain shortcut to the performance of plane heterogeneous perovskite devices.

Tailoring the d-band centers of FeP nanobelt arrays by fluorine doping for enhanced hydrogen evolution at high current density

Modulating the intrinsic activity of transition metal iron-based phosphates though tailoring d-band center has been effective strategy especially for large-scale hydrogen production at high current density. Herein, nonmetallic fluorine atoms are well doped into FeP nanobelt arrays by room temperatures immersion method for enhanced performance of hydrogen evolution reaction (HER) in alkaline solution. Significantly, the optimized fluorine-doped iron phosphide nanobelt array (3F-FeP) possess enhanced HER catalytic activity with low overpotentials of 191, 261 and 302 mV to achieve the 100, 500 and 1000 mA cm−2. Furthermore, the long-time stability test indicates that the NiFe-LDH/IF(+)//3F-FeP/IF(−) couple can last for more than 100 h at high current density of 1000 mA cm−2, which gives it a great potential in the practical electrolytic water industry. Density functional theory (DFT) calculations and ultraviolet photoemission spectroscopy (UPS) characterization consistently reveal that the doping of F can effectively regulate the electronic structure, promote electron transport, lower the d-band center position, optimize the hydrogen adsorption energy, reduce the water splitting energy and the H2 formation energy of iron phosphate. This work can provide a facile method for the designing strategy of materials with higher catalytic activity for HER.

Nitrogen and sulfur co-doping strategy to trigger the peroxidase-like and electrochemical activity of Ti3C2 nanosheets for sensitive uric acid detection

The development of functional nanomaterials based on the unique structure and morphology of MXene for biosensing has aroused great interest. In this work, using thiourea as the doping source, a new structure composed of nitrogen and sulfur co-doped on the surface of Ti3C2 nanosheets was synthesized through a simple one-step synthesis method. Fortunately, the obtained nitrogen and sulfur co-doped Ti3C2 nanosheets (NS–Ti3C2 NSs) showed excellent peroxidase-like activity and electrochemical activity. The catalytic mechanism of modified Ti3C2 nanosheets was explored. It is revealed that the catalytic mechanism of NS-Ti3C2 NSs is composed of two important parts: the dissociation and adsorption of H2O2 and the protonation of TMB. In addition, the fabricated NS-Ti3C2 NSs-based electrochemical biosensor is superior to the counterpart from Ti3C2 nanosheets, indicating that the doping of nitrogen and sulfur elements provides more active sites and promotes electron transport efficiency. Combining the unique advantages of colorimetry and electrochemical technology, we have developed a fast, accurate, intuitive and efficient UA detection method for uric acid in the range of 2 μM–400 μM with a detection limit (LOD) of 0.19 μM. The established sensing platform in this study prove the possibility of the doping method for the development of MXene-based biosensors with high sensitivity and high performance, and pave the way for the future development of biosensors for biomedical fields.

Core-shell Ni1.5Sn@Ni(OH)2 nanoflowers as battery-type supercapacitor electrodes with high rate and capacitance

Poor conductivity and aggregation of two-dimensional Ni(OH)2 nanosheets hinder their extensive applications in supercapacitors. In the current study, a core-shell nanoflower composite is successfully synthesized using a high conductivity Ni1.5Sn alloy and Ni(OH)2 nanosheets via a facile two-step hydrothermal reaction. The alloy material enhances the conductivity of the sample and promotes electron transport for Ni(OH)2. The as-prepared core-shell structure effectively restrains the clustering of nanosheets and improves the specific surface area of active materials. The optimized NS@NL-3 displays an outstanding specific capacitance (1002.2C g−1 at 1 A g−1) and satisfactory capacitance retention rate (80.63% at 20 A g−1) by adjusting the coating amount of Ni(OH)2 nanosheets, which is significantly higher compared with the performance of pure Ni(OH)2 (609.6C g−1 at 1 A g−1 and 55.64% at 20 A g−1). The all-solid-state hybrid supercapacitor (HSC) is fabricated with activated carbon (AC) as the negative electrode and NS@NL-3 as the positive electrode, which shows a high energy density of 57.4 Wh kg−1 at 803.6 W kg−1 as well as a superior cycling stability (88.45 % after 10,000 cycles). Experiment shows that 42 LEDs are effortlessly lit by two series-wound solid-state HSC devices, which indicates its high potential for practical applications.

Effect of TiO2 surface treatment on electron transfer in dye-sensitized solar cells

Defect states in the TiO2 nanoparticles can cause severe charge recombination and poor electron-transport efficiency when used as a photoanode in dye-sensitized solar cells (DSSCs). Herein, we report a simple and practical way to passivate the surface defects of TiO2 through hydrothermal treating with acetic acid and H2SO4, introducing a high percentage of 101 facets and sulfonic acid functional groups on the TiO2 surface. A high efficiency of 8.12% has been achieved, which is 14% higher than that of untreated TiO2 under the same condition. EIS results prove that the multiacid-treated TiO2 can promote electron transport and reduce charge recombination at the interface of the TiO2 and electrolyte. This work provides an efficient approach to engineer the electron-transport pathway in DSSCs.

Interface modification by formamidine acetate for efficient perovskite solar cells

Perovskite solar cells (PSCs) have received widespread attention due to their excellent photovoltaic characteristics. However, the nonradiative recombination of carriers induced by defects limits the stability and performance of PSCs. Interface and additive engineering are good medicine to cure the disease. Herein, formamidine acetate (FAAc) as interfacial additive is introduced to the TiO2/perovskite interface. The connection of the FA+ between the TiO2 and perovskite promotes electron transport, and the amino group (−NH2) and carboxyl group (−COOH) of FAAc passivates the defect at TiO2/perovskite interface. Meanwhile, the FAAc modification tunes the energy array and improves crystal quality of perovskite. In consequence, the PSC based on FAAc-modified TiO2 achieves the best power conversion efficiency (PCE) of 20.47%, accompanied with excellent stability and mitigated hysteresis, while PCE of the pristine PSC is 18.30%.

Vertically oriented Ni-doped MoS2 nanosheets supported on hollow carbon microtubes for enhanced hydrogen evolution reaction and water splitting

Developing efficient hydrogen evolution reaction (HER) electrocatalysts is extremely important for large-scale hydrogen production from water splitting. In this work, ultra-small MoS 2 nanosheets with 5% Ni doping grown on both sides of hollow carbon microtubes (5%-Ni-MoS 2 /aCMT) are prepared by a hydrothermal method . The vertically oriented Ni-doped MoS 2 nanosheets provide more active sites for HER, while open porous structure promotes ions transport, and hollow carbon microtube substrate accelerates electrons transport as well as hydrogen release. Density functional theory (DFT) analysis proves that the optimal amount of Ni doping can effectively adjust the electronic structure of MoS 2 . As a result, 5%-Ni-MoS 2 /aCMT electrode exhibits enhanced kinetics for HER in both acidic and alkaline conditions. To deliver the current density of 10 mA cm −2 , it requires overpotentials of 140 and 88 mV in 1 M KOH and 0.5 M H 2 SO 4 . 5%-Ni-MoS 2 /aCMT exhibits better stability than commercial Pt/C at a high current density of 200 mA cm −2 . Moreover, 5%-Ni-MoS 2 /aCMT/NF (nickel foam) || RuO 2 /NF electrolyzer exhibits ultra-long stability of 30 h at the current density of 100 mA cm −2 and excellent overall water splitting performance with requiring low cell voltages of 1.52 and 1.71 V to generate current densities of 10 and 50 mA cm −2 . • The Ni doping with an optimized content adjusted the electronic structure of MoS 2 , and improved the intrinsic activity. • The ultra-small vertically oriented and defect-rich Ni-doped MoS 2 nanosheets provide more active sites for HER. • The natural N-doped aCMT substrate promotes electron transport during the HER process. • 5%-Ni-MoS 2 /aCMT behaves an enhanced kinetics process based on EIS and DFT analysis.

Defect engineering induced heterostructure of Zn-birnessite@spinel ZnMn2O4 nanocrystal for flexible asymmetric supercapacitor

Defect engineering holds great promise to boost surface charge redox chemistry of pseudocapacitive materials. However, their innovative development on the heterogeneous structure is still lacking. Herein, defect-rich heterogeneous Zn-birnessite nanosheet@spinel ZnMn2O4 nanocrystal composites are designed via an in situ chemical reduction route at a low temperature. We explore the formation mechanism that the generated oxygen vacancy (Vo) in the Zn-birnessite triggers Mn cation migration, leading to birnessite-to-spinel phase transition. The defect-rich heterostructure supplies rich Mn2+/3+/4+ redox couples, multiple electrochemically active sites, and shortened ion-transport pathways. Moreover, the bandgap of the heterostructure is reduced from 1.54 eV to 1.06 eV after introducing Vo, which promotes electron transport and thus bolsters fast redox reaction kinetics. Accordingly, the heterostructure delivers a large areal capacitance of 1903 mF cm−2 at 3 mA cm−2 at a wide potential window of 1.2 V, high rate performance, and long cycle life (93.7% capacitance retention over 16,000 cycles). An asymmetric supercapacitor employing the heterostructure as a cathode and vanadium oxide as an anode exhibits a high voltage of 2.4 V, and possesses a maximum energy density of 6.24 mWh cm−3. This research offers a promising avenue to tailor the electrochemical reactivity of heterostructures through defect engineering.

Monodispersed ultra-thin BiOCl nanosheets with (110) facets exposed in situ self-assembled on reduced graphene oxide to enhance NO2 sensing performance at room temperature

In order to effectively increase gas adsorption active sites and boost the electrical conductivity of the materials, we synthesized ultra-thin BiOCl nanosheets with the uniform dispersion on reduced graphene oxide by a facile hot-injection method for detection of the concentration of the pollutant NO2. The size of BiOCl nanosheet was controlled within 25–30 nm. TEM, EPR and XPS unveil the presence of oxygen vacancy (VO) in the composite. The optimum BiG-3 sensor (the mass ratio of BiOCl/rGO is 1/3) exhibits a high sensitivity, elevated selectivity and remarkable long-term stability with the response (S = Ra/Rg) of 12.95–5 ppm NO2, response/recovery time of 9.3 s and 63 s, and as long as 60 days of stability at room temperature. The significant improvement in gas sensing performance of BiG-3 nanocomposite was mainly due to the highest selectivity with the higher adsorption energy of highly exposed (110) crystal planes for NO2, and a large number of oxygen vacancies providing additional active sites. Large areas of effective contact between ultra-thin BiOCl nanosheets and rGO can synergistically promote electron transport. Hence, the high sensing performance sensing material may be inspirations for actual productions.

PCBM/Ag interface dipole management in inverted perovskite solar cells

In inverted perovskite solar cells, the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/Ag back interface is quite important because serious recombination occurs and H2O/O2 directly attacks this interface to induce device instability. Here, bi-functional dipole layers are applied at the interface aiming at improving the charge transport and device stability simultaneously. Silane with -CF3 end group anchored on the PCBM surface induces more effective dipole effect than that with (CH2)7-CH3 end functional silane, bending the interface energy level to promote electron transport and reduce recombination. The hydrophobic nature of -CF3 also enhances the durability of the device. This work highlights the back surface dipole management method to achieve efficient and stable perovskite solar cells.

Self-doped TiO2 nanotube array photoanode for microfluidic all-vanadium photoelectrochemical flow battery

• Self-doped TiO 2 nanotube array photoanode is developed for μVPFB. • Visible-light response of TiO 2 is enabled by self-doping. • Nanotube array structure enhances separation of electron-hole pairs. • The developed photoanode shows enhanced solar energy storage performance. In this work, a self-doped TiO 2 nanotube array (SD-TNA) photoanode was developed through a facile method for a microfluidic all-vanadium photoelectrochemical flow battery (μVPFB) to achieve better solar energy storage performance. The TEM, XPS and XRD results confirmed successful self-doping, for which the light absorption range of the developed photoanode was extended to visible light. Meanwhile, one-dimensional nanotube structure promoted electron transport to enhance the separation of electrons and holes. The miniaturization of the flow battery reduced mass transfer resistance. Because of these merits, the μVPFB with the SD-TNA photoanode yielded a relatively stable photocurrent density as high as 0.10 mA cm −2 , which was much better than the conventional TNA photoanode, presenting about 100% improvement. The improvements in the photocurrent density and vanadium ion conversion rate could be achieved by upgrading both the intensity of light and concentration of vanadium ion.

Hierarchical N-doped carbon spheres anchored with cobalt nanocrystals and single atoms for oxygen reduction reaction

Carbon-supported transition metal catalysts have attracted intense interest for oxygen reduction reaction (ORR) due to their high activity and low cost. Herein, we report bimetallic zeolitic imidazole frameworks (BMZIF)-derived hierarchical N-doped carbon spheres anchored with graphene-encapsulated Co nanocrystals (Co@C) and spatially isolated single Co atoms (Co SAs) (denoted as Co-NCS) for highly efficient ORR. An ultrasonic strategy has been developed to uniformly anchor BMZIF on resin microspheres. The ultrasonic method significantly shortens the synthesis time and contributes to the homogeneous distribution of BMZIF. The inner resin spheres act as ideal support to anchor Zn/Co ions and prevent the aggregation of BMZIF nanocrystals, and the derived products provide adequate structural support and high conductivity after carbonization. Meanwhile, the outer BMZIF-derived porous carbon framework provides large specific surface area, promoted electron transport, and abundant exposed active sites. The co-existence of Co SAs and Co@C plays a vital role in the ORR process. The resultant catalyst demonstrates superior ORR performance with a half-wave potential (J 1/2 ) of 0.90 V, outperforming the commercial Pt/C. This work opens a new path to construct efficient Co-N-C based catalysts. • A fast ultrasonic method was developed to uniformly anchor BMZIF on resin spheres. • Resin spheres provide support for BMZIF, prevent aggregation, improve conductivity. • BMZIF-derived carbon framework increases transport pathways, exposes active sites. • Co-existence of Co single atoms and Co nanocrystals plays vital role in the ORR.

Enhanced heterogeneous photo-Fenton-like degradation of tetracycline over CuFeO2/biochar catalyst through accelerating electron transfer under visible light

The visible-light induced heterogeneous photo-Fenton-like (HPF-like) process is regarded as a promising technique for organic pollutants degradation due to its efficient utilization of solar energy and high H2O2 activation activity. This study prepared the CuFeO2/biochar catalysts via hydrothermal technique at no extra reductant and systematically investigated their band structure and photoelectric properties. The dispersed distribution of CuFeO2 particles in CuFeO2/biochar composites narrowed bandgap of CuFeO2 and promoted electron transport of CuFeO2. Compared with CuFeO2, the CuFeO2/biochar containing 1.0 g biochar in the preparation (CuFeO2/biochar-1.0) possessed higher carrier density and longer photoelectron lifetime, which is beneficial to higher catalytic performance. The apparent rate constant for tetracycline as target pollutant degradation by CuFeO2/biochar-1.0 was 2.0 times higher than that by CuFeO2. The acquired optimum conditions for tetracycline degradation were 220 mg L−1 CuFeO2/BC-1.0, 22 mM H2O2 and pH 6.4 using response surface methodology. The quenching experiments and ESR analysis revealed that OH was the predominant active species, and photoelectron and O2− were auxiliary species. The photoelectron could promote in-situ recycling of Cu2+ to Cu+ and Fe3+ to Fe2+, which significantly improved H2O2 activation by CuFeO2. The possible pathway of tetracycline was proposed according to intermediates identified by HPLC/MS. The toxicity analysis demonstrated that the overall toxicity of the identified intermediates was reduced in HPF-like system.

Enhancement Effects and Mechanisms of Microscale Zero Valent Iron on the Performance of Anaerobic Co-digestion of Waste Activated Sludge and Food Waste

Focusing on low biogas yields in the anaerobic co-digestion of waste activated sludge and food waste, the enhancing effects and mechanisms of microscale zero valent iron (mZVI) on anaerobic co-digestion was investigated. The results indicated that the addition of mZVI enhanced the methanogenesis stage of co-digestion but had no significant effect on the solubilization, hydrolysis, and acidification stages. With a dosage of 10 g·L-1 mZVI, the cumulative methane yield (based on VS) within 15 days reached 238.68 mL·g-1, which was 20.05% higher than the control group. The mechanism analysis showed that mZVI promoted electron transport system (ETS) activity (based on INTF/TS), which increased to 21.50 mg·(g·h)-1 with 10 g·L-1 mZVI compared to 13.43 mg·(g·h)-1 in the control group. Furthermore, mZVI enhanced direct interspecies electron transfer (DIET) between specific bacteria and methanogens. Microbial community analysis demonstrated that the abundance of DIET-related microorganisms, such as Syntrophomonas, Methanosarcina, and Methanobacterium, was higher in presence of mZVI.

Three-dimensional architectures based on carbon nanotube bridged Ti2C MXene nanosheets for Li–S batteries

Lithium–sulfur (Li–S) batteries are promising candidates for high density electrochemical energy storage systems. However, the poor conductivity of S and the shuttle effect of polysulfides are a bottleneck to practical applications. Herein, a three-dimensional architecture, based on carbon nanotube (CNT) bridged Ti2C MXene nanosheets, was constructed as a sulfur host. This architecture was based on Ti atoms, which can chemically absorb polysulfides. The CNTs are highly conductive and intercalate into the MXene nanosheets to prevent their stacking and construct an interspace for polysulfides. This hybrid, as a host of S, can effectively alleviate the shuttle effect through a combination of physical confinement and chemical adsorption. This resulted in an open internal space, which served as a cathode for the loaded S to promote electron transport and enhance electrochemical kinetics of the polysulfide conversion in Li–S batteries.

Hollow graphene fibres of highly ordered structure via coaxial wet spinning with application to multi-functional flexible wearables

Hollow graphene fibres have a large specific surface area with hollow, thereby increasing electrode electrolyte interfacial contact and promoting electron transport, have a layers structure of sheath as well as improving the mechanical properties. In this study, a one-step coaxial wet spinning method was adopted in which the core spinning solution was the same as the solidification solution. The graphene oxide (GO) dope in the shell was subjected to two-way solidification inside and outside and formed a dense shell. At the time, the injection speed ratio core/shell caused the core layer to pull rapidly on the shell, and the spinning dope was washed by the coagulation solution. The two opposite forces exerted a tug-of-war effect on the curved graphene sheet to gradually straighten it. Finally, a novel hollow graphene fibre with a dense and highly ordered shell was formed. Hollow fibres with a shell thickness of approximately 0.8 μm have a volume resistance of 1.14 × 10−2 Ω cm and a strength of 79.27 MPa, while non-hollow graphene fibres have a volume resistance of 2.69 × 10−2 Ω cm and a strength of 28.03 MPa. The hollow fibre also exhibited very stable electrical resistance during lateral compression cycles, providing a basis for the development of innovative hollow fibres for use in wearable flexible devices.

Vertically aligned architecture in the dense and thick TiO2-graphene nanosheet electrode towards high volumetric and areal capacities

2D nanomaterials have attracted intensive attention in the area of compact energy storage owing to their large packing densities. However, the highly tortuous and lengthy channels in conventional 2D nanomaterial electrodes cause sluggish ion diffusion kinetics and seriously reduce the capacity. Herein, we report a simple method adopting diamond wire saw cutting technology to construct a compact vertically aligned TiO2-graphene nanosheet electrode (VATiO2-G) with a large thickness of 130 μm. The vertical alignment not only provides short and less tortuous ion transport pathways to facilitate ion diffusion kinetics, but also improves the electronic conductivity to promote electron transport across the electrode. Accordingly, the VATiO2-G anode for lithium-ion batteries simultaneously exhibits high volumetric and areal capacities of 243 mA h cm−3 and 3.16 mA h cm−2 at 2.8 mA cm−2, respectively. This work exploits a general method to attain vertically aligned architecture in dense and thick 2D nanomaterial electrodes.

High performance lithium-sulfur batteries based on CoP nanoparticle-embedded nitrogen-doped carbon nanotube hollow polyhedra

Lithium‑sulfur (Li-S) battery with high theoretical energy density is regard as one of the most appealing competitors for the promising next-generation energy storage systems. However, the severe polysulfide shuttling and the low electrical conductivity of sulfur cathode limit the practical application of Li-S batteries. Therefore, the designing of sulfur host materials with high electrochemical activity and high sulfur content have great significance for Li-S batteries. Here, we reported a novel hybrid nanostructure (a new sulfide matrix material) through the pyrolytic reduction phosphorization strategy form ZIF-67, in which CoP nanoparticles were embedded into nitrogen-doped carbon nanotubes hollow polyhedron (NCNHP). Due to the synergistic effect of highly active Co, CoP and nitrogen-doped carbon nanotubes (NCNTs), the Co/CoP-NCNHP hybrid improved the adsorption of polysulfides. Micropores in Co/CoP-NCNHP effectively impregnate sulfur and inhibit the diffusion of polysulfides through physical constraint. In addition, the Co/CoP-NCNHP conductive network of nitrogen doping carbon nanotubes (NCNTs) interconnection promoted electron transport and electrolyte infiltration. Therefore, the specific capacity, rate capability and cycling stability of Li-S batteries are significantly improved. In particular, we delivered the Co/CoP-NCNHP based cathode (loaded with 74.09 wt% sulfur), which could main the specific capacity of 885 mAh g−1 after 500 cycles of 0.5C current.

Poly(dithieno[3,2-b:2’,3’-d]pyrrole) twisting redox pendants enabling high current durability in all-organic proton battery

Conducting polymers (CPs) bearing redox-active units are remarkable electrode materials for aqueous batteries. We report herein the elegant design of dithieno[3,2-b:2’,3’-d]pyrrole (DTP) twisted quinones repeating CPs for high-performance and robust all-organic proton battery in 1 M sulfuric acid electrolyte. The N-anthraquinone or naphthoquinone pendants act as superior redox sites by promoting electron transport along π-conjugated backbone via intermolecular charge transfer. The DTP-cored redox polymers exhibit high reversibility in charge/discharge cycling and withstand high current rate up to 50 C. The twist alignment of quinone pendants on DTP backbone facilitates charge transport and electrochemical reaction kinetics. By assembling two redox polymers with different energy levels as electrode pair, the all-polymer proton battery demonstrates a high capacity of 78 mAh g−1 (0.5 A g−1) and excellent rate capability (39 mAh g−1 at 20 A g−1). This proof-of-concept demonstration indicates we can develop more up-scalable, easily accessible, safe and environmentally benign organic electrodes for aqueous batteries through delicate materials design.

Compressible, anisotropic lamellar cellulose-based carbon aerogels enhanced by carbon dots for superior energy storage and water deionization

Heteroatom-doped carbon materials have received great attention for applications in electrode materials. However, conventional heteroatom-doping methods sacrifice conductivity, stability, and specific surface area (SSA). Here, the carbon quantum dots (CDs) are used as carriers of N, P, O to form electron-rich regions promoting electron transport without decreasing stability and SSA. The CDs promote the formation of graphitic nitrogen in the composite, which effectively reduces their internal resistance by increasing the dielectric constant. Moreover, the orderly growth of ice crystals generates a unique bridged layer structure under bidirectional freeze-casting in a mixture of GO/CDs/microfibrillated cellulose, which gives the composite super-compressibility. Notably, the optimal sample has a 117% increase in specific capacitance. The CDs also improve wettability and thus reduce the charge transfer resistance giving a large desalination capacity of 32.59 mg g−1 (504 mg L−1 NaCl). This work illustrates the unique role of CDs in improving the electrochemical performance of composites.