Showing papers by "Shihe Yang published in 2021"

Redirecting dynamic surface restructuring of a layered transition metal oxide catalyst for superior water oxidation

Abstract: Rationally manipulating the in situ formed catalytically active surface of catalysts remains a tremendous challenge for a highly efficient water electrolysis. Here we present a cationic redox-tuning method to modulate in situ catalyst leaching and to redirect the dynamic surface restructuring of layered LiCoO2–xClx (x = 0, 0.1 or 0.2), for the electrochemical oxygen evolution reaction (OER). Chlorine doping lowered the potential to trigger in situ cobalt oxidation and lithium leaching, which induced the surface of LiCoO1.8Cl0.2 to transform into a self-terminated amorphous (oxy)hydroxide phase during the OER. In contrast, Cl-free LiCoO2 required higher electrochemical potentials to initiate the in situ surface reconstruction to spinel-type Li1±xCo2O4 and longer cycles to stabilize it. Surface-restructured LiCoO1.8Cl0.2 outperformed many state-of-the-art OER catalysts and demonstrated remarkable stability. This work makes a stride in modulating surface restructuring and in designing superior OER electrocatalysts via manipulating the in situ catalyst leaching. Rationally manipulating the in-situ-formed catalytically active surface of catalysts is a challenging but promising endeavour. Now, the surface of LiCoO2 during water oxidation is engineered by Cl doping via a cationic redox-tuning method that modulates in situ leaching and redirects the dynamic surface restructuring.

Self-Driven Perovskite Narrowband Photodetectors with Tunable Spectral Responses

Abstract: Narrowband photodetectors with tunable spectral responses are highly desirable for applications in image sensing, machine vision, and optical communication. Herein, a filterless and self-driven perovskite narrowband photodetector (PNPD) based on the defect-assisted charge collection narrowing (CCN) mechanism is reported, which is enabled by a high-quality thick perovskite film. By adjusting the halide component of the perovskite layer, the bandgap is successfully modulated and the corresponding narrowband photodetectors show a wide spectral response range from the red to the near-infrared (NIR), all with full-widths at half maximum (FWHMs) below 30 nm. Specifically, the methylammonium lead iodide (MAPbI3 ) narrowband photodetector exhibits a characteristic detection peak at 800 nm with a very low noise current of ≈0.02 pA Hz-1/2 , a high specific detectivity up to 1.27 × 1012 Jones, and a fast response speed with rise/fall time of 12.7/6.9 µs. Impressively, these values are among the highest of their kind reported previously, and allow demonstration of narrowband imaging. The excellent performance of self-driven PNPDs lights up their prospect in high-efficiency optoelectronic devices without external power sources.

Activating Metal Oxides Nanocatalysts for Electrocatalytic Water Oxidation by Quenching-Induced Near-Surface Metal Atom Functionality.

Abstract: Developing a reliable strategy for the modulation of the texture, composition, and electronic structure of electrocatalyst surfaces is crucial for electrocatalytic performance, yet still challenging. Herein, we develop a facile and universal strategy, quenching, to precisely tailor the surface chemistry of metal oxide nanocatalysts by rapidly cooling them in a salt solution. Taking NiMoO4 nanocatalysts an example, we successfully produce the quenched nanocatalysts offering a greatly reduced oxygen evolution reaction (OER) overpotential by 85 mV and 135 mV at 10 mA cm-2 and 100 mA cm-2 respectively. Through detailed characterization studies, we establish that quenching induces the formation of numerous disordered stepped surfaces and the near-surface metal ions doping, thus regulating the local electronic structures and coordination environments of Ni, Mo, which promotes the formation of the dual-site active and thereby affords a low energy pathway for OER. This quenching strategy is also successfully applied to a number of other metal oxides, such as spinel-type Co3O4, Fe2O3, LaMnO3, and CoSnO3, with similar surface modifications and gains in OER activity. Our finding provides a new inspiration to activate metal oxide catalysts and extends the use of quenching chemistry in catalysis.

An aerosol-liquid-solid process for the general synthesis of halide perovskite thick films for direct-conversion X-ray detectors

Abstract: Summary Medical X-ray computed tomography requires imaging at a low dose rate and in a large area. Halide perovskites have shown high potential for X-ray detection, but a pressing challenge is the current lack of low-cost methods for large-scale fabrication of high-quality thick perovskite films. Here we demonstrate and elucidate an aerosol-liquid-solid process to enable continuous growth of uniform halide perovskite films at low temperature over a large area of 100 cm2, which are vertically monolithic, and thus beneficial to carrier transport. Direct-conversion X-ray detectors based on the representative CsPbI2Br films in conjunction with a deliberated, interface-engineered C-electrode have realized an unprecedented sensitivity (≥1.48 × 105 μC Gyair−1 cm−2) and a low limit of detection (280 nGyair s−1). We have further demonstrated the high-resolution radiographic imaging capability of these films. These results lay the groundwork for large-scale application of halide perovskites in radiation detectors.

Crystallization Kinetics Modulation of FASnI3 Films with Pre-nucleation Clusters for Efficient Lead-Free Perovskite Solar Cells.

Abstract: Tin halide perovskites are rising as promising materials for lead-free perovskite solar cells (PSCs). However, the crystallization rate of tin halide perovskites is much faster than the lead-based analogs, leading to more rampant trap states and lower efficiency. Here, we disclose a key finding to modulate the crystallization kinetics of FASnI3 through a non-classical nucleation mechanism based on pre-nucleation clusters (PNCs). By introducing piperazine dihydriodide to tune the colloidal chemistry of the FASnI3 perovskite precursor solution, stable clusters could be readily formed in the solution before nucleation. These pre-nucleation clusters act as intermediate phase and thus can reduce the energy barrier for the perovskite nucleation, resulting in a high-quality perovskite film with lower defect density. This PNCs-based method has led to a conspicuous photovoltaic performance improvement for FASnI3 -based PSCs, delivering an impressive efficiency of 11.39 % plus improved stability.

TM LDH Meets Birnessite: A 2D‐2D Hybrid Catalyst with Long‐Term Stability for Water Oxidation at Industrial Operating Conditions

Abstract: Efficient noble-metal free electrocatalyst for oxygen evolution reaction (OER) is critical for large-scale hydrogen production via water splitting. Inspired by Nature's oxygen evolution cluster in photosystem II and the highly efficient artificial OER catalyst of NiFe layered double hydroxide (LDH), we designed an electrostatic 2D-2D assembly route and successfully synthesized a 2D LDH(+)-Birnessite(-) hybrid. The as-constructed LDH(+)-Birnessite(-) hybrid catalyst showed advanced catalytic activity and excellent stability towards OER under a close to industrial hydrogen production condition (85 °C and 6 M KOH) for more than 20 h at the current densities larger than 100 mA cm-2 . Experimentally, we found that besides the enlarged interlayer distance, the flexible interlayer NiFe LDH(+) also modulates the electronic structure of layered MnO2 , and creates an electric field between NiFe LDH(+) and Birnessite(-), wherein OER occurs with a greatly decreased overpotential. DFT calculations confirmed the interlayer LDH modulations of the OER process, attributable to the distinct electronic distributions and environments. Upshifting the Fe-3d orbitals in LDH promotes electron transfer from the layered MnO2 to LDH, significantly boosting up the OER performance. This work opens a new way to fabricate highly efficient OER catalyst for industrial water oxidation.

Sequential Growth of 2D/3D Double-Layer Perovskite Films with Superior X-Ray Detection Performance.

Abstract: Perovskite materials in different dimensions show great potential in direct X-ray detection, but each with limitations stemming from its own intrinsic properties. Particularly, the sensitivity of two-dimensional (2D) perovskites is limited by poor carrier transport while ion migration in three-dimensional (3D) perovskites causes the baseline drifting problem. To circumvent these limitations, herein a double-layer perovskite film is developed with properly aligned energy level, where 2D (PEA)2 MA3 Pb4 I13 (PEA=2-phenylethylammonium, MA=methylammonium) is cascaded with vertically crystallized 3D MAPbI3 . In this new design paradigm, the 3D layer ensures fast carrier transport while the 2D layer mitigates ion migration, thus offering a high sensitivity and a greatly stabilized baseline. Besides, the 2D layer increases the film resistivity and enlarges the energy barrier for hole injection without compromising carrier extraction. Consequently, the double-layer perovskite detector delivers a high sensitivity (1.95 × 104 μC Gyair -1 cm-2 ) and a low detection limit (480 nGyair s-1 ). Also demonstrated is the X-ray imaging capacity using a circuit board as the object. This work opens up a new avenue for enhancing X-ray detection performance via cascade assembly of various perovskites with complementary properties.

Surface passivation of organometal halide perovskites by atomic layer deposition: an investigation of the mechanism of efficient inverted planar solar cells

Abstract: Interface passivation plays a pivotal role in achieving high-efficiency organic metal halide perovskite solar cells (PSCs). It has been recently revealed that atomic layer deposition (ALD) of wide-band gap oxides shows great potential to effectively passivate defects at the interface, and ALD is also of great technological promise for industrial upscaling. However, the conflicting observations of ALD passivation are often reported in the literature, even with very similar ALD conditions. To unveil the involved crucial mechanism, this work carefully investigates the evolution of a representative MAPbI3 perovskite surface during the ALD of Al2O3, by employing the technique of in situ X-ray photoelectron spectroscopy. The ALD at 125 °C was found to cause significant degradation of the perovskite; lowering the deposition temperature can largely minimize the degradation, and 75 °C was found to be the best ALD temperature. Following this conclusion, inverted planar perovskite solar cells were prepared in ambient conditions with ALD Al2O3 interlayers. Indeed, cells with the interlayer deposited at 75 °C exhibited a significantly enhanced power conversion efficiency from 18.8% (champion 19.2%) to 20.0% (champion 20.4%). Photoluminescence measurements further evidence that the ALD layer can effectively passivate defect states at the perovskite surface. Considering the great representativeness and broad applicability of MAPbI3 and ALD Al2O3, the mechanism and strategy reported herein should be of significant value for the perovskite interface engineering in general.

Conductive Polymer Intercalation Tunes Charge Transfer and Sorption-Desorption Properties of LDH Enabling Efficient Alkaline Water Oxidation.

Abstract: Controlling and tuning surface properties of a catalyst have always been a prime challenge for efficient hydrogen production via water splitting. Here, we report a facile method for tuning both charger transfer and sorption-desorption properties of NiFe layered double hydroxide (LDH) by intercalating a conductive polymer of polypyrrole (ppy) via an interlayer confined polymerization synthesis (ICPS) process. Ex situ characterizations and in situ electrochemical quartz-crystal microbalance with dissipation (EQCM-D) tracking experiments showed that the intercalated ppy not only improved the charge transfer property of the resulting hybrid catalyst LDH-ppy but also made it more flexible and adaptive for quick and reversible sorption-desorption of reactants and intermediates during the oxygen evolution reaction (OER) process. Consequently, the as-prepared LDH-ppy exhibited a doubled catalytic current density over the bare LDH, as visualized by in situ scanning electrochemical microscopy (SECM) at the subnanometer scale. This work sheds light on orchestrating the charge and sorbate transfer abilities of catalysts for efficient water splitting by smartly combining inorganic and organic layers.

Plasmonic Hot Hole Extraction from CuS Nanodisks Enables Significant Acceleration of Oxygen Evolution Reactions.

Abstract: Localized surface plasmon resonance (LSPR) is well known for its unique ability to tune the reactivity of plasmonic materials via photoexcitation; however, it is still an open question as to whether plasmonic holes can be directly extracted to drive valuable chemical reactions. Herein we give an affirmative answer by reporting an illumination-enhanced oxygen evolution reaction (OER) using CuS nanodisks (NDs) alone as the electrocatalyst. Impressively, under 1221 nm laser or xenon lamp illumination, an unprecedented reduction of OER overpotential was observed on the CuS ND-coated electrodes. Transient absorption combined with Mott-Schottky measurements disclosed that near-infrared (NIR) irradiation generated abundant hot holes from LSPR damping in the CuS NDs accounting for the remarkable OER performance enhancement. This is the first report on the direct utilization of plasmonic hot holes in CuS nanomaterials for boosting OER performance, opening up a new route to designing NIR-active photocatalysts/electrocatalysts by exploiting the unique LSPR properties.

Boosting the electrochemical performance of hematite nanorods via quenching-induced metal single atom functionalization

Abstract: Currently there is tremendous interest in supported metal single atom (MSA) materials owing to their remarkable performance in many fields. Typically MSA materials are prepared by co-precipitation or pyrolysis methods, and can be highly variable in terms of the spatial distribution of MSA sites created. Herein, we report a new method, quenching, as an effective synthetic strategy for loading MSA sites onto nanostructured supports. As a proof of concept, a hot α-Fe2O3@CNT fiber (CNT = carbon nanotube) was quenched rapidly by immersion in an aqueous solution of SnCl4 at 4 °C, to yield a fiber uniformly decorated with Sn single atoms (Sn-Fe2O3@CNT fiber). The resulting Sn-Fe2O3@CNT fiber electrode exhibits outstanding performance, offering a capacitance of 391.32 mF cm−2 at 0.24 mA cm−2, which is more than 1.5 times that of the α-Fe2O3@CNT fiber. Moreover, an all-solid-state fiber-shaped supercapacitor consisting of a Sn-Fe2O3@CNT fiber negative electrode and a MnO2@CNT fiber positive electrode affords a very high areal capacitance of 105.68 mF cm−2 and an exceptional energy density of 6.09 mW h cm−3. The surface quenching strategy is expected to be widely applicable for the synthesis of MSA functionalized materials, thus opening up new avenues for energy and catalysis research.

Trap-Assisted Charge Storage in Titania Nanocrystals toward Optoelectronic Nonvolatile Memory.

Abstract: Transistor-based memories are of particular significance in the pursuit of next-generation nonvolatile memories. The charge storage medium in a transistor-based memory is pivotal to the device performance. In this report, nitrogen doping titania nanocrystals (N-TiO2 NCs) synthesized through a low-temperature nonhydrolytic method are used as the charge storage medium in a graphene transistor-based memory. The decoration of the N-TiO2 NCs enables the device to perform as an ultraviolet (UV) light-programmable nonvolatile optoelectronic memory. Multilevel nonvolatile information recording can be realized through accurate control of the incident light dose, which is ascribed to the vast and firm hole trapping abilities of the N-TiO2 NCs induced by the N dopant. Accordingly, a positive gate voltage can be used to erase the programmed state by promoting the recombination of stored holes in N-TiO2 NCs. This study manifests the importance of trap engineering for information storage and provides an alternative path toward nonvolatile optoelectronic memory.

Unexpected high selectivity for acetate formation from CO2 reduction with copper based 2D hybrid catalysts at ultralow potentials

Abstract: Copper-based catalysts are efficient for CO2 reduction affording commodity chemicals. However, Cu(I) active species are easily reduced to Cu(0) during the CO2RR, leading to a rapid decay of catalytic performance. Herein, we report a hybrid-catalyst that firmly anchors 2D-Cu metallic dots on F-doped CuxO nanoplates (CuxOF), synthesized by electrochemical-transformation under the same conditions as the targeted CO2RR. The as-prepared Cu/CuxOF hybrid showed unusual catalytic activity towards the CO2RR for CH3COO− generation, with a high FE of 27% at extremely low potentials. The combined experimental and theoretical results show that nanoscale hybridization engenders an effective s,p-d coupling in Cu/CuxOF, raising the d-band center of Cu and thus enhancing electroactivity and selectivity for the acetate formation. This work highlights the use of electronic interactions to bias a hybrid catalyst towards a particular pathway, which is critical for tuning the activity and selectivity of copper-based catalysts for the CO2RR.

Activating Carbon Nitride by BP@Ni for the Enhanced Photocatalytic Hydrogen Evolution and Selective Benzyl Alcohol Oxidation.

Abstract: Two-dimensional (2D) semiconductors are promising photocatalysts; in order to overcome the relatively low efficiency of single-component 2D photocatalysts, heterostructures are fabricated for effective charge separation. Herein, a 2D heterostructure is synthesized by anchoring nickel nanoparticle-decorated black phosphorus (BP) nanosheets to graphitic carbon nitride (CN) nanosheets (CN/BP@Ni). The CN/BP@Ni heterostructure exhibits an enhanced charge separation due to the tight interfacial interaction and the cascaded electron-transfer channel from CN to BP and then to Ni nanoparticles. Possessing abundant active sites of Ni and P-N coordinate bonds, CN/BP@Ni shows a high visible-light-driven H2 evolution rate of 8.59 mmol·h-1·g-1 with the sacrificial agent EtOH, about 10-fold to that of CN/BP. When applying benzyl alcohol to consume photogenerated holes, CN/BP@Ni enables the selective production of benzaldehyde; therefore, two value-added products are obtained in a single closed redox cycle. This work provides new insights into the development of photocatalysts without non-noble metals.

Highly efficient and stable broadband near-infrared-emitting lead-free metal halide double perovskites

Abstract: Non-lead metal halide double perovskites (MHDPs), recognized as one of the most promising alternatives to lead-based metal halide perovskites (MHPs), have received enormous attention in recent years due to their nontoxicity and good thermodynamic stability. However, the development of a broadband near-infrared (NIR) emitting MHP with high optical efficiency and robust chemical stability remains a challenge. In this work, we report a broadband NIR emitting lead-free MHDP Cs2SnCl4Br2 activated by Sb3+ with the largest full width at half maximum of 164 nm. The morphology and particle size were controllably evolved via finely adjusting the preparation temperature. Most surprising is that the high-temperature post-treatment, which is to be avoided always, was applied for the as-obtained NIR MHDP, achieving an unexpectedly great boosting of the NIR emission efficiency by 13 times. Moreover, excellent stability was achieved, which showed that the broadband NIR emission intensity retains 90% of the initial level after continuous UV irradiation for 48 h, maintains 100% of the initial level after being immersed in water for 6 h, and increases up to 102% after being stored in air for 2 months. The origin of NIR emission from Sb3+ ionoluminescence was verified with the combination of experimental and DFT studies. As a proof-of-concept, a broadband NIR light emitting diode with a radiant flux of 17.23 mW was fabricated using the as-obtained broadband NIR MHDP for NIR spectroscopy applications. This work not only provides a method for the rational design of broadband NIR MHPs and extending their applications, but also prompts the steps to develop novel MHDPs with superior chemical and optical stability.

Recent advances in surface/interface engineering of noble-metal free catalysts for energy conversion reactions

Abstract: This article reviews recent advances in characterization techniques and material development strategies for the surface/interface engineering of energy conversion catalysts, with an emphasis on surface defect engineering, surface crystalline property modulation, surface microstructure tailoring and heterointerface construction. The material development strategies and their influences on the performance of the catalysts in energy conversion reactions are discussed in depth with representative examples. Finally, a summary of the review and perspectives on future developments together with ongoing challenges in this promising area are provided.

Organic metal-free halide perovskites tuned up for X-ray detection

Abstract: X-ray detectors are conventionally in the inorganic domain, but all-organic metal-free halide perovskites (O-PVSK) have also entered the scene recently. Now, a comprehensive study by Cui et al. unveils how halide anions influence the O-PVSK, guiding future efforts to building high-performance organic X-ray detectors.

High throughput screening of novel tribromide perovskite materials for high-photovoltage solar cells

Abstract: An efficient search for numerous novel mixed perovskite materials for high-performance solar cells leads to a strong demand for high throughput screening protocols. Highly efficient composition screening based on high throughput fabrication of discontinuous rather than compact perovskite films with comparable properties, which can save plenty of time and effort required for optimizing dense films and can significantly expand the applicability of the screening method to various perovskite compositions, has seldom been investigated. Especially, tribromide perovskites (∼2.3 eV bandgap) with promising applications in tandem and spectral splitting devices require the efficient screening of new constituents to yield a high open-circuit voltage (Voc). Herein, we develop a highly efficient composition screening protocol based on high throughput inkjet printing of discontinuous perovskite films with representative and comparable properties to accelerate the discovery of novel tribromide perovskites for high-photovoltage solar cells. 30 tribromide perovskite films with similar bandgaps are speedily and automatically inkjet-printed, and a very close grain size is acquired for all samples via optimizing the crystallization. Therefore, the corresponding photoluminescence (PL) lifetime database allows the efficient screening and identification of new constituents for high-photovoltage devices. To validate this, among the 30 samples, two compositions (HC(NH2)2)0.4(CH3NH3)0.6PbBr3 (FA0.4MA0.6) and (HC(NH2)2)0.1(CH3NH3)0.9PbBr3 (FA0.1MA0.9) with a long and short average PL lifetime, respectively, are screened out for device comparison. As expected, the FA0.4MA0.6 device delivers a high Voc of 1.60 V with a champion efficiency of 9.25%, which is among the highest reported Voc values for tribromide devices, much higher than that (1.45 V and 6.62%) of the FA0.1MA0.9 counterpart. Surprisingly, the Voc limit for both devices is determined to be as high as 2.01 V for the first time. The Voc and efficiency improvements principally result from the reduced trap states, lower level of energetic disorder, more efficient charge transport and decreased charge recombination losses. Additionally, the validity of the PL lifetime database is further confirmed by a high Voc of 1.55 V obtained for another novel composition. These findings open up a new avenue for accelerated discovery of new perovskites for advanced device applications.