Core-shell Nanospheres Research Articles

Asymmetric Heterodimer-Regulated Surface Plasmon Coupling ECL Polarization Strategy for MiRNA-182 Detection.

In this work, a novel plasmonic heterodimer with controllable hot spot was designed and applied to regulate surface plasmon coupling electrochemiluminescence (SPC-ECL) polarization sensing system. The heterodimer nanostructure consisted of individual Au-Ag core-shell nanocubes (Au@Ag NC) and Au nanospheres (Au NS), which were precisely assembled by thiol-DNA and biotin-streptavidin. The asymmetric nanostructure can significantly modulate the ECL intensity and emission polarization angle based on the synergy of the surface plasmon coupling (SPC) effect and the lightning rod effect with extraordinary field enhancement in the hot spot region. As a result, the isotropic ECL signal of zinc-doped nitrogen dots (Zn-N dots) was regulated in the directional emission. Furthermore, the SPC-ECL biosensor was successfully applied to detect miRNA-182 in triple-negative breast cancer (TNBC) tissues. The research on the established relationship between ECL polarization analysis and plasmonic heterodimers can provide a new pathway for the development of ECL sensing platforms.

Translocation and fate of nanospheres in pheochromocytoma cells following exposure to synchrotron-sourced terahertz radiation.

The routes by which foreign objects enter cells is well studied; however, their fate following uptake has not been explored extensively. Following exposure to synchrotron-sourced (SS) terahertz (THz) radiation, reversible membrane permeability has been demonstrated in eukaryotic cells by the uptake of nanospheres; nonetheless, cellular localization of the nanospheres remained unclear. This study utilized silica core-shell gold nanospheres (AuSi NS) of diameter 50 ± 5 nm to investigate the fate of nanospheres inside pheochromocytoma (PC 12) cells following SS THz exposure. Fluorescence microscopy was used to confirm nanosphere internalization following 10 min of SS THz exposure in the range 0.5-20 THz. Transmission electron microscopy followed by scanning transmission electron microscopy energy-dispersive spectroscopic (STEM-EDS) analysis was used to confirm the presence of AuSi NS in the cytoplasm or membrane, as single NS or in clusters (22% and 52%, respectively), with the remainder (26%) sequestered in vacuoles. Cellular uptake of NS in response to SS THz radiation could have suitable applications in a vast number of biomedical applications, regenerative medicine, vaccines, cancer therapy, gene and drug delivery.

Core-Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na-S Batteries.

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium-sulfur (RT Na-S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S8 →Na2 Sx →Na2 S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core-shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N4 ), where isolated Ni-N4 sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S8 into Na2 Sx (4<x≤8), while Ni-N4 sites realize the efficient conversion of Na2 Sx into Na2 S, bridged by the diffusion of Na2 Sx from the core to shell. Besides, Ni-N4 sites on the shell can also induce an inorganic-rich cathode-electrolyte interface (CEI) on ZnS-NC@Ni-N4 to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N4 /S cathode exhibits an excellent rate-performance (650 mAh g-1 at 5 A g-1 ) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na-S batteries.

Enhanced photocatalytic H2 production performance of Au@Cu2O-Ta3N5 discrete ternary core-shell spheres

Ta3N5 owns a theoretical band structure for photocatalytic H2 production. However, the practical production performance is unsatisfactory, which is probably attributed to fast electron-hole recombination. In this study, we design novel Au@Cu2O-Ta3N5 discrete core-shell ternary nanospheres for highly efficient photocatalytic H2 production by splitting water. This catalyst is prepared by coating Cu2O on the Au nanoparticles of Au-Ta3N5 nanospheres via an illumination method. The core-shell structure irradiated for 2 h (Au@Cu2O-Ta3N5 2 h) shows higher photocatalytic H2 production rate (65.78 μmol·g−1·h−1) than Au-Ta3N5 (0.5% Au-Ta3N5, 22.43 μmol·g−1·h−1), Au-Cu2O-Ta3N5 (32.24 μmol·g−1·h−1), and fully covered Au@Cu2O-Ta3N5 5 h sample (51.27 μmol·g−1·h−1). The enhanced performance is attributed to the unique discrete core-shell structure, designed appropriate band structure, low charge transfer resistance, and high electron-hole separation ability. This study provides a novel Ta3N5-based ternary core-shell structure for high-performance H2 production.

Construction of ZnO@ZIF-CoZn bimetallic core-shell nanospheres for enhanced ethanol sensing performance

In order to achieve highly sensitive, stable and preferential monitoring of ethanol, a new core-shell structure of ZnO@ZIF-CoZn (zeolite imidazole framework-CoZn) was hydrothermally synthesized to meet actual detection requirements. The micro-morphology, crystal phase and element composition of the synthesized materials were studied by SEM, TEM, XRD, XPS and other characterization methods. It was found that the porous ZIF-CoZn film (∼100 nm) was uniformly and densely coated on the surface of the ZnO nanospheres (∼400 nm), and a core-shell structure of ZnO@ZIF-CoZn was successfully synthesized. In the gas sensitivity test, the response of ZnO@ZIF-CoZn to 100 ppm ethanol reached 18.4 at 200 °C, which is almost 3.6 times than that of pure ZnO, and the optimal working temperature of ZnO@ZIF-CoZn was lower than that of pure ZnO (240 °C). In addition, ZnO@ZIF-CoZn exhibited excellent selectivity and stability to ethanol. A heterojunction model and surface sensing response are proposed to explain the enhanced sensing response. Therefore, based on the unique nanostructure, low cost, high sensitivity and excellent selectivity of ethanol sensing performance, ZnO@ZIF-CoZn is expected to become a promising candidate in the ethanol sensor market.

Synergistic S-doped biomass carbon and N-doped carbon for construction of interlayer expanded MoS2 core/shell nanospheres for potassium and sodium storage

The construction of high-performance anode materials is the critical technology for promoting the development and application for potassium-ion batteries (PIBs). Herein, we present the synthesis of S-doped biomass carbon/MoS2@N-doped carbon core-shell nanospheres with the expanded interlayer of 0.99 nm (S-BC/E-MoS2@N-C) via the combined hydrothermal and polymerized method. In the hydrothermal process, we firstly find that the biomass carbon is heteroatomic doped with sulfur in the hydrothermal process by the sulfur source for forming MoS2. The polymerized N-doped carbon is forming on surface of MoS2 nanosheets for construction sandwiched core-shell structure. The N-doped carbon layer and S-doped biomass carbon use cooperatively to establish an omnibearing conductive network on MoS2 by internal and external integration. In such a unique structure, high conductivity and excellent structural stability are achieved in the S-BC/E-MoS2@N-C composite. Consequently, the S-BC/E-MoS2@N-C electrodes exhibit superior potassium storage performances including enhanced rate capability and good cycled stability with high reversible capacities (156.6 mA h g−1 after 650 cycles at 100 mA g−1). And for sodium ion batteries, the S-BC/E-MoS2@N-C electrode delivers an initial reversible capacity of 538.9 mAh g−1 at 200 mA g−1 and maintains 371.1 mAh g−1 after 200 cycles. This work shed a kind of double heteratomic doping and core-shell hierarchical structure of MoS2 anodes in potassium/sodium storage.

CsPbBr3 Perovskite Quantum Dots Embedded in Polystyrene-poly2-vinyl Pyridine Copolymer for Robust and Light-Tunable Memristors

The development of a reliable optoelectronic memristor is crucial for the success of neuromorphic vision systems, but current devices are limited by stochastic resistance switching and uncontrollable ion dynamics. To address these challenges, a core–shell nanosphere composite was synthesized using CsPbBr3 quantum dots and block copolymer polystyrene-poly2-vinyl pyridine. This memristor exhibits both negative differential resistance and resistive switching memory behavior and has demonstrated exceptional stability, withstanding over 5000 cycles and remaining stable for over 5 million seconds. It is also tunable by light irradiation, making it ideal for optoelectronic logic operations and multi-derivative state applications. The memory behavior is attributed to an electrochemical metalization mechanism involving the formation and annihilation of pyridine groups, conductive metal filaments, and bromide ion vacancies in S2VP filaments. This work presents an effective method for fabricating robust multi-derivative perovskite optoelectronic devices for neuromorphic computing systems. Additionally, machine learning algorithms have demonstrated accurate digital image classification and recognition using photoelectric pulse-driven neuromorphic computation with an accuracy of over 97%.

Controllable reduction of NiCoO2@NiCo core–shell nanospheres on CNTs for high-performance electrochemical energy storage

The performances of energy storage devices are strongly dependent on the electrode materials. Owing to the high theoretical capacity, NiCoO2 is a promising transition metal oxide for supercapacitors. Despite many efforts have been devoted, it still lacks of effective methods to overcome its shortcomings such as low conductivity and poor stability, in order to achieve its theoretical capacity. Herein, utilizing the thermal reducibility of trisodium citrate and its hydrolyzate, a series of NiCoO2@NiCo/CNT ternary composites in which NiCoO2@NiCo core–shell nanospheres deposited on CNT surface with adjustable metal contents are synthesized. Benefiting from the enhanced synergistic effect of both metallic core and CNTs, the optimized composite exhibits an extremely high specific capacitance (2660 F g−1 at 1 A g−1, the effective specific capacitance of the loaded metal oxide is 4199 F g−1, close to the theoretical value), an excellent rate performance and stability, when the metal content is about 37%. After depolarized calculation, the energy storage mechanism of the composite is reasonably analyzed. By controlling the contents of hexamethylenetetramine, trisodium citrate and CNTs in the reactant, the roles of them are distinguished. This study reveals an efficient novel strategy for transition metal oxides to maximize the electrochemical performances.

Convenient hydrothermal treatment combining with “Ship in Bottle” to construct Yolk-Shell N-Carbon@Ag-void@mSiO2 for high effective Nano-Catalysts

More active sites will be exposed when noble metal particles are loaded on the core of yolk-shell nanospheres (NM-YSNS) to give higher metal utilization rate, catalytic activity, and good recycle stability. Herein, we adopt an efficient strategy to access the high-performance NM-YSNS via “ship in bottle” mindset on loading Ag nanoparticle on the core surface of core–shell structure accurately and the core shrinkage on forming yolk-shell structure. First, we systematically investigated the mechanism of SiO2 coating 3-aminophenol-co-formaldehyde nanoparticles to generate 3-aminophenol-co-formaldehyde@mesoporous SiO2 core–shell nanospheres (3-APF@mSiO2 CSNS). Interestingly, the core surface of 3-APF@mSiO2 CSNS became uneven after hydrothermal process, which provided positions for Ag, then additional Ag+ could reach the 3-APF surface through the mSiO2 shell and be in situ reduced into Ag particles by –NH- and –NH2 there. Similarly, the 3-APF@Au@mSiO2 CSNS were prepared successfully. After carbonizing 3-APF@Ag@mSiO2 CSNS, the N-Carbon@Ag-void@mSiO2 YSNS was obtained. The NM-YSNS catalyst had a high specific surface area of 258.8 m2g−1, mSiO2 shell of 3.8 nm mesoporous size, and core loaded with Ag particles firmly, showing a high turnover frequency of 137.08 h−1 and good recycle stability in catalytic reduction of 4-nitrophenol for preparing 4-aminophenol.

Superhydrophobic and Conductive Wire Membrane for Enhanced CO2 Electroreduction to Multicarbon Products.

Gas-liquid-solid triple-phase interfaces (TPI) are essential for promoting electrochemical CO2 reduction, but it remains challenging to maximize their efficiency while integrating other desirable properties conducive to electrocatalysis. Herein, we report the elaborate design and fabrication of a superhydrophobic, conductive, and hierarchical wire membrane in which core-shell CuO nanospheres, carbon nanotubes (CNT), and polytetrafluoroethylene (PTFE) are integrated into a wire structure (designated as CuO/F/C(w); F, PTFE; C, CNT; w, wire) to maximize their respective functions. The realized architecture allows almost all CuO nanospheres to be exposed with effective TPI and good contact to conductive CNT, thus increasing the local CO2 concentration on the CuO surface and enabling fast electron/mass transfer. As a result, the CuO/F/C(w) membrane attains a Faradaic efficiency of 56.8 % and a partial current density of 68.9 mA cm-2 for multicarbon products at -1.4 V (versus the reversible hydrogen electrode) in the H-type cell, far exceeding 10.1 % and 13.4 mA cm-2 for bare CuO.

Phase engineering of Cu@Cu2O core-shell nanospheres for boosting tandem electrochemical CO2 reduction to C2+ products

Cu-based CO2 electrochemical reduction (CO2ER) is promising for reducing greenhouse gas emission and producing high-value multicarbon (C2+) chemicals and fuels. Unfortunately, the C2+ selectivity is still quite low. In this work, well-defined Cu@Cu2O core–shell nanospheres with time-dependent evolution of phase composition, crystallinity and morphology were specifically designed by a facile chemically induced self-transformation strategy. A maximum C2+ Faradaic efficiency (FE) exceeding 79%, including FEC2H4 reaching 44%, was achieved using phase-engineered Cu@Cu2O nanospheres. Based on the temperature-programmed desorption analyses and in-situ Raman spectroscopy, the adsorption behaviors of both CO2 reactant and *CO intermediate can be synergistically tuned by phase engineering of Cu@Cu2O nanospheres: Cu2O shell enhances *CO2 and *CO adsorption coverage, while porous Cu core concentrate and strengthens *CO intermediates for subsequent CO-CO coupling towards C2+ products. This work will shed new light on the phase engineering of Cu-based tandem electrocatalysts for tuning CO2/CO-catalyst interaction and modulating CO2ER processes and selectivity.

Compensation behavior in (Fe–Ni) core–shell nanostructures: Heisenberg Monte Carlo simulations

By performing atomistic simulations, we have studied some features of classical Heisenberg model using the statistical Monte Carlo method MC under the Hinzke–Nowak algorithm. First, we have deeply explored magnetic and thermal properties of a core–shell nanosphere model and investigate the behaviors of the temperature-dependent magnetization, magnetic susceptibility and phase diagrams for different possible exchange interactions. The obtained results show the existence of diverse -types behaviors in the Néel classification nomenclature. Then, we have applied the same computational method to the real (Fe, Ni) nanostructure using experimental values of magnetic parameters for iron and nickel. It is demonstrated that (Fe, Ni) nanoparticle exhibits a compensation phenomenon compatible with those found in the experimental studies.

Nitrogen-Doped Core-Shell Mesoporous Carbonaceous Nanospheres for Effective Removal of Fluorine in Capacitive Deionization

Fluorine pollution of wastewater is a global environmental problem. Capacitive deionization has unique advantages in the defluorination of fluorine-containing wastewater; however, the low electrosorption capacity significantly restricts its further development. To overcome this limitation, nitrogen-doped core-shell mesoporous carbonaceous nanospheres (NMCS) were developed in this study based on structural optimization and polarity enhancement engineering. The maximal electrosorption capacity of NMCS for fluorine reached 13.34 mg g−1, which was 24% higher than that of the undoped counterpart. NMCS also indicated excellent repeatability evidenced by little decrease of electrosorption capacity after 10 adsorption-regeneration cycles. According to material and electrochemical measurements, the doping of nitrogen into NMCS resulted in the improvement of physicochemical properties such as conductivity and wettability, the amelioration of pore structure and the transformation of morphology from yolk-shell to core-shell structure. It not only facilitated ion transportation but also improved the available adsorption sites, and thus led to enhancement of the defluorination performance of NMCS. The above results demonstrated that NMCS would be an excellent electrode material for high-capacity defluorination in CDI systems.

Efficient and stable Fe3O4@SiO2 core–shell nanospheres for electrochemical water oxidation under neutral conditions

Fe3O4@SiO2 core–shell nanospheres were exploited for the first time to obtain a vigorous electrocatalyst for water oxidation under neutral conditions.

Manganese and selenium co-doped CeO2@Co3O4 porous core–shell nanospheres for enhanced oxygen evolution reactions

MnSe–CeO2@Co3O4 synthesised by a one-pot multi-step method, followed by calcination and selenization treatments, exhibits superior electrocatalytic activity and stability.

Reporter Molecules Embedded Au@Ag Core-Shell Nanospheres as SERS Nanotags for Cardiac Troponin I Detection

Rapid and accurate detection of acute myocardial infarction can improve patients' chances of survival. Cardiac troponin I (cTn I) is an important diagnostic biomarker for acute myocardial infarction. However, current immunoassays are insufficient to accurately measure cTn I, as they have limited detection sensitivity and are time-consuming. Surface-enhanced Raman scattering (SERS) is a brilliant fingerprints diagnostic technique characterised by ultrasensitivity, fast response, and qualitative and quantitative analysis capabilities. In this study, reporter molecules (4-Mercaptobenzoic acid, 4-MBA) embedded Au@Ag core-shell nanospheres as SERS nanotags were prepared for the detection of cTn I. As the Raman reporters were embedded between the core and the shell, they could be protected from the external environment and nanoparticle aggregation. Excellent SERS performances were obtained due to the enhanced local electromagnetic field in the gap of core and shell metals. In a standard phosphate buffered saline (PBS) environment, the limit of detection for cTn I was 0.0086 ng mL-1 (8.6 ppt) with a good linear relationship. The excellent Raman detection performance was attributed to the localized surface plasmon resonance effect and strong electromagnetic field enhancement effect produced by the gap between the Au core and the Ag shell. The SERS nanotags we prepared were facile to synthesize, and the analysis procedure could be completed quickly (15 min), which made the detection of cTn I faster. Therefore, the proposed SERS nanotags have significant potential to be a faster and more accurate tool for acute myocardial infarction diagnostics.

Air nanobubbles induced reversible self-assembly of 7S globulins isolated from pea (Pisum Sativum L.)

The interplay of food proteins and macro or microscopic bubbles at the air-water interface that shaped the ultimate structures of proteins is well-known, yet knowledge was blank on the interactions between food proteins and nanoscopic bubbles (i.e., nanobubbles). In this study, bulk air nanobubbles were successfully fabricated in the aqueous solutions following a facile “cyclic compression-expansion” method. Subsequently, the effects of generated air nanobubbles and various factors including pH, protein concentration, nanobubble concentration, and ionic strength on the self-assembly behavior of 7S globulins isolated from pea proteins were investigated. It was revealed that air nanobubbles acted as soft templates to trigger 7S globulins self-assembly into core-shell nanospheres adjacent to the protein isoelectric point (∼pH 5). An enhancement of ionic strength from 0 to 0.4 mol L −1 led to increased particle size, whereas attenuating interactions between 7S globulins and air nanobubbles. The particle size of nanoparticles was also demonstrated to be protein and nanobubble concentration-dependent. Protein secondary structures were modified by air nanobubbles with apparently increased contents in random coils and decreased contents in α-helix. Changes in protein tertiary structures demonstrated that 7S globulins are exposed to a more hydrophobic microenvironment with reduced surface hydrophobicity, after complexing with air nanobubbles through electrostatic and hydrophobic interactions. The nanoparticles at pH 6 slightly shrunk during the 30-day refrigeration at 4 °C compared to those at pH 4, and the original nanostructures could revive after replenishing with fresh air nanobubble suspensions, indicating their high stability for future potential applications in food structure design innovation. • Air nanobubbles were generated using a “cyclic compression and expansion” method. • Interplay of 7S globulins and nanobubbles was impacted by extrinsic factors. • Nanobubbles induced reversible protein self-assembly to core-shell nanoparticles. • Air nanobubbles modified secondary and tertiary structures of 7S globulins. • Protein self-assembly behavior were driven by ionic and hydrophobic interactions.

Efficient Lithium/Sodium-Ion Storage by Core-Shell Carbon Nanospheres@TiO2 Decorate by Epitaxial WSe2 Nanosheets Derived from Bimetallic Polydopamine Composites.

Metal-polydopamine coordination chemistry attracts great attention owing to the synergistic effect of adjustable components and advantageous structures. However, few efforts have been devoted to exploring bimetal-polydopamine composites, especially for multistructural composites with high-capacity components and high stability. In this regard, the TiO2 @C-WSe2 core-shell nanospheres are designed and fabricated based on Ti-W-polydopamine composites after selenization, in which the TiO2 nanoparticles are encapsulated or embedded in the carbon nanospheres and the external WSe2 nanosheets are grown epitaxially on the carbon surfaces, featuring multiple channels for ion diffusion and abundant active edges for electrochemical reactions. The introduction of WSe2 not only greatly improves the capacity but also results in exponential growth of the active edge. As a result, the as-prepared TiO2 @C-WSe2 displayed long-term cycling performance in lithium-ion batteries. Furthermore, the anode is assembled into sodium-ion batteries, manifesting a stable capacity of 352mA h g-1 at 1.0 A g-1 even after 2000 cycles, one of the best performances for polydopamine-based composites. Enhanced performance can be attributed to the synergies of high-capacity components and different dimensional materials. This work highlights that the rational design of functional structures provides a novel inspiration for electrodes with effective nanoarchitectures.

Assembly of Core/Shell Nanospheres of Amorphous Hemin/Acetone-Derived Carbonized Polymer with Graphene Nanosheets for Room-Temperature NO Sensing.

Implementing parts per billion-level nitric oxide (NO) sensing at room temperature (RT) is still in extreme demand for monitoring inflammatory respiratory diseases. Herein, we have prepared a kind of core-shell structural Hemin-based nanospheres (Abbr.: Hemin-nanospheres, defined as HNSs) with the core of amorphous Hemin and the shell of acetone-derived carbonized polymer, whose core-shell structure was verified by XPS with argon-ion etching. Then, the HNS-assembled reduced graphene oxide composite (defined as HNS-rGO) was prepared for RT NO sensing. The acetone-derived carbonized polymer shell not only assists the formation of amorphous Hemin core by disrupting their crystallization to release more Fe-N4 active sites, but provides protection to the core. Owing to the unique core-shell structure, the obtained HNS-rGO based sensor exhibited superior RT gas sensing properties toward NO, including a relatively higher response (Ra/Rg = 5.8, 20 ppm), a lower practical limit of detection (100 ppb), relatively reliable repeatability (over 6 cycles), excellent selectivity, and much higher long-term stability (less than a 5% decrease over 120 days). The sensing mechanism has also been proposed based on charge transfer theory. The superior gas sensing properties of HNS-rGO are ascribed to the more Fe-N4 active sites available under the amorphous state of the Hemin core and to the physical protection by the shell of acetone-derived carbonized polymer. This work presents a facile strategy of constructing a high-performance carbon-based core-shell nanostructure for gas sensing.

Magnetic electrode configuration with polypyrrole-wrapped Ni/NiFe2O4 core–shell nanospheres to boost electrocatalytic water splitting

The exploration of transition metal-based electrodes with high efficiency, low-budget and excellent stability for overall water splitting has attracted increasing attention. To optimize the metal oxides as efficient bifunctional electrocatalysts, it is necessary to design not only their atomic and electronic structures but also the macroscopical electrode configuration. Herein, we report the preparation of conductive polypyrrole (PPy)-wrapped Ni/NiFe2O4 (Ni/NiFe2O4@PPy) nanospheres as a promising bifunctional electrocatalyst for the OER and HER. In the material design strategy, the PPy coating improves the conductivity and modulates the ion transmission rate between the electrolyte and Ni/NiFe2O4. The interaction between PPy and Ni/NiFe2O4 regulates the electronic structure and enhances the reaction efficiency of active sites. Furthermore, Ni/NiFe2O4@PPy nanospheres are employed to construct a binder-free magnetic electrode, which can well avoid the blockage of active sites and accelerate the gas release through the loosely assembled catalysts. The Ni/NiFe2O4@PPy with paramagnetic characteristics can be easily recovered for recycling by demagnetizing the electrodes. The specially designed magnetic electrodes show superior electrocatalytic activity with low overpotentials of 127 mV@10 mA cm−2 and 236 mV@100 mA cm−2 for HER and 265 mV@10 mA cm−2 and 370 mV@100 mA cm−2 for OER. The overall water electrolytic cell with Ni/NiFe2O4@PPy electrodes can achieve 10 mA cm−2 at 1.64 V with an excellent long-term stability. This work provides a novel material design and magnetic electrode construction strategy to improve the water splitting performance.