Boosting Hydrogen Storage Performance of MgH_(2) by Oxygen Vacancy-Rich H-V_(2)O_(5) Nanosheet as an Excited H-Pump

MgH_(2) is a promising high-capacity solid-state hydrogen storage material,while its application is greatly hindered by the high desorption temperature and sluggish kinetics.Herein,intertwined 2D oxygen vacancy-rich V_(2)O_(5) nanosheets(H-V_(2)O_(5))are specifically designed and used as catalysts to improve the hydrogen storage properties of MgH_(2).The as-prepared MgH_(2)-H-V_(2)O_(5) composites exhibit low desorption temperatures(Tonset=185℃)with a hydrogen capacity of 6.54 wt%,fast kinetics(Ea=84.55±1.37 kJ mol^(-1) H_(2) for desorption),and long cycling stability.Impressively,hydrogen absorption can be achieved at a temperature as low as 30℃ with a capacity of 2.38 wt%within 60 min.Moreover,the composites maintain a capacity retention rate of~99%after 100 cycles at 275℃.Experimental studies and theoretical calculations demonstrate that the in-situ formed VH_(2)/V catalysts,unique 2D structure of H-V_(2)O_(5) nanosheets,and abundant oxygen vacancies positively contribute to the improved hydrogen sorption properties.Notably,the existence of oxygen vacancies plays a double role,which could not only directly accelerate the hydrogen ab/de-sorption rate of MgH_(2),but also indirectly affect the activity of the catalytic phase VH_(2)/V,thereby further boosting the hydrogen storage performance of MgH_(2).This work highlights an oxygen vacancy excited“hydrogen pump”effect of VH_(2)/V on the hydrogen sorption of Mg/MgH_(2).The strategy developed here may pave a new way toward the development of oxygen vacancy-rich transition metal oxides catalyzed hydride systems.

Nanostructuring of Mg-Based Hydrogen Storage Materials:Recent Advances for Promoting Key Applications

With the depletion of fossil fuels and global warming,there is an urgent demand to seek green,low-cost,and high-efficiency energy resources.Hydrogen has been considered as a potential candidate to replace fossil fuels,due to its high gravimetric energy density(142 MJ kg^(-1)),high abundance(H_(2)O),and environmentalfriendliness.However,due to its low volume density,effective and safe hydrogen storage techniques are now becoming the bottleneck for the"hydrogen economy".Under such a circumstance,Mg-based hydrogen storage materials garnered tremendous interests due to their high hydrogen storage capacity(~7.6 wt%for MgH_(2)),low cost,and excellent reversibility.However,the high thermodynamic stability(ΔH=-74.7 kJ mol^(-1)H_(2))and sluggish kinetics result in a relatively high desorption temperature(>300℃),which severely restricts widespread applications of MgH_(2).Nano-structuring has been proven to be an effective strategy that can simultaneously enhance the ab/de-sorption thermodynamic and kinetic properties of MgH_(2),possibly meeting the demand for rapid hydrogen desorption,economic viability,and effective thermal management in practical applications.Herein,the fundamental theories,recent advances,and practical applications of the nanostructured Mg-based hydrogen storage materials are discussed.The synthetic strategies are classified into four categories:free-standing nano-sized Mg/MgH_(2)through electrochemical/vapor-transport/ultrasonic methods,nanostructured Mg-based composites via mechanical milling methods,construction of core-shell nano-structured Mg-based composites by chemical reduction approaches,and multi-dimensional nano-sized Mg-based heterostructure by nanoconfinement strategy.Through applying these strategies,near room temperature ab/de-sorption(<100℃)with considerable high capacity(>6 wt%)has been achieved in nano Mg/MgH_(2)systems.Some perspectives on the future research and development of nanostructured hydrogen storage materials are also provided.

Exciting lattice oxygen of nickel–iron bi-metal alkoxide for efficient electrochemical oxygen evolution reaction

High efficiency,cost-effective and durable electrocatalysts are of pivotal importance in energy conversion and storage systems.The electro-oxidation of water to oxygen plays a crucial role in such energy conversion technologies.Herein,we report a robust method for the synthesis of a bimetallic alkoxide for efficient oxygen evolution reaction(OER)for alkaline electrolysis,which yields current density of 10 mA cm^(-2)at an overpotential of 215 mV in 0.1 M KOH electrolyte.The catalyst demonstrates an excellent durability for more than 540 h operation with negligible degradation in activity.Raman spectra revealed that the catalyst underwent structure reconstruction during OER,evolving into oxyhydroxide,which was the active site proceeding OER in alkaline electrolyte.In-situ synchrotron X-ray absorption experiment combined with density functional theory calculation suggests a lattice oxygen involved electrocatalytic reaction mechanism for the in-situ generated nickel–iron bimetal-oxyhydroxide catalyst.This mechanism together with the synergy between nickel and iron are responsible for the enhanced catalytic activity and durability.These findings provide promising strategies for the rational design of nonnoble metal OER catalysts.

Hydrogen-induced optical properties of FC/Pd/Mg films:Roles of grain size and grain boundary

Nanomodification is an effective method to solve the thermodynamic and kinetics limitation of Magnesium(Mg)-based materials,which shows promising application prospects in hydrogen energy field.However,the role of the grain size of pure Mg on the hydrogen-induced performance of the hydrogen sensitive thin film under cyclic hydrogen loading/unloading process at room temperature has rarely been studied systematically.To study the relationship between the structure of Mg layer and the hydrogen-induced optical performance of fluorocarbon(FC)/Pd/Mg films,a series of Mg with different internal structures were prepared by changing the velocity of sputtered atoms under different sputtering powers.The FC/Pd/Mg(40 W)film with fine nanostructure showed faster hydrogenation/dehydrogenation kinetics as well as a larger optical conversion range,which can be attributed to the large population of grain boundaries with high grain boundary energy and more hydrogen diffusion path.As sputtering power gradually increased from 40 W to 300 W,the grain inside films grew larger.The FC/Pd/Mg(300 W)film had more columnar-like regions inside and less grain boundaries with lower energy contributing to slower hydrogen absorption/desorption kinetics and lower optical conversion range.

Oxygen Vacancy-Rich 2D TiO_(2) Nanosheets:A Bridge Toward High Stability and Rapid Hydrogen Storage Kinetics of Nano-Confined MgH_(2)

MgH_(2) has attracted intensive interests as one of the most promising hydrogen storage materials.Nevertheless,the high desorption temperature,sluggish kinetics,and rapid capacity decay hamper its commercial application.Herein,2D TiO_(2) nanosheets with abundant oxygen vacancies are used to fabricate a flower-like MgH_(2)/TiO_(2) heterostructure with enhanced hydrogen storage performances.Particularly,the onset hydrogen desorption temperature of the MgH_(2)/TiO_(2) heterostructure is lowered down to 180℃(295℃ for blank MgH_(2)).The initial desorption rate of MgH_(2)/TiO_(2) reaches 2.116 wt% min^(-1) at 300℃,35 times of the blank MgH_(2) under the same conditions.Moreover,the capacity retention is as high as 98.5% after 100 cycles at 300℃,remarkably higher than those of the previously reported MgH_(2)-TiO_(2) composites.Both in situ HRTEM observations and ex situ XPS analyses confirm that the synergistic effects from multi-valance of Ti species,accelerated electron transportation caused by oxygen vacancies,formation of catalytic Mg-Ti oxides,and stabilized MgH_(2) NPs confined by TiO_(2) nanosheets contribute to the high stability and kinetically accelerated hydrogen storage performances of the composite.The strategy of using 2D substrates with abundant defects to support nano-sized energy storage materials to build heterostructure is therefore promising for the design of high-performance energy materials.

In situ One-Pot Fabrication of MoO3-x Clusters Modified Polymer Carbon Nitride for Enhanced Photocatalytic Hydrogen Evolution

Developing low-cost and high-efficient noble-metal-free cocatalysts has been a challenge to achieve economic hydrogen production.In this work,molybdenum oxides(MoO3-x)were in situ loaded on polymer carbon nitride(PCN)via a simple one-pot impregnation-calcination approach.Different from post-impregnation method,intimate coupling interface between high-dispersed ultra-small MoO3-xnanocrystal and PCN was successfully formed during the in situ growth process.The MoO3-x-PCN-X(X=1,2,3,4)photocatalyst without noble platinum(Pt)finally exhibited enhanced photocatalytic hydrogen performance under visible light irradiation(λ>420 nm),with the highest hydrogen evolution rate of 15.6μmol/h,which was more than 3 times that of bulk PCN.Detailed structure-performance revealed that such improvement in visible-light hydrogen production activity originated from the intimate interfacial interaction between high-dispersed ultra-small MoO3-xnanocrystal and polymer carbon nitride as well as efficient charge carriers transfer brought by Schottky junction formed.

Machine Learning-Assisted Low-Dimensional Electrocatalysts Design for Hydrogen Evolution Reaction

Efficient electrocatalysts are crucial for hydrogen generation from electrolyzing water.Nevertheless,the conventional"trial and error"method for producing advanced electrocatalysts is not only cost-ineffective but also time-consuming and labor-intensive.Fortunately,the advancement of machine learning brings new opportunities for electrocatalysts discovery and design.By analyzing experimental and theoretical data,machine learning can effectively predict their hydrogen evolution reaction(HER)performance.This review summarizes recent developments in machine learning for low-dimensional electrocatalysts,including zero-dimension nanoparticles and nanoclusters,one-dimensional nanotubes and nanowires,two-dimensional nanosheets,as well as other electrocatalysts.In particular,the effects of descriptors and algorithms on screening low-dimensional electrocatalysts and investigating their HER performance are highlighted.Finally,the future directions and perspectives for machine learning in electrocatalysis are discussed,emphasizing the potential for machine learning to accelerate electrocatalyst discovery,optimize their performance,and provide new insights into electrocatalytic mechanisms.Overall,this work offers an in-depth understanding of the current state of machine learning in electrocatalysis and its potential for future research.

Doping of group IVB elements for nickel-rich cobalt-free cathodes

Hetero-element doping is a promising strategy to improve the cycling stability of nickel-rich cobalt-free cathodes for the next-generation high energy-density Li ion batteries.To make doping effective,it is important to understand the mechanism of how the dopants regulate the electronic band,lattice parameter adjusting,or hetero-phase formation to achieve high stability.In this study,we investigate LiNi_(0.9)Mn_(0.1)O_(2)cathodes doped with IVB grouping elements via multiple characterization techniques.By utilizing in situ XRD and TEM methods,we found that the stronger Ti-O bond effectively improves the cathode stability via a dual protection mechanism.Specifically,the bulk lattice of cathode is wellpreserved during cycling as a result of the suppressed H_(2)-H_(3)phase transition,while a in situ formed Ti-rich surface layer can prevent continuous surface degradation.As a result,the 5%Ti doped LiNi_(0.9)Mn_(0.1)O_(2)cathode exhibits a high capacity retention of 96%after 100 cycles.Whereas,despite IVB group elements Zr and Hf have stronger bonding energy with oxygen,their larger ionic radii actually impede their diffusion into the cathode,thereby they can not improve the cycling stability.Our findings uncover the functional origin of doped elements with their dynamic modification on cathode structure,providing mechanistic insights into the design of nickel-rich cobalt-free cathodes.

Optimizing the morphology of all-polymer solar cells for enhanced photovoltaic performance and thermal stability

Due to the complicated film formation kinetics, morphology control remains a major challenge for the development of efficient and stable all-polymer solar cells(all-PSCs). To overcome this obstacle, the sequential deposition method is used to fabricate the photoactive layers of all-PSCs comprising a polymer donor PTzBI-oF and a polymer acceptor PS1. The film morphology can be manipulated by incorporating amounts of a dibenzyl ether additive into the PS1 layer. Detailed morphology investigations by grazing incidence wide-angle X-ray scattering and a transmission electron microscope reveal that the combination merits of sequential deposition and DBE additive can render favorable crystalline properties as well as phase separation for PTzBI-oF:PS1 blends. Consequently, the optimized all-PSCs delivered an enhanced power conversion efficiency(PCE) of 15.21%along with improved carrier extraction and suppressed charge recombination. More importantly, the optimized all-PSCs remain over 90% of their initial PCEs under continuous thermal stress at 65 °C for over 500 h. This work validates that control over microstructure morphology via a sequential deposition process is a promising strategy for fabricating highly efficient and stable all-PSCs.

A review on photocatalysis in antibiotic wastewater:Pollutant degradation and hydrogen production

Surveys on antibiotics have become one of the most popular topics in the recent two decades. From 1998 to 2018, more than 5,000 articles concentrated on the research of antibiotic wastewater treatment have been published. Among them, photocatalysis has received much attention due to its green and environmental-friendly properties. In this mini-review, the recent progress of photocatalysis in antibiotic wastewater was summarized, including antibiotics degradation and hydrogen energy conversion. The photocatalysts commonly used were also discussed. It can be mainly classified as TiO2-based materials, sulfides and polymeric carbon nitride-based materials and bismuth-contained materials. Four major types of antibiotics, tetracycline, sulfonamide, β-lactam and quinolone, were involved. Furthermore, perspectives concentrated on future development and challenges, especially converting antibiotics into hydrogen energy, were also proposed.

Simultaneous visible-light-induced hydrogen production enhancement and antibiotic wastewater degradation using MoS2@ZnxCd1-xS: Solid-solution-assisted photocatalysis

In this study,a ZnxCd1-xS solid solution was successfully synthesized using a hydrothermal method.MoS2 serving as a co-catalyst for hydrogen evolution was also prepared through a one-pot hydrothermal method.The structures,morphology,chemical states,and optical properties were characterized using powder X-ray diffraction,scanning electron microscopy,high-angle annular dark field-scanning transmission electron microscopy,elemental mapping,X-ray photoelectron spectroscopy,and UV-Vis diffuse reflection spectroscopy.Visible-light-driven photocatalytic experiments were conducted to simultaneously achieve hydrogen production and amoxicillin antibiotic wastewater degradation.The results indicated 8%MoS2/ZnxCd1-xS achieves the best photocatalytic performance.The ZnxCd1-xS samples illustrated a superior performance to that of CdS,which can be attributed to a thermodynamic improvement.Based on the results of PL and TRPL analyses,the enhancement of the hydrogen production mechanisms can be ascribed to the prolonged separation process of the photocarriers.Furthermore,the degradation results were analyzed using the HPLC method and the possible degradation pathways were determined through the HPLC-MS techniques.

Structural evolution of Pt‐based oxygen reduction reaction electrocatalysts

The commercialization of proton exchange membrane fuel cells(PEMFCs)could provide a cleaner energy society in the near future.However,the sluggish reaction kinetics and harsh conditions of the oxygen reduction reaction affect the durability and cost of PEMFCs.Most previous reports on Pt-based electrocatalyst designs have focused more on improving their activity;however,with the commercialization of PEMFCs,durability has received increasing attention.In-depth insight into the structural evolution of Pt-based electrocatalysts throughout their lifecycle can contribute to further optimization of their activity and durability.The development of in situ electron microscopy and other in situ techniques has promoted the elucidation of the evolution mechanism.This mini review highlights recent advances in the structural evolution of Pt-based electrocatalysts.The mechanisms are adequately discussed,and some methods to inhibit or exploit the structural evolution of the catalysts are also briefly reviewed.

In-situ monitoring of dynamic behavior of catalyst materials and reaction intermediates in semiconductor catalytic processes

Semiconductor photocatalysis, as a key part of solar energy utilization, has far-reaching implications for industrial, agricultural, and commercial development. Lack of understanding of the catalyst evolution and the reaction mechanism is a critical obstacle for designing efficient and stable photocatalysts. This review summarizes the recent progress of in-situ exploring the dynamic behavior of catalyst materials and reaction intermediates. Semiconductor photocatalytic processes and two major classes of in-situ techniques that include microscopic imaging and spectroscopic characterization are presented. Finally, problems and challenges in in-situ characterization are proposed, geared toward developing more advanced in-situ techniques and monitoring more accurate and realistic reaction processes, to guide designing advanced photocatalysts.

Impact of Methanol Photomediated Surface Defects on Photocatalytic H2 Production Over Pt/TiO2

Co-catalysts play a critical role in enhancing the efficiency of inorganic semiconductor photocatalysts;however,synthetic approaches to tailoring cocatalyst properties are rarely the focus of research efforts.A photomediated route to control the dispersion and oxidation state of a platinum(Pt)cocatalyst through defect generation in the P25 titania photocatalyst substrate is reported.Titania photoirradiation in the presence of methanol induces longlived surface defects which subsequently promote the photodeposition of highly dispersed(2.2±0.8 nm)and heavily reduced Pt nanoparticles on exposure to H2 PtCl6.The optimal methanol concentration of 20 vol%produces the highest density of metallic Pt nanoparticles.Photocatalytic activity for water splitting and associated hydrogen(H2)production under UV irradiation mirrors the methanol concentration employed during the P25 photoirradiation pretreatment and resulting Pt loading resulting in a common mass-normalized H2 productivity of 3800±130 mmol gpt-1 h-1.Photomediated surface defects(arising in the presence of a methanol hole scavenger)provide electron traps that regulate subsequent photodeposition of a Pt co-catalyst over P25,offering a facile route to tune photocatalytic efficiency.

In situ revealing the reconstruction behavior of monolayer rocksalt CoO nanosheet as water oxidation catalyst

The reconstruction during oxygen evolution reaction (OER) significantly affects the electronic and local geometry structure of metal sites in electrocatalyst.Compared with well-investigated cobalt-based materials,the reconstruction of rocksalt CoO with purely Co^(2+) in octahedral (Oh) coordination has not been revealed in detail.Herein,monolayer Co O supported on reduced graphene oxide (r GO) was synthesized via a one-pot hydrothermal strategy with calcinating in Ar atmosphere.The structure evolution of twodimension (2D) Co O/r GO during OER was revealed by in situ X-ray absorption spectroscopy (XAS).The transition from Co O toward Co3O_(4) already occurred at open circuit potential,further enhanced at 1.23 V (vs.RHE).The Co Ox(OH)ywas determined as the active phase at 1.53 V,displaying a tetrahedral Co coordination defective spinel Co_(3)O_(4) with the Co-O shell that featured the (oxy)hydroxide,not the standard Co OOH.After OER,the irreversible transition from CoO to Co_(3)O_(4) was observed.In contrast,in situ Raman spectra revealed a reversible amorphization process on Co_(3)O_(4)/r GO under operation conditions.Furthermore,this study indicated that the reconstruction behavior could be more effectively revealed by XAS using 2D materials.

Intelligent microneedle patch with prolonged local release of hydrogen and magnesium ions for diabetic wound healing

Diabetes mellitus,an epidemic with a rapidly increasing number of patients,always leads to delayed wound healing associated with consistent pro-inflammatory M1 polarization,decreased angiogenesis and increased reactive oxygen species(ROS)in the microenvironment.Herein,a poly(lactic-co-glycolic acid)(PLGA)-based microneedle patch loaded with magnesium hydride(MgH_(2))(MN-MgH_(2))is manufactured for defeating diabetic wounds.The application of microneedle patch contributes to the transdermal delivery and the prolonged release of MgH_(2) that can generate hydrogen(H_(2))and magnesium ions(Mg^(2+))after reaction with body fluids.The released H_(2) reduces the production of ROS,transforming the pathological microenvironment induced by diabetes mellitus.Meanwhile,the released Mg^(2+)promotes the polarization of pro-healing M2 macrophages.Consequently,cell proliferation and migration are improved,and angiogenesis and tissue regeneration are enhanced.Such intelligent microneedle patch provides a novel way for accelerating wound healing through steadily preserving and releasing of H_(2) and Mg^(2+)locally and sustainably.

Fe-porphyrin:A redox-related biosensor of hydrogen molecule

Hydrogen molecule(H_(2))exhibits broad-spectrum but microenvironment-dependent biomedical effects in varied oxidation stress-related diseases,but its molecular mechanism is unclear and its targeting molecule is unknown so far.Herein,we originally reveal that Fe-porphyrin is a H_(2)-targeted molecule.We have demonstrated that the oxidized Fe-porphyrin in both free and protein-confining states can self-catalyze the hydrogenation/reduction by reacting with H_(2)to catalytically scavenge∙OH,and can also catalytically hydrogenate to reduce CO_(2)into CO in the hypoxic microenvironment of in vitro simulation and in vivo tumor,confirming that Fe-porphyrin is a redox-related biosensor of H_(2)and H_(2)is an upstream signaling molecule of CO.These discoveries are favorable for deep understanding and exploration of profound biomedical effects of H2,and helpful for development of innovative drugs and hydrogen energy/agricultural materials.

Organic cathode materials for rechargeable magnesium-ion batteries:Fundamentals, recent advances, and approaches to optimization

Rechargeable magnesium-ion batteries(MIBs) are favorable substitutes for conventional lithium-ion batteries(LIBs) because of abundant magnesium reserves, a high theoretical energy density, and great inherent safety. Organic electrode materials with excellent structural tunability,unique coordination reaction mechanisms, and environmental friendliness offer great potential to promote the electrochemical performance of MIBs. However, research on organic magnesium battery cathode materials is still preliminary with many significant challenges to be resolved including low electrical conductivity and unwanted but severe dissolution in useful electrolytes. Herein, we provide a detailed overview of reported organic cathode materials for MIBs. We begin with basic properties such as charge storage mechanisms(e.g., n-, p-, and bipolartype), moving to recent advances in various types of organic cathodes including carbonyl-, nitrogen-, and sulfur-based materials. To shed light on the diverse strategies targeting high-performance Mg-organic batteries, elaborate summaries of various approaches are presented.Generally, these strategies include molecular design, polymerization, mixing with carbon, nanosizing and electrolyte/separator optimization.This review provides insights on exploring high-performance organic cathodes in rechargeable MIBs.

In situ High-Energy Synchrotron X-ray Studies in Thermodynamics of Mg-In-Ti Hydrogen Storage System

Achieving dual regulation of the kinetics and thermodynamics of MgH_(2) is essential for the practical applications.In this study,a novel nanocomposite(In@Ti-MX)architected from single-/few-layered Ti_(3)C_(2) MXenes and ultradispersed indium nanoparticles was prepared by a bottom-up self-assembly strategy and introduced into MgH_(2) to solve the above-mentioned problems.The MgH_(2)+In@Ti-MX composites demonstrate excellent hydrogen storage performance:The resultant In@Ti-MX demonstrated a positive effect on the hydrogen storage performance of MgH_(2)/Mg:the dehydrogenated rate of MgH_(2)+15 wt%In@Ti-MX reached the maximum at 330°C,which was 47°C lower than that of commercial MgH_(2);The hydrogenation enthalpy of the dehydrided MgH_(2)+15 wt%In@Ti-MX and MgH_(2)+25 wt%In@Ti-MX were determined to be−66.2±1.1 and−61.7±1.4 kJ·mol^(−1) H_(2).In situ high-energy synchrotron x-ray diffraction technique together with other microstructure analyses revealed that synergistic effects from Ti_(3)C_(2) MXenes and In nanoparticles(NPs)contributed to the improved kinetics and thermodynamics of MgH_(2)(Mg):Ti/TiH_(2) derived from Ti_(3)C_(2) MXenes accelerated the dissociation and recombination of hydrogen molecule/atoms,while In NPs reduced the thermodynamic stability of MgH_(2) by forming the Mg-In solution.Such a strategy of using dual-active hybrid structures to modify MgH_(2)/Mg provides a new insight for tuning both the hydrogen storage kinetics and thermodynamics of Mg-based hydrides.

In-situ transformed Mott-Schottky heterointerface in silver/manganese oxide nanorods boosting oxygen reduction,oxygen evolution,and hydrogen evolution reactions

The development of non-platinum group metal(non-PGM)and efficient multifunctional electrocatalysts for oxygen reduction reaction(ORR),oxygen evolution reaction(OER),and hydrogen evolution reaction(HER)with high activity and stability remains a great challenge.Herein,by in-situ transforming silver manganese composite oxide heterointerface into boosted Mott-Schottky heterointerface through a facile carbon reduction strategy,a nanorod-like silver/manganese oxide with superior multifunctional catalytic activities for ORR,OER and HER and stability was obtained.The nanorod-like silver/manganese oxide with Mott-Schottky heterointerface(designated as Ag/Mn_(3)O_(4))exhibits an ORR half-wave potential of 0.831 V(vs.RHE)in 0.1 M KOH,an OER overpotential of 338 mV and a HER overpotential of 177 mV at the current density of 10 mA·cm^(-2)in 1 M KOH,contributing to its noble-metal benchmarks comparable performance in aqueous aluminum-air(Al-air)battery and laboratorial overall water splitting electrolytic cell.Moreover,in-situ electrochemical Raman and synchrotron radiation spectroscopic measurements were conducted to further illustrate the catalytic mechanism of Ag/Mn_(3)O_(4)Mott-Schottky heterointerface towards various electrocatalytic reactions.At the heterointerface,the Ag phase serves as the electron donor and the active phase for ORR and HER,while the Mn_(3)O_(4)phase serves as the electron acceptor and the active phase for OER,respectively.This work deepens the understanding of the Mott-Schottky effect on electrocatalysis and fills in the gap in fundamental physical principles that are behind measured electrocatalytic activity,which offers substantial implications for the rational design of cost-effective multifunctional electrocatalysts with Mott-Schottky effect.