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For the first time, a series of MXene (Ti3C2Tx)/Bi2WO6 Schottky junction piezocatalysts were constructed, and the piezocatalytic hydrogen evolution activity was explored. Optimal Ti3C2Tx/Bi2WO6 exhibits the highest piezocatalytic hydrogen evolution rate of 764.4 µmol g-1 h-1, which is nearly 8 times higher than that of pure Ti3C2Tx and twice as high as that of Bi2WO6. This value also surpasses that of most recently reported typical piezocatalysts. Moreover, related experimental results and density functional theory calculations reveal that Ti3C2Tx/Bi2WO6 can provide unique channels for efficient electron transfer, enhance piezoelectric properties, optimize the adsorption Gibbs free energy of water, reduce activation energy for hydrogen atoms, endow robust separation capacity of charge carrier, and restrict the electron-hole recombination rate, thus significantly promoting the efficiency of hydrogen evolution reaction. Ultimately, we have unraveled an innovative piezocatalytic mechanism. This work broadens the scope of MXene materials in a sustainable energy piezocatalysis application.
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Designing highly efficient, stable, and pH-universal perovskites for hydrogen evolution reaction (HER) is urgently needed yet remains a grand challenge. Herein, a titanium-containing strontium ruthenate (SrTi0.5Ru0.5O3, STRO) is developed as an excellent HER electrocatalyst in a wide pH range. The introduction of Ti into SrRuO3 significantly reduces the size of STRO, endowing with a high reactivity that facilitates a deep surface-reconstruction during HER. Furthermore, Sr2+ leaching triggered reconstruction leads to STRO breaking into tiny nanoparticles accompanied by high-valence ruthenium (Ru) species reducing to metallic Ru. The generated active species, increased accessible sites, and improved electrical conductivity greatly boost HER. The reconstructed STRO displays remarkable HER activities with exceptional low overpotentials of 18, 24, and 55 mV at 10 mA cm-2 in 1 m KOH, 0.5 m H2SO4, and 1 m PBS, respectively, surpassing most perovskites reported previously and comparable to or even outperforming that of commercial Pt/C. Moreover, the STRO exhibits excellent stabilities over 200 h in alkaline and acidic media, superior to that of Pt/C. This work not only provides insights into structure reconstruction of perovskites during HER, but also opens new perspectives for developing high-efficiency and pH-universal electrocatalysts for future energy applications.
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Constructing quantum dot-scale metal sulfides with defects and strongly coupled with carbon is significant for advanced sodium-ion batteries (SIBs). Herein, Se substituted V3S4 quantum dots with anionic defects confined in nitrogen-doped carbon matrix (V3S4-xSex/NC) are fabricated. Introducing element Se into V3S4 crystal expands the interlayer distance of V3S4, and triggers anionic defects, which can facilitate Na+ diffusions and act as active sites for Na+ storage. Meanwhile, the quantum dots tightly encapsulated by conductive carbon framework improve the stability and conductivity of the electrode. Theoretical calculations also unveil that the presence of Se enhances the conductivity and Na+ adsorption ability of V3S4-xSex. These properties contribute to the V3S4-xSex/NC with high specific capacity of 447 mAh g-1 at 0.2 A g-1, and prominent rate and cyclic performance with 504 mAh g-1 after 1000 cycles at 10 A g-1. The sodium-ion hybrid capacitors (SIHCs) with V3S4-xSex/NC anode and activated carbon cathode can achieve high energy/power density (maximum 144 Wh kg-1/5960 W kg-1), capacity retention ratio of 71% after 4000 cycles at 2 A g-1. This work not only synthesizes V3S4-xSex/NC, but also provides a promising opportunity for designing quantum dots and utilizing defects to improve the electrochemical properties.
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Developing low-cost electrocatalysts with excellent activity and durability in urea-assisted water splitting is urgently needed in order to achieve sustainable hydrogen production. Herein, we in situ synthesized a robust coupled heterostructured electrocatalyst (CoP/MoO2) on a nickel foam (NF) substrate and explored its electrocatalytic performances in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and urea oxidation reaction (UOR). The overpotential of CoP/MoO2/NF is found to be only 11 mV at 10 mA cm-2 during the HER process, which is significantly lower than that of commercial Pt/C. Meanwhile, the UOR catalytic performance of CoP/MoO2/NF indicates fast reaction kinetics, along with a considerable low driving potential (1.26 V) compared to that of the OER (1.51 V). In situ and ex situ techniques demonstrate that these excellent electrocatalytic properties are mainly ascribed to the effective synergistic coupled effect and strong electronic interactions between single-component CoP and MoO2, which can tune electronic states of Co and Mo, expose more active sites, enhance intrinsic catalytic activity, and accelerate charge transfer. Moreover, when used in electrochemical overall water splitting and urea-assisted water electrolysis, CoP/MoO2/NF can reach a current density of 10 mA cm-2 at only 1.46 and 1.32 V. This outperforms Pt/C||RuO2 and numerous nonprecious metal electrocatalysts and maintains a stable long-term electrolytic operation for 84 h. This work provides a promising pathway for the development of efficient catalysts during urea-assisted water electrolysis for hydrogen production.
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The energy gap and conduction band position of catalysts play crucial roles in solar-to-hydrogen (STH) transformation technology. Unfortunately, although an increase in the conduction band position can effectively promote the photoreduction capacity of the photocatalyst, it will inevitably widen the band gap, thus reducing the light-absorption scale. It seems that there is a contradiction between the reduction of band gap and the improvement of conduction band position, which is that "You can't have your cake and eat it too." Herein, an ultrasimple molecular adsorption strategy was engineered by adsorbing hydrazine hydrate on the surface of TiO2. The theoretical and experimental results indicated that the strong electron-donating effect of amino groups in hydrazine hydrate can promote the redistribution of photogenerated electrons and form surface electron networks on the surface of TiO2 photocatalysts, which can bend the conduction band upward and significantly improve its photoreduction ability. Besides, the adsorption of -NH2 can narrow the band gap width of TiO2 and promote the separation efficiency of photogenerated carriers. More interestingly, it can also effectively enhance the adsorption of H2O and H+, thus greatly elevating the STH efficiency. The STH rate of the as-prepared T-N-3 can be increased by ≈530%. This work sheds light on a new approach for resolving the contradiction between photoreduction and light absorption capabilities to effectively enhance photocatalytic performance.
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The development of electrode materials with excellent performance serves as the key for researchers to enhance the energy density of supercapacitors. Cobalt molybdate (CoMoO4) nanomaterials have been regarded as one of the most prospective electrode materials for supercapacitors due to their high theoretical capacitance and excellent electrical conductivity. In this paper, three kinds of CoMoO4 nanorods were prepared directly via simple and environmentally friendly solid-phase chemical reactions with solid inorganic salts as raw materials. According to X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) test results, different reagents had certain effects on the size and morphology of CoMoO4, and these affected its electrochemical performance. In particular, the samples prepared with Co(NO3)2·6H2O as raw material took on a more uniform micromorphology, with a better crystallinity. Simultaneously, electrochemical test results showed that the samples synthesized with Co(NO3)2·6H2O presented relatively good electrical conductivity and a large specific capacitance (177 F g-1). This may be due to the nitrates reacting more slowly during the reaction and the crystals having difficulty aggregating during growth. Therefore, the structure of the prepared CoMoO4 nanomaterial was more uniform, and it was resistant to collapse during the charging and discharging process; thus, the capacitor presents the best performance.
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The exploitation of electrode materials with ability to balance capacity and kinetics between cathode and anode is a challenge for sodium-ion hybrid capacitors (SIHCs). Mn-based anode materials are limited by poor electrical conductivity, sluggish reaction kinetics, large volume variation, weak cycling stability, and inferior reversible capacity. Herein, MnS nanocubes encapsulated in S-doped porous carbon matrix (MSC) with strong sulfur-bridged bond interactions (CSMn) are successfully synthesized by solvent-free tactics. The CSMn bonds generated between MnS and carbon significantly inhibit the aggregation of nanostructural MnS cubes, restrict the volume expansion, and stabilize the nanostructure, which improves the Na+ storage reversibility and stability. Moreover, S-doped porous carbon enhances the electrical conductivity and electrons/ions diffusion rate, which boosts a fast kinetic reaction. As expected, MSC anode presents an outstanding reversible capacity of 600 mAh g-1 at 0.2 A g-1 and a long-term stable capacity of 357 mAh g-1 for 1000 cycles at a high current density of 10 A g-1 in sodium-ion batteries (SIBs). The as-assembled SIHCs deliver a high energy density of 109 W h kg-1 and a high power output of 98 W kg-1 , with 88% capacity retention at 2 A g-1 after 2000 cycles and practical applications (55 LEDs can be lighted for 10 min).
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Nickel-iron based hydroxides have been proven to be excellent oxygen evolution reaction (OER) electrocatalysts, whereas they are inactive toward hydrogen evolution reaction (HER), which severely limits their large-scale applications in electrochemical water splitting. Herein, a heterostructure consisted of NiFeV hydroxide and iron oxide supported on iron foam (NiFeV@FeOx /IF) has been designed as a highly efficient bifunctional (OER and HER) electrocatalyst. The V doping and intimate contact between NiFeV hydroxide and FeOx not only improve the entire electrical conductivity of the catalyst but also afford more high-valence Ni which serves as active sites for OER. Meanwhile, the introduction of V and FeOx reduces the electron density on lattice oxygen, which greatly facilitates desorption of Hads . All of these endow the NiFeV@FeOx /IF with exceptionally low overpotentials of 218 and 105 mV to achieve a current density of 100 mA cm-2 for OER and HER, respectively. More impressively, the electrolyzer requires an ultra-low cell voltage of 1.57 V to achieve 100 mA cm-2 and displays superior electrochemical stability for 180 h, which outperforms commercial RuO2 ||Pt/C and most of the representative catalysts reported to date. This work provides a unique route for developing high-efficiency electrocatalyst for overall water splitting.
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Electrocatalytic water splitting is still circuitous and controversial because of the lack of highly active electrocatalysts to decrease the overpotential. Herein, we report a feasible method for constructing heterojunctions of MnO2-Co3O4 nanosheets on Co@NCNT support surfaces (MnO2-Co3O4/Co@NCNT) by spontaneous redox reactions. Experimental results indicate that Co embedded in Co@NCNT can be used as the carbon support and anchoring sites for heterojunctions, thus exposing a large number of active sites, adjusting the surface electronic structure, changing the OER rate-determining step of the catalyst, and reducing the reaction energy barrier. Besides, the in situ formation of MnO2-Co3O4 nanosheets on Co@NCNT inhibits the loss and aggregation of the catalyst, leading to robust structural stability. Therefore, the synergistic effects of these factors provide multi-functional active sites to enhance the intrinsic activity and achieve maximum catalytic performances. To deliver a current density of 10 mA cm-2, the catalyst of MnO2-Co3O4/Co@NCNT achieves an overpotential (η) of 303 mV in 1.0 M KOH media for OER. This simple redox strategy can be easily extended to prepare other ultrathin transition-metal oxide heterojunctions, which could be applied not only for water splitting but also for other energy conversion and storage technologies.
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Transition metal nitrides are promising electrocatalysts for hydrogen evolution reaction (HER) owing to their Pt-like electronic structure. However, the harsh nitriding conditions greatly limit their large-scale applications. Herein, ultrafine Co3Mo3N-Mo2C (<1 nm)-decorated carbon nanofibers (Co3Mo3N-Mo2C/CNFs) were prepared by electrostatic spinning followed by pyrolysis treatment, in which the MoCo-MOF simultaneously serves as the precursor and nitrogen source. The generated synergistic interactions between Mo2C and Co3Mo3N significantly adjust the electronic structure of Mo2C and afford a fast charge transfer, which endows the resultant hybrid with superior HER electrocatalytic performances. Specifically, the as-obtained Co3Mo3N-Mo2C/CNF delivers a low overpotential of only 76 mV to achieve a current density of 10 mA cm-2 and superior durability with no obvious degradation for 200 h in acidic media. This performance outperforms most of the transition metal-based electrocatalysts reported to date. This work paves a new way for the design of catalysts with ultrasmall size and high efficiency in energy conversion.
RESUMEN
Developing high-efficiency, low-cost, and earth-abundant electrocatalysts toward the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is highly desirable for boosting the energy efficiency of water splitting. Herein, we adopted an interfacial engineering strategy to enhance the overall water splitting (OWS) activity via constructing a bifunctional OER/HER electrocatalyst combining MoS2-Ni3S2 with NiFe layered double hydroxide (NiFe-LDH) on a nickel foam substrate. The NiFe-LDH/MoS2-Ni3S2/NF electrocatalyst delivers superior OER/HER activity and stability, such as low overpotentials (220 and 79 mV for OER and HER at current densities of 50 and 10 mA cm-2, respectively) and a low Tafel slope. This excellent electrocatalytic performance mainly benefits from the electronic structure modulation and synergistic effects between NiFe-LDH and MoS2-Ni3S2, which provides a high electrochemical activity area, more active sites, and strong electron interaction. Furthermore, the assembly of NiFe-LDH/MoS2-Ni3S2/NF into a two-electrode system only requires an ultra-low cell voltage of 1.50 V at a current density of 10 mA cm-2 and exhibits outstanding stability with a decay of current density of only 2.11% @50 mA cm-2 after 50 h, which is far superior to numerous other reported transition metal NiFe-LDH and MoS2-Ni3S2-based as well as RuO2||Pt-C electrocatalysts. This research highlights the rational design of heterostructures to efficiently advance electrocatalysis for water splitting applications.
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Constructing heterojunctions with strong interfacial interactions can accelerate the transfer and separation of photogenerated charge carriers. However, finding a simple strategy to construct tightly connected heterojunctions remains a major challenge. In this work, AgBr/BiOBr S-scheme heterojunctions were designed via a straightforward co-anionic strategy without using a solvent. The experimental results indicate that the AgBr/BiOBr heterojunction with a close contact interface can extend the use of visible light, accelerate the separation, and induce the transfer of photoelectrons and holes while maintaining an excellent redox capacity. Undoubtedly, the photocatalytic reduction rate of carbon dioxide to carbon monoxide by 1.0 AgBr/BiOBr is 87.73 µmol·g-1·h-1 (quantum efficiency is 0.57%), which is 12.15 times and 4.45 times higher than that of pure AgBr and BiOBr, respectively. The present work provides insights into a simple strategy for the preparation of strongly interacting interfacial heterojunctions for photocatalytic CO2 reduction.
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Direct formic acid fuel cells (DFAFCs) are one of the most promising power sources due to its high conversion efficiency; relatively low carbon emissions, toxicity, and flammability; convenience; and low-cost storage and transportation. However, the key challenge to large-scale commercial applications is its poor power performance and the catalyst's high preparation cost. In this study, a new sandwich-structured Pd/polypyrrole-graphene/Pd (Pd/PPy-Gns/Pd)-modified glassy carbon electrode (GCE) was prepared using a simple constant potential (CP) electrodeposition technique. On the basis of the unique synthetic procedure and structural advantages, the Pd/PPy-Gns/Pd shows a fast charge/mass transport rate, high electrocatalytic activity, and great stability for formic acid electro-oxidation (FAO). The mass activity of Pd/PPy-Gns/Pd electrode reaches 917 mA·mg-1Pd. The excellent catalytic activity is mainly due to the uniform embedding of Pd nanoparticles on the polypyrrole-graphene (PPy-Gns) support, which exposes more active sites, and prevents the shedding and inactivation of Pd nanoparticles. At the same time, the introduction of graphene (Gns) in the PPy further improved the conductivity of the catalyst and accelerated the transfer of electrons.
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Defects play a vital role in improving photocatalytic performance. However, the specific influence mechanism of sulfur defects (DSS) on sulfide photocatalytic performance and stability is still unclear. In this work, an ingenious solvent-free self-overflow strategy is designed to introduce DSS into ZnS nanoparticles and explore the specific promotion mechanism of photocatalytic performance and photostability. The results indicate that the introduced DSS in ZnS nanoparticles can simultaneously boost the photocatalytic hydrogen production (PHE) performance and photostability of ZnS: the PHE rate of the defective ZnS can increase up to 21350.23 µmol·h-1·g-1, which is roughly 4.7 times higher than that of pristine ZnS. Both experiments and theoretical calculationsshow that the enhanced photocatalytic performance could be attributed to the change of energy band position after introducing DSS. Specifically, the introduction of DSS can raise the conduction band (CB) position of ZnS to enhance the reducing ability of photogenerated electrons. Besides, the valence band (VB) position can also be raised to boost the light absorption ability of ZnS and restrain the photocorrosion by weakening the oxidation capacity of the photogenerated holes. The ingenious strategy and interesting mechanism in this job provide a simple artful tactic to fabricate other defective sulfide photocatalysts and open up a particular path to promote the photostability of the photocatalysts.
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Simultaneous boosting electrochemical methanol oxidation reaction (MOR) for direct methanol fuel cells and production of hydrogen is meaningful but challenging. Herein, a sea urchin-shaped cobalt-embedded N-doped carbon nanotubes (Co@NCNT) encapsulated CoPt3 @Co2 P heterojunction (CoPt3 @Co2 P/Co@NCNT) is fabricated. Theoretical calculations confirm that electrons at the interfaces transfer from CoPt3 to Co2 P, where electron hole region on CoPt3 is beneficial to improving the MOR activity, whereas accumulation region on Co2 P favors to the optimization of H2 O and H* absorption energies for hydrogen evolution reaction (HER). Benefitting from its interfacial electronic reconfiguration, the CoPt3 @Co2 P/Co@NCNT heterojunction exhibits excellent electrocatalytic performances for MOR and HER, in which the mass activity (2981 mA mgPt -1 ) for MOR is 14.2 times than that of Pt/C (20%), and the smallest overpotentials only requires 19 mV to deliver a current density of 10 mA cm-2 for HER. Moreover, the electrolyzer employing CoPt3 @Co2 P/Co@NCNT for anodic MOR and cathodic H2 production only requires a low voltage of 1.43 V at 10 mA cm-2 with impressive long-life cycling stability, which is obviously better than that of commercial Pt/C//RuO2 . This study offers a novel strategy for other organics oxidation reaction coupled with HER catalyzed production of hydrogen.
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2D piezoelectric catalysts with strong piezoresponse and high piezoelectric potential have valuable applications in catalytic degradation of organic pollutants and antibiotics, but the development of novel nanomaterials with powerful piezopotential still remains a serious challenge. Bismuth oxysulfide (Bi2O2S) nanosheets possessing large piezoelectric potentials were prepared using a low-heating solid-state chemical reaction and used for the first time for piezoelectric catalysis in this work. Moreover, Bi2O2S nanosheets can degrade pollutants universally, and the degradation efficiencies of methyl blue and rhodamine B are as high as 97.7% and 92.9% within 60 min under ultrasonication, respectively, which is superior to most piezoelectric materials reported in the literature.
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Building efficient and stable bifunctional electrocatalysts toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for the advancement of rechargeable zinc-air batteries (ZABs). Here, a convenient in situ strategy is reported to controllably encapsulate CoFe alloy nanoparticles within N-doped carbon nanotubes (CoFe@NCNT). The abundant Co(Fe)-Nx active sites and the synergistic interaction between CoFe alloys and carbon nanotubes facilitate mass transfer and interfacial charge transfer, resulting in excellent dual functional electrocatalytic activity of OER/ORR with minor potential difference (ΔE = 0.73 V). Thus, the corresponding rechargeable ZAB displays high power density (194 mW cm-2), excellent specific capacity (795 mAh gZn-1), and favorable stability (900 cycles@5 mA cm-2). This work provides an approach for establishing low-cost bultifunctional electrocatalysts with excellent performance of non-noble metal nanoalloys.
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The ingenious architectural structural engineering is extensively identified as a cogent means for facilitating the electrochemical properties of conversion-type anode materials for sodium-ion storage. Herein, a delicate, scalable and controllable solvent-free strategy is proposed to synthesize ultrafine Mn2O3 quantum dots embedded into N-doped carbon to generate two-dimensional (2D) composites (MNC) with robust interfacial heterostructural interactions for high sodium ion storage and fast reaction kinetics, which averts the use of solvents and environmental pollution, greatly reduces time and production costs. The introduction of metallic Mn species simultaneously achieves the construction of ultrafine Mn2O3 quantum dots and strong interfacial heterostructural COMn bonds between metal species and 2D N-doped carbon matrix. The synergistic effect of the formation of oxide quantum dots, the combination of 2D N-doped carbon and the construction of robust interfacial interactions provides the stable electrode structure, fast reaction kinetics and high electrochemical storage capability of anode materials. Hence, MNC composites in SIBs convey remarkable reversible rate capability. Its superior capacity reaches 215 mAh g-1 for 50 cycles at 0.2 A g-1 and 155 mAh g-1 for 1000 cycles at a high current density of 5 A g-1, which shows good long-term stability. The assembled sodium-ion hybrid capacitors (SIHCs) device delivers outstanding energy density of 138 Wh kg-1 at a power density of 126 W kg-1 and 98% capacity retention after 2000 cycles at 2 A g-1, and tremendous capability for practical applications (69 LEDs can be easily lighted). This work not merely offers guidance for the rational interfacial engineering design of high-capacity Mn-based electrode materials in a feasible and scalable solvent-free tactics for Na+ storage, but also broadens the routes for projecting a better electrode material for other battery systems.
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Cerium-doped bismuth oxybromide (1%, 5% and 10% Ce-BiOBr) piezocatalysts were synthesized. The piezocatalytic activity was efficiently regulated by defect and morphology engineering. Among them, the 5% Ce-BiOBr exhibits the highest piezocatalytic hydrogen production property with an evolution rate of 1147.6 µmol g-1 h-1, nearly twice that of the original BiOBr. Additionally, the MO dye degradation efficiency of 5% Ce-BiOBr reaches 91.9% within 60 min, with a higher reaction kinetic constant (0.0376 min-1) that was 6.1 times larger than that of pure BiOBr. These outstanding performances of 5% Ce-BiOBr surpass those of most other piezocatalytic material systems.
RESUMEN
Introducing the appropriate vacancies to augment the active sites and improve the electrochemical kinetics while maintaining high cyclability is a major challenge for its widespread application in electrochemical energy storage. Here, core-shell structured Bi2S3@C with sulfur vacancies was prepared by hydrothermal method and one-step carbonization/sulfuration process, which significantly improves the intrinsic electrical conductivity and ion transport efficiency of Bi2S3. Additionally, the uniform protective carbon layer around surface of composite maintains structural stability and effectively alleviates volume expansion during alloying/dealloying. As a result, the BSC-500 anode exhibits a brilliant reversible capacity of 636 mAh/g at 0.2 A/g and a long-term stable capacity of 524 mAh/g for 500 cycles at a high current density of 3 A/g in lithium-ion batteries. In addition, the assembled Bi2S3@C//LiCoO2 full cell delivered a capacity of 184 mAh/g at 1 A/g and excellent cyclability (125 mAh/g after 1000 cycles). The proposed strategy of combining sulfur vacancies with a core-shell structure to improve the electrochemical kinetics of Bi2S3 in lithium-ion batteries off the prospect for practical applications of transition metal sulfide anodes.