Deformable Catalytic Material Derived from Mechanical Flexibility for Hydrogen Evolution Reaction

Deformable catalytic material with excellent flexible structure is a new type of catalyst that has been applied in various chemical reactions,especially electrocatalytic hydrogen evolution reaction(HER).In recent years,deformable catalysts for HER have made great progress and would become a research hotspot.The catalytic activities of deformable catalysts could be adjustable by the strain engineering and surface reconfiguration.The surface curvature of flexible catalytic materials is closely related to the electrocatalytic HER properties.Here,firstly,we systematically summarized self-adaptive catalytic performance of deformable catalysts and various micro–nanostructures evolution in catalytic HER process.Secondly,a series of strategies to design highly active catalysts based on the mechanical flexibility of lowdimensional nanomaterials were summarized.Last but not least,we presented the challenges and prospects of the study of flexible and deformable micro–nanostructures of electrocatalysts,which would further deepen the understanding of catalytic mechanisms of deformable HER catalyst.

Recent advances in photothermal effects for hydrogen evolution

Photothermal effect has been widely employed in the H2 evolution process at the advantage of using clean energy sources to produce another one of higher benefits.The solar-to-heat conversion have various forms and heat can facilitate reactions in a variety of dimensions.Hence,summarizing the sources and destinations of heat is important for constructing hydrogen production systems of higher efficiency.This view mainly focuses on the recent state-of-art progress of hydrogen evolution reaction(HER)based on photothermal effect.First,we introduce the main pathways of photothermal conversions applied in H2 evolution.Then,the functions of the photothermal effect are clearly summarized.Furthermore,we go beyond the catalytic reaction and introduce a method to improve the catalytic system by changing the catalytic bulk phase through thermal means.In the end,we sort out the challenges and outlook to offer some noble insights for this promising area.

Effective strategies to promote Z(S)-scheme photocatalytic water splitting

Artificial Z(S)-scheme photocatalytic water splitting systems have attracted extensive attention due to their advantages such as wide light absorption range,high charge separation efficiency and strong carrier redox ability.However,it is still challenging to design and prepare Z(S)-scheme photocatalysts with low-cost and highly stability for efficiently photocatalytic overall water splitting using solar energy.This review mainly introduces various strategies to improve the photocatalytic water splitting performance of Z(S)-scheme systems.These strategies mainly focus on enhancing or extending the range of light absorption,promoting charge separation,and enhancing surface redox reaction in Z(S)-scheme systems.Finally,the main challenges of Z(S)-scheme photocatalytic water splitting systems and their future development directions are pointed out.This review would be beneficial to understanding the challenges and opportunities faced by the research field of Z(S)-scheme photocatalytic systems,and has important guiding significance for the development and utilization of high-performance Z(S)-scheme photocatalytic reaction system in the future.

Strategies to accelerate bubble detachment for efficient hydrogen evolution

In the process of electrocatalytic water splitting, the management of gaseous products is an important task. Timely detachment of gaseous products from the electrode surface and the electrolyte is beneficial to the reduction of energy consumption of the electrolytic cell. In the existing industrial electrolytic cells, the circulating pump drives the electrolyte flowing to discharge the gaseous products. Up to now, several much more advanced strategies have been explored to deal with the negative effects of bubbles. In this review, we summarized various strategies for bubble detachment, including electrode design, external field imposing and system upgrading. We also elaborated the principle, functional features, practicability, advantages and limitations of each method. Finally, challenges and perspectives are also provided for the further development of advanced bubbles detachment strategies for efficient hydrogen evolution.

Recent advances on liquid intercalation and exfoliation of transition metal dichalcogenides: From fundamentals to applications

The weak van der Waals gap endows two dimensional transition metal dichalcogenides(2D TMDs)with the potential to realize guest intercalation and host exfoliation.Intriguingly,the liquid intercalation and exfoliation is a facile,low-cost,versatile and scalable strategy to modulate the structure and physiochemical property of TMDs via introducing foreign species into interlayer.In this review,firstly,we briefly introduce the resultant hybrid superlattice and disperse nanosheets with tailored properties fabricated via liquid intercalation and exfoliation.Subsequently,we systematically analyze the intercalation phenomenon and limitations of various intercalants in chemical or electrochemical methods.Afterwards,we intensely discuss diverse functionalities of resultant materials,focusing on their potential applications in energy conversion,energy storage,water purification,electronics,thermoelectrics and superconductor.Finally,we highlight the challenges and outlooks for precise and mass production of 2D TMDs-based materials via liquid intercalation and exfoliation.This review enriches the overview of liquid intercalation and exfoliation strategy,and paves the path for relevant high-performance devices.

Designing multi-heterogeneous interfaces of Ni-MoS_(2)@NiS_(2)@Ni_(3)S_(2)hybrid for hydrogen evolution

The transition metal chalcogenides represented by MoS_(2)are the ideal choice for non-precious metal-based hydrogen evolution catalysts.However,whether in acidic or alkaline environments,the catalytic activity of pure MoS_(2)is still difficult to compete with Pt.Recent studies have shown that the electronic structure of materials can be adjusted by constructing lattice-matched heterojunctions,thus optimizing the adsorption free energy of intermediates in the catalytic hydrogen production process of materials,so as to effectively improve the electrocatalytic hydrogen production activity of catalysts.However,it is still a great challenge to prepare heterojunctions with lattice-matched structures as efficient electrocatalytic hydrogen production catalysts.Herein,we developed a one-step hydrothermal method to construct Ni-MoS_(2)@NiS_(2)@Ni_(3)S_(2)(Ni-MoS_(2)on behalf of Ni doping MoS_(2))electrocatalyst with multiple heterogeneous interfaces which possesses rich catalytic reaction sites.The Ni-MoS_(2)@NiS_(2)@Ni_(3)S_(2)electrocatalyst produced an extremely low overpotential of 69.4 mV with 10 mA·cm^(−2)current density for hydrogen evolution reaction(HER)in 1.0 M KOH.This work provides valuable enlightenment for exploring the mechanism of HER enhancement to optimize the surface electronic structure of MoS_(2),and provides an effective idea for constructing rare metal catalysts in HER and other fields.

Diverse atomic structure configurations of metal-doped transition metal dichalcogenides for enhancing hydrogen evolution

Doping foreign metal atoms into the substrate of transition metal dichalcogenides(TMDs)enables the formation of diverse atomic structure configurations,including isolated atoms,chains,and clusters.Therefore,it is very important to reasonably control the atomic structure and determine the structure-activity relationship between the atomic configurations and the hydrogen evolution reaction(HER)performance.Although numerous studies have indicated that doping can yield diverse atomic structure configurations,there remains an incomplete understanding of the relationship between atomic configurations within the lattice of TMDs and their performance.Here,diverse atomic structure configurations of adsorptive doping,substitutional doping,and TMDs alloys are summarized.The structure-activity relationship between different atomic configurations and HER performance can be determined by micro-nanostructure devices and density functional theory(DFT)calculations.These diverse atomic structure configurations are of great significance for activating the inert basal plane of TMDs and improving the catalytic activity of HER.Finally,we have summarized the current challenges and future opportunities,offering new perspectives for the design of highly active and stable metal-doped TMDs catalysts.

Atom elimination strategy for MoS_(2) nanosheets to enhance photocatalytic hydrogen evolution

The regulation of the basic properties of atom-economic catalysts at the atomic scale and atomic-level insights into the underlying mechanism of catalysis are less explored. We engineer the surface of vertical immobilized MoS_(2) on dispersible TiO_(2) nanofibers via atomic subtraction to precisely manipulate active sites at the atomic level. The photocatalytic performances of TiO_(2) @MoS_(2) after H_(2) reduction towards the hydrogen production under visible light irradiation(>420 nm) are about 4 times that of TiO_(2) @MoS_(2) before H_(2) reduction. Importantly, the enhanced stability of TiO_(2) @MoS_(2) lasts for at least 30 h. Promising catalytic activity that is attributed to omnidirectional exposed active sites located defects, edges, corners that are transformed from the subtractive atomic sites could be exhumed comprehensively. This work will provide an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity at the atomic level by atom elimination strategy. To get rid of a few atomics on the surface of atomically-thin MoS_(2) nanosheet could be a prudent avenue for enabling the basal plane of MoS_(2) catalytically active.

Flexible electronics based on one-dimensional inorganic semiconductor nanowires and two-dimensional transition metal dichalcogenides

Flexible electronics technology is considered as a revolutionary technology to unlock the bottleneck of traditional rigid electronics that prevalent for decades,thereby fueling the next-generation electronics.In the past few decades,the research on flexible electronic devices based on organic materials has witnessed rapid development and substantial achievements,and inorganic semiconductors are also now beginning to shine in the field of flexible electronics.As validated by the latest research,some of the inorganic semiconductors,particularly those at low dimension,unexpectedly exhibited excellent mechanical flexibility on top of superior electrical properties.Herein,we bring together a comprehensive analysis on the recently burgeoning low-dimension inorganic semiconductor materials in flexible electronics,including one-dimensional(1D)inorganic semiconductor nanowires(NWs)and two-dimensional(2D)transition metal dichalcogenides(TMDs).The fundamental electrical properties,optical properties,mechanical properties and strain engineering of materials,and their performance in flexible device applications are discussed in detail.We also propose current challenges and predict future development directions including material synthesis and device fabrication and integration.

External field assisted hydrogen evolution reaction

As a clean,efficient,and sustainable energy,hydrogen is expected to replace traditional fossil energy.A series of studies focusing on morphology regulation,surface modification,and structural reconstruction have been devoted to improving the intrinsic catalytic activity of non-noble metal catalysts.However,complex system structure design and the mutual interference of various chemical components would hinder the further improvement of hydrogen evolution performance.In recent years,external field assisted hydrogen evolution reaction(HER)has become a new research hotspot.Herein,we systematically summarize the promoting effects of various external fields on catalytic hydrogen production from the aspects of system design and catalytic mechanism,including electric field,thermal field,optical field,magnetic field,and acoustic field.Ultimately,we discuss the key challenges facing this external field regulation strategy and put forward the prospect of future research topics.We sincerely expect that this review could not only provide a new insight into the basic mechanism of external-assisted catalysis,but also promote further research on improving HER performance from a more diverse and comprehensive perspective.

Moirésuperlattice engineering of two-dimensional materials for electrocatalytic hydrogen evolution reaction

Vertically stacking two-dimensional(2D)materials with small azimuthal deviation or lattice mismatch generate distinctive global structural periodicity and symmetry,revealed as the moirésuperlattices(MSLs).Manipulating the interlayer twist angle enables the modification of the electronic structure of 2D materials to explore the advanced applications.Although extraordinary progress has been achieved in the unique structure and emergent properties of MSLs,the investigation of the catalytic applications of MSLs materials is still in its infancy.It is therefore very urgent to summarize the advanced development of MSLs in the field of catalysis.In this review,we firstly summarize the advanced fabrication and high-resolution characterization techniques of the MSLs materials,as well as their novel properties related to catalysis represented by electrocatalytic hydrogen evolution reaction(HER).Then,all the MSLs materials such as MoS_(2),WS_(2),and Ru serving as electrocatalysts for HER are further reviewed in detail.Finally,we outline the current challenges as well as the experimental and theoretical strategies to advance the development of function-oriented MSLs materials for catalysis.This review aims to provide profound insight into the wide applications of this novel material platform in catalytic field.

Activation of hydrogen peroxide by molybdenum disulfide as Fenton-like catalyst and cocatalyst:Phase-dependent catalytic performance and degradation mechanism

Molybdenum disulfide(Mo S_(2))has attracted great attention in hydrogen peroxide(H_(2)O_(2))activation as a Fenton-like catalyst and cocatalyst,but the distinct mechanism of generating^(·)OH remains unclear.In this paper,the metallic 1T phase and semiconducting 2H phase of Mo S_(2)nanosheets were prepared and applied in MoS_(2)/H_(2)O_(2)and MoS_(2)/Fe^(2+)/H_(2)O_(2)systems with and without light irradiation.Compared with2H-MoS_(2),1T-MoS_(2)exhibited superior removal rates in degrading organic pollutants in the two systems under light irradiation.However,the phase had little effect on activating H_(2)O_(2)in the Mo S_(2)/H_(2)O_(2)system under dark conditions.This is because it was difficult for the surface^(·)OH_(ads)generated in the Mo S_(2)/H_(2)O_(2)system to diffuse into solution,while the^(·)OH_(free)radicals were mainly responsible for degrading organic pollutants.When introducing light irradiation,external energy may accelerate the desorption of^(·)OH_(ads)into^(·)OH_(free.)Interestingly,the conversion between Mo^(4+)and Mo^(5+)triggered the decomposition of H_(2)O_(2)in the Fenton-like reaction,while the cycle of Mo^(4+)/Mo^(6+)promoted the regeneration of Fe^(3+)when employing 1T-MoS_(2)as a cocatalyst.Meanwhile,the 1T-MoS_(2)catalysts exhibited excellent stability and ability to degrade various organics in the two systems.This work offers deeper insight into the Mo S_(2)-based Fenton-like and cocatalytic mechanisms.

Recent status and future perspectives of ZnIn_(2)S_(4) for energy conversion and environmental remediation

Zinc indium sulfide (ZnIn_(2)S_(4)),a novel photocatalyst,has attracted considerable attention and been extensively studied over the past few years owing to its various advantages such as nontoxicity,structural stability,easy availability,suitable band gap and fascinating photocatalytic activity.This review mainly focuses on the recent state-of-art progress of ZnIn_(2)S_(4)-based photocatalysts.First,we briefly introduced preparation methods of ZnIn_(2)S_(4) with diverse morphological structures.Then,considering the photocatalytic activity of pristine ZnIn_(2)S_(4) would be confined by rapid recombination of photo-generated electronhole pairs and limited light absorption range,different modulation strategies such as layer and size control,doping,vacancy engineering and hetero-nanostructures were expounded in detail.Afterwards,the applications of ZnIn_(2)S_(4) in various fields such as H_(2) production,CO_(2) reduction,value-added products synthesis,pollutant purification and N_(2) fixation are clearly summarized.In the end,we sorted out the conclusions and outlook,aiming to provide some new insights for this fascinating material.

Recent status and advanced progress of tip effect induced by micro-nanostructure

The unique structural features represented by micro-nanoneedle tip structure reflect wonderful physical and chemical properties.The tip effect includes the concentration of energy such as electrons,photons and magnetism in the tip region,which has promising applications in the fields of energy conversion,water capture,environmental restoration and so on.In this review,a comprehensive and systematic summary of the latest advances in the application of the tip effect in different fields is provided.Utilizing advanced Finite Difference Time Domain simulation,we further propose our understanding of the fundamental mechanism of the tip effect induced by micro-nanostructure.However,we need to forge the present study to further reveal the essential law of the tip effect from the perspective of theoretical calculations.This review would provide a solid foundation for further development and application of the tip effect.

Revisited electrochemical gas evolution reactions from the perspective of gas bubbles

Electrochemical gas evolution reactions are common but essential in many electrochemical processes including water electrolysis.During these processes,gas bubbles are constantly nucleating on reaction interfaces in electrolyte and consequently exert an impact on catalysts and the performance.In the past few decades,extensive studies have been conducted to characterize bubbles with emerging advanced technologies,manage behaviors of bubbles,and apply bubbles to various domains.In this review,we summarize representative discoveries as well as recent advancements in electrochemical gas evolution reactions from the perspective of gas bubbles.Finally,we end up this review with a profound outlook on future research topics from the combination of experiments and theoretical techniques,non-negligible bubble effects,gravity-free situation,and reactions under practical industrial conditions.

Ingeniously designed Ni-Mo-S/ZnIn_(2)S_(4) composite for multi-photocatalytic reaction systems

Molybdenum disulfide (MoS_(2)) with low cost, high activity and high earth abundance has been found to be a promising catalyst for the hydrogen evolution reaction (HER), but its catalytic activity is considerably limited due to its inert basal planes. Here, through the combination of theory and experiment, we propose that doping Ni in MoS_(2) as catalyst can make it have excellent catalytic activity in different reaction systems. In the EY/TEOA system, the maximum hydrogen production rate of EY/Ni-Mo-S is 2.72 times higher than that of pure EY, which confirms the strong hydrogen evolution activity of Ni-Mo-S nanosheets as catalysts. In the lactic acid and Na_(2)S/Na_(2)SO_(3) systems, when Ni-Mo-S is used as co-catalyst to compound with ZnIn_(2)S_(4) (termed as Ni-Mo-S/ZnIn_(2)S_(4)), the maximum hydrogen evolution rates in the two systems are 5.28 and 2.33 times higher than those of pure ZnIn_(2)S_(4), respectively. The difference in HER enhancement is because different systems lead to different sources of protons, thus affecting hydrogen evolution activity. Theoretically, we further demonstrate that the Ni-Mo-S nanosheets have a narrower band gap than MoS_(2), which is conducive to the rapid transfer of charge carriers and thus result in multi-photocatalytic reaction systems with excellent activity. The proposed atomic doping strategy provides a simple and promising approach for the design of photocatalysts with high activity and stability in multi-reaction systems.

Revisiting lithium-storage mechanisms of molybdenum disulfide

Molybdenum disulfide(MoS_(2)),a typical two-dimensional transition metallic layered material,attracts tremendous attentions in the electrochemical energy storage due to its excellent physicochemical properties.However,with the deepening of the research and exploration of the lithium storage mechanism of these advanced MoS_(2)-based anode materials,the complex reaction process influenced by internal and external factors hinders the exhaustive understanding of the lithium storage process.To design stable anode material with high performance,it is urgent to review the mechanisms of reported anode materials and summarize the related factors that influence the reaction processes.This review aims to dissect all possible side reactions during charging and discharging process,uncover internal and external factors inducing various anode reactions and finally put forward strategies of controlling high cycling capacity and super-stable lithium storage capability of MoS_(2).This review will be helpful to the design of MoS_(2)-based lithium-ion batteries(LIBs) with excellent cycle performance to enlarge the application fields of these advanced electrochemical energy storage devices.

Ultrathin Ti_(3)C_(2) nanowires derived from multi-layered bulks for high-performance hydrogen evolution reaction

One-dimensional ultrathin nanowires(NWs)offer a great deal of promising properties for electrochemical energy storage and conversion due to their nanoscale confinement effect and high surface-to-volume ratios.It is highly desirable to precisely design and synthesize ultrathin Ti_(3)C_(2)NWs in the aspect of size,crystalline structure and composition.Here,we report a simple alkalization strategy to design the ultrathin Ti_(3)C_(2)NWs for hydrogen evolution reaction(HER)by modulating the surface-active sites.The design principle can well improve the amount of the defect sites and ion accessibility to increase the interactions between Ti_(3)C_(2)NWs and H^(*).The optimized Ti_(3)C_(2)NWs achieve an overpotential of 476 mV at the current density of 10 mA/cm^(2)and a Tafel slope of 129 mV/dec for HER catalysis,which are superior to that of Ti_(3)C_(2)nanosheets and m-Ti_(3)C_(2).It paves an avenue for the rational transformation of MXene bulks to one-dimensional NWs catalysts for HER.

Dislocation-strained MoS_(2)nanosheets for high-efficiency hydrogen evolution reaction

Defect engineering is one of the effective strategies to optimize the physical and chemical properties of molybdenum disulfide(MoS_(2))to improve catalytic hydrogen evolution reaction(HER)performance.Dislocations,as a typical defect structure,are worthy of further investigation due to the versatility and sophistication of structures and the influence of local strain effects on the catalytic performance.Herein,this study adopted a low-temperature hydrothermal synthesis strategy to introduce numerous dislocation-strained structures into the in-plane and out-of-plane of MoS_(2)nanosheets.Superior HER catalytic activity of 5.85 mmol·g^(−1)·h^(−1)under visible light was achieved based on the high-density dislocations and the corresponding strain field.This work paves a new pathway for improving the catalytic activity of MoS_(2)via a dislocation-strained synergistic modulation strategy.

Amorphous molybdenum sulfide and its Mo-S motifs:Structural characteristics,synthetic strategies,and comprehensive applications

Amorphous materials are one kind of nonequilibrium materials and have become one of the most active research fields.Compared with crystalline solids,the theory of amorphous materials is still in infancy because their characteristic of atomic arrangement is more like liquid and has no long-range periodicity.Recently,as the representative of amorphous materials,amorphous molybdenum sulfide(a-MoS_(x))with unique physical and chemical properties has been studied extensively.However,considerable debate surrounds the structure–property relationships of a-MoS_(x)owing to its diverse Mo-S motifs.Herein,we summarize recent discoveries and research results regarding a-MoS_(x),whose structural characteristics,synthetic strategies,formation criteria,and comprehensive applications are discussed in detail.Finally,this review is ended with our personal insights and critical outlooks over the development of a-MoS_(x).