優(yōu)化結(jié)晶度的CrS/CoS2少層異質(zhì)結(jié)非晶/晶態(tài)界面耦合增強水裂解和甲醇輔助節(jié)能制氫

摘要：由于電催化劑中的非晶區(qū)和結(jié)晶區(qū)具有不同的物理化學(xué)性質(zhì)，因此非晶化/結(jié)晶化工程成為提高電解水催化動力學(xué)的重要策略。然而，在微觀環(huán)境中有效地調(diào)控催化劑的結(jié)晶度仍然是一個嚴峻的挑戰(zhàn)。本文介紹了一種可調(diào)節(jié)結(jié)晶度的新型CrS/CoS2異質(zhì)結(jié)構(gòu)，該異質(zhì)結(jié)對氫氣析出反應(yīng)（HER）和氧氣析出反應(yīng)（OER）都具有高效的催化活性。Cr―S―Co鍵的重新分配引起的d帶中心移動有助于調(diào)節(jié)中間體H*和OOH*在催化劑表面的吸附能力，從而優(yōu)化HER和OER的決速步驟。在最佳條件下，非晶態(tài)CrS和高度結(jié)晶的CoS2異質(zhì)結(jié)（A-CrS/HC-CoS2）在HER和OER均表現(xiàn)出優(yōu)異的催化活性，分別為90.6 mV （10 mA?cm?2，HER）和370.5 mV （50 mA?cm?2，OER）。非晶/高晶結(jié)構(gòu)有利于A-CrS/HC-CoS2在水電解過程中的結(jié)構(gòu)和成分演變，因此具有出色的穩(wěn)定性。作為甲醇輔助節(jié)能制氫裝置中的雙功能催化劑，A-CrS/HC-CoS2僅需1.51 V的低槽電壓即可達到10 mA?cm?2的電流密度，證明其是理想的金屬基催化劑的候選材料。本研究為雙功能過渡金屬化合物電催化劑在非晶態(tài)/晶態(tài)異質(zhì)結(jié)構(gòu)中通過結(jié)晶度調(diào)控來提高催化活性和穩(wěn)定性提供了重要啟示。

關(guān)鍵詞：非晶態(tài)-晶態(tài)耦合界面；異質(zhì)結(jié)構(gòu)；結(jié)晶度調(diào)控；水分解；節(jié)能制氫裝置

中圖分類號：O643

Abstract： Large-scale hydrogen production through theelectrochemical water splitting technique is an important way foraddressing the impending energy and environmental crisis. Thisapproach requires highly efficient and robust bifunctional cost-effectiveelectrocatalysts. Engineering amorphous and crystalline phases withinelectrocatalysts is a key method for enhancing the catalytic kinetics ofwater electrolysis， due to their unique physicochemical properties. Theinterface and amorphous regions constructed within heterostructuresserve as highly active sites that play a crucial role in electrochemicalreactions. On the other hand， highly crystalline regions within theheterostructure demonstrated high tolerance in harsh environments，which helps to improve the stability of the overall catalyst. However， effectively tailoring the crystalline state of catalystswithin a microenvironment presents a significant challenge. Herein， construction of a novel CrS/CoS2 heterojunction withprecise control over crystallinity were presented. The optimized amorphous CrS/highly crystalline CoS2 heterojunction （ACrS/HC-CoS2） exhibits a low overpotential of 90.6 mV （at 10 mA?cm?2） and 370.5 mV （at 50 mA?cm?2） for hydrogenevolution reaction （HER） and oxygen evolution reaction （OER）， respectively. X-ray photoelectron spectroscopy （XPS） anddensity functional theory （DFT） calculations reveal that charge redistribution induces variations in the d-band center valueat the A-CrS/HC-CoS2 heterostructure interface， enhancing the catalytic activity for both HER and OER. The displacementof the d-band due to charge redistribution in the Cr―S―Co bond within A-CrS/HC-CoS2 contributes to the modulation ofthe adsorption capacity of H* and OOH* intermediates on the catalyst surface， thereby optimizing the rate-determiningstep for HER and OER. The amorphous/highly crystalline structure also facilitates the structural and compositionalevolution of A-CrS/HC-CoS2 during water electrolysis， ensuring excellent stability. As a bifunctional catalyst in a methanolassistedenergy-saving hydrogen production device， A-CrS/HC-CoS2 operates at a low cell voltage of 1.51 V to deliver acurrent density of 10 mA?cm?2， making it a promising candidate among metal-based catalysts. The well-preservedamorphous/crystalline heterointerfaces in A-CrS/HC-CoS2， along with favorable changes in surface composition， contributeto robust HER and OER stability. This work provides valuable insights into the manipulation of catalytic activity throughcrystalline control within amorphous/crystalline heterojunctions for bifunctional transition metal compound electrocatalysts.

Key Words： Amorphous-crystalline interface; Heterostructure; Crystalline degree modulation; Water-splitting;Energy-saving hydrogen device

1 Introduction

The booming growth of clean and sustainable energy torestrain the immoderate depletion of fossil fuels is one of thevital approaches to addressing pollution incidents andenvironmental risks while striving for carbon neutrality 1?5.Given hydrogen’s high calorific value （142 MJ?kg?1） andcarbon-free properties， the large-scale production of cleanhydrogen fuel via water electrolysis powered by electricity hasgarnered widespread attention as a crucial element in futureenergy supply 2，6，7. However， the broader adoption of waterelectrolysis has been hampered by the inefficiencies in both thecathodic hydrogen evolution reaction （HER） and the anodicoxygen evolution reaction （OER）， necessitating robust andhighly active catalysts to reduce overpotentials and consequentlyreduce operational costs of electrolytic water systems 8，9.

Despite their effectiveness， precious metal-based catalysts（e.g.， Pt-based metal catalysts for HER， Ir/Ru-based metalcatalysts for OER） face inherent limitations such as escalatingcosts， limited elemental resources， and compatibility issues，which severely hinder their scalable utilization 10，11. Therefore，there is a pressing need for the design of earth-abundant，bifunctional alternatives characterized by high activity andstability， such as metal phosphides， metal chalcogenides， metalnitrides， metal carbides， and metal oxides/hydroxides 12?20.

Among these alternatives， cobalt sulfides （CoS2）， as a type of metal chalcogenides， stand out due to their unique physical andchemical properties 21. Notably， the abundant d orbital electronsin cobalt （Co）， with an electron configuration of 3d74s2， and itsmetallic conductivity （6.7 × 103 S?cm?1 at 300 K） have garneredsignificant attention in the field of electrocatalytic hydrogenproduction. CoS2， with its high active component content，provides a conducive channel for ion adsorption and transport，thereby accelerating the kinetics of HER and OER 22，23.However， CoS2 faces challenges related to the inadequateadsorption energies of reactive species （H*/OH*） andinsufficiently catalytically active surfaces 15.

To address these challenges， hybridizing appropriateconstituents to construct heterostructure materials can mitigatethe weakness of individual components， harness their merits，optimize electronic properties， and modify structuralconfigurations. This approach increases active sites and inducesthe restructuring of electron nearby active centers， regulating theadsorption energies of reactive species on the catalyst.Moreover， the amorphous and crystalline regions within theheterostructure play distinct roles： the interface and amorphousportions contain abundant coordination-unsaturated sites andvacancies， serving as highly active sites for electrochemicalreactions， while the highly crystalline regions exhibitrobustness in harsh environments， enhancing the overallcatalyst’s stability 24?26. Therefore， designing and constructing amorphous/crystalline heterostructures represent an effectiveand promising strategy for achieving both high activity andstability in catalysts.

The element chromium （Cr）， known for its unique electronicconfiguration （t2g3eg0）， has garnered attention as a specificdopant in electrocatalysts， which alters the charge balance，disrupts the continuousness of local chemical field， and thusmodifies the electronic structure of electrocatalysts 27. Recenttheoretical predictions have suggested that monolayer 2H-CrS2exhibits noble metal-like properties in HER 28. Consequently，the Cr-based sulfide/cobalt sulfide heterojunction holds thepromise of serving as an overall water-splitting catalyst withhigh activity and stability， but no synthesis or study has exploredthe relationship between composition/structure and catalyticperformance for this heterojunction.

In this study， we synthesized a series of CrS/CoS2heterojunctions with varying degrees of crystallinity using acontrollable sulfurating approach on cobaltous hydroxide/chromic acetate nanosheets. The charge redistribution at the interfaces， mediated by Cr ―S― Co bonding， optimizes theadsorption of H* and OOH* intermediates on the CrS/CoS2heterojunction， thereby accelerating the rate-determining stepsof HER and OER. The amorphous/highly crystalline structure inthe amorphous CrS/highly crystalline CoS2 heterojunction （ACrS/HC-CoS2） not only facilitates the generation of richinterfaces and exposes more active sites， resulting in high HERand OER activities， but also supports the structural andcompositional evolution of A-CrS/HC-CoS2 during waterelectrolysis， ensuring high HER and OER stability. This workillustrates the value of controllable amorphous-crystallinecoupling in enhancing both catalytic activity and durability，offering a versatile strategy to improve the performance of otherbifunctional transition metal compound electrocatalysts.

2 Results and discussion

The supplemental material includes a description of theexperimental portion. As illustrated in Fig. 1a， we employed astraightforward two-step strategy to prepare CrS/CoS2 heterojunctions with varying degrees of crystallinity. First， wesynthesized cobaltous hydroxide/chromic acetate precursors viaa facile hydrothermal procedure. Field-emission scanningelectron microscopy （FESEM） images of the cobaltoushydroxide/chromic acetate precursor （Fig. S1） confirmed that itconsisted of nanoflower-like structures with 2D wrinklednanosheets interconnected to each other. Then， the CrS/CoS2heterojunctions with different crystallinity were obtained byprecisely controlling the sulfurization process of the cobaltoushydroxide/chromic acetate precursor using sulfur powder as asource， conducted at varying temperatures for 2 h.

X-ray diffraction （XRD） technology was used to analyze thecomposition and crystal structure of the prepared catalysts. Forthe A-CrS/HC-CoS2 sample at 500 °C， the peaks located at32.3°， 36.3°， and 39.9° can be assigned to the （002）， （021）， and（112） planes of CoS2 （JCPDS No. 98-062-4832）， and the peakslocated at 29.9°， 45.7° and 53.2° can associated to the （010），（012） and （110） planes of CrS （JCPDS No. 98-004-9666），indicating the successful formation of A-CrS/HC-CoS2heterojunction （Fig. S2）. Conversely， there was no discernibleXRD diffraction peak for A-CrS/A-CoS2 （sulfurated at 300 °C），indicating the formation of an amorphous CrS/amorphous CoS2heterojunction （Fig. S3a）. The XRD pattern of A-CrS/LC-CoS2（sulfurated at 400 °C） closely resembled that of A-CrS/HC-CoS2but exhibited lower crystallinity in CoS2. Interestingly， uponsulfurization at 600 °C， a significant phase transformation wasobserved， resulting in the formation of the CoCr2S4/CoS1.097heterojunction （Fig. S3b）.

To facilitate comparison， single compounds of CoS2 and CrSwere synthesized by using a similar procedure. The XRDanalysis confirmed that the single-phase CoS2 exhibited highcrystallinity （Fig. S3c）， while the XRD pattern of single-phaseCrS appeared amorphous （Fig. S3d）， indicating that theformation of the CoS2/CrS heterojunction promoted the crystallization of CrS.

Transmission electron microscopy （TEM） images confirmedthe flexible nanosheet morphology of A-CrS/HC-CoS2 （Fig. 1b，c）.High-resolution TEM （HR-TEM） images further verified that ACrS/HC-CoS2 nanosheets had a few-layer structure with athickness of 8.35 nm （Fig. 1d） and consisted of both amorphousCrS and crystalline CoS2 （Fig. 1e，f）. The amorphous CrS domainwas surrounded by crystalline CoS2， creating numerousheterojunction interfaces that facilitated the exposure of moreactive sites. Energy-dispersive spectroscopy （EDS） mappingimages confirmed the uniform distribution of Co， Cr and Selements in A-CrS/HC-CoS2 （Fig. 1g）. Both pure CoS2 and CrSexhibited lamellar morphology， with the distinction being thatCoS2 displayed a highly crystalline state （Fig. S4）， while CrSappeared amorphous （Fig. S5）. In A-CrS/A-CoS2 （Fig. S6）， asignificant number of disordered regions were observed.Similarly， TEM images of A-CrS/LC-CoS2 revealed bothamorphous and crystalline region， with CoS2 exhibiting lowercrystallinity compared to A-CrS/HC-CoS2 （Fig. S7）.Corresponding EDS mapping images of A-CrS/A-CoS2 and ACrS/LC-CoS2 further conformed the uniform distribution of Co，Cr and S elements in CrS/CoS2 heterojunctions. Notably， in theCoCr2S4/CoS1.097 heterojunction （Fig. S8）， two morphologieswere observed： nanowires and nanoparticles. CorrespondingEDS mapping images of CoCr2S4/CoS1.097 indicated unevendistribution of Co， Cr and S elements. These results suggestedthat high-temperature treatment induced Cr to blend into theCoS2 structure， forming a Cr-Co binary metal sulfide. The XRDand TEM findings strongly supported the precise control overthe crystallinity of CrS/CoS2 heterojunctions.

X-ray photoelectron spectroscopy （XPS） was employed toinvestigate the surface chemical compositions and surfacecharge states of the prepared catalysts. The full XPS spectrum（Figs. 2a and S9a） confirms that A-CrS/A-CoS2， A-CrS/LCFig CoS2 A-CrS/HC-CoS2 and CoCr2S4/CoS1.907 all contain Co， Cr，and S elements. Notably， no signal of Cr was detected in CoS2，and no signal of Co was detected in CrS. High-resolution XPSspectra of Co 2p （Fig. 2b） reveal peaks at 782.5 and 798.7 eV，corresponding to the 2p3/2 and 2p1/2 doublets， respectively 29?31.Compared to pure CoS2， the Co 2p3/2 and 2p1/2 peaks in ACrS/HC-CoS2 exhibit a positive shift， which is consistent withother CrS/CoS2 heterojunction （Fig. S9b）. This shift suggests themain existence of Co2+ and strong interactions between CrS andCoS2 32，33. Additionally， low-valence Co was detected inCoCr2S4/CoS1.907 34. The high-resolution XPS spectra of Cr 2pwere split into Cr 2p3/2 and Cr 2p1/2 orbitals， located at 576.2 and585.8 eV， respectively （Fig. 2c） 35?38. The Cr 2p3/2 and Cr 2p1/2peaks in the A-CrS/HC-CoS2 spectra， situated at 577.9 and 587.0eV， respectively （Fig. S9c）， can be assigned to high-valenceCr3+. This may contribute to accelerating the reaction kinetics forboth HER and OER 39. The positive shift of ～1.7 eV in thebinding energy of Cr 2p compared to that of CrS implies electronredistribution in A-CrS/HC-CoS2 40，41. In Fig. 2d， the S 2pspectrum exhibits two prominent peaks at 162.4 and 163.8 eV，corresponding to S 2p3/2 and S 2p1/2， respectively 42. Notably， theS 2p peak in A-CrS/HC-CoS2 slightly shifted toward lowerbinding energy compared to that of CoS2 and CrS. This shift canbe attributed to the lower electronegativity of Cr， leading tocharge redistribution on the CoS2 and CrS interface through theCo―S―Cr bond.

To illustrate the effect of different crystallinities on thecatalytic performance of CrS/CoS2 heterostructures， the aspreparedcatalysts was detected in 1.0 mol?L?1 KOH using atypical three-electrode setup. Fig. 3a，b present the HERpolarization curves and overpotential comparison of A-CrS/HCCoS2，CoS2， CrS， and commercial Pt/C catalysts in alkalinemedia. A-CrS/HC-CoS2 displayed excellent electrochemicalperformance for HER， with overpotentials of only 90.6 and176.1 mV at current densities of 10 and 100 mA?cm?2，respectively， compared with CoS2 （165.9 mV@10mA?cm?2/312.1 mV@100 mA?cm?2） and CrS （173.1 mV@10mA?cm?2/325.4 mV@100 mA?cm?2）. The performance of ACrS/HC-CoS2 also surpassed that of A-CrS/A-CoS2 （173.2mV@10 mA?cm?2/341.1 mV@100 mA?cm?2）， A-CrS/LC-CoS2（155.5 mV@10 mA?cm?2/278.1 mV@100 mA?cm?2） andCoCr2S4/CoS1.097 （167.3 mV@10 mA?cm?2/312.1 mV@100mA?cm?2） （Figs. 3c and S10a）. Notably， the catalyticperformance of A-CrS/HC-CoS2 exceeded that of Pt/C at highcurrent density of ～70 mA?cm?2. The corresponding Tafel slopeof A-CrS/HC-CoS2 （76 mV?dec?1） was also smaller than those of CoCr2S4/CoS1.907 （114 mV?dec?1）， CoS2 （106 mV?dec?1）， CrS（117 mV?dec?1） and other CrS/CoS2 heterojunctions， such as ACrS/A-CoS2 （135 mV?dec?1） and A-CrS/LC-CoS2 （95mV?dec?1）， indicating the faster HER rate of A-CrS/HC-CoS2（Fig. S10b）. The A-CrS/HC-CoS2 catalyst also exhibitedsuperior HER activity compared to CoS2， CrS， A-CrS/A-CoS2，and A-CrS/LC-CoS2 catalysts， suggesting enhanced HERactivity through the synergistic effect between amorphous CrSand highly crystalline CoS2. The stability of the A-CrS/HC-CoS2catalyst was confirmed by long-term Chronoamperometry （CP）testing （Fig. 3d）. The catalytic performance of A-CrS/HC-CoS2catalysts shows significant enhancement during the 20-h test atcurrent density of 50 and 100 mA?cm?2， respectively.Furthermore， the HER performance of A-CrS/HC-CoS2demonstrated competitiveness with most state-of-the-art HERcatalysts （Fig. 3e， Table S1）.

Inspired by the excellent HER activity of the A-CrS/HC-CoS2，its OER performance was further evaluated in alkalineelectrolytes. A-CrS/HC-CoS2 only requires a minimaloverpotential of 370.5 mV to achieve a current density of 50mA?cm?2. This overpotential is not only significantly lower thanthat needed for CoS2 （390.8 mV）， CrS （450.5 mV） and RuO2（410.4 mV）， respectively （Fig. 4a，b）， but also much smaller than415.2， 397.5 and 399.5 mV required for the A-CrS/A-CoS2， ACrS/LC-CoS2 and CoCr2S4/CoS1.097 （Fig. S11a）， respectively.The Tafel slopes， calculated from polarization curves， werefound to be 106 mV?dec?1 for CoS2， 137 mV?dec?1 for CrS， 112mV?dec?1 for RuO2， 80 mV?dec?1 for A-CrS/A-CoS2， 70mV?dec?1 for A-CrS/LC-CoS2， 66 mV?dec?1 for A-CrS/HCCoS2，and 74 mV?dec?1 for CoCr2S4/CoS1.907 （Figs. 4c andS11b）. The lower Tafel slope of A-CrS/HC-CoS2 indicates fasterOER kinetics. The electrochemical stability of A-CrS/HC-CoS2was confirmed by CP curves recorded at a constant currentdensity of 50 and 100 mA?cm?2 （Fig. 4d）， which showed nosignificant potential decay for at least 20 h. Additionally， theOER performance of A-CrS/HC-CoS2 was competitive withmost reported cobalt-based sulfide OER catalysts （Fig. 4e andTable S2）.

Electrochemical impedance spectroscopy （EIS） wasperformed to gain a better understanding of the improved HERand OER performance for A-CrS/HC-CoS2 （Fig. S12）. The EISplots revealed that the charge-transfer resistance （Rct） ofCrS/CoS2 heterojunction， such as A-CrS/A-CoS2 （0.52 Ω）， ACrS/LC-CoS2 （0.33 Ω） and CoCr2S4/CoS1.907 （0.43 Ω） weresmaller than that of CoS2 （0.58 Ω） and CrS （0.66 Ω）. Notably，the Rct of A-CrS/HC-CoS2 （0.12 Ω） is much smaller than that of other CrS/CoS2 heterojunction. These results indicated thathybrid of CrS and CoS2 can significantly reduce impedanceduring electron transport， and optimization of crystallinity inCrS/CoS2 heterojunctions can efficiently minimize chargetransfer resistance 43.

The electrochemical active surface area （ECSA） of theprepared catalysts was also calculated based on the double-layercapacitance obtained from cyclic voltammetry （CV） plots atvarious scan rates （Figs. S13 and S14）. A-CrS/HC-CoS2exhibited a larger Cdl of 12.9 mF?cm?2 compared to CoS2 （7.7mF?cm?2）， CrS （7.1 mF?cm?2）， A-CrS/A-CoS2 （2.6 mF?cm?2）， ACrS/LC-CoS2 （11.2 mF?cm?2） and CoCr2S4/CoS1.907 （10.8mF?cm?2）. The higher Cdl of A-CrS/C-CoS2 can be attributed toits unique amorphous/crystalline few-layer nanosheet structure，which facilitates mass transfer and provides more active sitesduring the HER and OER processes， resulting in enhanced HERand OER activity. These findings suggest that the presence ofamorphous CrS and highly crystalline CoS2 in A-CrS/HC-CoS2not only increases the number of active sites but also improvesintrinsic catalytic ability， leading to enhanced HER and OERperformance.

DFT calculations were conducted to provide further insightsinto the mechanisms underlying the enhanced electrocatalyticactivity achieved by constructing the CrS-CoS2 heterojunction.Based on the XRD and HRTEM analyses， highly exposed CoS2（002） and CrS （012） crystal facets were selected to construct theheterojunction （Figs. S15 and S16）， with a bridge formed by Co-S-Cr interface bonds at the interface （Fig. 5a）. Due to theelectronegativity difference between Cr and Co elements （Co：1.88， Cr： 1.66）， there was a noticeable redistribution of chargedensity at the interface region in the CrS-CoS2 heterojunction 44.Fig. 5b，e show charge density difference plots that illustrate theelectronic density variation at the CrS-CoS2 heterojunctioninterface. These plots reveal that there is stronger electronaccumulation inside the Co―S bond， indicating that electronswere injected into Co sites once the CrS-CoS2 interface wasformed. Conversely， electron depletion can be observed at theCr-S side， which gives Cr centers in CrS species a highervalence， making them more favorable for adsorption of H*，OOH*， and other adsorbed reaction intermediates. This isconsistent with previous experimental results based on XPSanalysis. In conclusion， the DFT calculations successfullydemonstrated that the CrS/CoS2 few-layer heterojunctioneffectively facilitates interface electron transport.

The geometrical configurations and free energy of hydrogenadsorption （ΔGH*） on different reaction sites of CoS2， CrS andCrS/CoS2 heterostructure were shown in Figs. 5c and S17. TheΔGH* on the CrS/CoS2 surface was ?0.08 eV， which is closer tothe thermoneutral state compared to both CoS2 and CrS. Theresult indicates that both fast proton transfer and rapid hydrogenrelease processes occur on CrS/CoS2 heterostructure. Asdepicted in （Fig. 5d）， the Gibbs free energy （ΔG） during the OERprocess with four-electrons pathway were calculated （theproposed reaction pathway of OER process were shown in Figs.S18–S20）. Apparently， the third electron transfer step （*O +H2O → *OOH + H+ + e?） determines the potential determiningstep （PDS） for three catalysts. For pure CrS， the overpotential is2.48 eV， indicating that the nucleophilic attack of OH? is verydifficult in Cr centers. However， after introducing the Cr-S-Cointerface by combining it with CoS2， the overpotential is reducedto 0.43 eV， demonstrating the significant role of constructingCrS/CoS2 heterointerfaces in lowering the thermodynamicenergy barrier and optimizing reaction activity. The d bandcenter is a well-accepted descriptor， which has been widely usedto understand variations in chemisorption energies of variousadsorbates on catalyst surfaces. In general， a high d-band center implies a strong affinity to adsorbates due to less filling ofadsorbate-metal antibonding states. As shown in （Figs. 5f， S21and S22）， Cr sites in CrS possess higher d-band center than Cosites in CoS2， indicating that stronger interaction with reactionintermediate， including OH*， H* and other adsorbates. In otherword， the desorption of H* is difficult in CrS catalyst surfaces.The results are consistent with the previous ΔGH* analysis. ForHER process， an appropriate ΔGH （≈ 0 eV） is vital for effectivecatalytic performance. As a result， when the CrS/CoS2heterojunction has formed， the charge redistribution in theinterface could improve the electronic structure by altering dband center value， which is in favor of water splitting processes.

The performance of the A-CrS/HC-CoS2 catalyst wasevaluated in an overall water splitting and methanol-assisted H2production device consisted of two-electrode configurationswith A-CrS/HC-CoS2 both as cathode and anode were evaluatedin 1 mol?L?1 KOH solution. The bi-functional A-CrS/HC-CoS2demonstrated excellent performance， requiring a cell voltage of1.74 V to achieve a stable current density of 10 mA?cm?2 inoverall water splitting， which was very close to a commercialPt/C//RuO2 counterpart （1.73 V@10 mA?cm?2） （Fig. 6a，b）. Moreimportantly， in methanol-assisted H2 production， the deviceequipped with A-CrS/HC-CoS2 as both cathode and anodeexhibited a low cell voltage of 1.51 V to achieve a currentdensity of 10 mA?cm?2， significantly outperforming thePt/C//RuO2 device （1.70 V@10 mA?cm?2）. The water-splittingdevice equipped with bifunctional A-CrS/HC-CoS2 could beeasily powered by a small solar cell （Fig. 6c）. Moreover， thelong-term stability of the A-CrS/HC-CoS2-based device （Fig.6d） was evaluated， and it exhibited superior stability after 20 h，while the counterpart device （Pt/C//RuO2） exhibited significantperformance degradation within just a few hours. These resultssuggest that A-CrS/HC-CoS2 has the potential to replaceprecious metal catalysts in achieving high-efficiency watersplitting and methanol-assisted H2 production devices. Theassembled A-CrS/HC-CoS2//A-CrS/HC-CoS2 electrolyzer also demonstrated competitiveness compared to other electrolyzersreported in previous studies （Fig. 6e and Table S3）.

To gain a deeper understanding of the electrocatalyticbehaviors， ex situ analyses of structure robustness and surfacecomposition changes of A-CrS/HC-CoS2 after long-termstability tests for both HER and OER were conducted. The XRDpatterns of A-CrS/HC-CoS2 after electrolysis showed that themain peaks of CoS2 and CrS were still present， indicating thatthe crystal structure of the catalyst remained intact duringelectrolysis （Fig. S23）. In the survey spectrum （Fig. S24）， thesignal of Cr in A-CrS/HC-CoS2 after HER decreased comparedto that of fresh A-CrS/HC-CoS2， suggesting partial dissolutionof Cr during the HER process. Interestingly， the fine spectrumof Co in A-CrS/HC-CoS2 after HER and OER exhibited only aslight negative shift compared to fresh A-CrS/HC-CoS2 （Fig.7a）， indicating that the low oxidation state of Co induced by thepotential has high activity， which corresponds to the enhancedactivity observed during HER and OER stability. The highresolutionXPS spectrum of Cr slightly shifts after OER，indicating that the high valence state of Cr was maintainedduring the OER process， while the signal of Cr in A-CrS/HCCoS2after HER was too low to be detected （Fig. 7b）. Partialdissolution of Cr from A-CrS/HC-CoS2 during the HER processwould produce a large number of Cr vacancies， which likelycontributed to the significant enhancement of catalyticperformance during HER. In addition， the S―S bond in ACrS/HC-CoS2 after HER and OER fully transformed into S―Obonds on the surface of A-CrS/HC-CoS2 （Fig. 7c）. The TEMimages showed that the A-CrS/HC-CoS2 nanosheet structurewas well-maintained after HER （Fig. 7d） and OER （Fig. 7h）， andthe STEM images and corresponding mappings of A-CrS/HCCoS2after HER （Fig. 7g） and OER （Fig. 7k） confirmed theelemental distribution of Co， Cr， and S in the A-CrS/HC-CoS2.After the HER process， A-CrS/HC-CoS2 exhibited themorphology of amorphous nanosheets with some CoS2 dotsanchored （Fig. 7e，f）， while after the OER process， A-CrS/HCCoS2underwent restructuring， with amorphous regions formingat the surface edges of the nanosheets （Fig. 7i，j）. This indicatedthe formation of a Co/Cr oxyhydroxides layer. It’s worthemphasizing that the well-maintained amorphous/crystallineheterointerfaces in A-CrS/HC-CoS2 and favorable changes insurface composition contributed to the robust HER and OERstability.

3 Conclusions

In summary， we have prepared CrS/CoS2 heterojunction withvarying degrees of crystallinity and systematically investigatedthe relationship between their microstructure， electronicproperties， electrocatalytic HER/OER performance anddurability. Thanks to the synergistic effect of theamorphous/highly crystalline structure and heterojunction，electronic coupling at the interfaces via the Cr―S―Co bond has been significantly strengthened， and the d-band center has beenfinely tuned. It optimizes H*/OOH* intermediate adsorption andreduces the kinetic barriers of the HER and OER processes，resulting in outstanding HER and OER activity. Theheterojunction interface， coupling amorphous and highlycrystalline morphologies， fully exposes the active sites， therebysignificantly enhancing the HER and OER performance， whichalso facilitates the structural and composition evolution of ACrS/HC-CoS2 during water electrolysis， enabling excellentstability. The HER and OER overpotential of A-CrS/HC-CoS2surpasses that of most other related Co-based compoundcatalysts. As a bifunctional catalyst in a methanol-assistedenergy-saving hydrogen production device， it achieves a currentdensity of 10 mA?cm?2 at a low cell voltage of 1.51 V， making itan excellent candidate among metal-based catalysts. This workprovides a strategy for finely tuning the catalytic activity ofamorphous-crystalline heterojunction electrocatalysts， whichcan be applied to enhance the activity and durability of otherrelated electrocatalysts.

Author Contributions： Conceptualization， S. Lu and M. Jin;Methodology， W. Dou， J. Zhang， L. Wang， C. Wu and H. Yi;Software， R. Wang; Investigation， W. Dou， J. Zhang， L. Wang C.Wu and H. Yi; Writing-Original Draft Preparation， S. Lu， W. Dou，R. Wang， M. Jin; Writing-Review amp; Editing， S. Lu， W. Dou， R.Wang， M. Jin; Supervision， S. Lu and M. Jin; FundingAcquisition， S. Lu， R. Wang and M. Jin. The manuscript waswritten through contributions of all authors. All authors havegiven approval to the final version of the manuscript.

Supporting Information： available free of charge via the internet at http：//www.whxb.pku.edu.cn.

References

（1） Faber， M. S.; Dziedzic， R.; Lukowski， M. A.; Kaiser， N. S.; Ding， Q.;Jin， S. J. Am. Chem. Soc. 2014， 136 （28）， 10053.doi： 10.1021/ja504099w

（2） Huang， G.; Xiao， Z.; Chen， R.; Wang， S. ACS Sustain. Chem. Eng.2018， 6 （12）， 15954. doi： 10.1021/acssuschemeng.8b04397

（3） Liu， Z.; Zhao， L.; Liu， Y.; Gao， Z.; Yuan， S.; Li， X.; Li， N.; Miao， S.Appl. Catal. B-Environ. 2019， 246， 296.doi： 10.1016/j.apcatb.2019.01.062

（4） Lu， S.-Y.; Jin， M.; Zhang， Y.; Niu， Y.-B.; Gao， J.-C.; Li， C. M. Adv.Energ. Mater. 2018， 8 （11）， 1702545. doi： 10.1002/aenm.201702545

（5） Yu， Y.; Rao， P.; Feng， S.; Chen， M.; Deng， P.; Li， J.; Miao， Z.; Kang，Z.; Shen， Y.; Tian， X. Acta Phys. -Chim. Sin. 2023， 39 （8）， 2210039.[于彥會， 饒鵬， 封蘇陽， 陳民， 鄧培林， 李靜， 苗政培， 康振燁，沈義俊， 田新龍. 物理化學(xué)學(xué)報， 2023， 39 （8）， 2210039.]doi： 10.3866/PKU.WHXB202210039

（6） Yu， L.; Huang， X.; Zhang， Q.; Zhang， Z. Acta Phys. -Chim. Sin. 2022，38 （6）， 2109020. [于樂， 黃小清， 張橋保， 張志成. 物理化學(xué)學(xué)報，2022， 38 （6）， 2109020.] doi： 10.3866/PKU.WHXB202109020

（7） Tang， S.; Wang， C.; Pu， X.; Gu， X.; Chen， Z. Acta Phys. -Chim. Sin.2023， 39 （8）， 2212037. [唐生龍， 王春蕾， 蒲想俊， 顧向奎，陳重學(xué). 物理化學(xué)學(xué)報， 2023， 39 （8）， 2212037.]doi： 10.3866/PKU.WHXB202212037

（8） Sun， K.; Zhao， Y.; Yin， J.; Jin， J.; Liu， H.; Xi， P. Acta Phys. -Chim.Sin. 2022， 38 （6）， 2107005. [孫軻， 趙永青， 殷杰， 靳晶， 劉翰文，席聘賢. 物理化學(xué)學(xué)報， 2022， 38 （6）， 2107005.]doi： 10.3866/PKU.WHXB202107005

（9） Feng， L. L.; Yu， G.; Wu， Y.; Li， G. D.; Li， H.; Sun， Y.; Asefa， T.;Chen， W.; Zou， X. J. Am. Chem. Soc. 2015， 137 （44）， 14023.doi： 10.1021/jacs.5b08186

（10） Gao， Z.; Li， M.; Wang， J.; Zhu， J.; Zhao， X.; Huang， H.; Zhang， J.;Wu， Y.; Fu， Y.; Wang， X. Carbon 2018， 139， 369.doi： 10.1016/j.carbon.2018.07.006

（11） Li， Y.; Sun， Y.; Qin， Y.; Zhang， W.; Wang， L.; Luo， M.; Yang， H.;Guo， S. Adv. Energy Mater. 2020， 10 （11）， 1903120.doi： 10.1002/aenm.201903120

（12） Zhang， L.; Zhang， J.; Fang， J.; Wang， X. Y.; Yin， L.; Zhu， W.; Zhuang，Z. Small 2021， 17 （28）， 2100832. doi： 10.1002/smll.202100832

（13） Wang， S. Acta Phys. -Chim. Sin. 2021， 37 （7）， 2011013. [王雙印.物理化學(xué)學(xué)報， 2021， 37 （7）， 2011013.]doi： 10.3866/PKU.WHXB202011013

（14） Guo， Y.; Gan， L.; Shang， C.; Wang， E.; Wang， J. Advan. Funct. Mater.2017， 27 （5）， 1602699. doi： 10.1002/adfm.201602699

（15） Zhu， Y.; Song， L.; Song， N.; Li， M.; Wang， C.; Lu， X. ACS Sustain.Chem. Eng. 2019， 7 （3）， 2899. doi： 10.1021/acssuschemeng.8b05462

（16） Chen， B.; Wang， J.; He， S.; Shen， Y.; Huang， S.; Zhou， H. J. Alloy.Compd. 2023， 948， 169655. doi： 10.1016/j.jallcom.2023.169655

（17） Lu， S.-Y.; Li， S.; Jin， M.; Gao， J.; Zhang， Y. Appl. Catal. B-Environ.2020， 267， 118675. doi： 10.1016/j.apcatb.2020.118675

（18） Peng， W.; Wang， Z.; Lu， R.; Li， Q.; Wang， Z.; Zhao， Y.; Xu， L.; Mai，L. Chem. Eng. J. 2023， 457， 141173. doi： 10.1016/j.cej.2022.141173

（19） Han， L.; Wu， Y.; Zhao， B.; Meng， W.; Zhang， D.; Li， M.; Pang， R.;Zhang， Y.; Cao， A.; Shang， Y. ACS Appl. Mater. Interfaces 2022， 14（27）， 30847. doi： 10.1021/acsami.2c06122

（20） Xu， H.; Zhang， W. D.; Yao， Y.; Yang， J.; Liu， J.; Gu， Z. G.; Yan， X.J. Colloid Interface Sci. 2022， 629， 501.doi： 10.1016/j.jcis.2022.09.072

（21） Jin， M.; Lu， S.-Y.; Ma， L.; Gan， M.-Y.; Lei， Y.; Zhang， X.-L.; Fu， G.;Yang， P.-S.; Yan， M.-F. J. Power Sources 2017， 341， 294.doi： 10.1016/j.jpowsour.2016.12.013

（22） Zhang， J.; Xiao， B.; Liu， X.; Liu， P.; Xi， P.; Xiao， W.; Ding， J.; Gao，D.; Xue， D. J. Mater. Chem. A 2017， 5 （33）， 17601.doi： 10.1039/c7ta05433e

（23） Zhang， J.; Liu， Y.; Sun， C.; Xi， P.; Peng， S.; Gao， D.; Xue， D. ACSEnergy Lett. 2018， 3 （4）， 779. doi： 10.1021/acsenergylett.8b00066

（24） Xie， M.; Li， C.; Zhang， S.; Zhang， Z.; Li， Y.; Chen， X. B.; Shi， Z.;Feng， S. Small 2023， 2301436. doi： 10.1002/smll.202301436

（25） Yang， L.; Huang， L.; Yao， Y.; Jiao， L. Appl. Catal. B-Environ. 2021，282， 119584. doi： 10.1016/j.apcatb.2020.119584

（26） Han， K. H.; Seok， J. Y.; Kim， I. H.; Woo， K.; Kim， J. H.; Yang， G. G.;Choi， H. J.; Kwon， S.; Jung， E. I.; Kim， S. O. Adv. Mater. 2022， 34（34）， 2203992. doi： 10.1002/adma.202203992

（27） Shifa， T. A.; Gradone， A.; Yusupov， K.; Ibrahim， K. B.; Jugovac， M.;Sheverdyaeva， P. M.; Rosen， J.; Morandi， V.; Moras， P.; Vomiero， A.Chem. Eng. J. 2023， 453， 139781. doi： 10.1016/j.cej.2022.139781

（28） Sun， F.; Hong， A.; Zhou， W.; Yuan， C.; Zhang， W. Mater. Today 2020，25， 101707. doi： 10.1016/j.mtcomm.2020.101707

（29） Fang， B.; He， N.; Li， Y.; Lu， T.; He， P.; Chen， X.; Zhao， Z.; Pan， L.Electrochim. Acta 2023， 448， 142187.doi： 10.1016/j.electacta.2023.142187

（30） Wu， Q.; Liu， L.; Guo， H.; Li， L.; Tai， X. J. Alloy. Compd. 2020， 821，153219. doi： 10.1016/j.jallcom.2019.153219

（31） Ma， X.; Wang， J.; Liu， D.; Kong， R.; Hao， S.; Du， G.; Asiri， A. M.;Sun， X. New J. Chem. 2017， 41 （12）， 4754. doi： 10.1039/c7nj00326a

（32） Hao， J.; Yang， W.; Peng， Z.; Zhang， C.; Huang， Z.; Shi， W. ACSCatal. 2017， 7， 4214. doi： 10.1021/acscatal.7b00792

（33） Jin， M.; Wang， R.; Jia， B.; Zhang， J.; Liu， H.; Lu， S.-Y. Appl. Surf.Sci. 2022， 591， 153201. doi： 10.1016/j.apsusc.2022.153201

（34） Wang， P.; Bai， P.; Mu， J.; Jing， J.; Wang， L.; Su， Y. J. ColloidInterface Sci. 2023， 642， 1. doi： 10.1016/j.jcis.2023.03.133

（35） Cao， X.; Wang， T.; Qin， H.; Lin， G.; Zhao， L.; Jiao， L. Nano Res.2022， 16 （3）， 3665. doi： 10.1007/s12274-022-4635-5

（36） Cao， F.; Li， M.; Hu， Y.; Wu， X.; Li， X.; Meng， X.; Zhang， P.; Li， S.;Qin， G. Chem. Eng. J. 2023， 472， 144970.doi： 10.1016/j.cej.2023.144970

（37） Zhang， S.-H.; Wu， M.-F.; Tang， T.-T.; Xing， Q.-J.; Peng， C.-Q.; Li， F.;Liu， H.; Luo， X.-B.; Zou， J.-P.; Min， X.-B.; et al. Chem. Eng. J. 2018，335， 945. doi： 10.1016/j.cej.2017.10.182

（38） Wu， Y.; Tao， X.; Qing， Y.; Xu， H.; Yang， F.; Luo， S.; Tian， C.; Liu， M.;Lu， X. Adv. Mater. 2019， 31 （15）， 1900178.doi： 10.1002/adma.201900178

（39） Dong， C.; Yuan， X.; Wang， X.; Liu， X.; Dong， W.; Wang， R.; Duan，Y.; Huang， F. J. Mater. Chem. A 2016， 4 （29）， 11292.doi： 10.1039/c6ta04052g

（40） Liu， D.; Tong， R.; Qu， Y.; Zhu， Q.; Zhong， X.; Fang， M.; Ho Lo， K.;Zhang， F.; Ye， Y.; Tang， Y.; et al. Appl. Catal. B-Environ. 2020， 267，118721. doi： 10.1016/j.apcatb.2020.118721

（41） Zhu， L.; Susac， D.; Teo， M.; Wong， K.; Wong， P.; Parsons， R.;Bizzotto， D.; Mitchell， K.; Campbell， S. J. Catal. 2008， 258 （1）， 235.doi： 10.1016/j.jcat.2008.06.016

（42） Jin， M.; Lu， S.-Y.; Zhong， X.; Liu， H.; Liu， H.; Gan， M.; Ma， L. ACSSustain. Chem. Eng. 2020， 8 （4）， 1933.doi： 10.1021/acssuschemeng.9b06329

（43） Lu， S. Y.; Wang， J.; Wang， X.; Yang， W.; Jin， M.; Xu， L.; Yang， H.;Ge， X.; Shang， C.; Chao， Y.; et al. Small Methods 2022， 6 （6），2101551. doi： 10.1002/smtd.202101551

（44） Fu， T.; Li， Z. Chem. Eng. Sci. 2015， 135， 3.doi： 10.1016/j.ces.2015.03.007

中國科協(xié)青年人才托舉工程（2021QNRC001）， 重慶市自然科學(xué)基金（CSTB2022NSCQ-MSX0557， cstc2020jcyj-msxmX0670， 2023NSCQ-MSX3724）， 重慶科技學(xué)院人才引進項目（ckrc2021050， ckrc20230401， ckrc2021053）， 重慶市教委科學(xué)技術(shù)研究計劃項目（KJQN202001525， KJQN202201532，KJQN202301542），國家自然科學(xué)基金（22109016）及中國材料基因工程高通量計算平臺開放研究基金（CNMGE2023016）資助