Effect of graphene templated fluorides of Ce and La on the de/rehydrogenation behavior of MgH2

The present investigation describes the hydrogen storage properties of MgH₂ ball milled with different additives i.e. graphene templated rare earth metal (La and Ce) fluorides, CeF₄ and LaF₃. MgH₂ ball milled with graphene templated CeF₄ (MgH₂:CeF₄@Gr) has onset desorption temperature of 245 °C, which is 50 °C, 52 °C and 75 °C lower than MgH₂ ball milled with LaF₃ templated graphene, CeF₄ and LaF₃ respectively. CeF₄@Gr also shows the superior effect amongst all additives during rehydrogenation where MgH₂:CeF₄@Gr absorbs 5.50 wt% within 2.50 min at 300 °C under 15 atm H₂ pressure. Dual tuning effect, i.e. lowering of thermodynamic (62.77 kJ/mol H₂: lower from 74 kJ/mol for pristine MgH₂) and kinetics barrier (93.01 kJ/mol) has been observed for MgH₂:CeF₄@Gr. Additionally, MgH₂ ball milled with CeF₄@Gr shows good reversibility up to 24 cycles of de/rehydrogenation. The feasible working mechanism of CeF₄@Gr as additive for MgH₂ has been studied in detail with the help of Transmission Electron Microscope (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction characterizations (XRD).     

Multiple improvements of hydrogen sorption and their mechanism for MgH2 catalyzed through TiH2@Gr

The present investigation reports the effect of TiH₂ templated over graphene (TiH₂@Gr) on the hydrogen sorption characteristics of MgH₂/Mg. The as synthesized TiH₂@Gr leads to significant effect on sorption in MgH₂ by the following effects: the first is dehydrogenation of MgH₂–TiH₂@Gr, which leads to the conversion of some part of TiH₂ into TiH_1.924. TiH₂ together with TiH_1.924 works as a better catalyst than TiH₂ alone. The second is ball-milling of TiH₂@Gr, which produces defective graphene, which also works as co-catalyst. The third is anchoring of TiH₂ on graphene, which does not allow the catalyst to agglomerate. The catalytic effect of TiH₂@Gr on MgH₂ is found to be better than Ti@Gr and TiO₂@Gr. The onset desorption temperature for MgH₂–TiH₂@Gr is ~204 °C, which is 31 °C and 36 °C lower than MgH₂–Ti@Gr, MgH₂–TiO₂@Gr respectively. The better catalytic behavior of TiH₂@Gr also persists during de/re-hydrogenation kinetics and cycling study of MgH₂. The feasible mechanism for superior catalytic for TiH₂@Gr on MgH₂ has been put forward.     

S,N co-doped graphene quantum dots decorated TiO2 and supported with carbon for oxygen reduction reaction catalysis

Sluggish kinetics and catalyst instability in oxygen reduction reaction are the central issues in fuel cell and metal-air battery technologies. For that, highly active, stable, and low-cost non-platinum based electrocatalysts for oxygen reduction reaction are an immediate requirement in fuel cell and metal-air battery technologies. A new composite (S,N-GQD/TiO₂/C-800) is synthesized, made of sulfur (S) and nitrogen (N) co-doped graphene quantum dot (GQD) with TiO₂. This composite is supported on carbon on heating at 800 °C under N₂ atmosphere and is explored for oxygen reduction reaction (ORR) catalyst. The synthesized composite S,N-GQD/TiO₂/C-800, shows outstanding catalytic activity with an onset potential of 0.91 V and a half-wave potential of 0.82 V vs. RHE, an alkaline medium. The Tafel slope of the catalyst is 61 mV dec^?1. The catalyst is an excellent methanol tolerant and shows good stability in an alkaline medium. The excellent ORR activity of S,N-GQD/TiO₂/C-800 is ascribed to well-built interactivity between the S,N-GQD/TiO₂, and the carbon support. The unique structure offers advantages, with outstanding electrical conductivity, high surface area, and excellent charge transfer kinetics between the doped GQD and TiO₂ interface and subsequently from the carbon surface to the S,N-GQD/TiO_2.     

Branched multiphase TiO2 with enhanced photoelectrochemical water splitting activity

An efficient hierarchical structure, nano-branch containing anatase TiO₂ nanofibers and rutile nanorods, was prepared via the combination of the electrospinning and hydrothermal processes. This novel configuration of TiO₂ multiphase possessed higher surface area, roughness, and fill factors compared with each single phase component prepared in the same condition, which significantly enhanced its light absorption. Our experimental results showed that within the interface of multiphase TiO₂, the heterojunction promoted the charge separation and improved the charge transfer rate, leading to higher efficiency for photoelectrochemical water splitting. The photocurrent density of the nano-branched TiO₂ electrode could reach 0.95 mA/cm², which was almost twice as large as that of the pristine TiO₂ nanorod. Our work provides a simple and feasible routine to synthesize complex TiO₂ nanoarchitectures, which lays a foundation for improving energy storage and conversion efficiency of TiO₂-based photoelectrodes.     

Novel synthesis of graphene oxide/In2S3/TiO2 NRs heterojunction photoanode for enhanced photoelectrochemical (PEC) performance

Novel heterostructure photocatalyst built from titanium dioxide (TiO₂), graphene oxide (GO) and indium sulfide (In₂S₃) has been successfully prepared for photoelectrochemical hydrogen production. The stepwise introduction of three materials on conductive glass substrate has been realized through hydrothermal, electrochimical and spin coating deposition methods, respectively. The structure, morphology, composition, optical and photoelectrochemical properties of the resultant photoanodes were investigated in detail. The presence of GO in the heterostructure film was confirmed by Raman analysis with D and G band intensity. Surface morphology analysis of the GO/In₂S₃/TiO₂ NRs structure reveal the homogenous distribution of graphene oxide on In₂S₃/TiO₂ NRs surface. From UV–Vis analysis, band gap energy of the samples decreases gradually from 3.34 eV (TiO₂ NRs) to 3.12 eV, with In₂S₃ and GO addition. The electrochemical impedance spectroscopy (EIS) further confirmed that GO/In₂S₃/TiO₂NRs heterostructure possessed the lowest charge-transfer resistance, revealing that In₂S₃ and GO could significantly accelerate the electron mobility compared with bare TiO₂. From Mott-Schottky plots, several parameters such as flat-band potential and free carrier concentration were determined. Next, The GO/In₂S₃/TiO₂ NRs electrode achieved remarkably improved current density (0.45 mAcm² at 0.8 V vs Ag/AgCl) compared to pure TiO₂ NRs or In₂S₃/TiO₂ NRs electrodes, which attributes to the uniform structure and excellent electrical conductivity of GO, which could reduce the combination rate of the photo electron-hole pairs. These results reveal that GO/In₂S₃/TiO₂ NRs possesses great potential toward the development of newly synthesizable catalysts in the field of photoelectrochemical water splitting.     

Hydrothermal synthesis of mixed crystal phases TiO2–reduced graphene oxide nanocomposites with small particle size for lithium ion batteries

A rutile and anatase mixed crystal phase of nano-rod TiO₂ and TiO₂–reduced graphene oxide (TiO₂–RGO) nanocomposites with small particle size were prepared via a facile hydrothermal approach with titanium tetrabutoxide and graphene oxide as the precursor. Hydrolysis of titanium tetrabutoxide and mild reduction of graphene oxide were simultaneously carried out. Compared with traditional multistep methods, a novel green synthetic route to produce TiO₂–RGO without toxic solvents or reducing agents was employed. TiO₂–RGO as anode of lithium ion batteries was characterized by extensive measurements. The nanocomposites exhibited notable improvement in lithium ion insertion/extraction behavior compared with TiO₂, indicating an initial irreversible capacity and a reversible capacity of 295.4 and 112.3 mA h g⁻¹ for TiO₂–RGO after 100 cycles at a high charge rate of 10 C. The enhanced electrochemical performance is attributed to increased conductivity in presence of reduced graphene oxide in TiO₂–RGO, a rutile and anatase mixed crystal phase of nano-rod TiO₂/GNS composites, small size of TiO₂ particles in nanocomposites, and enlarged electrode–electrolyte contact area, leading to more electroactive sites in TiO₂–RGO.     

A green and facile synthesis of TiO2/graphene nanocomposites and their photocatalytic activity for hydrogen evolution

This work reports a green and facile approach to synthesize chemically bonded TiO₂/graphene sheets (GS) nanocomposites using a one-step hydrothermal method. The as-prepared composites were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and ultraviolet visible (UV-Vis) diffuse reflectance spectra. The photocatalytic activity was evaluated by hydrogen evolution from water splitting under UV-Vis light illumination. An enhancement of photocatalytic hydrogen evolution was observed over the TiO₂/GS composite photocatalysts, as 1.6 times larger for TiO₂/2.0 wt%GS than that of Degussa P25. This fabrication process features the reduction of graphene oxide and formation of TiO₂ simultaneously leading to the well dispersion of generated TiO₂ nanoparticles on the surface of GS.     

Photocatalytic hydrogen evolution on graphene quantum dots anchored TiO2 nanotubes-array

The inversely structured TiO₂ nanotubes-array (TiO₂-NA) and CdS-modified TiO₂ nanotubes-array (CdS/TiO₂-NA) with graphene quantum dots (GQDs) anchored inside were prepared through a facile impregnation method. The catalysts were characterized by multiple techniques of SEM, TEM, XRD, Raman spectroscopy, XPS, TG and diffuse reflectance UV/Vis absorption spectroscopy. The results of TEM, XPS and Raman spectroscopy indicate that the GQDs were really formed and successfully anchored into the TiO₂-NA and CdS/TiO₂-NA. The activity evaluation results show that the hydrogen evolution rate during photocatalytic water splitting was greatly improved after loading GQDs into TiO₂-NA and CdS/TiO₂-NA. By breaking graphene into GQDs, the light-filtering effect of graphene was remarkably inhibited as compared with that of conventional large graphene sheets. Moreover, the overall morphology of TiO₂ nanotube array could be well maintained after anchoring GQDs inside, which is favorable to mass transfer. The catalyst design strategy proposed in present work can be extended to other photocatalytic systems.     

Enhanced performance for photocatalytic hydrogen evolution using MoS2/graphene hybrids

A MoS₂/graphene hybrid (MSG) is synthesized by microwave hydrothermal method. Both of the charge transfer resistance and the photocurrent are tuned in graphene modified MoS₂ by enhancing photocatalytic nature, where the charge transfer resistance significantly decreases from 36,000 Ω–8.49 Ω and the photocurrent promotes from 0.29 mA cm^?2 to 16.47 mA cm^?2. In this article, the result reveals that the appropriate modification of graphene can reach the maximum yield of hydrogen gas. In addition, the appropriate conditions, such as the concentration of 0.32 M formic acid and the MoS₂ photocatalyst with 0.8 wt% graphene (MSG_0.8) dose of 0.013 g L^?1, can complete the outstanding photocatalytic hydrogen evolution, where the hydrogen evolution using MSG_0.8 composite photocatalyst has the maximum yield of 667.2 μmol h^?1 g^?1.     

Enhanced photocatalytic hydrogen evolution from reduced graphene oxide-defect rich TiO2-x nanocomposites

Solar-driven photocatalytic hydrogen generation by splitting water molecules requires an efficient visible light active photocatalyst. This work reports an improved hydrogen evolution activity of visible light active TiO_2-x photocatalyst by introducing reduced graphene oxide via an eco-friendly and cost-effective hydrothermal method. This process facilitates graphene oxide reduction and incorporates intrinsic defects in TiO₂ lattice at a one-pot reaction process. The characteristic studies reveal that RGO/TiO_2-x nanocomposites were sufficiently durable and efficient for photocatalytic hydrogen generation under the visible light spectrum. The altered band gap of TiO_2-x rationally promotes the visible light absorption, and the RGO sheets present in the composites suppresses the electron-hole recombination, which accelerates the charge transfer. Hence, the noble metal-free RGO/TiO_2-x photocatalyst exhibited hydrogen production with a rate of 13.6 mmol h^?1g^?1_cat. under solar illumination. The appreciable photocatalytic hydrogen generation activity of 947.2 μmol h^?1g^?1_cat with 117 μAcm^?2 photocurrent density was observed under visible light (>450 nm).     

A ternary Ag/TiO2/CNT photoanode for efficient photoelectrochemical water splitting under visible light irradiation

A ternary Ag/TiO₂/CNT photoanode was prepared by grafting Ag nanoparticles on the surface of as-synthesized TiO₂/CNT nanocomposite for the photoelectrochemical (PEC) water splitting under visible light irradiance. The ternary composite photoanode was observed to generate four times higher photocurrent density compared to binary TiO₂/CNT nanocomposite under visible light irradiance. The Ag nanoparticles on the surface of nanocomposite act as a surface plasmon resonance (SPR) photosensitizer under visible light. The enhanced photocurrent density of Ag/TiO₂/CNT ternary photoanode is attributed to the increased light absorption in the visible region, decrease in band-bending and effective interfacial electron transfer due to the synergetic effect of Ag nanoparticles and CNTs. The enhanced charge transfer within the Ag/TiO₂/CNT was also confirmed by the electrochemical impedance spectroscopy. This work demonstrates a feasible route to improve the PEC performance of TiO₂ towards water splitting under sunlight irradiation.     

Eosin Y functionalized graphene for photocatalytic hydrogen production from water

Chemically reduced graphene oxide (RGO) can be functionalized by eosin Y (EY). The formation of the stable aqueous EY functionalized graphene (EY-RGO) suspension is due to the non-covalent interaction between EY and RGO surface via hydrogen bonding and π-π stacking. EY-RGO was characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Spectral and photoelectrochemical studies indicate that photoinduced electron transfer occurs from EY to RGO. The EY-RGO is photocatalytic active for water reduction to produce hydrogen. The average production rate of H₂ for the photocatalyst (w_EY/w_RGO = 1) in a 10 vol% triethanolamine aqueous solution can reach 3.35 mmol g⁻¹ h⁻¹ and 0.40 mmol g⁻¹ h⁻¹ under 30 h UV-vis and 10 h visible light irradiation, respectively. The photocatalytic activity of EY-RGO is superior to that of RGO, graphene oxide (GO), and EY-GO. Modification EY-RGO with Pt nanoparticles can further improve photocatalytic activity. All these features demonstrated that organic sensitizers functionalized graphene provided a nice candidate as a photocatalyst for H₂ generation from water under solar light irradiation.     

Single-step anodization for synthesis of hierarchical TiO2 nanotube arrays on foil and wire substrate for enhanced photoelectrochemical water splitting

A hierarchical nanoporous-TiO₂ nanotube composite structure consisting of a nanoporous top layer with smooth underlying nanotubes was obtained by a single-step anodization technique. The growth of such composite structure has also been applied to Ti wire substrate for the first time. The photoelectrochemical performance was examined under AM 1.5 simulated solar irradiation in 1 M KOH electrolyte. In general, the hierarchical architecture demonstrated improved photoelectrochemical activity over plain TiO₂ nanotubes. Furthermore, the composite structure on a wire substrate was also found to enhance photoelectrochemical activity over a foil substrate. Under optimized conditions, over a 40% increase in hydrogen generation for hierarchical nanotubes over plain nanotubes is observed and over 25% increase in hydrogen generation using a wire substrate over a foil substrate is observed.     

Enhanced photocatalytic activities of three-dimensional graphene-based aerogel embedding TiO2 nanoparticles and loading MoS2 nanosheets as Co-catalyst

A novel graphene-based three-dimensional (3D) aerogel embedded with two types of functional nanomaterials had been prepared by a facile one-pot hydrothermal process. During the hydrothermal reaction, graphene, TiO₂ nanoparticles and MoS₂ nanosheets were self-assembled into the 3D interconnected networks aerogel, where the uniformly dispersed TiO₂ nanoparticles were densely anchored onto the graphene nanosheets and decorated with the ultrathin MoS₂ nanosheets. The UV–vis DRS and PL spectra measurement shows that the MoS₂/P25/graphene aerogel exhibits enhanced light absorption and efficient charge separation properties. As a new photocatalyst, the photocatalytic activity was evaluated by photoelectrochemical test and photodegradation methyl orange (MO) under UV irradiation, an improvement of photocurrent was observed, as 6 times higher for MoS₂/P25/graphene aerogel (37.45 mA/cm²) than pure P25 at +0.6 V, and the fastest photodegradation of MoS₂/P25/graphene aerogel was found within 15 min. The improved photocatalytic activity is attributed to the porous structure, good electrical conductivity and the maximization of accessible sites of the unique 3D graphene aerogel, the increasing active adsorption sites and photocatalytic reaction centers for the introduction of MoS₂ nanosheets, and the positive synergetic effect between the three components in this hybrid. This work demonstrates that the as-prepared MoS₂/P25/graphene aerogel may have a great potential application in photoelectrochemical hydrogen production and pollution removal.     

TiO2 nanoparticles modified with ZnIn2S4 nanosheets and Co-Pi groups: Type II heterojunction and cocatalysts coexisted photoanode for efficient photoelectrochemical water splitting

The optimization of photoelectrode is the key issue for the efficient photoelectrochemical water splitting process. In this work, the TiO₂ photoanode is synthesized and modified with ZnIn₂S₄ nanosheets and Co-Pi cocatalyst (TiO₂/ZnIn₂S₄/Co-Pi) for a favorable photoelectrochemical performance. The synthesis and modification process of the TiO₂ photoanode are optimized. The physical and chemical characterizations indicate that the TiO₂ has a nano-cauliflower-like structure and rutile crystal form modified with a network hexagonal ZnIn₂S₄ nanosheets and amorphous Co-Pi groups. After optimization of the hydrothermal and annealing process, the optimized TiO₂ photoanode manifests a photocurrent density of 1.82 mA cm^?2, 1.73-fold of the pristine TiO₂ photoanode (1.05 mA cm^?2). With the surficial ZnIn₂S₄ and Co-Pi modification, the photocurrent density of the TiO₂/ZnIn₂S₄/Co-Pi photoanode is raised to 5.05 mA cm^?2, 5.32-fold of the optimized TiO₂ photoanode (1.82 mA cm^?2). The applied bias photon-to-current efficiency, the charge separation and injection efficiencies of the TiO₂/ZnIn₂S₄/Co-Pi photoanodes are 8.79, 3.40, and 1.64-folds of the optimized TiO₂ photoanode. Combined the Tauc plot, valence band XPS spectra, EIS and Mott-Schottky analysis, the PEC water splitting mechanism could be that: (i) the type II heterojunction formed by the TiO₂ and ZnIn₂S₄ semiconductors improves the charge separation/injection efficiencies; (ii) the Co-Pi groups facilitate the oxygen evolution kinetics; (iii) the Co-Pi groups and 2D ZnIn₂S₄ nanosheets synergistically enhance the charge separation efficiency. This investigation could offer a prospect of practical implementation for photoelectrochemical water splitting.     

TiO2 nanotubes for hydrogen generation by photocatalytic water splitting in a two-compartment photoelectrochemical cell

Highly ordered TiO₂ nanotube arrays for hydrogen production have been synthesized by electrochemical anodization of titanium sheets. Under solar light irradiation, hydrogen generation by photocatalytic water splitting was carried out in the two-compartment photoelectrochemical cell without any external applied voltage. The hydrogen gas and oxygen generated on Pt side and on TiO₂ nanotubes side respectively were efficiently separated. The effect of anodization time on the morphology structures, photoelectrochemical properties and hydrogen production was systematically investigated. Due to more charge carrier generation and faster charge transfer, a maximum photoconversion efficiency of 4.13% and highest hydrogen production rate of 97 μmol h⁻¹cm⁻² (2.32 mL h⁻¹cm⁻²) were obtained from TiO₂ nanotubes anodized for 60 min.     

Nanocomposite of graphene oxide with nitrogen-doped TiO2 exhibiting enhanced photocatalytic efficiency for hydrogen evolution

The application of hydrogen energy potentially addresses energy and environmental problems. In order to improve the photocatalytic efficiency, nanocomposite of N-doped TiO₂ with graphene oxide (NTG) is prepared and characterized with Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), photoluminescent spectra. The application of NTG to hydrogen evolution exhibits high photocatalytic efficiency of 716.0 or 112.0 μmol h⁻¹ g⁻¹ under high-pressure Hg or Xenon lamp, which is about 9.2 or 13.6 times higher than P25 photocatalyst. This is mainly attributed to the N-doping of TiO₂ and the incorporation of graphene oxide resulting in narrow band gap, together with the synergistic effect of fast electron-transporting of photogenerated electrons and the efficient electron-collecting of graphene oxide retarding charge recombination. These results provide a significant theoretical foundation for the potential application of N-doping photocatalysts to hydrogen evolution.     

Direct Z-scheme anatase/rutile bi-phase nanocomposite TiO2 nanofiber photocatalyst with enhanced photocatalytic H2-production activity

Design and preparation of direct Z-scheme anatase/rutile TiO₂ nanofiber photocatalyst to enhance photocatalytic H₂-production activity via water splitting is of great importance from both theoretical and practical viewpoints. Herein, we develop a facile method for preparing anatase and rutile bi-phase TiO₂ nanofibers with changing rutile content via a slow and rapid cooling of calcined electrospun TiO₂ nanofibers. The phase structure and composition, surface morphology, specific surface area, surface chemical composition and element chemical states of TiO₂ nanofibers were analyzed by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), nitrogen adsorption and X-ray photoelectron spectroscopy (XPS). By a rapid cooling of 500 °C-calcined electrospun TiO₂ precursor, anatase/rutile bi-phase TiO₂ nanofibers with a roughly equal weight ratio of 55 wt.% anatase and 45 wt.% rutile were prepared. The enhanced H₂ production performance was observed in the above obtained anatase/rutile composite TiO₂ nanofibers. A Z-scheme photocatalytic mechanism is first proposed to explain the enhanced photocatalytic H₂-production activity of anatase/rutile bi-phase TiO₂ nanofibers, which is different from the traditional heterojunction electron–hole separation mechanism. This report highlights the importance of phase structure and composition on optimizing photocatalytic activity of TiO₂-based material.     

Correlation between microstructural defects and photoelectrochemical performance of 1D Ti–Nb composite oxide photoanodes for solar water splitting

We report on the optimized fabrication of ultrathin wall nanotubes grown on Ti–Nb alloy via anodization in organic-based electrolytes. The nanotubes are vertically aligned with wall thicknesses of 5–8 nm, diameters of 180–200 nm, and lengths of 2–2.8 μm. Raman spectroscopy and glancing angle x-ray diffraction (GAXRD) measurements indicated the formation of composite oxides of anatase TiO₂ and monoclinic Nb₂O₅. The composite oxides showed better stability at elevated temperatures up to 650 ᵒC and with much smaller induced microstrain compared to the TiO₂ counterpart. X-ray photoelectron spectroscopy (XPS) analysis confirmed the composition of the fabricated nanotubes as a mixed TiO₂–Nb₂O₅ composite. Upon their use as photoanodes to split water, the composite TiO₂–Nb₂O₅ NTs showed almost 2-fold increase in the obtained photocurrent compared to that of bare TiO₂ NTs prepared under the same conditions. Moreover, the incident photon to current efficiency (IPCE) of the mixed oxide nanotubes was higher than that of bare TiO₂ with a positive shift towards longer wavelengths, indicating improved electron mobility and charge collection. Hence, the addition of Nb resulted in the formation of thermally stable and photoactive photoanodes for solar fuel production.     

Preparation and electrochemical hydrogen storage properties of Co9S8 alloy coated with cobalt/graphene composite

A facile one-pot reduction process is used to obtain the cobalt/graphene composite (CoRGO). The CoRGO materials exhibit unique reticular globular morphology. Co₉S₈ hydrogen storage alloy is fabricated via mechanical alloying method. Different amounts of CoRGO are coated on the surface of Co₉S₈ alloy by ball milling. The electrochemical characterizations of the composites are conducted in the standard tri-electrode system. Ultimately, the CoRGO coated Co₉S₈ electrode shows preferable performance than the RGO modified alloy (603.6 mAh/g) and original alloy (577.3 mAh/g). As the additive content of CoRGO is 6 wt%, a maximum discharge capacity of 637.5 mAh/g is obtained. Furthermore, the cycle stability and high-rate dischargeability of the electrode are also enhanced. The Co particles in the CoRGO participate in the reversible redox reactions and the graphene provides high conductivity. The CoRGO with distinctive structure and morphology can not only improve the electrocatalytic activity but also increase the specific surface area of Co₉S₈ alloy. The cobalt and graphene species in the CoRGO composite serve a synergistic effect in further facilitating the hydrogen diffusion, expediting the charge transfer in/on the alloy and improving the corrosion resistance, thus enhancing the electrochemical performance and reaction kinetics of Co₉S₈ alloy.