Electrochemical reduction induced self-doping of oxygen vacancies into Ti–Si–O nanotubes as efficient photoanode for boosted photoelectrochemical water splitting

Self-doping of oxygen vacancies (V_O) states into TiO₂-based nanotubes was an efficient way for improving photoelectrochemical (PEC) water splitting properties. Here we induced oxygen vacancies into Si-doped TiO₂ (Ti–Si–O) nanotubes on Ti–Si alloy via a facile electrochemical surface reduction, and applied it for PEC water splitting. Systematic studies revealed that the self-doped oxygen vacancies not only promoted optical absorption of the doped nanotubes but also enhanced separation-transport processes of the photo-generated charge carriers, and thus resulted in improved PEC water splitting properties. The V_O/Ti–Si–O co-doping system exhibited a higher photocurrent density of 1.63 mA/cm² at 0 V vs. Ag/AgCl. Corresponding solar-to-hydrogen efficiency could reach 0.81%, which was about 5.4 times that of undoped TiO₂. It's believed that elements doping and oxygen vacancies self-doping synergistic strategy employed in this work, may provide theoretical and practical significance for designing and fabricating efficient TiO₂-based nanostructures photoanodes in PEC water splitting for boosted solar-to-hydrogen conversion.     

Core-shell hetero-phase reduced Ti–Ni–O nanotubes photoanode with enhanced optical absorption and charge transport for boosted photoelectrochemical water splitting

Bulk-phase doping and surface oxygen-defective engineering of TiO₂-based nanostructures are identified as effective routes for enhanced photoelectrochemical (PEC) water splitting. Here, we reported a reduced Ti–Ni–O nanotubes photoanode with anatase-rutile crystalline-core and oxygen vavancies amorphous-shell for boosted PEC water splitting. The core-shell hetero-phase reduced Ti–Ni–O nanotubes were fabricated through phase-structure modulation by a thermal treatment of anodized Ti–Ni–O nanotubes on Ti–Ni alloy and with one-step electrochemical reduction. Microstructure, optical and PEC measurement results confirmed effective bulk-phase Ni-doping and surface oxygen vacancies self-doping into the reduced mixed-phase Ti–Ni–O nanotubes, which enabled high capability of optical-absorption and simultaneously favored charge separation-transfer for remarkably improved the PEC water splitting. A higher photocurrent density of 1.66 mA/cm² at 0 V vs. Ag/AgCl and solar-to-hydrogen efficiency of 0.79% were achieved for the reduced Ti–Ni–O system, which was 5.35 and 5.27 times that of undoped TiO₂, respectively. This work may shed an insight view on fabricating high-performance Ti-based nano-photoanodes with enhanced light harvesting and carrier kinetics for efficient PEC water splitting, through synergistic strategy of bulk-phase elements doping and surface oxygen vacancies self-doping.     

Enhanced photoelectrochemical performance of an α-Fe2O3 nanorods photoanode with embedded nanocavities formed by helium ions implantation

Hematite is a prospective semiconductor in photoelectrochemical (PEC) water oxidation field due to its suitable bandgap for the solar spectrum absorption. Nevertheless, the low transfer and separation efficiency of the charge carriers are restricted by its diffusion length of hole which is 2–4 nm and further reduce the PEC performance. Here, we report an innovative method, by introducing nanocavities into the α-Fe₂O₃ nanorod arrays photoanodes through helium ions implantation, to improve the charge carriers' transfer and separation efficiency and further to enhance water oxidation performance. The result indicates that, the photocurrent density of nanocavities embedded α-Fe₂O₃ photoanode (S2-A sample) reaches 1.270 mA/cm² at 1.6 V vs. RHE which is 1-fold higher than that of the pristine α-Fe₂O₃ (0.688 mA/cm²) and the photocurrent density of S2-A sample reaches 0.652 mA/cm² at 1.23 V vs. RHE. In this work, the ion implantation combined with post annealing method is found to be a valid method to improve the photoelectrochemical performance, and it also can be further used to modify the other semiconductor photoelectrodes materials.     

Design of efficient Mn-doped α-Fe2O3/Ti-doped α-Fe2O3 homojunction for catalyzing photoelectrochemical water splitting

To produce clean chemical fuel of hydrogen efficiently, applying photocatalysts for conducting photoelectrochemical water splitting is indispensable. Hematite (α-Fe₂O₃) has been considered as one of the most effective photocatalysts for water oxidation due to excellent visible-light responses, high stability and source abundance properties, but low electrical conductivity and slow oxidation evolution kinetics limit its application. In this study, a novel α-Fe₂O₃ homojunction is constructed via doping Ti and Mn in two layers using two-step hydrothermal synthesis followed by one-step annealing process. Co-doping effect of Ti and Mn in α-Fe₂O₃ and growing sequence of Mn doped α-Fe₂O₃ (Mn:Fe₂O₃) and Ti doped α-Fe₂O₃ (Ti:Fe₂O₃) are also investigated to illustrate the efficient design of Mn:Fe₂O₃/Ti:Fe₂O₃ homojunction. The optimized Mn:Fe₂O₃/Ti:Fe₂O₃ electrode shows the highest photocurrent density of 2.10 mA/cm² at 1.60 V_RHE respectively comparing to those of 0.10, 1.20 and 0.22 mA/cm² for Ti:FeOOH, Ti:Fe₂O₃ and α-Fe₂O₃ electrodes. The outstanding performance of Mn:Fe₂O₃/Ti:Fe₂O₃ homojunction is attributed to the smaller charge-transfer resistance, higher carrier density, and less charge recombination. This work gives a rational design for hematite-based photocatalysts and successfully attains greatly improved photocatalytic ability for water oxidation. Development of homojunction using heteroatom doping in thus verified to be highly applicable on synthesizing promising photocatalysts.     

Reasonable regulation of kinetics over BiVO4 photoanode by Fe–CoP catalysts for boosting photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting using earth-abundant semiconductor offer a promising strategy to produce the sustainable clean energy. Herein, we successfully engineered BiVO₄ photoanode with Fe-doped CoP oxygen evolution catalysts (BiVO₄–Fe/CoP) for the first time. Fe/CoP catalysts could significantly break the kinetic limitations of BiVO₄, contributing to the enhanced charge injection efficiencies and charge carrier density. The rational heterostructure has boosted the photocurrent density and incident photon-to-current conversion efficiency (IPCE) to 2.16 mA/cm² and 43% (7 times than that of the bare BiVO₄), respectively. Meanwhile, the BiVO₄–Fe/CoP photoanode also exhibited the desirable long-term stability during PEC water oxidation for 4 h. The results prove the feasibility of BiVO₄–Fe/CoP configuration, which further provided a novel approach towards the development of efficient PEC water oxidation system.     

Enhanced photoelectrochemical performance of anatase TiO2 by metal-assisted S–O coupling for water splitting

In this study, hybrid density functional theory calculations have been used to investigate the electronic structures of (Mg, S), (2Al, S), (Ca, S), and (2Ga, S) codoped anatase TiO₂, aiming at improving their photoelectochemical performance for water splitting. It is found that the acceptor metals (Mg, Al, Ca, and Ga), assisting the coupling of the incorporated S with the neighboring O in TiO₂, lead to the fully occupied energy levels in the forbidden band of TiO₂, which is driven by the antibonding state π* of the S–O bond. It is also found that the metal-assisted S–O coupling can prevent the recombination of the photo-generated electron–hole pairs and effectively reduce the band gap of TiO₂. Among these systems, the (Mg, S) codoped anatase TiO₂ has the narrowest band gap of 2.206 eV, and its band edges match well with the redox potentials of water. We propose that this metal-assisted S–O coupling could improve the visible light photoelectrochemical activity of anatase TiO₂.     

Electrodeposited Cr-Doped α-Fe2O3 thin films active for photoelectrochemical water splitting

Polycrystalline hematite (α-Fe₂O₃) Chromium (Cr)-doped thin films were electrodeposited on fluorine-doped tin oxide-coated glass substrates. The electrodeposition bath comprised an aqueous solution containing FeCl₃·6H₂O, NaCl, and H₂O₂.Chromium was added to the electrolyte at such a proportion that the Cr/(Cr + Fe) ratio remained within the 2–8 at. % range. The as-deposited films were subsequently annealed in air at 650 °C for 2 h. The structure and morphological characteristics of the undoped and Cr-doped α-Fe₂O₃ thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectroscopy. Cr doping led the main XRD lines to shift to lower angles, which mostly resulted from substituting Fe³⁺ for Cr⁴⁺ ions that leads to α-Fe₂O₃ lattice contraction. The SEM observations showed that the roughness and aspect of surfaces changed with the Cr doping level. The photoelectrochemical (PEC) performance of the α-Fe₂O₃ films was examined by chronoamperometry and linear sweep voltammetry techniques. The Cr-doped films exhibited greater photoelectrochemical activity than the undoped α-Fe₂O₃ thin films. The highest photocurrent density was obtained for the 8% Cr-doped α-Fe₂O₃ films in 1 M NaOH electrolyte. All the samples achieved their best IPCE at 400 nm. The IPCE values for the 8 at.% Cr-doped hematite films were 20-fold higher than that of the undoped sample.This Cr-doped hematite films ‘excellent photoelectrochemical performance was mainly attributed to improved charge carrier properties. Such high photoactivity was attributed to the large active surface area and increased donor density caused by increasing the Cr doping in the α-Fe₂O₃ films.     

Fabrication of hollow g-C3N4@α-Fe2O3/Co-Pi heterojunction spheres with enhanced visible-light photocatalytic water splitting activity

For the first time, g-C₃N₄@α-Fe₂O₃/Co-Pi heterojunctional hollow spheres were successfully fabricated via thermal condensation method followed by solvothermal and photo-deposition treatment, which showed excellent photocatalytical property. Except for the Z-scheme charge transfer between α-Fe₂O₃ and g-C₃N₄, the Co-Pi could further reduce the combination of photogenerated electrons and holes as a hole storage agent, resulting in remarkably enhanced visible-light photocatalytic water splitting activity with the H₂ production rate of 450 μmol h⁻¹g⁻¹, which is 15.7 times higher than that of g-C₃N₄. Moreover, the photocatalytic activity of the prepared ternary hollow photocatalysts showed almost no significant weakness after five cycles, which indicated their good performance stability. The as-prepared g-C₃N₄@α-Fe₂O₃/Co-Pi also possessed good activity for overall water splitting with the hydrogen production rate reaching 9.8 μmol h⁻¹g⁻¹. This synthesized g-C₃N₄@α-Fe₂O₃/Co-Pi composite is expected to be a promising candidate for water splitting.     

High-throughput characterization of Ag–V–O nanostructured thin-film materials libraries for photoelectrochemical solar water splitting

Ag–V–O thin-film materials libraries, with both composition (Ag_22-77V_23-78O_x) and thickness (123–714 nm) gradients were fabricated using combinatorial reactive magnetron co-sputtering aiming on establishing relations between composition, structure, and functional properties. As-deposited libraries were annealed in air at 300 °C for 10 h. High-throughput characterization methods of composition, structure and functional properties were used to identify photoelectrochemically active regions. The phases AgV₆O₁₅, Ag₂V₄O₁₁, AgVO₃, and Ag₄V₂O₇ were observed throughout the composition gradient. The photoelectrochemical properties of Ag–V–O films are dependent on composition and morphology. An enhanced photocurrent density (~300–554 μA/cm²) was obtained at 30 to 45 at.% Ag along the thickness gradient. Thin films of these compositions show a nanowire morphology, which is an important factor for the enhancement of photoelectrochemical performance. The photoelectrochemically active regions were further investigated by high-throughput synchrotron-X-ray diffraction and transmission electron microscopy (Ag₃₂V₆₈O_x) which confirmed the presence of Ag₂V₄O₁₁ as the dominating phase along with the minor phases AgV₆O₁₅ and AgVO₃. This enhanced photoactive region shows bandgap values of ~2.30 eV for the direct and ~1.87 eV for the indirect bandgap energies. The porous nanostructured films improve charge transport and are hence of interest for photoelectrochemical water splitting.     

Recent trends in development of hematite (α-Fe2O3) as an efficient photoanode for enhancement of photoelectrochemical hydrogen production by solar water splitting

Solar-assisted water splitting using photoelectrochemical (PEC) cell is an environmentally benign technology for the generation of hydrogen fuel. However, several limitations of the materials used in fabrication of PEC cell have considerably hindered its efficiency. Extensive efforts have been made to enhance the efficiency and reduce the hydrogen generation cost using PEC cells. Photoelectrodes that are stable, efficient and made of cost-effective materials with simple synthesizing methods are essential for commercially viable solar water splitting through PEC technology. To this end, hematite (α-Fe₂O₃) has been explored as an excellent photoanode material to be used in the application of PEC water oxidation owing to its suitable bandgap of 2.1 eV that can utilize almost 40% of the visible light. In this study, we have summarized the recent progress of α-Fe₂O₃ nanostructured thin films for improving the water oxidation. Strategic modifications of α-Fe₂O₃ photoanodes comprising nanostructuring, heterojunctions, surface treatment, elemental doping, and nanocomposites are highlighted and discussed. Some prospects related to the challenges and research in this innovative research area are also provided as a guiding layout in building design principles for the improvement of α-Fe₂O₃ photoanodes in photoelectrochemical water oxidation to solve the increasing environmental issues and energy crises.     

Photoelectrochemical hydrogen generation with nanostructured CdS/Ti–Ni–O composite photoanode

Composite photocatalysts have aroused great interest due to combination of favorable electronic and optical properties. Herein, novel CdS/Ti–Ni–O composite photoanodes were constructed through anodic fabrication of nanostructured Ni-doped TiO₂ (Ti–Ni–O) oxide films and CdS deposition by successive ionic layer adsorption and reaction (SILAR). The morphology and composition evolution, optical properties and photoelectrochemical (PEC) performance of the photoanodes were investigated. The composite nanofilms mainly consisted of micropores and nanotubes. The CdS/Ti–Ni–O composite photoanode demonstrated remarkable PEC hydrogen generation properties with a high photocurrent density (6.72 mA·cm^?2 at 0 V vs Ag/AgCl) which was 18.2 times to that of the bare Ti–Ni–O photoanode. The synergy of Ni-doping and CdS-coupling on the enhancement of PEC performance offers useful ideas to the exploitation of effective photocatalysts and contributes to the development of solar-driven PEC hydrogen generation.     

Convex-nanorods of α-Fe2O3/CQDs heterojunction photoanode synthesized by a facile hydrothermal method for highly efficient water oxidation

Morphology controlling and surface modification of semiconductors is the key for efficient photoelectrochemical (PEC) water splitting systems. This work provides a new strategy for achieving morphology control and heterojunction construction simultaneously by one-step hydrothermal method. The α-Fe₂O₃/CQDs heterojunction photoanode with convex-nanorods morphology is successfully prepared by hydrothermal method in CQDs (Carbon Quantum Dots) aqueous contained iron precursor followed by low temperature annealing treatment. Compared with bare hematite photoanode, the α-Fe₂O₃/CQDs photoanode has 8.5 time higher photocurrent density (at 1.23 V vs. RHE) of 0.35 mA cm^?2 and a negative shift of onset potential about 300 mV. The enhanced photoelectrochemical response is attributed to the convex-nanorods which benefit higher absorbance of light and the formed α-Fe₂O₃/CQDs heterojunction, which can efficiently enhance the electron-hole separation and reduce the surface charge recombination. The morphology and properties of the sample were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fouriertrans form infrared spectroscopy (FTIR), UV–vis spectra, X-ray diffractometry (XRD), X-ray photoelectron spectra (XPS), and photoelectrical measurements.     

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.     

Novel synthesis of Ti–Fe2O3/MIL-53(Fe) via the in situ process for efficient photoelectrochemical water oxidation

The slow kinetics of water oxidation has become a challenge for photoelectrochemical hydrogen production. Here, a novel organic-inorganic integrated photoanode system was constructed by using MIL-53(Fe) formed during the in-situ etching process as a cocatalyst to modify Ti–Fe₂O₃. The photocurrent density of Ti–Fe₂O₃/MIL-53(Fe) reaches 2.5 mA/cm², 10 times that of bare Ti–Fe₂O₃ at 1.23 V vs. RHE, and the water oxidation photocurrent onset potential shifts 105 mV negatively. Ti–Fe₂O₃/MIL-53(Fe) reaches 52% at 390 nm for IPCE. The excellent photoelectrochemical performance is due to iron oxide clusters boost charge separation and transfer, in-situ etching exposes more reactive sites, and the tight connection reduces interfacial resistance, which greatly accelerates the surface kinetics of Ti–Fe₂O₃. The in-depth understanding is provided for in-situ modification of photoanodes by metal organic frameworks in this work.     

Electrodeposited zirconium-doped α-Fe2O3 thin film for photoelectrochemical water splitting

Nanostructured hematite thin films were doped with zirconium successfully using electrodeposition method for their implementation as photoanode in photoelectrochemical (PEC) cell for hydrogen generation. XRD, Raman, XPS, SEM and UV-visible spectroscopy techniques were used to characterize the thin films. Highest photocurrent density of 2.1 mA/cm² at 0.6 V/SCE was observed for 2.0 at.% Zr⁴⁺ doped α-Fe₂O₃ sample with solar to hydrogen conversion efficiency of 1.43%. Flatband potential (−0.74 V/SCE) and donor density (2.6 × 10²¹ cm⁻³) were found to be maximum for the same sample. These results suggest substantial potential of hematite thin films with controlled doping of zirconium in PEC water splitting applications.     

α-Fe2O3 nanoarrays photoanodes decorated with Ni-MOFs for enhancing photoelectrochemical water oxidation

Owing to severe recombination of photogenerated charges, sluggish kinetics of oxygen evolution reaction (OER) and high overpotential, the efficiency of photoelectrocatalytic (PEC) water splitting is severely restricted currently. Herein, a metal-organic framework (Ni-MOF) as cocatalyst has been introduced onto Fe₂O₃ nanoarrays for PEC water oxidation. The new Ni-MOFs/Fe₂O₃ photoanode obviously improves the PEC water oxidation performance with respect to the Fe₂O₃. Specifically, a high photocurrent density is achieved on the Ni-MOF/Fe₂O₃ film, which corresponds to two-fold over the pristine Fe₂O₃ film at 1.23 V vs. RHE. Moreover, the photoanode also exhibits a significant cathodic shift of the onset potential (~240 mV) relative to the bare Fe₂O₃. The enhanced PEC performance is attributed to effective utilization the surface-reaching holes and reduction of the surface charge recombination, which are confirmed by electrochemical impedance spectroscopy and the derived Bode analysis. This study brings new insight into the development of MOF-based materials in the field of PEC water splitting.     

Role of sputtered WO3 underlayer and NiFeCr-LDH co-catalyst in WO3–BiVO4 heterojunction for enhanced photoelectrochemical water oxidation

WO₃–BiVO₄ (WO-60s/BVO) heterojunction was synthesized by radio-frequency sputtered WO₃ onto FTO substrate, followed by spin-coating of BiVO₄ layer. Furthermore, Cr incorporated NiFe-LDH (NiFeCr-LDH) oxygen evolution reaction (OER) co-catalyst was electrodeposited onto WO-60s/BVO. The sputtered WO₃ underlayer in the WO-60s/BVO facilitated enhanced electron-hole separation and less transient time for the electron to arrive at back contact than conventional spin-coated WO₃ layers. Incorporating Cr into NiFe-LDH increased the electrical conductivity of LDH, which resulted in an enhanced transfer of photogenerated charge-carrier and significant promotion of the OER kinetics. The heterojunction with sputtered WO₃ underlayer and NiFeCr-LDH co-catalyst attained photocurrent density of 4.9 mA cm⁻² at 1.23 V vs. RHE with an IPCE value greater than 56% in the 350–470 nm wavelength range. Moreover, the WO-60s/BVO-NiFeCr photoanode showed only 7% decay in photocurrent after 6 h with H_2, and O₂ evolution of 98 and 47 μmol cm⁻² h, respectively, suggesting high stability for OER.     

Metallic nanoparticles loaded Al–SrTiO3 supported with RhCr2O3 and CoOOH cocatalysts for overall water splitting

Developing new renewable, carbon-neutral fuels to diminish the amount of released CO₂ in the atmosphere and to solve global challenges such as global warming and climate change is significant. Among them, hydrogen (H₂) is attracting much attention due to its high energy density, ease of transportation, and multiple means of production. To meet the global demand of H_2, photocatalytic water splitting is one of the most promising methods for large scale production. Herein, Al-doped SrTiO₃ photocatalyst (Al–SrTiO₃) was prepared by a molten flux method. Then, plasmonic metal nanoparticles (Au, Cu, Pt), and cocatalysts Rh/Cr₂O₃ and CoOOH were selectively deposited onto the reductive and oxidative active sites of Al–SrTiO₃ using multi-step photodeposition-impregnation methods for water splitting and H₂ production under UV-rays, UV–Vis. Light, and visible light (λ ≥ 400 nm). Our results showed that, compared with Pt and Cu loaded Al–SrTiO₃ photocatalyst supported with Rh/Cr₂O₃ and CoOOH cocatalysts, Au-loaded samples showed the highest H₂ production efficiency under both UV (920 μmol/h - EQE = 41% at 365 nm) and UV–Vis (100.5 μmol/h) rays. In addition, the amount of evolved H₂ decreased by increasing the weight ratio of Au nanoparticles (NPs) due to the overlap between Au NPs and Rh/Cr₂O₃ cocatalyst. Although Au 0.3 wt%-loaded sample showed high activity under both UV and UV–Vis. Rays, it exhibited almost no efficiency under visible light because of the large bandgap of Al–SrTiO₃ (3.1 eV) and the poor absorption in the visible region. Visible light absorption was then enhanced by increasing the loaded amount of Au NPs and by separating Au NPs and Rh/Cr₂O₃ cocatalyst responsible for H₂ evolution by combining both photodeposition and impregnation methods. Under visible light, Rh/Cr₂O₃-loaded Al–SrTiO₃ with 4 wt % Au NPs showed the highest H₂ evolution efficiency (41 μmol/3 h). This was attributed to the efficient hot electron transfer from Au NPs to Al–SrTiO₃ then to RhCr₂O₃, resulting in charge separation needed for efficient H₂ generation.     

Fabrication of 0D/1D/2D ZnS–CuS nanodots/GNRs/g-C3N4 heterojunction photocatalyst for efficient photocatalytic overall water splitting

Photocatalytic water splitting has become a significant challenge in modern chemistry. In this process, the rate-determining step is the hydrogen evolution reaction (HER). In the present work, a surface modification approach for graphitic carbon nitride (g-C₃N₄) was applied to improve its photocatalytic HER. 0D ZnS–CuS nanodots were synthesized with the hydrothermal method as a co-catalyst to enhance the capability and stability of water splitting in the presence of visible light irradiation. Also, graphene nanoribbons were synthesized from CNTs unzipping to reduce the energy barrier of HER, improve the HE kinetic, and enhance the catalytic performance of the g-C₃N₄. By using ZnS–CuS/GNRs₍₂₎/g-C₃N₄ photocatalyst, a low onset potential of 130 mV, slight Tafel slope of 41 mV dec^?1, as well as excellent stability of 2000 s was obtained in acidic media. This efficient performance is attributed to the increased visible light absorption level in the proposed photocatalyst and the high stability in electron-hole pairs.     

Homogeneous core–shell NiCo2S4 nanorods as flexible electrode for overall water splitting

Exploring low-cost and highly efficient Water splitting electrocatalyst has been recognized as one of the most challenging and promising ways. NiCo₂S₄ core-shell nanorods supported on nickel foam (NF) have been fabricated by a facile hydrothermal method. The electrochemical performance of NiCo₂S₄@NiCo₂S₄ for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is studied. NiCo₂S₄@NiCo₂S₄/NF exhibits a significantly improved OER and HER performance with an overpotential of 200 mV at 40 mA/cm² and an overpotential of 190 mV at 10 mA/cm². The combination of low charge-transfer resistance, enhanced interaction and charge transport as well as large electrochemical double-layer capacitance enables superior OER and HER. The NiCo₂S₄@NiCo₂S₄/NF nanorod electrode shows excellent electrocatalytic activity with a low voltage 1.57 V and stability with long hour electrolysis, which is highly satisfactory for a prospective bifunctional electrocatalyst.