Facile one-pot synthesis of binder-free nano/micro structured dendritic cobalt activated nickel sulfide: a highly efficient electrocatalyst for oxygen evolution reaction

Reasonable design and preparation of non-noble metal electrocatalysts with predominant catalytic activity and long-term stability for oxygen evolution reaction (OER) are essential for electrocatalytic water splitting. Ni foam (NF) is highlighted for its 3D porous structure, impressive conductivity and large specific surface area. Herein, nano/micro structured dendritic cobalt activated nickel sulfide grown on 3D porous NF (Co–Ni₃S₂/NF) has been successfully synthesized by one-step hydrothermal method. Due to the ingenious incorporation of Co, Co–Ni₃S₂/NF electrode shows auspicious electrocatalytic performance for OER compared with Ni₃S₂/NF electrode. As a result, Co–Ni₃S₂/NF needs overpotential of only 274 and 459 mV at current density of 10 and 50 mA cm⁻², respectively, while Ni₃S₂/NF requires overpotential of 344 and 511 mV. At potential of 2.0 V (vs. RHE), Co–Ni₃S₂/NF displays current density of 191 mA cm⁻², while Ni₃S₂/NF just attains current density of only 135 mA cm⁻². Moreover, Co–Ni₃S₂/NF demonstrates excellent stability for uninterrupted OER in alkaline electrolyte. The strategy of designing and preparing cobalt activated nickel sulfide grown on NF renders a magnificent prospect for the development of metal-sulfide-based oxygen evolution catalysts with excellent electrocatalytic performances.     

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.     

Ni3S2-MoSx nanorods grown on Ni foam as high-efficient electrocatalysts for overall water splitting

In order to solve the problem of large overpotential in water electrolysis for hydrogen production, transition metal sulfides are promising bifunctional electrocatalysts for hydrogen evolution reaction/oxygen evolution reaction that can significantly reduce overpotential. In this work, Ni₃S₂ and amorphous MoS_x nanorods directly grown on Ni foam (Ni₃S₂-MoS_x/NF) were prepared via one-step solvothermal process, which were used as a high-efficient electrocatalyst for overall water splitting. The Ni₃S₂-MoS_x/NF composite exhibits very low overpotentials of 65 and 312 mV to reach 10 mA cm⁻² and 50 mA cm⁻² in 1.0 M KOH for HER and OER, respectively. Besides, it exhibits a low Tafel slope (81 mV dec⁻¹ for HER, 103 mV dec⁻¹ for OER), high exchange current density (1.51 mA cm⁻² for HER, 0.26 mA cm⁻² for OER), and remarkable long-term cycle stability. This work provides new perspective for further the development of highly effective non-noble-metal materials in the energy field.     

A nano-spherical structure Ni3S2/Ni(OH)2 electrocatalyst prepared by one-step fast electrodeposition for efficient and durable water splitting

Developing non-noble metal catalysts with excellent electrocatalytic performance and stability is of great significance to hydrogen production by water electrolysis, but there are still problems of low activity, complex preparation and high cost. Herein, we fabricated a novel Ni₃S₂/Ni(OH)₂ dual-functional electrocatalyst by a one-step fast electrodeposition on nickel foam (NF). While maintaining the electrocatalytic performance of Ni₃S₂, the existence of heterostructure and Ni(OH)₂ co-catalyst function greatly improves the overall water splitting performance of Ni₃S₂/Ni(OH)₂–NF. Hence, It shows a low overpotential of 66 mV at 10 mA cm^?2 for HER and 249 mV at 20 mA cm^?2 for OER. The dual-functional electrocatalyst needs only 1.58 V at 20 mA cm^?2 when assembled two-electrode electrolytic cell. Impressively, the electrocatalyst also shows outstanding catalytic stability for about 800 h when 20 and 50 mA cm^?2 constant current was applied, respectively which demonstrates a potential electrocatalyst for overall water splitting.     

CdS/CuCo2S4 dots-on-rods boosting charge separation and hydrogen evolution

Herein, we report a new class of CdS/CuCo₂S₄ dots-on-rods nanostructures that exhibit efficient visible-light-induced H₂ evolution from water. The material CuCo₂S₄ nanodots over CdS nanorods are fabricated through controlled loading in a facile hydrothermal process and formed a heterojunction, maximizing the energy conversion, that shows advanced performance in photochemical H₂ evolution (rate: 33.32 mmol g^?1h^?1 and AQY: 13.2% at λ = 420 ± 15 nm) from water. The experimental and theoretical results on physical and chemical properties revealed that the photocatalytic system is positively correlated with the H₂ production rate and suggest that CuCo₂S₄ nanodots in CdS nanorods plays a critical role in relative efficiency of the H₂ generation. The surprisingly high activity was attributed to enhanced charge carriers’ separation and transfer efficiency, confirmed by the kinetic measurements (TAS) and further reinforced from the Kelvin probe force microscopy (KPFM) analysis and theoretical understanding.     

Flower-shaped and sea urchin-shaped structures coexisting in cobalt-based phosphate and oxides achieve efficient electrochemical overall water electrolysis

Active site engineering for electrocatalysts is an essential strategy to improve their intrinsic electrocatalytic capability for practical applications and it is of great significance to develop a new excellent electrocatalyst for overall water splitting. Here, Co₃O₄/nickel foam (NF) and Co₂(P₄O₁₂)/NF electrocatalysts with flower-shaped and sea urchin-shaped structures are synthesized by a simple hydrothermal process and followed by a post-treatment method. Among them, Co₂(P₄O₁₂)/NF shows good catalytic activity for hydrogen evolution reaction (HER), and at the current density of 10 mA cm^?2, the overpotential is only 113 mV Co₃O₄/NF exhibits good catalytic activity for oxygen evolution reaction (OER), and the overpotential is 327 mV at 20 mA cm^?2. An alkaline electrolyzer with Co₃O₄/NF and Co₂(P₄O₁₂)/NF catalysts respectively as anode and cathode displays a current density of 10 mA cm^?2 at a cell voltage of 1.59 V. This work provides a simple way to prepare high efficient, low cost and rich in content promising electrocatalysts for overall water splitting.     

Phosphate ions-functionalized and wettability-tuned nickel ferrite for boosted oxygen evolution performance

Nickel ferrite (NiFe₂O₄) has been explored as a promising oxygen evolution reaction (OER) electrocatalyst for water splitting owning to its earth-abundant and considerable water oxidation catalytic activity. Nevertheless, its practical electrocatalytic performance towards OER is still undesirable due to the sluggish OER kinetics and high overpotential gap on the water oxidation anode side. In this work, in order to enhance the electrochemical water oxidation performance of NiFe₂O₄, the surface of NiFe₂O₄ is functionalized with phosphate ions (Pi) by using a facile incipient impregnation and following calcination process. Results demonstrate that the OER properties of NiFe₂O₄ under alkaline conditions can be dramatically boosted by the surface Pi functionalization. In 1.0 M KOH solution, the resulting NiFe₂O₄-Pi on glassy carbon (GC) electrode demonstrates quite lower overpotential of 332 mV (10 mA/cm²) and Tafel slope of 57 mV/dec compared to that of pristine NiFe₂O₄ (443 mV@10 mA/cm² and 96 mV/dec), which is also better than that of commercial RuO₂ electrocatalysts (348 mV@10 mA/cm² and 80 mV/dec). Moreover, such electrocatalyst on nickel foam electrode also realizes superior OER durability to afford a current density of 70 mA/cm² at overpotential of only 300 mV for at least 28 h. The excellent electrocatalytic water oxidation activities of NiFe₂O₄-Pi can be attributed to the tuning electronic property and surface wettability by Pi ions functionalization. This work provides us a novel and effective approach to modify the photo-/electrocatalytic activity for transition metal oxides.     

Nickel foam-supported Fe,Ni-Polyporphyrin microparticles: Efficient bifunctional catalysts for overall water splitting in alkaline media

Developing highly active, stable and sustainable electrocatalysts for overall water splitting is of great importance to generate renewable H₂ for fuel cells. Herein, we report the synthesis of electrocatalytically active, nickel foam-supported, spherical core-shell Fe-poly(tetraphenylporphyrin)/Ni-poly(tetraphenylporphyrin) microparticles (FeTPP@NiTPP/NF). We also show that FeTPP@NiTPP/NF exhibits efficient bifunctional electrocatalytic properties toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Electrochemical tests in KOH solution (1 M) reveal that FeTPP@NiTPP/NF electrocatalyzes the OER with 100 mA cm⁻² at an overpotential of 302 mV and the HER with 10 mA cm⁻² at an overpotential of 170 mV. Notably also, its catalytic performance for OER is better than that of RuO₂, the benchmark OER catalyst. Although its catalytic activity for HER is slightly lower than that of Pt/C (the benchmark HER electrocatalyst), it shows greater stability than the latter during the reaction. The material also exhibits electrocatalytic activity for overall water splitting reaction at a current density of 10 mA cm⁻² with a cell voltage of 1.58 V, along with a good recovery property. Additionally, the work demonstrates a new synthetic strategy to an efficient, noble metal-free-coordinated covalent organic framework (COF)-based, bifunctional electrocatalyst for water splitting.     

Co3O4–C@FeMoP on nickel foam as bifunctional electrocatalytic electrode for high-performance alkaline water splitting

Exploring low-cost, highly efficient, and sustainable non-precious electrocatalysts for electrolytic H₂ generation is driving research for the sustainable green urban development. Herein, we present a simple synthetic approach, through a two-step process, to prepare the bifunctional electrode of Co₃O₄–C@FeMoP hybrid micro rods/nanosheets anchored on nickel foam (NF), in which the Co₃O₄–C microrods grown on NF surface are decorated by FeMoP nanosheet layers, which is directly grown through a simple hydrothermal followed by post-phosphorization processes. The obtained hybrid hierarchical Co₃O₄–C@FeMoP/NF shows a significant enhancement in the electrocatalytic activities of oxygen/hydrogen evolution reactions (OER/HER) in comparison to the individual Co₃O₄–C and FeMoP nanostructures, thanks to more heterointerface active sites provided by FeMoP nanostructures with three-dimensional (3-D) layered architectures. The Co₃O₄–C@FeMoP/NF catalyst exhibits a relatively small overpotential of 200 mV vs. RHE for OER to achieve 20 mA/cm² and 123 mV vs RHE at 10 mA/cm² for HER along with excellent durability in alkaline electrolytes. We demonstrate the bifunctional electrocatalytic electrode as the electrolyzer for the generation of H₂ via water splitting at small applied voltage of 1.61 V to achieve 10 mA/cm² and good stability for 24-h continuous running.     

Controlled synthesis of N–CuCo2S4@Ni3S2 nanoarrays as promising urea oxidation electrocatalyst

One of the most attractive means for mitigation of environmental pollution is to produce hydrogen by electrocatalytic urea splitting. In the paper, the heterogeneous interfacial rich N–CuCo₂S₄@Ni₃S₂ material was in situ synthesized on nickel foam through a typical hydrothermal and sulfuration process. This N–CuCo₂S₄@Ni₃S₂ electrode displays excellent urea oxidation performance (potential of 1.38 V@50 mA cm⁻²), which is one of the best reactivity reported so far. Experimental results show that the superior catalytic activity is attributed to the rapid charge transfer, more reaction center exposed and superior electrical conductivity. Density functional theory shows that this Ni₃S₂ material accelerates the reaction rate in the catalytic process, the introduction of this N–CuCo₂S₄ material improves the conductivity of the material, and the synergistic catalysis of the N–CuCo₂S₄ and Ni₃S₂ makes this N–CuCo₂S₄@Ni₃S₂ material exhibit superior urea oxidation activity. Notably, long-term tests have shown a decrease in catalytic activity, which suggests that the surface of the sulfide is in situ generated to oxides or hydroxides, which are truly active species. This work provides a new idea for the development of efficient and stable urea oxidation catalysts for sulfides.     

Coupling NixSy-Ni2P heterostructure nanoarrays on Ni foam as environmentally friendly electrocatalyst for overall water splitting

The development of efficient, cheap and stable electrodes is the key to achieve the industrialization of hydrogen production from electrochemical water splitting. In this paper, Ni_xS_y-Ni₂P mixtures on Ni foam (Ni_xS_y-Ni₂P/NF) were synthesized by hydrothermal process followed by sulfurization and phosphorization approach. The combination of Ni_xS_y and Ni₂P exposes a large number of active sites, thus greatly improving the catalytic activity of the material. As expected, the Ni_xS_y-Ni₂P/NF material exhibits ultra-small overpotentials of 211 and 320 mV for water oxidation reaction at the current densities of 10 and 100 mA/cm², respectively. What is noteworthy is that the material also present superior hydrogen evolution reaction properties (122 mV@10 mA cm^?2). Moreover, when the material is acted as a bifunction electrode to drive the overall water splitting, only a cell voltage of 1.54 V is required to drive a current density of 10 mA/cm², which is one of the superior catalytic properties reported up to now. Experimental results show that the good electrochemistry performance of the Ni_xS_y-Ni₂P/NF material is attributed to the improved charge transfer rate, exposure of more active site and superior electrical conductivity. This work provides an effective way to explore environmentally friendly catalysts based on transition metal sulfide and phosphide.     

Modulating interfacial charge redistribution of Ni2P/CuCo2S4 p-n nano-heterojunctions for efficient electrocatalytic overall water splitting

Fabricating effective yet inexpensive catalysts is an important target in the research of water electrolysis and clean energy generation. Key challenges still remaining in this area are the rich density of surface-active sites, efficient interfacial charge transfer and improved reaction kinetics. Herein, Ni₂P/CuCo₂S₄ p-n junctions are constructed via an in situ hydrothermal growth of Ni₂P nanoparticles on CuCo₂S₄ nanosheets. Extensive X-ray photoelectron, optical absorption and electrochemical spectroscopy studies coupled with density functional theory calculations provide a mechanistic understanding of the electrochemical behaviour of these catalysts. The integrated Ni₂P/CuCo₂S₄ p-n junctions, owing to the intimate interfacial interactions, offer interesting possibilities to purposively modulate the electronic structure of active sites at the interface, and thus to improve the hydrogen adsorption energetics and electrochemical reaction kinetics. As a result, the catalyst with 30 wt% Ni₂P content displays high intrinsic electrocatalytic activity, requiring overpotentials of 183 and 360 mV to deliver 10 mA cm⁻² for HER and 40 mA cm⁻² for OER in alkaline media, respectively, far lower than those of individual Ni₂P (400 and 520 mV) and CuCo₂S₄ (348 and 380 mV), further showing remarkable durability for 30 h. In addition, an alkaline two-electrode water electrolyzer assembled by Ni₂P/CuCo₂S₄ nano-heterojunctions exhibits a relatively low cell potential of 1.67 V at 10 mA cm⁻². These Ni₂P-modified CuCo₂S₄ heterostructures demonstrate great potential for renewable hydrogen production technologies, including water electrolysis.     

Fe-doped NiCo2S4 catalyst derived from ZIF – 67 towards efficient hydrogen evolution reaction

The development of economical, efficient and stable non-noble metal catalysts plays a key role in electrocatalytic hydrogen evolution. NiCo₂S₄ has been proved to be an efficient non-noble catalyst, to further improve its electrocatalytic performance is a meaningful work. In this paper, the effects of Fe doping on electrochemical performance of NiCo₂S₄ is investigated. The Fe-doped NiCo₂S₄ catalyst is prepared by a facile solvothermal method with metal-organic-framework (MOF, ZIF-67) as template, and it exhibits an improved hydrogen evolution reaction (HER) performance with an overpotential of 181 mV at 10 mA cm^?2, a Tafel slope of 125 mV dec^?1 compared with that of NiCo₂S₄ (252 mV overpotential and 149 mV dec^?1 Tafel slope). The combination of improved conductivity, mesopores architecture retained with the ZIF-67 template, which result the reduced internal resistance, enhanced charge transportation as well as large electrochemical double-layer capacitance. This work provides an effective and synergistic strategy for fabricating NiCo₂S₄-based catalysts toward electrochemical water splitting.     

NiCo-sulfide hetero-structured interface induced highly active nickel-dominated metal sites for oxygen evolution reaction

The development of sustainable energy is of great significance for relieving the energy shortage crisis, where the oxygen evolution reaction (OER) in water electrolysis plays a crucial role in efficient energy conversion technology. Hetero-structured transition metal sulfides are regarded as quite promising electrocatalytic materials, considering their intrinsic activity and prominent synergistic effect. However, the essential surface reconstruction process of transition metal sulfides renders a great challenge to reveal the real active sites and the relative electrocatalytic reaction mechanism. Herein, novel sea urchin-like NiCo bimetallic sulfide (denoted as NiS/Co₃S₄) catalysts with highly exposed heterogeneous interface is designed for efficient OER. The high electrochemical active surface as well as effectual charge-transfer effect ensures NiS/Co₃S₄ catalysts with superior activity and durability, such as a low overpotential of 285 mV at 100 mA/cm², a small Tafel slope of 66 mV/dec as well as the long-term stability for 60 h. The post OER characterizations confirm that high valence of Ni dominated metal sites expedite the surface reconstruction process and the formed Ni (oxy)hydroxides significantly accelerate the process of oxygen evolution reaction.     

CuCo2S4 integrated multiwalled carbon nanotube as high-performance electrocatalyst for electroreduction of nitrogen to ammonia

Ammonia synthesis based on electrocatalytic nitrogen reduction reaction (NRR) by using renewable sources of energy under ambient conditions has attracted wide research attentions. Herein, we report that the noble-metal-free CuCo₂S₄/multiwalled carbon nanotube nanocomposite, which is synthesized via a facile one-step hydrothermal and sulfuration approach, can work as the high active and durable catalyst for electrocatalytic NRR. This nanocomposite achieves a high NH₃ yield of 137.5 μg h⁻¹ mg_cat⁻¹ and a high Faradaic efficiency of 8.7% at −0.5 V vs reversible hydrogen electrode (RHE) in 0.1 M Na₂SO₄ solution, which outperforms CuCo₂S₄ counterpart and most reported NRR catalysts. These results reveal that the MWCNT in nanocomposite not only suppresses the aggregation of CuCo₂S₄ nanoparticles and maximizes the exposure of active sites, but also contributes to the synergistic effect between CuCo₂S₄ nanoparticles and MWCNT, and facilitates the interfacial reaction kinetics.     

Overall noble metal free Ni and Fe doped Cu2ZnSnS4 (CZTS) bifunctional electrocatalytic systems for enhanced water splitting reactions

Herein, we report an inexpensive synthesis of sonochemical nickel and iron (M = Ni, Fe) doped Cu₂ZnSnS₄ (CZTS) and their utility as a nanoelectrodes for improved electrocatalytic water splitting performance. The as-synthesized electrode materials were characterized further by Transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman and X-ray photoelectron (XP) spectroscopic studies. Significantly, Ni doped CZTS electrocatalyst exhibits low overpotential approximately 214 and 400 mV for the hydrogen evolution reactions (HER) in 0.5 M H₂SO₄ and 1 M KOH electrolyte solutions respectively, and 1.29 V vs RHE for the oxygen evolution reactions (OER) in 1 M KOH at 10 mA/cm² current density. Small Tafel slopes and tested durability for longer time i.e. upto 500 min for water splitting, demonstrates that Ni doped CZTS is efficient bifunctional electrocatalyst having high activity along with extraordinary current/potential stability. Moreover, Fe doped CZTS electrocatalyst shows relatively poor response, i.e. overpotential 300 mV in 0.5 M H₂SO₄ and 445 mV in 1.0 M KOH towards HER and overpotential 1.54 V for the OER in 1 M KOH reaches at 10 mA/cm². This highly efficient bifunctional electrocatalysts that can meet the existing energy anxiety.     

Size-dependent electrocatalytic activities of printed Co3O4 films for a monolithic photovoltaic-electrolytic hydrogen generation system

As an electrocatalyst in a monolithic PV-electrolytic cell for water splitting hydrogen generation Co₃O₄ films were prepared by a paste coating method using Co₃O₄ particles. Different sized Co₃O₄ particles with average diameters of 145.9, 63.3 and 36.5 nm were prepared using a supercritical hydrothermal synthesis method. Electrochemical properties with respect to the particle size in the film were investigated by evaluating overpotential, charge transfer resistance (R_ct), and number of active sites (q∗). The relation between overpotential in water oxidation at 5 mA/cm² and BET surface area showed a slope of −73.8 ± 6.6, implying strong particle size dependence on electrocatalytic activity. Moreover, the R_ct and q^∗ values and the actual hydrogen evolution rate indicated that the electrocatalytic activity of Co₃O₄ is attributed to physical properties (e.g. particle size) of the film. Whereas, intrinsic single site activity of the film was not significantly changed with respect to the particle size in the film.     

One-pot preparation of Ni3S2@3-D graphene free-standing electrode by simple Q-CVD method for efficient oxygen evolution reaction

Efficient non-noble metal catalysts for the oxygen evolution reaction (OER) are particularly important in the practical applications of electrocatalytic water splitting (ECWS). Herein, based on a simple quasi chemical vapor deposition (Q-CVD) method, we fabricate a newly Ni₃S₂@3-D graphene free-standing electrode for efficient OER applications. The Ni₃S₂@3-D graphene integrates the advantageous features of 3-D graphene and Ni₃S₂ towards OER, such as more interfacial catalytic sites, pore-rich structure, N-doped structure and good electrical conductivity. Benefiting from the favorable features, the Ni₃S₂@3-D graphene (especially 900 °C sample) exhibits excellent OER performances in alkaline medium, which includes a low on-set potential (1.53 V), low overpotential of 305 mV at a current density of 10 mA cm⁻², and a smaller Tafel slope (50 mV dec⁻¹). This catalyst also shows ultrahigh stability after chronoamperometry response at 10 mA cm⁻² for 48 h with 30% increase in the current density. The present work opens a new approach for the one-pot construction of hybrid materials between metal sulfide and graphene to increase the electrocatalytic activity of non-noble metal OER catalysts.     

MnxCo3-xO4 spinel oxides as efficient oxygen evolution reaction catalysts in alkaline media

The design of efficient electrocatalysts for oxygen evolution reaction (OER) is an essential task in developing sustainable water splitting technology for the production of hydrogen. In this work, manganese cobalt spinel oxides with a general formula of Mn_xCo_3-xO₄ (x = 0, 0.5, 1, 1.5, 2) were synthesised via a soft chemistry method. Non-equilibrium mixed powder compositions were produced, resulting in high electrocatalytic activity. The oxygen evolution reaction was evaluated in an alkaline medium (1 M KOH). It was shown that the addition of Mn (up to x ≤ 1) to the cubic Co₃O₄ phase results in an increase of the electrocatalytic performance. The lowest overpotential was obtained for the composition designated as MnCo₂O₄, which exhibited a dual-phase structure (∼30% Co₃O₄ + 70% Mn_1.4Co_1.6O₄): the benchmark current density of 10 mA cm⁻² was achieved at the relatively low overpotential of 327 mV. The corresponding Tafel slope was determined to be ∼79 mV dec⁻¹. Stabilities of the electrodes were tested for 25 h, showing degradation of the MnCo₂O₄ powder, but no degradation, or even a slight activation for other spinels.     

Fe7S8/FeS2/C as an efficient catalyst for electrocatalytic water splitting

Exploring effective bi-functional catalysts is of great significance to enhance the electrochemical activity for overall water splitting. To date, Fe₇S₈ has been rarely reported to realize electrochemical overall water splitting because of its intrinsic poor conductivity. In this paper, Fe₇S₈/FeS₂ heterostructured nanosheets with interface structures and defect sites are prepared via a facile hydrothermal method. Fe₇S₈/FeS₂/C electrocatalysts are constructed through the addition of carbon powder to weaken the electron transfer barrier. As expected, Fe₇S₈/FeS₂/C requires the overpotential of 262 mV and 198 mV to reach 10 mA/cm² toward oxygen evolution reaction and hydrogen evolution reaction, respectively. Moreover, Fe₇S₈/FeS₂/C attains a voltage of 1.67 V at 10 mA/cm² and maintains long-term stability for 24 h toward overall water splitting in a two-electrode system. The excellent activity can be related to interface structures and surface defect sites, which boost the charge transfer rate owing to the rich active sites.