Efficient bifunctional hydrogen and oxygen evolution reaction electrocatalyst based on the NU-1000/CuCo2S4 heterojunction

One of the current necessities to produce clean energy is the logical design of inexpensive noble-metal free electrocatalysts with developed structure and composition for electrochemical water splitting. In this study, we introduce a new core-shell-structured bifunctional electrocatalyst of NU-1000/CuCo₂S₄ for oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and overall water splitting for the first time. Own to unique structure with rich porosity, high electrical conductivity, high stability and larger density of active sites, this nanocomposite can produce water electrolysis in a 1 M KOH solution. The electrochemical measurements show overpotentials of 335 mV for OER and 93 mV for HER at a current density of 10 mAcm⁻². Also, the NU-1000/CuCo₂S₄ nanocomposite exhibits Tafel slope values of 110 mV dec⁻¹ and 103 mV dec⁻¹ for HER and OER, respectively. Besides, NU-1000/CuCo₂S₄ presents a significant long-term stability in a 72 h run. Additionally, NU-1000/CuCo₂S₄ requires 1.55 V to deliver 10 mA cm⁻² current density in overall water splitting. According to these results, we hope to use this electrocatalyst in producing oxygen and hydrogen from water.     

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.     

Effect of cation substitution on the water splitting performance of spinel cobaltite MCo2S4 (M = Ni,Cu and Co)

The introduction of different ions is an effective method for regulating electron distribution and increasing the electrocatalytic activity of spinel cobalt sulfide (Co₃S₄). However, the effect of doping different ions on water splitting performance has not been systematically clarified. Therefore, a detailed research is done to illuminate the doping of different ions on the water splitting performance of spinel cobalt sulfide MCo₂S₄ (M = Ni, Cu and Co) nanorods grown on Ni foam. To drive the electrocatalytic current of 50 mA/cm² and 10 mA/cm², the CuCo₂S₄/NF material only requires an overpotential of 240 mV for oxygen evolution reaction (OER) and an overpotential of 142 mV for hydrogen evolution reaction (HER). The results of density functional theory and experiment demonstrate that the strong water adsorption energy and the large electrochemical activity area make CuCo₂S₄/NF show good catalytic activity. The CuCo₂S₄/NF nanorods material presents superior electrochemistry performance with a small voltage 1.53 V. The water oxidation activity increases linearly before nonlinearly improving with the increasing of pH, indicating that the substrate changes from water to hydroxyl. It is noteworthy that CuCo₂S₄/NF will be transformed into amorphous oxide active species, which will act as a stable catalyst during the reaction.     

Co3O4 nanoparticles decorated Polypyrrole/carbon nanocomposite as efficient bi-functional electrocatalyst for electrochemical water splitting

An effective bi-functional electrocatalyst of Co₃O₄/Polypyrrole/Carbon (Co₃O₄/Ppy/C) nanocomposite was prepared through a simple dry chemical method and used to catalyze the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Three types of carbon support as Vulcan carbon, reduced graphite oxide (RGO) and multi-walled carbon nanotubes (MCNTs) were used to study the influence on electrochemical reactions. Spherical shaped Co₃O₄ nanoparticles with 8–10 nm was found uniformly distributed on Ppy/C composite, which were analyzed by X-ray diffraction and transmission electron microscopy techniques. Amongst, Co₃O₄/Ppy/MWCNT shows improved bifunctional electrocatalytic activity towards both OER and HER with relatively low over potential (340 mV vs. 490 mV at 10 mA cm⁻²) and Tafel slope (87 vs. 110 mV dec⁻¹). In addition to that, MWCNT supported Co₃O₄/Ppy nanocomposite exhibits good electronic conductivity and electrochemical stability up to 2000 potential cycles. The results clearly indicate that the Co₃O₄/Ppy/MWCNT nanocomposite could be the promising bi-functional electrocatalyst for efficient water electrolysis.     

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.     

High-performance hybrid supercapacitor based on the porous copper cobaltite/cupric oxide nanosheets as a battery-type positive electrode material

In this work, CuCo₂O₄/CuO nanosheets (NSs) and CuCo₂O₄ oblique prisms (OPs) were synthesized at 130 °C with different amounts of hexamethyltetramine (HMTA) and reaction time through a hydrothermal method, and followed by an annealing treatment of precursors in air. The CuCo₂O₄/CuO NSs with 40 nm in thickness possessed a large specific surface area of 43.34 m² g⁻¹ and a mean pore size of 18.14 nm. The electrochemical tests revealed that the CuCo₂O₄/CuO NSs were belonged to the battery-type electrode material and exhibited a specific capacity of 395.55 C g⁻¹ at the current density of 1 A g⁻¹, higher than 258.16 C g⁻¹ for CuCo₂O₄ OPs. A hybrid supercapacitor (HSC) was assembled with activated carbon (AC) as negative electrode and CuCo₂O₄-based materials as positive electrode. The CuCo₂O₄/CuO NSs//AC HSC exhibited a high energy density of 30.18 Wh kg⁻¹ at a power density of 869.62 W kg⁻¹, and showed a fantastic cycling performance with 105.22% capacity retention over 5000 cycles. In contrast, the CuCo₂O₄ OPs//AC HSC delivered an energy density 26.27 Wh kg⁻¹ at 916.74 W kg⁻¹. These impressive electrochemical properties indicate that CuCo₂O₄/CuO NSs may serve as a promising electrode material for the highly capable hybrid supercapacitors in the near future.     

Preparation of Cu atom doped LaFeO3/activated porous carbon composites and their electrocatalytic nitrogen reduction performance

The electrocatalytic N₂ reduction reaction (NRR) under ambient conditions is a green and sustainable method for ammonia (NH₃) synthesis, and the development of efficient electrocatalysts for NRR is a top priority. In recent years, LaFeO₃ has been widely used in the field of catalysis because of its high stability, low cost, and green advantages. Through strategies such as heteroatom doping and carbon loading, we can effectively increase the content of oxygen vacancies and improve the electrical conductivity of the material to produce composites with unique electronic structures and excellent catalytic properties. In the present work, we prepared single-atom doped LaFeO₃/activated porous carbon composites (LFC/AC) for electrocatalytic NRR. The NH₃ yield and Faraday efficiency of LFC/AC were the highest at 23.876 μg h⁻¹ mg⁻¹ and 6.53% in 0.1 M Na₂SO₄ electrolyte solution, both of which were higher than those of LFC. A series of characterizations and tests have shown that LFC/AC has excellent stability, electrical conductivity, and electrocatalytic properties. The density flooding theory (DFT) simulations were performed to explore the main mechanisms to improve the NRR performance of the materials.     

Ambient electrosynthesis of NH3 from N2 using Bi-doped CeO2 cube as electrocatalyst

The synthesis of ammonia (NH₃) from electrochemical nitrogen reduction reaction (NRR) under environmental conditions is a promising technology. Compared with the traditional artificial nitrogen fixation process by the Haber-Bosch process, electrochemical nitrogen reduction reaction (NRR) requires no harsh reaction conditions. In this work, we report that Bi-doped CeO₂ nanocubes show high NRR activity as electrocatalysts. The NH₃ yield of 17.83 μgh⁻¹ mg⁻¹_cat. and the Faradaic Efficiency (FE) of 1.61% at −0.9 V are achieved in 0.1 M Na₂SO₄. The performance is much higher than that for the traditional CeO₂ nanoparticles. The detailed analysis indicates that both the Bi doping and the cube morphology are critical for this encouraging NRR performance. The mechanism for improving NRR is further explored with first-principle calculations, demonstrating the importance of Bi-doping for performance enhancement.     

Construction of NiCo2S4/Ni3S2 nanoarrays on Ni foam substrate as an enhanced electrode for hydrogen evolution reaction and supercapacitors

Developing a multifunctional and sustainable electrode material for hydrogen evolution reaction and supercapacitors is a highly feasible avenue for producing the high energy density and renewable energies. In our study, nanostructured NiCo₂S₄/Ni₃S₂/NF nanoarrays are rational developed in experiments via a simple hydrothermal reaction. Ascribed to the 3D nanostructured NiCo₂S₄/Ni₃S₂ with numerous exposure active sites and large contact areas for the electrolyte, the binder-free feature of NiCo₂S₄/Ni₃S₂/NF facilitates a low charge transfer resistance, as well as the synergetic effect of NiCo₂S₄ and Ni₃S₂. The obtained electrocatalyst showed ultrahigh electrocatalytic activity with an overpotential of 111 mV at 10 mA cm⁻² and a Tafel slope of 57 mV dec⁻¹. In addition, the electrode showed an area specific capacity of 6.13 F cm⁻² at 10 mA cm⁻² and superior rate capability (2.72 F cm⁻² at 80 mA cm⁻²), accompanied by excellent cycling stability. This results presented in our work can provide an effective strategy for rational design of other hybrid materials with excellent electrochemical performance in the application of electrocatalysis and supercapacitors.     

Ni–Co–S nanosheets supported by CuCo2O4 nanowires for ultra-high capacitance hybrid supercapacitor electrode

Recently, constructing core-shell arrays directly on conductive substrates is proved as a promising strategy for energy storage devices, due to the abundant active sites and fast electrons transport paths. In this work, we design core-shelled CuCo₂O₄@Ni–Co–S arrays directly on Ni foam substrate by the hydrothermal and electrodeposition processes. The core-shelled arrays can possess the large accessible surface area, fast charge transfer kinetics and the synergistic effect from both components, leading to better electrochemical performances. Consequently, core-shell CuCo₂O₄@Ni–Co–S arrays can deliver a high specific capacitance of 12.10 F cm⁻² (corresponding to 2897 F g⁻¹ mass specific capacitance), and good cycle stability with 82.5% capacitance retention after 8000 cycles of charging and discharging at 20 mA cm⁻². In addition, a battery-supercapacitor hybrid device made of CuCo₂O₄@Ni–Co–S and activated carbon displays a high energy density of 0.65 mWh cm⁻² at 32 mW cm⁻² power density, and the capacitance loss less than 20% (~83.6%) after 8000 cycles.     

MoS2-graphene-CuNi2S4 nanocomposite an efficient electrocatalyst for the hydrogen evolution reaction

We present a facile methodology for the synthesis of a novel 2D-MoS₂, graphene and CuNi₂S₄ (MoS₂-g-CuNi₂S₄) nanocomposite that displays highly efficient electrocatalytic activity towards the production of hydrogen. The intrinsic hydrogen evolution reaction (HER) activity of MoS₂ nanosheets was significantly enhanced by increasing the affinity of the active edge sites towards H⁺ adsorption using transition metal (Cu and Ni₂) dopants, whilst also increasing the edge sites exposure by anchoring them to a graphene framework. Detailed XPS analysis reveals a higher percentage of surface exposed S at 17.04%, of which 48.83% is metal bonded S (sulfide). The resultant MoS₂-g-CuNi₂S₄ nanocomposites are immobilized upon screen-printed electrodes (SPEs) and exhibit a HER onset potential and Tafel slope value of – 0.05 V (vs. RHE) and 29.3 mV dec⁻¹, respectively. These values are close to that of the polycrystalline Pt electrode (near zero potential (vs. RHE) and 21.0 mV dec⁻¹, respectively) and enhanced over a bare/unmodified SPE (– 0.43 V (vs. RHE) and 149.1 mV dec⁻¹, respectively). Given the efficient, HER activity displayed by the novel MoS₂-g-CuNi₂S₄/SPE electrochemical platform and the comparatively low associated cost of production for this nanocomposite, it has potential to be a cost-effective alternative to Pt within electrolyser technologies.     

Post-synthetic Ti exchanged UiO-66-NH2 metal-organic frameworks with high faradaic efficiency for electrochemical nitrogen reduction reaction

Electrochemical nitrogen reduction reaction (NRR) is a promising approach for NH₃ production to take place of the traditional Haber-Bosch process, which is still limited by the low NH₃ yield rate and low Faradaic efficiency. Herein, Ti was post-synthetic exchanged into Zr-based metal organic frameworks to synthesize UiO-Zr-Ti as NRR electrocatalysts. The incorporated Ti is found to function as active sites for NRR and benefit the improved charge-transfer efficiency, which has a positive effect on the high NH₃ yield rate. Moreover, the existence of Zr and Ti species can effectively suppress the competing HER, thus leading to high Faradaic efficiency. Therefore, the modified UiO-Zr-Ti-5d shows the highest NH₃ yield rate of 1.16 × 10⁻¹⁰ mol cm⁻² s⁻¹ and the highest Faradaic efficiency of 80.36%, which is comparable to recently reported NRR electrocatalysts.     

Electrocatalytic ammonia synthesis on Fe@MXene catalyst as cathode of intermediate-temperature proton-conducting solid oxide cell

As the only carbon-free energy carrier without CO₂ emission upon decomposition, ammonia is an ideal storage medium for H₂. However, the current low efficiency of ammonia synthesis is a main challenge on intermediate-temperature proton-conducting electrochemical cells. Herein, we develop a novel non-precious cathode catalyst consisting of Fe nanoparticles loaded on two-dimensional MXene nanosheets (Fe@MXene) that can achieve a high Faradaic efficiency of 8.4% and an NH₃ yield of 8.24 × 10⁻⁹ mol. s⁻¹·cm⁻² on an anode-supported Ba_0·95Ce_0·6Tb_0·1Y_0·2Zr_0·1O_3-δ-based electrolyte. The resultant catalyst with high specific surface area and catalytic active sites is beneficial to N₂ reduction, resulting from the effective activation of N₂ molecules imposed by the transported protons. The mechanism of catalytic NRR reveals that Fe@MXene catalyst can increase the electrocatalytic efficiency because of the improvement in the reaction rate constant. These show a promising catalyst of Fe@MXene for N₂ reduction reaction using intermediate-temperature proton-conducting solid oxide cell.     

Phase controlled synthesis and the phase dependent photo-and electrocatalysis of CdS@CoMo2S4/MoS2 catalyst for HER

Herein we report a heterostructure with ultrathin nanosheets of Co-doped molybdenum sulfide on CdS nanorod array (donated as CdS@CoMo₂S₄/MoS₂) by hydrothermal synthesis. Firstly, elemental Co doping MoS₂ (CoMo₂S₄) delivers the double benefits of increased active sites and enhanced conductivity. Secondly, the structural characteristics maximally exposes the MoS₂ edges and enlarges interfacial contact area between the composite catalyst and electrolyte, as well as the efficient interfacial charge transfer. The ratio of CoMo₂S₄/MoS₂ in CdS@CoMo₂S₄/MoS₂ plays a crucial role for the enhanced photo-assistant electrocatalytic hydrogen evolution reaction (HER). We can tune the ratio of CoMo₂S₄/MoS₂ by controlling the preparation time or the ratio of precursor of Co/Mo. The catalyst with predominant MoS₂ phase shows superior photocatalytic HER performance with a high H₂ production rate of 46.60 μmol mg⁻¹ h⁻¹. Meanwhile, the catalyst with predominant CoMo₂S₄ phase exhibits not only relatively low overpotential of 172 mV at 10 mA cm⁻², which outperforms most values that have been reported on catalyst supported on ITO substrate, but also possesses H₂ production rate of 23.47 μmol mg⁻¹ h⁻¹. The superior photo-assistant electrocatalytic HER activity results from the synergistically structural and electronic modulations, as well as the proper energy band alignment between MoS₂ and CdS. This investigation could provide an approach to integrate the electro- and photocatalytic activities for HER, especially the photo responding behaviour at a bias potential which is meaningful to produce H₂ for actual application.     

Construction of heterostructure interface with FeNi2S4 and CoFe nanowires as an efficient bifunctional electrocatalyst for overall water splitting and urea electrolysis

The design of high-performance non-noble-metal-based electrocatalysts for electrooxidation reactions involving splitting of water molecule for energy and environmental applications is the need of the hour. In this study, we report the electrocatalytic performance of a nanocomposite catalyst of FeNi₂S₄ nanoparticles/CoFe nanowires supported on nickel foam that was prepared by a simple hydrothermal method. The electrocatalyst has several advantages, such as the nanocomposite structure, relatively high electrical conductivity, and synergistic effect between FeNi₂S₄ and CoFe. These characteristics enhanced the catalytic efficiency of FeNi₂S₄/CoFe electrode, gaining small overpotentials of 380 and 207 mV for oxygen and hydrogen evolution reactions, respectively, at a current density of 100 mA cm^?2. The charge transfer processes are significantly improved by the electron pairs from FeNi₂S₄ and CoFe, as well as by the enhanced active sites at the electrode-electrolyte interface and their bonding interactions. The electrooxidation of urea was also explored, which showed a lower overpotential of 230 mV to reach 100 mA cm^?2 current density. Interestingly, FeNi₂S₄/CoFe was successfully employed as cathode and anode for urea-assisted water electrolysis, utilizing 1.56 V to produce 10 mA cm^?2 current density, which is approximately 160 mV below that for water electrolysis, thus verifying the lower energy consumption during electrolysis. These results indicate that nanoparticle and nanowire composite catalysts can be used for wastewater treatment and green energy production applications.     

NiCoP coated on NiCo2S4 nanoarrays as electrode materials for hydrogen evolution reaction

It is very important to exploit robust electrocatalysts for the urea splitting in an alkaline medium. Hence, the NiCo₂S₄@NiCoP nanoarrays on Ni foam (NiCo₂S₄@NiCoP/NF) was successfully synthesized for the first time and used as an efficient and stable difunctional electrocatalyst for the overall urea splitting. As one of the most promising bifunctional electrocatalysts reported, NiCo₂S₄@NiCoP only needs 108 mV to reach current density of 10 mA cm⁻² for hydrogen evolution reaction. Moreover, such NiCo₂S₄@NiCoP//NiCo₂S₄@NiCoP electrodes couple display superior urea splitting performance with the requirement of a cell voltage of 1.53 V to drive a catalytic current density of 10 mA cm⁻². In addition, the NiCo₂S₄@NiCoP material presents high long-term electrocatalytic stability keeping its performance at 11 mA cm⁻² for 12 h. The experimental results demonstrate that the sluggish Volmer step has been improved by incorporating the NiCoP to the NiCo₂S₄.     

One-step synthesis of CuCo2O4-Sm0.2Ce0.8O1.9 nanofibers as high performance composite cathodes of intermediate-temperature solid oxide fuel cells

One-dimensional nanostructured CuCo₂O₄-Sm_0.2Ce_0.8O_1.9 (SDC) nanofibers are prepared by the electrospinning method and one step sintering as a cathode with low polarization resistance for intermediate temperature solid oxide fuel cells (IT-SOFC). The CuCo₂O₄-SDC nanofibers cathodes form a porous network structure and have large triple-phase boundaries. Correspondingly, the electrochemical performance of the CuCo₂O₄-SDC nanofibers composite cathodes shows significantly improve, achieving the polarization resistance of 0.061 Ω cm² and the maximum power densities of 976 mW·cm⁻² at 750 °C. Thus, these results suggest that CuCo₂O₄-SDC nanofiber could be a highly active cathode material for IT-SOFCs.     

Facile electrochemical fabrication of magnetic Fe3O4 for electrocatalytic synthesis of ammonia used for hydrogen storage application

Ammonia (NH₃) offers extensive applications in industrial production; moreover, it is a potential carrier for hydrogen energy and an eco-friendly fuel. Electrocatalytic synthesis of NH₃ has drawn increasing research attention, wherein an excellent electrocatalyst plays a vital role. Iron (Fe) oxide nanomaterials with their high activity and cost effectiveness of its raw material Fe, have received significant attention in electrocatalytic N₂ reduction reaction (NRR) to synthesize NH₃. This study reports a rapid and cost-effective electrochemical method for synthesizing magnetic Fe₃O₄ nanoparticles, achieving gram-level production under ambient conditions. The synthesized magnetic Fe₃O₄ nanoparticles as electrocatalyst for NRR, achieved excellent faradaic efficiency of 16.9% and an optimal NH₃ yield of 12.09 μg h^?1 mg^?1_cat. at ?0.15 V (versus the reversible hydrogen electrode (RHE)) in 0.1 M Na₂SO₄. Besides, density functional theory (DFT) calculations indicate that the N≡N bond was fully activated, and the NRR proceeds mainly along the alternating hydrogenation pathway.     

Amorphous ATO and amorphous ATO based composite anodes for Li-ion batteries

In this study, amorphous antimony doped tin oxide (ATO) coatings on Cr coated stainless steel and multiwall carbon nanotube (MWCNT) buckypaper substrates were prepared using a radio frequency (RF) magnetron sputtering process as anode materials in lithium-ion batteries. The MWCNT anode, amorphous SnO₂:Sb anode and amorphous SnO₂:Sb-MWCNT nanocomposite anode have shown first discharge capacities of 446 mA h g⁻¹, 1064 mA h g⁻¹ and 1462 mA h g⁻¹, respectively. The best cycling performance were observed for amorphous SnO₂:Sb-MWCNT nanocomposite anode.     

Reduced CoFe2O4/graphene composite with rich oxygen vacancies as a high efficient electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) is regarded as a limit-efficiency process in electrochemical water splitting generally, which needs to develop the effective and low-cost non-noble metal electrocatalysts. Oxygen vacancies have been verified to be beneficial to enhance the electrocatalytic performance of catalysts. Herein, we report the facile synthesis of reduced CoFe₂O₄/graphene (r-CFO/rGO) composite with rich oxygen vacancies by a citric acid assisted sol-gel method, heat treatment process and the sodium borohydride (NaBH₄) reduction. The introduction of graphene and freezing dry technique prevents the restacking of GO and the aggregation of CFO nanoparticles (NPs) and increases the electronic conductivity of the catalyst. Fast heating rate and low anneal temperature favors to obtain low crystallinity and lattice defects for CFO. NaBH₄ reduction treatment further creates the rich oxygen vacancies and electrocatalytic active sites. The obtained r-CFO/rGO with high specific surface area (108 m² g⁻¹), low crystallinity and rich oxygen vacancies demonstrates a superior electrocatalytic activity with the smaller Tafel slope (68 mV dec⁻¹), lower overpotential (300 mV) at the current density of 10 mA cm⁻², and higher durability compared with the commercial RuO₂ catalyst. This green, low-cost method can be extended to fabricate similar composites with rich defects for wide applications.