Bifunctional Electrode Materials Research Articles

Enhanced catalytic activity of novel sea urchin-like spinel for advanced electrochemical energy conversion

Through precise morphological engineering, novel sea urchin-like spinel NiCo2O4 (NCO) was successfully synthesized and thoroughly investigated as a bifunctional electrode for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In contrast to traditional NCO, the distinctive scattered nanofiber microstructure of NCO prepared via hydrothermal at 100 ℃ (HT100) increases the specific surface area, introduces more oxygen vacancies, reduces the bandgap, enhances the diffusion, adsorption, and dissociation processes of oxygen molecules, thereby promoting rapid electron transfer and augmenting the number of active sites for both ORR and OER. At 800 °C, under the ORR model, NCO-HT100 exhibits an impressive output performance of 920 mW cm−2, surpassing traditional NCO by 47.8 %. Simultaneously, under the OER model, NCO-HT100 achieves a current density of 134.29 mA cm−2. Compared with conventional NCO, sea urchin-like NCO-HT100 displays lower Tafel slopes and overpotentials in alkaline solution at room temperature, indicating superior OER performance. These findings highlight that the sea urchin-like NCO-HT100 stands out as an advanced bifunctional electrode material for both ORR and OER. The insights gained from this research provide pivotal guidance for the future development of multifunctional electrode materials in energy conversion device applications.

Ultrathin, large area β-Ni(OH)2 crystalline nanosheet as bifunctional electrode material for charge storage and oxygen evolution reaction

Bifunctional electrode materials are highly desirable for meeting increasing global energy demands and mitigating environmental impact. However, improving the atom-efficiency, scalability, and cost-effectiveness of storage systems, as well as optimizing conversion processes to enhance overall energy utilization and sustainability, remains a significant challenge for their application. Herein, we devised an optimized, facile, economic, and scalable synthesis of large area (cm2), ultrathin (∼2.9 ± 0.3 nm) electroactive nanosheet of β-Ni(OH)2, which acted as bifunctional electrode material for charge storage and oxygen evolution reaction (OER). The β-Ni(OH)2 nanosheet electrode shows the volumetric capacity of 2.82 Ah.cm−3(0.82 µAh.cm−2) at the current density of 0.2 mA.cm−2. The device shows a high capacity of 820 mAh.cm−3 with an ultrahigh volumetric energy density of 0.33 Wh.cm−3 at 275.86 W.cm−3 along with promising stability (30,000 cycles). Furthermore, the OER activity of ultrathin β-Ni(OH)2 exhibits an overpotential (η10) of 308 mV and a Tafel value of 42 mV dec-1 suggesting fast reaction kinetics. The mechanistic studies are enlightened through density functional theory (DFT), which reveals that additional electronic states near the Fermi level enhance activity for both capacitance and OER.

Moss-like Ti3C2Tx based Fe/H2V3O8 composite as bifunctional electrode material for ammonium ion and zinc ion storage

The research on aqueous energy storage system is of significance due to its high security and economic friendliness. Herein, a moss-like Ti3C2Tx@Fe/H2V3O8 is synthesized by a simple hydrothermal method, in which Ti3C2Tx layers can act as scaffold to boost electric conductivity and suppress vanadium solution, H2V3O8 nanorods can expand electrode/electrolyte contact area and prevent aggregation, while Fe doping can optimize electric band structure effectively. Due to the cooperative effect of three components and distinctive structure of material, the Ti3C2Tx@Fe/H2V3O8 shows superior NH4+ storage capacity with superior capacity of 284.4 mAh g−1 at 0.5 A g−1 and high energy density of 48.64 mAh g−1 at power density of 166.9 W g−1. In addition, the Ti3C2Tx@Fe/H2V3O8 shows high capacity of 356 mAh g−1 at 0.1 A g−1 and stable long-cycling durability with outstanding capacity retention after 2000 cycles in Zn2+ storage application. The results reveal the great potential of Ti3C2Tx@Fe/H2V3O8 in aqueous ion battery application through rational structure design and synergistic effect of each component.

Samarium-doped vanadium pentoxide nanorods anchored reduced graphene oxide nanocomposite as a bi-functional electrode material for supercapacitor and direct methanol oxidation fuel cell applications

In this work, we demonstrate a novel, facile synthesis of reduced graphene oxide nanosheets decorated samarium-doped vanadium pentoxide (RGO/Sm:V2O5) nanocomposite material and explore its application toward supercapacitor and direct methanol oxidation process. As-fabricated material and electrode were well-characterized to evaluate its surface morphology and functionalities. Results indicate a maximum capacitance value of 544 F/g for RGO/Sm:V2O5 modified electrode than the 2% Sm:V2O5 (346 F/g) and V2O5 (133 F/g) modified electrodes. In addition, an excellent Rct value (3.2 Ω) was achieved for the RGO-loaded Sm:V2O5 electrode than the 2% Sm:V2O5 electrode (4.7Ω). The RGO/Sm:V2O5 electrode also shows higher cyclic efficiency (98 %) at the 1000th cycle than the non-RGO loaded Sm:V2O5 electrodes. Furthermore, the fabricated electrodes were also examined for the direct methanol oxidation performances, and the results indicate a higher current density value of 181 mA/cm2 for RGO/Sm:V2O5 electrode than 2% Sm:V2O5 electrode (139 mA/cm2). The excellent electrochemical performance of the RGO/Sm: V2O5 electrode is mainly due to the presence of RGO nanosheet in the synthesized nanocomposite material. Therefore, as-prepared material can be applied as an excellent alternative electrode material for energy storage and conversion systems.

Large-area ultrathin 2D Co(OH)2 nanosheets: a bifunctional electrode material for supercapacitor and water oxidation

Ultrathin film of active materials having thickness <5 nm emerged as a promising candidate for miniaturized energy storage and conversion devices. However, the small lateral size restricts its real device applications. Herein, we report large area, 2D, ultrathin (thickness: 4.3 ± 0.3 nm) Co(OH)2 nanosheets as bifunctional electrode material for supercapacitor and oxygen evolution reaction developed by ionic layer epitaxy method at the water-air interface. The symmetric supercapacitor device exhibited excellent volumetric capacitance of 2313 F/cm3 at 0.4 mA/cm2 current density. Additionally, it exhibited a remarkable volumetric energy density of 0.205 Wh/cm3 at a power density of 0.145 W/cm3, which is better than reported 2D electrode materials. Furthermore, the cobalt hydroxide (Co(OH)2) ultrathin-film electrodes showed improved oxygen evolution reaction electrocatalytic activity with low overpotential (ƞ10, 330 mV) and Tafel slope (47 mV/dec). The structural and morphological investigations after long-term operations show substantial stability of the electrode material. The theoretical investigations of electronic structures, quantum capacitance, and free energy profiles for the oxygen evolution reaction mechanism corroborate the experimental results.

Self-Supporting np-AlFeNiO Bifunctional Electrode Material for Electrochemical Water Splitting Prepared by Electrooxidation

Hydrogen production through water splitting is a promising path to develop renewable green energy. Effective, stable, and low-cost catalysts are the key to water splitting. In the present work, a series of self-supporting nanoporous alloys are prepared by using a dealloying process followed by electrooxidation. Among them, the np-AlFeNiO-4s sample exhibits remarkable activity (10 mA cm−2 at 32 mV for the HER and 278 mV for the OER) and good long-term stability (100 h) in alkaline conditions for both the HER and the OER. It only requires 1.56 V to reach 10 mA cm−2 current density for total water splitting performance. The very short time of electrooxidation can significantly improve the HER performance. Electrooxidation makes the metal and metal oxide sites on the electrode surface effectively coupled, which greatly enhances the kinetic rate of the Volmer and Heyrovsky steps. Appropriate electrooxidation is a rapid and easy way to improve the activity of the electrocatalyst, which has a broad application prospect in electrochemical water splitting.

Synthesis of nickel phosphate nanowires as a bifunctional catalyst for water electrolysis in alkaline media

The electrocatalytic water splitting (WS) process for hydrogen (H2) and oxygen (O2) production is known for its high efficiency, necessitating the development of bifunctional electrode materials. These materials must possess strong catalytic activity, significant active sites, high stability, and an abundance of earth-friendly components to ensure efficient and prolonged H2 and O2 generation. In this study, we employed a hydrothermal method to synthesize unique one-dimensional (1D) nickel phosphate (NiPO) nanoneedles directly grown on nickel foam (NF). The in-situ synthesis of the NiPO/NF catalyst offers favorable streamlining, facilitating electrode production and improving the contact between active sites and the conductive substrate. Under alkaline conditions, the NiPO/NF electrodes demonstrated low overpotentials of 374 mV and 377 mV at a high current density (J) of 250 mAcm−2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. These values indicate efficient and stable electrocatalytic activity. Moreover, the NiPO/NF catalyst exhibited continuous bifunctional catalytic activity for 12 hours with a J exceeding 20 mAcm−2. These findings suggest that NiPO/NF has the potential to be a cost-effective and sustainable option for large-scale WS applications.

Electrochemically Induced Ru/CoOOH Synergistic Catalyst as Bifunctional Electrode Materials for Alkaline Overall Water Splitting.

Efficient and affordable price bifunctional electrocatalysts based on transition metal oxides for oxygen and hydrogen evolution reactions have a balanced efficiency, but it remains a significant challenge to control their activity and durability. Herein, a trace Ru (0.74 wt.%) decorated ultrathin CoOOH nanosheets (≈4 nm) supported on the surface of nickel foam (Ru/CoOOH@NF) is rationally designed via an electrochemically induced strategy to effectively drive the electrolysis of alkaline overall water splitting. The as-synthesized Ru/CoOOH@NF electrocatalysts integrate the advantages of a large number of different HER (Ru nanoclusters) and OER (CoOOH nanosheets) active sites as well as strong in-suit structure stability, thereby exhibiting exceptional catalytic activity. In particular, the ultra-low overpotential of the HER (36mV) and the OER (264mV) are implemented to achieve 10mAcm-2. Experimental and theoretical calculations also reveal that Ru/CoOOH@NF possesses high intrinsic conductivity, which facilitates electron release from H2O and H-OH bond breakage and accelerates electron/mass transfer by regulating the charge distribution. This work provides a new avenue for the rational design of low-cost and high-activity bifunctional electrocatalysts for large-scale water-splitting technology and expects to help contribute to the creation of various hybrid electrocatalysts.

Optimizing Oxygen Electrode Bifunctionality with Platinum and Nickel Nanoparticle-Decorated Nitrogen-Doped Binary Metal Oxides

Developing bifunctional oxygen electrode materials with superior activity for oxygen reduction (ORR) and oxygen evolution (OER) reactions is essential for advancing regenerative fuel cell and rechargeable metal–air battery technologies. This present work deals with the synthesis and characterization of electrocatalysts containing Pt and Ni nanoparticles supported on nitrogen-doped mixed metal oxides (Mn2O3-NiO) and the systematic evaluation of their bifunctional ORR/OER performance in an alkaline medium. These electrocatalysts have been successfully synthesized by a simple and fast microwave method. PtNi/Mn2O3-NiO-N with a binary metal oxide-to-N ratio of 1:2 demonstrated the best performance among the studied materials regarding bifunctional electrocatalytic activity (∆E = 0.96 V) and robust stability.

Mn-doped nickel–cobalt sulfides as bifunctional electrodes for high-performance supercapacitors and electrocatalysts for hydrogen evolution reactions

The development of active electrode materials with dual functions of energy storage and electrocatalyst is important for future energy storage and energy conversion devices. In this work, manganese-doped nickel cobalt sulfide (Mn-NCS) mesoporous microspheres were prepared via a simple two-step solvent-thermal method and the effects of different Mn2+ doping levels on the electrochemical properties and hydrogen evolution reactions (HER) of the prepared samples were investigated. As a supercapacitor electrode material, optimized Mn0.5-NCS had a maximum specific capacitance of 1175 C g−1 at a current density of 1 A/g and remained an outstanding capacitance retention rate of 81 % at a current density of 20 A/g. The asymmetric supercapacitor was assembled with the optimal electrode material as the positive electrode and activated carbon as the negative electrode, and a high energy density of 55.4Wh kg−1 was achieved at a power density of 797 W kg−1. The Mn0.5-NCS exhibited the best HER performance in alkaline electrolyte, shown as the lowest overpotential of 95 mV and the smallest Tafel slope of 71 mV dec−1 at a current density of 10 mA cm−2. Experimental tests and density functional theory (DFT) calculations revealed that manganese preferentially occupies nickel sites and acted as an electron donor in the electrochemical process to realize the electron redistribution, increasing electron density and accelerating charge transfer. The results indicated that manganese-doped nickel–cobalt sulfides have great potential as bifunctional electrode materials for high-performance supercapacitors and HER.

Efficient processed carbon Soot@MoS2 hybrid Bi-functional electrode for dye-sensitized solar cell and asymmetric supercapacitor devices

A feasible approach to rectify the world's energy demand using sustainable development of adequate energy generation and storage technologies in a single channel. In this respect, we made a holistic approach with a bi-functional electrode material to perform effectively in energy generation and storage applications. MoS2 nanosheets were produced by the eco-friendly method and reduced graphene oxide is used to prepared by carbon soot which is derived from castor oil. The prepared soot and rGO were combined with MoS2 nanosheets using a simple sonication method. The as-prepared sample was introduced in the supercapacitor and DSSC application. The combination MoS2@rGO provides an enhanced conversion efficiency of 11.81 ​% and the reproducibility of DSSC is also studied. Further, MoS2@rGO is used to fabricate an asymmetric supercapacitor to investigate its real-time application. The device produced the maximum power density (1666.6 ​mW/kg) and energy density (25.69 ​mWh/Kg) at 1 A/g. The asymmetric supercapacitor device holds a cyclic stability of 81.4 % for 5000 cycles and it powered up an LED device for 4 ​min.

Manganese-cobalt hydroxide nanosheets anchored on a hollow sulfur-doped bimetallic MOF for high-performance supercapacitors and the hydrogen evolution reaction in alkaline media.

Nonmetallic doping and in situ growth techniques for designing electrode materials with excellent electrocatalytic activity are effective strategies to enhance the electrochemical performance. Bifunctional electrode materials for supercapacitors (SCs) and the hydrogen evolution reaction (HER) have attracted great interest due to their potential applications in green energy storage and conversion. Herein, the bimetallic MnCo LDH is anchored on a hollow sulfur (S)-doped MnCo-MOF-74 surface, forming a poplar flower-like 3D composite which is used for SCs and the HER in alkaline media. The fabricated S-MnCo-MOF-74@MnCo LDH/NF electrode exhibits a favorable specific capacitance of 1875.4 F g-1 at 1 A g-1 and steady long-term cycling performance. Moreover, the assembled HSC using S-MnCo-MOF-7@MnCo LDH/NF as the cathode material and active carbon (AC) as the anode material shows 546.4 F g-1 capacitance (1 A g-1) with a maximum energy density of 58 W h kg-1 at 14 000 W kg-1 power density. As an electrocatalyst, S-MnCo-MOF-7@MnCo LDH/NF exhibits excellent HER properties with a small Tafel slope of 128.9 mV dec-1 a low overpotential of 197 mV at 10 mA cm-2 and durable performance for 10 hours in alkaline media. The present work provides insights into understanding and designing active electrode materials for stable hydrogen evolution and high-performing supercapacitors in an alkaline environment.

ZIF-67 Grown in Situ over Carbon Fiber Felt (CFF) for Alkaline Water Splitting

Aiming for clean and affordable energy through green chemistry, water splitting emerges as one of the most effective and promising methods of producing high-purity hydrogen and oxygen without emitting harmful greenhouse gases into the atmosphere. As a result, the design and construction of low-cost, highly active, and long-term stable electrocatalysts is a challenge that must be highlighted. Considering their crystalline structure, morphological feature with high surface area, well defined pores, and tunable functionality, Metal-Organic Frameworks (MOFs) have attracted attention as materials in the development of highly efficient electrocatalysts for energy conversion and storage applications. The MOF used in this case is known as ZIF-67, which is a 3D self-assembled structure with Co(II) ions interconnected with 2-methylimidazole (Hmim) and has the same ligation angle as sodalite zeolites (145°). The ZIF-67 was anchored in situ on a carbon fiber felt (CFF; a great current collector), promoting the construction of a bottom-up electrode with MOF nanoparticles, which allows the electrode surface to have greater exposure of active sites due to interaction with the polar surface of the substrate in question. Nanoparticles also allow for greater electrocatalytic impacts by having surface effects that are enhanced when compared to bulk effects. Such prepared electrode was tested for water splitting in alkaline (1 M KOH) media, i.e., for hydrogen evolution as anodic reaction and oxygen evolution as cathodic reaction. Low onset potential accompanied by high current densities was observed under anodic polarization conditions. Thus, current density of 10 mA cm-2 was reached at potential of ca. 1.6 V vs RHE and current density as high as ca. 140 mA cm-2 at 2 V vs RHE. Such high performance could be attributed to the low charge-transfer resistance observed during electrochemical impedance measurements. The charge-transfer resistance further decreased with shift of potential to more positive values. Current density of 10 mA cm-2 was recorded at -0.2 V and current density of ca. 40 mA cm-2 at -0.4 V vs RHE under the cathodic polarization conditions. High performance suggests application of the herein prepared CFF/ZIF-67 as bifunctional electrode material for alkaline water electrolyzers. References Zhong, D. Liu, J. Zhang, J. Mater. Chem. A 2018, 6, 1887M. Birkholtz, DJ. Liu, Mater. Horiz. 2017, 4, 20Li, C.; Ma, D.; Zhu, Q, Angew. Chem. 2022, 12, 848. Figure 1

Interface engineering of N, P and S-doped hollow/porous Co3O4@Co3V2O8 heterostructure nanocube for high-activity supercapacitor and oxygen evolution reaction

Cobalt-based materials exhibit high theoretical specific capacitance and desirable electrocatalytic activity. However, their practical specific capacitance and electrocatalytic activity are significantly constrained by a lack of active sites and limited conductivity. Herein, N, P and S-doped hollow Co3O4@Co3V2O8 heterostructure nanocube is reasonably constructed via in-situ ion exchange method combined with calcination strategy. Besides, the relationship of heterogeneous interface and heteroatom doping on electrochemical performance is explored. The heterogeneous interface provides rich active sites and accelerates electron transfer. Additionally, N, P, and S-doping regulate the internal electronic structures, boost ion transfer rates, and increase active sites. The hollow structure accelerates the adsorption and desorption processes due to the increased electrochemical reaction sites. Benefiting from internal electronic structure and structural advantages, N, P, S-Co3O4@Co3V2O8 exhibits low overpotentials (561 mV and 649 mV at the current density of 50 mA/cm2 and 100 mA/cm2), low Tafel slopes (100.9 mV/dec), prospective specific capacitance (550.2 F/g) and outstanding charge/discharge behavior with remarkable life span. N, P, S-Co3O4@Co3V2O8 based device delivers favorable energy density (21.3 Wh/kg at 802.3 W/kg), which surpasses most of the latest cobalt-based materials. Overall, this work provides novel insights into the development of highly active and durable bifunctional electrode materials.

Mo-doped Ni3S2 nanosheet arrays for boosting hydrogen evolution activity and supercapacitor energy storage

The design and preparation of bifunctional electrode materials play a vital role in the field of energy storage and conversion. Herein, Mo-doped Ni3S2 nanosheet arrays assembled on nickel foam (named as Mo-Ni3S2) are designed through three-step continuous hydrothermal methods for enhanced hydrogen evolution reaction (HER) and supercapacitor storage characteristics. The ultrathin Mo-Ni3S2 nanosheets structure could modulate electronic structure and offer rich actives sites, thereby expediting the mobility of charge carriers and engendering a greater density of active sites. Consequently, the Mo-Ni3S2 exhibits low overpotential both in alkaline and acidic solution with the value of 53 and 65 mV at the current density of 10 mA cm−2, respectively. Meanwhile, the HER activity can be well maintained after 17 h of continuous operation at 10 mA cm−2, demonstrating its excellent stability. Furthermore, the as-prepared Mo-Ni3S2 as pseudocapacitive materials exhibits a specific capacitance of 3528 F g−1 at 1 A g−1, implying outstanding long durability with 96.5% capacity retention after 3000 charge–discharge cycles. Overall, this work provides a viable strategy for the development of transition metal-based materials as efficient bifunctional catalysts.

Co/Ni-MOF as a bifunctional electrode material for electrochemical sensor and oxygen evolution reaction

In recent years, the demand for economical multifunctional materials has increased significantly. In this paper, Co/Ni-based bimetallic-organic frameworks (Co/Ni-MOFs) materials were prepared, which showed good electrochemical recognition and oxygen evolution bifunctional activity in alkaline environment. The electrochemical test showed that the response time of the material to glucose was less than 3 s, the sensitivity was 2.0826 μAmM−1 cm−2, and the detection limit was 8.84 μM. The material also exhibits a good overpotential of 410 mV at a current density of 100 mA cm−2 and Tafel slope of 451 mV dec−1. The results show that Co/Ni-MOFs can be used as an electrocatalyst for electrochemical sensors and water splitting reactions.

Rational design of microflower-like manganese-doped ultrathin cobalt hydroxide nanosheets as bifunctional electrode materials for electrochemical sensing and supercapacitor applications

Noble metal-based electrocatalyst must be replaced for electrochemical applications by earth-rich, highly active, low-cost, and highly efficient dual-function electrocatalysts. In this study, transition metal-based hydroxides (TMHs), such as 2D manganese-doped cobalt hydroxide (Mn-Co(OH)2) ultrafine nanosheets, are investigated using a very simple large-scale co-precipitation method for efficient electrochemical sensing (nitrofurantoin (NFT)) and supercapacitor (SC) applications. The characterization results show that the porous and large surface area, polycrystalline nature, confinement of the 2D orientation, and strong synergistic effect contribute to the admirable electrochemical concert of Mn-Co(OH)2 for both sensing and SC applications. CV, GCD, EIS, and DPV techniques are used to thoroughly investigate electrochemical and physicochemical properties. As an electrochemical sensor, the Mn-Co(OH)2 modified disposable screen-printed carbon electrode (Mn-Co(OH)2/SPCE) shows excellent electrochemical assets for NFT detection with broad linear ranges (0.05–219 μM and 262–641 μM), low detection limit (0.012 μM) and good anti-interference ability. The obtained specific capacitance of Mn-Co(OH)2 is 348.8 F g−1 at 1 A g−1 with a maintenance capacitance of 80.76 % after 5000 cycles at 10 A g−1. The enhanced electrochemical behavior of Mn-Co(OH)2 may be related to the fast diffusion pathways of Mn doping and the enhanced redox reaction (cobalt ions) of the flower-like ultrathin nanosheets owing to their high surface area (214 m2/g). The characterization results and electrochemical performance (sensing and SCs) provide important and noteworthy insights into the synthesis of noble metal-free and high-efficiency transparent 2D TMHs nanosheets with high performance that can be widely used in various applications.

Zeolitic Imidazolate Framework-Derived Zn/Co-S@Ni(OH)2 Nanoarrays with Excellent Energy Storage and Electrocatalytic Performance.

The design and development of high-performance electrochemical electrode materials are crucial for energy storage and conversion systems. This work reports a facile preparation of a self-supported Zn/Co-S@Ni(OH)2 array electrode in which a Zn/Co-S nanosheet is derived from a leaf-like zeolitic imidazolate framework (Zn/Co-ZIF-L). The core-shell structure provides multiple benefits such as enhanced electrical conductivity, an abundance of exposed active sites, and strong electronic interactions between Zn/Co-S and ultra-thin Ni(OH)2 nanosheets, facilitating faster charge transfer. Consequently, Zn/Co-S@Ni(OH)2 demonstrates remarkable electrochemical characteristics as an electrode material for supercapacitors with an area capacitance of 12.9 F cm-2 at a current density of 2 mA cm-2 in 2 M KOH. The assembled asymmetric supercapacitor device achieves a high energy density of 0.95 mW h cm-2, while showing excellent longevity with a retention of 90.9% over 5000 cycles. Additionally, the Zn/Co-S@Ni(OH)2 arrays demonstrate significant oxygen evolution reaction activity with an overpotential of 242 mV at 10 mA cm-2 in 1 M KOH and significant stability for more than 100 h. This work provides a valuable approach for synthesizing bifunctional electrode materials for both energy storage and electrocatalysis applications.

Hierarchical dessert plant-like CoNiO2 nanowires decoration on MoS2 nano-petals for enhanced bi-functional overall water splitting reactions

To produce hydrogen, overall water splitting is the extremely effective method and their one of the key factors is the fabrication of bifunctional electrode materials with high catalytic activity, rotational design with a high active site, easy mass transfer, stability, and earth abundance. In this work, CoNiO2 nanowires (NWs)-embedded MoS2 hybrids were prepared using the hydrothermal synthesis method. The developed CoNiO2@MoS2 hybrid electrode achieved superior bifunctional catalytic activity with an overpotential of 43 mV and 220 mV for hydrogen evolution and oxygen evolution reactions, respectively, and more than 24 h span stability. Furthermore, the assembled CoNiO2@MoS2║CoNiO2@MoS2 electrocatalyst exhibited an overpotential of 1.47 V for overall splitting process at 10 mA cm−2, with improved electronic conductivity and stability. Density functional theory approximations revealed that the CoNiO2 NWs and MoS2 in the CoNiO2@MoS2 hybrid exhibited a strong interfacial contact, which enabled the preferable ΔGH⁎ and ΔGn values, thus significantly improving the electrocatalytic performance. The development of cobalt-based oxides with transition metal dichalcogenides-carrier bifunctional electrocatalysts will provide a novel approach to enhance overall water splitting.

Coordination Engineering of Dual Co, Ni Active Sites in N-Doped Carbon Fostering Reversible Oxygen Electrocatalysis.

The development of affordable and non-noble-metal-based reversible oxygen electrocatalysts is required for renewable energy conversion and storage systems like metal-air batteries (MABs). However, the nonbifunctionality of most of the catalysts impedes their use in rechargeable MAB applications. Moreover, the loss of active sites also affects the long-term performance of the electrocatalyst toward oxygen electrocatalysis. In this work, we report a simplistic yet controllable chemical approach for the synthesis of dual transitional metals such as cobalt, nickel, and nitrogen-doped carbon (CoNi-NC) as bifunctional electrode materials for rechargeable zinc-air batteries (ZABs). The spatially isolated Ni-N4 and Co-N4 active units were rendered for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. The individual efficacy of both reversible reactions enables an ΔE value of ∼0.72 V, which outperforms several bifunctional electrocatalysts reported in the literature. The half-wave potential (E1/2) and overpotential were achieved at 0.83 V and 330 mV (vs RHE) for ORR and OER, respectively. The peak power density of ZAB equipped with the CoNi-NC catalyst was calculated to be 194 mW cm-2. The present strategy for the synthesis of bifunctional electrocatalysts with dual active sites offers prospects for developing electrochemical energy storage and conversion systems.