Ultrathin NiFeZn-MOF nanosheets containing few metal oxide nanoparticles grown on nickel foam for efficient oxygen evolution reaction of electrocatalytic water splitting

Metal-Organic-Framework-Based Nanoarrays for Oxygen Evolution Electrocatalysis

The development of highly active and stable electrode materials for the oxygen evolution reaction (OER) is essential for the widespread application of electrochemical energy conversion systems. In recent years, various metal-organic frameworks (MOFs) with self-supporting array structures have been extensively studied because of their high porosity, abundant metal sites, and flexible and adjustable structures. This review provides an overview of the recent progress in the design, preparation, and applications of MOF-based nanoarrays for the OER, beginning with the introduction of the architectural advantages of the nanoarrays and the characteristics of MOFs. Subsequently, the design principles of robust and efficient MOF-based nanoarrays as OER electrodes are highlighted. Furthermore, detailed discussions focus on the composition, structure, and performance of pristine MOF nanoarrays (MOFNAs) and MOF-based composite nanoarrays. On the one hand, the effects of the two components of MOFs and several modification methods are discussed in detail for MOFNAs. On the other hand, the review emphasizes the use of MOF-based composite nanoarrays composed of MOFs and other nanomaterials, such as oxides, hydroxides, oxyhydroxides, chalcogenides, MOFs, and metal nanoparticles, to guide the rational design of efficient OER electrodes. Finally, perspectives on current challenges, opportunities, and future directions in this research field are provided.

Facile formation of Zn-incorporated NiFe layered double hydroxide as highly-efficient oxygen evolution catalyst

Electrochemical water splitting is the primary method to produce green hydrogen, which is considered an efficient alternative to fossil fuels for achieving carbon neutrality. For meeting the increasing market demand for green hydrogen, high-efficiency, low-cost, and large-scale electrocatalysts are crucial. In this study, we report a simple spontaneous corrosion and cyclic voltammetry (CV) activation method to fabricate Zn-incorporated NiFe layered double hydroxide (LDH) on commercial NiFe foam, which shows excellent oxygen evolution reaction (OER) performance. The electrocatalyst achieves an overpotential of 565 mV and outstanding stability of up to 112 h at 400 mA cm^-2. The active layer for OER is shown to be β-NiFeOOH according to the results of in-situ Raman. Our findings suggest that the NiFe foam treated by simple spontaneous corrosion has promising industrial applications as a highly efficient OER catalyst.

Rationally Reconstructed Metal-Organic Frameworks as Robust Oxygen Evolution Electrocatalysts

Reconstructing metal-organic framework (MOFs) toward a designed framework structure provides breakthrough opportunities to achieve unprecedented oxygen evolution reaction (OER) electrocatalytic performance, but has rarely, if ever, been proposed and investigated yet. Here, the first successful fabrication of a robust OER electrocatalyst by precision reconstruction of an MOF structure is reported, viz., from MOF-74-Fe to MIL-53(Fe)-2OH with different coordination environments at the active sites. Due to the radically reduced e_g -t_2g crystal-field splitting in Fe-3d and the much suppressed electron-hopping barriers through the synergistic effects of the O species the efficient OER of in MIL-53(Fe)-2OH is guaranteed. Benefiting from this desired electronic structure, the designed MIL-53(Fe)-2OH catalyst exhibits high intrinsic OER activity, including a low overpotential of 215 mV at 10 mA cm^-2 , low Tafel slope of 45.4 mV dec^-1 and high turnover frequency (TOF) of 1.44 s^-1 at 300 mV overpotential, over 80 times that of the commercial IrO₂ catalyst (0.0177 s^-1 ).Consistent with the density functional theory (DFT) calculations, the real-time kinetic simulation reveals that the conversion from O* to OOH* is the rate-determining step on the active sites of MIL-53(Fe)-2OH.

One-Dimensional Co-Carbonate Hydroxide@Ni-MOFs Composite with Super Uniform Core-Shell Heterostructure for Ultrahigh Rate Performance Supercapacitor Electrode

The insufficient contact between two phases in the heterostructure weakens the coupling interaction effect, which makes it difficult to effectively improve the electrochemical performance. Herein, a Co-carbonate hydroxide@ Ni-metal organic frameworks (Co-CH@Ni-MOFs) composite with super uniform core-shell heterostructure is fabricated by adopting 1D Co-CH nanowires as structuredirecting agents to induce the coating of Ni-MOFs. Both experimental and theoretical calculation results demonstrate that the heterostructure plays a vital role in the high performance of the as-prepared materials. On the one hand, the construction of super uniform core-shell heterostructure can create a large number of interfacial active sites and take advantages of the electrochemical characteristics of each component. On the other hand, the heterostructure can increase the adsorption energy of OH^- ions and promote the electrochemical activity for improving the reversible redox reaction kinetics. Based on the aforementioned advantages, the as-fabricated Co-CH@Ni-MOFs electrode exhibits a high specific capacity of 173.1 mAh g^-1 (1246 F g^-1 ) at 1 A g^-1 , an ultrahigh rate capability of 70.3% at 150 A g^-1 and excellent cycling stability with 90.1% capacity retention after 10 000 cycles at 10 A g^-1 . This study may offer a versatile design for fabricating a MOFs-based heterostructure as energy storage electrodes.

Nanosheet-assembled NiCo-LDH hollow spheres as high-performance electrodes for supercapacitors

Layered double hydroxides (LDHs) have been considered as favorable pseudocapacitive electrode materials for supercapacitors due to their tunable layered structure/compositions and low cost. Here, we report the NiCo-LDH hollow spheres prepared with Co-glycerate as the sacrificial template and cobalt source. The hollow spheres are assembled with frizzy NiCo-LDH nanosheets, where the hollow structure can inhibit agglomeration of the LDH nanosheets to expose more active sites and shorten the diffusion path of electrolyte ions. The prepared NiCo-LDH hollow spheres show a high specific capacitance of 1962 F g^-1 at 1 A g^-1 and good capacitance retention rate of 66.4 % at 30 A g^-1. The asymmetric supercapacitors fabricated using NiCo-LDH hollow spheres as positive electrode yields a large energy density 62.9 Wh kg^-1 at the power density of 0.8 kW kg^-1. This research may develop a facile synthesis way to prepare LDH hollow spheres for supercapacitors.

Ultrathin 2D flower-like CoP@C with the active (211) facet for efficient electrocatalytic water splitting

Due to the more exposed (211) facet, the electrocatalytic water splitting activity of 2D CoP@C is superior to that of its counterpart 3D structure.

Assembly of ZIF-67 nanoparticles and in situ grown Cu(OH)2 nanowires serves as an effective electrocatalyst for oxygen evolution

Due to the slow kinetics of oxygen evolution at the anode, the efficiency of electrocatalytic water decomposition is critically reduced, and its large-scale application is severely restricted. Therefore, it is urgent to develop electrocatalysts with excellent performance and stability to accelerate the oxygen evolution reaction (OER) reaction kinetics. Herein, a self-supporting binder-free electrocatalyst was successfully prepared using in situ grown Cu(OH)2 nanowires on CF as the carrier to grow ZIF-67 via a room temperature immersion method. The combination of Cu(OH)2 nanowires and the unique structure of ZIF-67 forms a three-dimensional nanostructured catalyst, in which the unique structure and the existence of synergy may contribute to a larger electrochemical active surface area, expose more electrochemically active sites, adjust the electronic structure, and accelerate the rate of electron transfer, thus greatly improving the electrocatalytic activity and durability for OER. The as-prepared Cu(OH)2@ZIF-67/CF exhibited excellent OER performance under alkaline conditions and required overpotentials of 205 mV and 276 mV to drive current densities of 10 mA cm-2 and 100 mA cm-2, respectively, with a small Tafel slope of 70.5 mV dec-1 for OER. The stability test of Cu(OH)2@ZIF-67/CF at the current density of 10 mA cm-2 displayed excellent stability for 22 h. This study provides a feasible strategy for the rapid preparation of low-cost and efficient electrocatalysts in alkaline media.

Recent development of two-dimensional metal-organic framework derived electrocatalysts for hydrogen and oxygen electrocatalysis

Developing efficient and low-cost electrocatalysts with unique nanostructures is of great significance for improved electrocatalytic reactions, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Two-dimensional (2D) metal-organic frameworks (MOFs) have attracted recent attention because of their unique dimension-related properties, such as ultrathin thickness, large specific surface area, and abundant accessible active sites that can act as good precursors for the derivation of a variety of nanocomposites as active materials in electrocatalysis and energy-related devices. In this review, we present recent developments in 2D MOF-derived nanomaterials for hydrogen and oxygen reactions in overall water-splitting and rechargeable Zn-air batteries. The advantages of various synthetic strategies are summarized and discussed in detail. Finally, we discuss the main challenges and future perspectives of the development of 2D MOF-derived electrocatalysts.

Two-dimensional metal-organic frameworks and their derivatives for electrochemical energy storage and electrocatalysis

Two-dimensional (2D) metal-organic frameworks (MOFs) and their derivatives with excellent dimension-related properties, e.g. high surface areas, abundantly accessible metal nodes, and tailorable structures, have attracted intensive attention as energy storage materials and electrocatalysts. A major challenge on the road toward the commercialization of 2D MOFs and their derivatives is to achieve the facile and controllable synthesis of 2D MOFs with high quality and at low cost. Significant developments have been made in the synthesis and applications of 2D MOFs and their derivatives in recent years. In this review, we first discuss the state-of-the-art synthetic strategies (including both top-down and bottom-up approaches) for 2D MOFs. Subsequently, we review the most recent application progress of 2D MOFs and their derivatives in the fields of electrochemical energy storage (e.g., batteries and supercapacitors) and electrocatalysis (of classical reactions such as the HER, OER, ORR, and CO2RR). Finally, the challenges and promising strategies for the synthesis and applications of 2D MOFs and their derivatives are addressed for future development.