Surface engineering of 2D MOF to construct high-density Co9S8 nanoparticles supported on nitrogen doped carbon for efficient oxygen evolution reaction

Transition metal sulfides and their hybrids are promising alternative to precious metal catalyst for the oxygen evolution reaction (OER). Herein, the high-density Co₉S₈ nanoparticles (NPs) embedded in N-doped carbon has been prepared by using surface-engineered zeolitic imidazolate framework-9 (ZIF-9) nanosheets as precursor. The surface of ZIF-9 was modified with TAA, which is able to create chemical barrier and prevents metal from aggregation in the subsequent pyrolysis, thus making small Co₉S₈ NPs densely anchored on carbon layers. Arising from the unique structure, Co₉S₈@NC affords an optimized electronic structure and rich effective reactive sites for OER. As expected, Co₉S₈@NC exhibits small overpotential of 264 mV at 10 mA cm⁻², low Tafel slope of 68.4 mV dec⁻¹, and superior stability for alkaline OER (0.1 M KOH). The electrolysis cell, which was equipped with Co₉S₈@NC cathode and Pt/C anode, shows low water splitting voltage of 1.58 V at 10 mA cm⁻² in 1.0 M KOH. This work employs an efficacious surface engineering strategy to design metal sulfide-based electrocatalysts for enhancing OER performance.     

ZIF-67-derived Mn doped Co9S8 supported on N-Enriched porous carbon polyhedron as an efficient electrocatalyst for oxygen evolution reaction

Rational design of efficient oxygen evolution reaction (OER) electrocatalysts plays a significant role in various applications like water splitting and metal-air batteries. Simultaneous modulation of geometric and electronic structure is a promising strategy for boosting the electrocatalytic active of OER catalysts. Herein, a novel type of Mn doped Co₉S₈ supported on N-enriched porous carbon polyhedron composite material (Mn–Co₉S₈/NC) is constructed via absorption-pyrolysis-sulfurization treatment of Zeolitic-imidazolate frameworks (ZIF-67). ZIF-67 derived N-enriched porous carbon polyhedron serves as the porous skeleton for anchoring numerous Co₉S₈ nanoparticles. The results confirm that the incorporation of Mn in Co₉S₈/NC can improve the degree of graphitization compared with Co₉S₈/NC, implying the enhancement of the conductivity. Meanwhile, the incorporation of Mn can lead to electronic modulation of Co species to bump up the intrinsic activity of active site in Mn–Co₉S₈/NC. Due to the synergistic effect of Mn, Co₉S₈ and porous carbon structure, the specific surface area and electronic structure are optimized, endowing the maximum utilization of active sites. The Mn–Co₉S₈/NC electrocatalyst exhibits superior OER activity with the overpotential of 286 mV at current density of 10 mA cm⁻² in 1.0 M KOH electrolyte. This work provides prospective insights into the synergistic coupling of geometric and electronic structure of Metal-Organic Frameworks (MOFs) material for efficient electrocatalysts.     

Controlled synthesis of Mn3O4/Co9S8–Ni3S2 on nickel foam as efficient electrocatalyst for oxygen evolution reaction

Advances in electrochemical interfaces have greatly facilitated the development of new energy systems that can replace traditional fossil fuels. Oxygen evolution reaction (OER) is the core reaction in the new energy conversion system to produce hydrogen. Here, nanorods structure of Mn₃O₄/Co₉S₈–Ni₃S₂/NF-4 was designed and assembled. The Mn₃O₄ has served as an appropriate matrix to build a composite structure with Co₉S₈–Ni₃S₂ to enhance the stability of catalyst. And the introduction of Mn regulated the electronic structure of Ni and Co, which increased the OER activity of matericals. Further characterization and electrochemical testing have suggested that between polymetallic can effectively optimize conductivity and enhance reaction kinetics. Mn₃O₄/Co₉S₈–Ni₃S₂/NF-4 can achieve overpotential of 188 mV at the current density of 10 mA cm^?2 in alkaline solution, with small Tafel slope of 43.2 mV dec^?1 and satisfactory stability of 30 h at 10 mA cm^?2. This work may show a feasible reference in the design of high-efficient OER catalysts.     

Assembly of Fe7S8 and Co9S8 nanosheets coupled with Cu(OH)2 nanorods as highly efficient oxygen evolution catalyst

Traditional fossil fuels can be replaced with hydrogen, and electrolysis of water is thought to be one of the most efficient ways to produce hydrogen that is also pollution-free. The oxygen evolution reaction (OER), which is thought to be the bottleneck of the entire water decomposition, is a result of the intricate electrochemical mechanism and the slow kinetic process. In this paper, Cu(OH)₂ forerunners with nanorods structure were combined on copper froth by straightforward submersion technique. Then, in a standard three-electrode system Fe₇S₈ and Co₉S₈ nanosheets with 3D structures were assembled on Cu(OH)₂ precursors by electrodeposition. At an alkaline environment of 1 M KOH, Cu(OH)₂/CF requires an overpotential of only 235 mV when the current density reaches 10 mA cm^?2, which is lower than that of other reported catalysts. In addition, Fe₇S₈–Co₉S₈@Cu(OH)₂/CF also showed excellent OER performance after long-term stability test, because bimetallic synergism can adjust the electronic structure of the catalyst and optimize its electrical conductivity. A feasible method for the design of a highly efficient oxygen evolution catalyst based on copper foam is reported in this paper.     

Hollow structured Zn0.76Co0.24S–Co9S8 composite with two-phase synergistic effect as bifunctional catalysts

It is of great significance to develop efficient and inexpensive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts for the current energy crisis. But this is still a long-term and formidable challenge. In this work, a two-phase synergistic effect between transition metal sulfides is applied in the design of ORR/OER bifunctional catalysts. Co-based zeolite imidazolate framework (MOF) is used as a precursor to prepare the hollow Co₉S₈ through vulcanization and heat treatment. At the same time, the phase transformation occurs to form some Zn_0.76Co_0.24S on surface during the heat treatment due to the Zn-polydopamine coating. The hollow structure Zn_0.76Co_0.24S–Co₉S₈ composite has been verified and promotes the diffusion of reactants and products, and the interaction between two phases greatly promotes the catalytic reactions. The coating of Zn-polydopamine forms uniform carbon layer on surface, enhancing the conductivity of Zn_0.76Co_0.24S–Co₉S₈ composite. The Zn_0.76Co_0.24S–Co₉S₈ composite shows much better performance of ORR and OER compared to any of them. The overpotential of OER at a current density of 10 mA/cm² is 330 mV, and the half-wave potential of ORR is 0.83 V. Additionally, the Zn_0.76Co_0.24S–Co₉S₈ composite displays better cyclic stability. The synergistic effect of Zn_0.76Co_0.24S and Co₉S₈ can be considered as the foremost factor for the improvement of catalyst performance, which provides new possibilities for the development of non-precious metal bifunctional catalysts.     

Zeolitic-imidazolate frameworks-derived Co3S4/NiS@Ni foam heterostructure as highly efficient electrocatalyst for oxygen evolution reaction

Transition metals sulfide-based nanomaterials have recently received significant attention as a promising cathode electrode for the oxygen evolution reaction (OER) due to their easily tunable electronic, chemical, and physical properties. However, the poor electrical conductivity of metal-sulfide materials impedes their practical application in energy devices. Herein, firstly nano-sized crystals of cobalt-based zeolitic-imidazolate framework (Co-ZIF) arrays were fabricated on nickel-form (NF) as the sacrificial template by a facile solution method to enhance the electrical conductivity of the electrocatalyst. Then, the Co₃S₄/NiS@NF heterostructured arrays were synthesized by a simple hydrothermal route. The Co-ZIFs derived Co₃S₄ nanosheets are grown successfully on NiS nanorods during the hydrothermal sulfurization process. The bimetallic sulfide-based Co₃S₄/NiS@NF-12 electrocatalyst demonstrated a very low overpotential of 119 mV at 10 mA cm^?2 for OER, which is much lower than that of mono-metal sulfide NiS@NF (201 mV) and ruthenium-oxide (RuO₂) on NF (440 mV) electrocatalysts. Furthermore, the Co₃S₄/NiS@NF-12 electrocatalyst showed high stability during cyclic voltammetry and chronoamperometry measurements. This research work offers an effective strategy for fabricating high-performance non-precious OER electrocatalysts.     

Highly active Ni/Co-metal organic framework bifunctional electrocatalyst for water splitting reaction

Rational design of electrocatalycally active materials with excellent performance for renewable energy conversion is of great interest. We have developed a nanosheet array of Ni/Co metal-organic framework (MOF) grown on CoO modified Ni foam (CoO/NF) substrate via the solvothermal process. The high surface area and low resistance of Ni/Co-MOF@CoO/NF (NC@CoO/NF) catalyst contribute to efficient water splitting. We have prepared a series of NC-n/CoO/NF (n = 1–4) catalysts to optimize the molar ratio of the Co atom in Ni MOF-74. Among them, NC-2@CoO/NF shows an excellent electrochemical performance in alkaline medium, i.e., low overpotential of 290 and 139 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. For a two-electrode system with NC-2@CoO/NF, a low cell voltage of 1.54 V at 10 mA cm^?2 has been obtained for overall water splitting which is much smaller than that with commercial Ir/C– Pt/C pair. This excellent performance can be attributed to the synergistic effects of Ni/Co-MOF and CoO/NF. In addition, the as-prepared NC-2@CoO/NF exhibits excellent long-term stability. The computational simulation also supports experimental results.     

Interface engineering of NixSy@MoS2 heterostructured nanorods as high-efficient electrocatalysts for water splitting

Robust and low-cost oxygen evolution reaction (OER) electrocatalysts at low overpotentials play an increasingly pivotal role in clean energy storage and conversion systems. The emerging catalyst with core-shell heterostructure has excited the potentiality of non-noble-metal candidates. Herein, in order to enhance the sufficient exposure and utilization of actives sites and accelerate the electron transfer rate of catalyst, Ni_xS_y@MoS₂ core-shell nanorods decorated NiSe₂ framework (Ni_xS_y@MoS₂/NiSe₂) electrocatalyst has been successfully prepared via interface engineering. As expected, the as-prepared catalyst shows an outstanding OER activity with a small overpotential of 360 mV to drive 100 mA cm⁻² and a Tafel slope of 64 mV dec⁻¹. More importantly, a low cell voltage of 1.40 V is achieved for the Ni_xS_y@MoS₂/NiSe₂ based water splitting electrolyzer at 10 mA cm⁻², and it shows negligible decrement after continuous operation for 100 h. Furthermore, density functional theory (DFT) calculations further uncovered the synergetic catalytic effect between the Ni_xS_y@MoS₂ core-shell nanorods and the NiSe₂ framework played a key role in generating more charge carriers and declining the energy barriers in the process of forming intermediates.     

Electrodeposition of NiFe layered double hydroxide on Ni3S2 nanosheets for efficient electrocatalytic water oxidation

The oxygen evolution reaction (OER) plays a vital role in various energy conversion applications. Up to now, the highly efficient OER catalysts are mostly based on noble metals, such as Ir- and Ru-based catalysts. Thus, it is extremely urgent to explore the non-precious electrocatalysts with great OER performance. Herein, a simple electrodeposition combined with hydrothermal method is applied to synthesize a non-precious OER catalyst with a three-dimensional (3D) core-shell like structure and excellent OER performance. In our work, NiFe layered double hydroxide (LDH) was electrodeposited on Ni₃S₂ nanosheets on nickel foam (NF), which exhibits a better performance compared with RuO₂, and a low overpotential of 200 mV is needed to reach the current density of 10 mA/cm² in 1 M KOH. Notably, the Ni₃S₂/NiFe LDH only need an overpotential of 273 mV to reach the current density of 200 mA/cm².     

Co0.85Se on three-dimensional hierarchical porous graphene-like carbon for highly effective oxygen evolution reaction

Designing an efficient, cheap and abundant catalyst for oxygen evolution reaction (OER) is crucial for the development of sustainable energy sources. A novel catalyst which could be a promising candidate for such electrocatalysts is described. Co_0.85Se supported on three-dimensional hierarchical porous graphene-like carbon (HPG) exhibits outstanding catalytic performances for OER in alkaline medium. It is found that the onset overpotential is 311 mV on the Co_0.85Se/HPG electrode, which is more 28 and 41 mV negative than that on the Co/HPG and Co₃O₄/HPG electrodes. What's more, the value of Tafel slope is 61.7 mV dec⁻¹ and the overpotential at the current density of 10 mA cm⁻² is 385 mV on this electrode. The Co_0.85Se/HPG of this work is an appealing electrocatalyst for OER in basic electrolyte.     

One-pot solvothermal synthesis of Co2P nanoparticles: An efficient HER and OER electrocatalysts

Development of an inexpensive electrocatalyst for hydrogen evolution (HER) and oxygen evolution reactions (OER) receives much traction recently. Herein, we report a facile one-pot ethyleneglycol (EG) mediated solvothermal synthesis of orthorhombic Co₂P with particle size ~20–30 nm as an efficient HER and OER catalysts. Synthesis parameters like various solvents, temperatures, precursors ratios, and reaction time influences the formation of phase pure Co₂P. Investigation of Co₂P as an electrocatalyst for HER in acidic (0.5 M H₂SO₄) and alkaline medium (1.0 M KOH), furnishes low overpotential of 178 mV and 190 mV, respectively to achieve a 10 mA cm^?2 current density with a long term stability and durability. As an OER catalyst in 1.0 M KOH, Co₂P shows an overpotential of 364 mV at 10 mA cm^?2 current density. Investigation of Co₂P NP by XPS analysis after OER stability test under alkaline medium confirms the formation of amorphous cobalt oxyhydroxide (CoOOH) as an intermediate during OER process.     

Amorphous CoFeP/NC hybrids as highly efficient electrocatalysts for water oxidation

The rational design and regulate structure and composition are pivotal for the development of highly efficient oxygen evolution reaction (OER) catalysts for water splitting. In this study, amorphous CoFeP/NC hybrid electrocatalyst has been synthesized by a simple and effective phosphorization of a CoFe-based coordination polymer under N₂ atmosphere. The synergistic effects between the CoFeP and N-doped carbon has led to high electronic conductivity attributed to the optimal Fe contents with N-doped carbon and enlarged electrocatalytic active surface area aroused by the nanostructure of CoFeP/NC, as well as the surface structural evolution of oxyhydroxide/phosphate during OER process. The resulting Co_0.35Fe_0.17P_0.48/NC electrocatalyst can attain a current density of 10 mA/cm² at an overpotential of 275 mV with a Tafel slope of 31 mV/dec on glassy carbon electrode and 228 mV on Ni foam electrode in 1 M KOH solution, long-term OER stability of this Co_0.35Fe_0.17P_0.48/NC under the applied potential of 1.53 V vs. RHE demonstrates no obvious decline in current densities of 110 mA/cm² within 17 h, which outperforms those of the contrast electrocatalysts in this work and also comparable to that of many of the reported electrocatalysts in the literatures. This Co_0.35Fe_0.17P_0.48/NC electrocatalyst highlights the rational modulation of optimal composition and electronic structure with homogeneous incorporation of the foreign metal-doped and N-doped carbon for the synthesis of highly efficient electrocatalysts toward to the water oxidation reactions.     

Iron-doped cobalt nitride nanoparticles (Fe–Co3N): An efficient electrocatalyst for water oxidation

The exploration of efficient, low-cost and earth-abundant oxygen-evolution reaction (OER) electrocatalysts and the understanding of the intrinsic mechanism are important to advance the clean energy conversion technique based on electrochemical water oxidation. In this work, Fe-doping Co₃N catalysts were successfully synthesized by a simple nitridation reaction of the Co_3-xFe_xO₄ precursor. This material exhibited a low overpotential of 294 mV at a current density of 10 mA cm^?2, and a small Tafel slope of 49 mV dec^?1 in 1 M KOH solution, superior to the performance of Co₃N and IrO₂. As revealed by the spectroscopic and electrochemical analyses, the enhanced OER performance mainly originates from the electronic modulation induced by the incorporation of Fe into Co₃N, benefitting the formation of CoOOH as active surface species and thus facilitating the OER process. These findings also demonstrate the introduction of heterogeneous element is a simple and effective strategy to regulate the OER property of the cobalt nitrides (Co₃N) catalysts.     

Tailoring the activity of NiFe layered double hydroxide with CeCO3OH as highly efficient water oxidation electrocatalyst

Owing to the efficient modulation of the electronic structure of nanomaterials, rare earth elements introduction as promoters into nanomaterials has attracted great attention in oxygen evolution reaction (OER). This work demonstrates the cerium carbonate hydroxide (CeCO₃OH) in situ grown on nickel foam (NF) supported NiFe layered double hydroxide (LDH) as a novel promoter in OER process. The hybrid material (Ni_0.75Fe_0.15Ce_0.10/NF) possesses excellent performance for OER where the overpotentials at the current densities of 10 mA cm^?2 and 100 mA cm^?2 are 228 mV and 270 mV, respectively, along with the Tafel slope of 38.3 mV dec^?1. Such performance is comparable in activity to many state-of-the-art electrocatalysts. The enhanced performance in the NiFe LDH can be ascribed to the synergetic interaction between CeCO₃OH and NiFe LDH by utilizing the advantages of cerium and carbonate in OER. The novelty of our work is the exploration of CeCO₃OH as a promoter to enhance the OER performance, which expands the application of cerium-based compounds in energy storage and conversion.     

Three-dimensional ZnCo/MoS2–Co3S4/NF heterostructure supported on nickel foam as highly efficient catalyst for hydrogen evolution reaction

Exploring inexpensive and earth-abundant electrocatalysts for hydrogen evolution reactions is crucial in electrochemical sustainable chemistry field. In this work, a high-efficiency and inexpensive non-noble metal catalysts as alternatives to hydrogen evolution reaction (HER) was designed by one-step hydrothermal and two-step electrodeposition method. The as-prepared catalyst is composed of the synergistic MoS₂–Co₃S₄ layer decorated by ZnCo layered double hydroxides (ZnCo-LDH), which forms a multi-layer heterostructure (ZnCo/MoS₂–Co₃S₄/NF). The synthesized ZnCo/MoS₂–Co₃S₄/NF exhibits a small overpotential of 31 mV and a low Tafel plot of 53.13 mV dec^?1 at a current density of 10 mA cm^?2, which is close to the HER performance of the overpotential (26 mV) of Pt/C/NF. The synthesized ZnCo/MoS₂–Co₃S₄/NF also has good stability in alkaline solution. The excellent electrochemical performance of ZnCo/MoS₂–Co₃S₄/NF electrode originates from its abundant active sites and good electronic conductivity brought by the multilayer heterostructure. This work provides a simple and feasible way to design alkaline HER electrocatalysts by growing heterostructures on macroscopic substrates.     

3D V–Ni3S2@CoFe-LDH core-shell electrocatalysts for efficient water oxidation

Studying cheap and efficient electrocatalysts is of great significance to promote the sluggish kinetics of oxygen evolution reaction (OER). Here, we adopted a simple two-step method to successfully prepare the 3D V–Ni₃S₂@CoFe-LDH core-shell electrocatalyst. The V–Ni₃S₂@CoFe-LDH/NF shows excellent OER performance with low overpotential (190 mV at 10 mA/cm² and 240 mV at 50 mA/cm²), small Tafel slope (26.8 mV/dec) and good long-term durability. Excitingly, to reach the same current density, V–Ni₃S₂@CoFe-LDH/NF electrode even needs much smaller overpotential than RuO₂. Furthermore, the outstanding OER activity of V–Ni₃S₂@CoFe-LDH/NF is ascribed to the following reasons: (1) V–Ni₃S₂ nanorod cores improve the conductivity and ensure the fast charge transfer; (2) CoFe-LDH nanosheets interconnected with each other provide more exposed active sites; (3) the unique 3D core-shell structures are favorable for electrolyte diffusion and gas releasing. Our work indicates that building 3D core-shell heterostructure will be a useful way to design good electrocatalysts.     

Spherical Co/Co9S8 as electrocatalyst for hydrogen production from alkaline solution and alkaline seawater

Cobalt-based sulfide catalysts are considered as potential materials for electrocatalytic hydrogen production from seawater. Here, we have successfully prepared a Co/Co₉S₈ electrocatalyst with hollow spherical structure. As-prepared material exhibited excellent electrocatalytic activity in hydrogen evolution reaction (HER) in alkaline seawater. The overpotentials for Co/Co₉S₈ in alkaline seawater were measured as low as 136.2 mV, when reached a current density of 10 mA cm^{− 2}. It also had good stability and could be maintained for 24 h in 1.0 M KOH and alkaline seawater. The results of SEM and TEM confirmed that the catalyst had excellent reaction structure. Due to the hollow structure, Co/Co₉S₈ showed remarkable catalytic performance for HER. The construction method of Co/Co₉S₈ hollow structure is an effective strategy to improve the performance of HER for seawater splitting.     

CNT-interconnected iron-doped NiP2/Ni2P heterostructural nanoflowers as high-efficiency electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) plays a decisive role in electrolytic water splitting. However, it is still challengeable to develop low-cost and efficient OER electrocatalysts. Herein, we present a combination strategy via heteroatom doping, hetero-interface engineering and introducing conductive skeleton to synthesize a hybrid OER catalyst of CNT-interconnected iron-doped NiP₂/Ni₂P (Fe-(NiP₂/Ni₂P)@CNT) heterostructural nanoflowers by a simple hydrothermal reaction and subsequent phosphorization process. The optimized Fe-(NiP₂/Ni₂P)@CNT catalyst delivers an ultralow Tafel slope of 46.1 mV dec^?1 and overpotential of 254 mV to obtain 10 mA cm^?2, which are even better than those of commercial OER catalyst RuO₂. The excellent OER performance is mainly attributed to its unique nanoarchitecture and the synergistic effects: the nanoflowers constructed by a 2D-like nanosheets guarantee large specific area and abundant active sites; the highly conductive CNT skeleton and the electronic modulation by the heterostructural NiP₂/Ni₂P interface and the hetero-atom doping can improve the catalytic activity; porous nanostructure benefits electrolyte penetration and gas release; most importantly, the rough surface and rich defects caused by phosphorization process can further enhance the OER performance. This work provides a deep insight to boost catalytic performance by heteroatom doping and interface engineering for water splitting.     

Oxygen vacancy-based ultrathin Co3O4 nanosheets as a high-efficiency electrocatalyst for oxygen evolution reaction

Enhancing the catalytic activity of Co₃O₄ electrocatalysts featuring abundant oxygen vacancies is required to enable their application in oxygen evolution reaction (OER). However, developing a harmless defect engineering strategy based on mild conditions to realize such an enhancement remains a challenge. Here, ultrathin Co₃O₄ nanosheets with abundant oxygen vacancies were prepared through a simple two-step method comprising a hydrothermal process and pre-oxidation to study the catalytic activity of the nanosheets toward OER. The ultrathin sheet structure and the Co₃O₄ nanosheets surface provide abundant active sites. The oxygen vacancy not only improves the catalyst activity, but also improves the electron transfer efficiency. These advantages make ultrathin Co₃O₄ nanosheets with abundant oxygen vacancies an excellent electrocatalyst for oxygen evolution. In an alkaline medium, ultrathin Co₃O₄ nanosheets exhibited excellent OER catalytic activity, with a small overpotential (367 mV for 10 mA/cm²) and faster reaction kinetics (65 mV/dec).Moreover, the electrocatalyst still maintained 68% of its original catalytic activity after 24 h operation. This work provides an extensive and reliable method for the preparation of low-cost and highly efficient OER electrocatalysts.     

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.