Bimetal metal-organic framework hollow nanoprisms for enhanced electrochemical oxygen evolution

Carboxylate-based metal-organic frameworks (MOFs) have emerged as promising electrocatalyst candidates for the water splitting and metal-air batteries. Hierarchical porous structure and redox-active metal centers with unsaturated coordination sites in MOFs facilitate the enhanced catalytic activity of oxygen evolution reaction (OER). Herein, uniform hollow structured Fe-free bi-metal (Co, Ni) MOF-74 nanoprisms are successfully synthesized using a solvothermal method and (Co₁Ni₁)₃(OH)(CH₃COO)₅ as the sacrificial templates, where Co and Ni are the metal nodes and 2,5-dihydroxyterephthalic acid (H₄DOBDC) serves as the organic ligand. At an overpotential of 300 mV, CoNi MOF-74 shows a high electrocatalytic activity towards OER in 0.1 M KOH, where the current density is 10 mA cm^?2 and the Tafel slope is 65.6 mV dec^?1. Meanwhile, CoNi MOF-74 is durable that sustains in alkaline for 100 h with 83.25% retention of current density. The improved catalytic activity can be associated with the in-situ generated amorphous Ni–Co (oxy)hydroxide, as well as the electron transfer from Ni²⁺ to Co²⁺. This work elucidates the potential application of MOF materials as efficient electrocatalysts for OER.     

High throughput preparation of Ni–Mo alloy thin films as efficient bifunctional electrocatalysts for water splitting

The synthesis of cost-effective and high-performance electrocatalysts for water splitting is the main challenge in electrochemical hydrogen production. In this study, we adopted a high throughput method to prepare bi-metallic catalysts for oxygen/hydrogen evolution reactions (OER/HER). A series of Ni–Mo alloy electrocatalysts with tunable compositions were prepared by a simple co-sputtering method. Due to the synergistic effect between Ni and Mo, the intrinsic electrocatalytic activity of the Ni–Mo alloy electrocatalysts is improved, resulting in excellent HER and OER performances. The Ni₉₀Mo₁₀ electrocatalyst shows the best HER performance, with an extremely low overpotential of 58 mV at 10 mA cm^?2, while the Ni₄₀Mo₆₀ electrocatalyst shows an overpotential of 258 mV at 10 mA cm^?2 in OER. More significantly, the assembled Ni₄₀Mo₆₀//Ni₉₀Mo₁₀ electrolyzer only needs a cell voltage of 1.57 V to reach 10 mA cm^?2 for overall water splitting.     

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.     

Porous NiFe alloys synthesized via freeze casting as bifunctional electrocatalysts for oxygen and hydrogen evolution reaction

Binder-free NiFe-based electrocatalyst with aligned pore channels has been prepared by freeze casting and served as a bifunctional catalytic electrode for oxygen and hydrogen evolution reaction (OER and HER). The synergistic effects between Ni and Fe result in the high electrocatalytic performance of porous NiFe electrodes. In 1.0 M KOH, porous Ni₇Fe₃ attains 100 mA cm⁻² at an overpotential of 388 mV with a Tafel slope of 35.8 mV dec⁻¹ for OER, and porous Ni₉Fe₁ exhibits a low overpotential of 347 mV at 100 mA cm⁻² with a Tafel slope of 121.0 mV dec⁻¹ for HER. The Ni₉Fe₁//Ni₉Fe₁ requires a low cell voltage of 1.69 V to deliver 10 mA cm⁻² current density for overall water splitting. The excellent durability at a high current density of porous NiFe electrodes has been confirmed during OER, HER and overall water splitting. The fine electrocatalytic performances of the porous NiFe-based electrodes owing to the three-dimensionally well-connected scaffolds, aligned pore channels, and bimetallic synergy, offering excellent charge/ion transfer efficiency and sizeable active surface area. Freeze casting can be applied to design and synthesize various three-dimensionally porous non-precious metal-based electrocatalysts with controllable multiphase for energy conversion and storage.     

NiCo-BDC derived Co3+ enriched NiCoxOy/NF nanosheets for oxygen evolution reaction

In recent years, transition metal catalysts due to their low price, excellent conductivity and high activity have been extensively studied in OER. It is worth noting that Co³⁺ plays a vital role in the process of oxygen evolution catalysis, because Co³⁺ ions are considered to be active sites. The development of catalysts with high Co³⁺ content has important application prospects for improving water oxidation efficiency. This paper uses a simple ligand-assisted synthesis method to promote the transformation of two-dimensional layered double hydroxides (LDHs) into two-dimensional metal organic frameworks (MOFs). MOF-OH/NF are quickly and easily prepared by electrooxidation, which exhibit superior OER properties, with a low overpotential of 260 mV and 420 mV for the oxygen evolution reaction (OER) at 100 mA cm^?2 and 1000 mA cm^?2. Moreover, the MOF-OH/NF has good stability in 1.0 M KOH electrolyte solution. This study provides a new idea for the design and synthesis of novel composite electrocatalysts.     

Core-shell Ni3Fe-based nanocomposites for the oxygen evolution reaction

To deal with energy and environmental issues, it is necessary to exploit efficient and stable electrocatalysts for the generation of clean hydrogen. Herein, we describe the synthesis of bimetallic Fe/Ni alloy encapsulated by amorphous carbon shells via a facile annealing strategy for electrocatalytic oxygen evolution reaction (OER). The ferric nickel tartrate annealed at 800 °C (Ni₃Fe₁O_x@C-800) exhibits a low OER overpotential of 264 mV at 10 mA cm^?2 and good stability in alkaline media. Compared with monometallic counterpart, bimetallic Ni₃Fe-based nanocomposites show lower OER barrier (ca. 324 kJ mol^?1) due to a cooperation mechanism between Ni and Fe sites in promoting electrocatalytic water oxidation. Compared with those annealed at other temperatures, the enhanced OER performance of Ni₃Fe₁O_x@C-800 can be ascribed to the large electrochemical surface area for exposing more active sites, smaller charge transfer, and better intrinsic activity of Ni₃Fe-based sites.     

Cobalt/cerium-based metal-organic framework composites for enhanced oxygen evolution electrocatalysis

Rational design of multivariate metal-organic framework (MOF)-based electrocatalysts with favorably heterostructures is highly desirable for the oxygen evolution reaction (OER). In this work, we report the rational construction of a series of CoCe-based MOFs (Co_1-xCe_x-BTC, x = 0, 0.1, 0.15 and 0.2) for OER electrocatalysis, and demonstrate the catalytically inactive Ce-BTC as a new OER promoter greatly boosts the electroctalaytic performance of Co-BTC. The resulting Co_0·9Ce_0.1-BTC exhibits the outstanding OER performances with a low overpotential of 308 mV at a current density of 10 mA cm^?2 and a long-term stability within 25 h, which is favorably comparable to those of the commercial IrO₂ and other previously reported MOF-based OER electrocatalysts.     

Cu2S/Ni3S2 ultrathin nanosheets on Ni foam as a highly efficient electrocatalyst for oxygen evolution reaction

It is an inevitable choice to find efficient and economically-friendly electrocatalysts to reduce the high overpotential of oxygen evolution reaction (OER), which is the key to improve the energy conversion efficiency of water splitting. Herein, we synthesized Cu₂S/Ni₃S₂ catalysts on nickel foam (NF) with different molar ratios of Ni/Cu by a simple two-step hydrothermal method. Cu₂S/Ni₃S₂-0.5@NF (CS/NS-0.5@NF) effectively reduces the overpotential of OER, displaying small overpotentials (237 mV@100 mA cm^?2 and 280 mV@500 mA cm^?2) in an alkaline solution, along with a low Tafel slope of 44 mV dec^?1. CS/NS-0.5@NF also presents an excellent durability at a relatively high current density of 100 mA cm^?2 for 100 h. The excellent performance is benefited by the prominent structural advantages and desirable compositions. The nanosheet has a high electrochemical active surface area and the porous structure is conducive to electrolyte penetration and product release. This work provides an economically-friendly Cu-based sulfide catalyst for effective electrosynthesis of OER.     

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

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

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.     

Multi-active site CoNi-MOFs as non-noble bifunctional electrocatalysts for highly efficient overall water splitting

The high-efficiency non-precious metal catalysts for oxygen evolution (OER) and hydrogen evolution (HER) are of great significance to the development of renewable energy technologies. Herein, a multiple active sites CoNi-MOFs-DBD electrocatalyst modified by low temperature plasma (DBD) was successfully synthesized by converting metal hydroxyfluoride on nickel foam into a well-arranged MOFs array using vapor deposition. The as-prepared CoNi-MOFs-DBD electrode showed better HER and OER catalytic activity, super hydrophilicity, and excellent stability. In an alkaline medium, the overpotential of HER is 203 mV at 10 mA cm^?2 and that of OER is 168 mV at 40 mA cm^?2. When CoNi-MOFs-DBD was used as a bifunctional electrocatalyst for overall water splitting in a two-electrode system, a current density of 10 mA cm^?2 can be achieved at a low voltage of 1.42 V, which shows great potential in electrocatalytic water splitting.     

Hydrogen production via highly efficient electrocatalyst based on 3D NixCo1-x(OH)2/NiFe-AM induce overall water splitting

The main factors limiting water splitting producing hydrogen production are overpotential, activity and persistence of electrocatalysts. Herein, a novel Ni_xCo_1-x(OH)₂ coupled with NiFe amorphous compound array growing on nickel foam substrate (expressed as Ni_xCo_1-x(OH)₂/NiFe-AM) was developed by facile hydrothermal and electrodeposition methods. Significantly, Ni_xCo_1-x(OH)₂/NiFe-AM with this unique structural exhibits superior activity and stability in the two half reactions of water electrolysis. In addition, when tested in an alkaline electrolyte with a current density of 10 mA cm⁻², the overpotentials of HER and OER was 157 mV and 196 mV (60 mA cm⁻²), respectively. The stability can up to 60 h. These test results show through constructing hierarchical nano-thron architecture enhanced electrocatalytic activity to produce hydrogen and oxygen.     

In situ growth of NiCoFe-layered double hydroxide through etching Ni foam matrix for highly enhanced oxygen evolution reaction

It is of great significance to develop the nonprecious metal oxide electrocatalysts toward oxygen evolution reaction (OER) for water splitting. Herein we report an in-situ growth of the ternary NiCoFe-layered double hydroxide nanosheets on surface etching nickel foam (NiCoFe LDHs/NF) without adding any nickel precursor. In this method, etching Ni matrix by Fe³⁺ not only provides the slowly released nickel ions, but also intensifies the Fe–Ni interaction between the directly grown active species and Ni foam. Therefore the composition, electronic structure, and morphology of the electrocatalysts can be easily regulated only by adjusting Co²⁺:Fe³⁺ ratio in the precursor solution. The obtained NiCo₁Fe₁ LDH/NF, which is formed in 1:1 Co²⁺:Fe³⁺ solution, has highest content of Ni³⁺ and Co³⁺ active sites and the largest electrochemical active area. It exhibits an outstanding OER performance with a small overpotential of 231 mV at 10 mA cm^?2 and excellent durability at 50 mA cm^?2 in 1.0 M KOH solution.     

Facile construction of heterostructural Ni3(NO3)2(OH)4/CeO2 bifunctional catalysts for boosted overall water splitting

Interface engineering has aroused vitally widespread concern since it could be an effective strategy for exploring high-performance and low-cost water oxidation electrocatalysts. Herein, we report a hetero-structured Ni₃(NO₃)₂(OH)₄/CeO₂/NF (NNO/CeO₂/NF) electrode, exhibiting superior performance owning to the NO₃^? anion substitution for the OH^? in nickel hydroxide to form Ni₃(NO₃)₂(OH)₄, together with its interface synergy with ceria. In alkaline solution, the NNO/CeO₂/NF electrocatalyst could catalyze the OER with an overpotential of 330 mV to approach 50 mA cm^?2. Also, it needs only an overpotential of 120 mV to reach 10 mA cm^?2 for HER. Additionally, when a standard two-electrode water electrolyzer is fabricated by employing NNO/CeO₂/NF as both the cathode and anode, it can generate 10 mA cm^?2 at 1.64 V and operate steadily without performance degradation after 25 h. This research provides a novel perspective for reasonable design of advanced catalytic materials with improvements in the field of electrocatalysis.     

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

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

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.     

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

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

Fe/Ni bimetallic organic framework with varying anions as robust electrocatalyst for oxygen evolution reaction

The performance of the metal?organic frameworks (MOFs) will be affected when the anions added were different. Herein, bimetallic FeNi-MOF was synthesized by hydrothermal method with nickel foam as substrate, the effects of four anions (Cl^?, NO₃^?, CH₃COO^?, SO₄^2?) on the materials performance of MOF were investigated. The MOF prepared when added chloride ion with the overpotential at 100 mA?cm^?2 as 247 mV. Meanwhile, the stability test at 100 mA cm^?2 for 12 h had no obvious change which exhibited high electrochemical stability. The analysis demonstrated that the superior performance of the MOF prepared when added chloride ion was attributed to the low charge transfer resistance, increased active area, exposure more active sites. This work would shed some lights for facile synthesis of ultrahigh performance OER catalyst by adjusting the anion of the precursor.     

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.     

PBA derived FeCoP nanoparticles decorated on NCNFs as efficient electrocatalyst for water splitting

Transition metal phosphides have been known as promising electrocatalysts for hydrogen evolution and oxygen evolution reactions (HER and OER) due to their high catalytic activity. In this work, the FeCoP nanoparticles decorated on N-doped electrospun carbon nanofibers (FeCoP@NCNFs) was successfully synthesized through depositing Fe, Co-based Prussian blue analogue Co₃[Fe(CN)₆]₂·10H₂O (FeCo-PBA) onto the electrospun PVP/PAN nanofibers via layer-by-layer approach, followed by carbonization and phosphorization treatments. Benefiting from the high electrical conductivity, abundant catalytic active sites and the synergistic effect between FeCoP nanoparticles and N-doped carbon nanofibers network, the obtained FeCoP@NCNFs displays good bifunctional electrocatalytic activity. In 1 M KOH, the FeCoP@NCNFs achieves 10 mA cm^?2 at an overpotential of 290, 226 mV for OER and HER, respectively. Moreover, it demands overpotential of 196 mV to achieve 10 mA cm^?2 for HER in 0.5 M H₂SO₄. The FeCoP@NCNFs is used as both anode and cathode for overall water splitting, it requires a low voltage of 1.65 V to achieve a current density of 10 mA cm^?2 and maintains outstanding stability over 10 h. Herein, a strategy for preparing bifunctional electrocatalysts of compositing transition metal phosphides with carbon nanofibers is proposed, and the application of metal-organic framework in electrocatalytic field is further extended.