Electrochemical fabrication of FeSx films with high catalytic activity for oxygen evolution

Electrochemical decomposition of water to produce oxygen (O₂) and hydrogen (H₂) through an anodic oxygen evolution reaction (OER) and a cathodic hydrogen evolution reaction (HER) is a promising green method for sustainable energy supply. Here, we demonstrate that cauliflower-like S-doped iron microsphere films are materials that can efficiently decompose water as an electrocatalyst for the oxygen evolution reaction. FeS_x films are prepared by a simple one-step electrodeposition method and directly grow on copper foam from a deep eutectic solvent, ethaline (mixture of choline chloride and ethylene glycol), as a durable and highly efficient catalyst for the OER in 1.0 M KOH. The prepared FeS_x/CF, as an oxygen-evolving anode, shows remarkable catalytic performance toward the OER with a moderate Tafel slope of 105 mV dec⁻¹, and require an overpotential of only 340 mV to drive a geometrical catalytic current density of 10 mA cm⁻². In addition, this catalyst also demonstrates strong long-term electrochemical durability. This study provides a simple synthesis route for practical applications of limited transition metal nano catalysts.

Electrochemical decomposition of water to produce oxygen (O₂) and hydrogen (H₂) through an anodic oxygen evolution reaction (OER) and a cathodic hydrogen evolution reaction (HER) is a promising green method for sustainable energy supply.     

An efficient and stable iodine-doped nickel hydroxide electrocatalyst for water oxidation: synthesis,electrochemical performance,and stability

The design of oxygen evolution reaction (OER) catalysts with higher stability and activity by economical and convenient methods is considered particularly important for the energy conversion technology. Herein, a simple hydrothermal method was adopted for the synthesis of iodine-doped nickel hydroxide nanoparticles and their OER performance was explored. The electrocatalysts were structurally characterized by powder X-ray diffraction analysis (P-XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and BET analysis. The electrochemical performance of the electrocatalysts was assessed by cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The abundant catalytic active sites, oxygen vacancies, low charge-transfer resistance, and a high pore diameter to pore size ratio of iodine-doped Ni(OH)₂ were responsible for its excellent catalytic activity, whereby OER was initiated even at 1.52 V (vs. RHE) and a 330 mV overpotential was needed to reach a 40 mV cm⁻² current density in 1 M KOH solution. The material also exhibited a low Tafel slope (46 mV dec⁻¹), which suggests faster charge-transfer kinetics as compared to its counterparts tested under the same electrochemical environment. It is worth noting that this facile and effective approach suggests a new way for the fabrication of metal hydroxides rich in oxygen vacancies, thus with the potential to boost the electrochemical performance of energy-related systems.

Oxygen evolution reaction mechanism under alkaline conditions over the iodine-doped Ni(OH)₂ surface.     

Enhancing bifunctional catalytic activity of cobalt–nickel sulfide spinel nanocatalysts through transition metal doping and its application in secondary zinc–air batteries

Developing large-scale and high-performance OER (oxygen evolution reaction) and ORR (oxygen reduction reaction) catalysts have been a challenge for commercializing secondary zinc–air batteries. In this work, transition metal-doped cobalt–nickel sulfide spinels are directly produced via a continuous hydrothermal flow synthesis (CHFS) approach. The nanosized cobalt–nickel sulfides are doped with Ag, Fe, Mn, Cr, V, and Ti and evaluated as bifunctional OER and ORR catalyst for Zn–air battery application. Among the doped spinel catalysts, Mn-doped cobalt–nickel sulfides (Ni_1.29Co_1.49Mn_0.22S₄) exhibit the most promising OER and ORR performance, showing an ORR onset potential of 0.9 V vs. RHE and an OER overpotential of 348 mV measured at 10 mA cm⁻², which is attributed to their high surface area, electronic structure of the dopant species, and the synergistic coupling of the dopant species with the active host cations. The dopant ions primarily alter the host cation composition, with the Mn(iii) cation linked to the introduction of active sites by its favourable electronic structure. A power density of 75 mW cm⁻² is achieved at a current density of 140 mA cm⁻² for the zinc–air battery using the manganese-doped catalyst, a 12% improvement over the undoped cobalt–nickel sulfide and superior to that of the battery with a commercial RuO₂ catalyst.

Transition metal-doped cobalt–nickel sulfide spinel (Ni_1.29Co_1.49Mn_0.22S₄) nanocatalysts for secondary Zn–air batteries with an efficient and stable electrochemical performance.     

Spinel oxide CoFe2O4 grown on Ni foam as an efficient electrocatalyst for oxygen evolution reaction

The effect of the oxygen evolution reaction (OER) is important in water splitting. In this work, we develop sphere-like morphology spinel oxide CoFe₂O₄/NF by hydrothermal reaction and calcination, and the diameter of the spheres is about 111.1 nm. The CoFe₂O₄/NF catalyst exhibits excellent electrocatalytic performance with an overpotential of 273 mV at a current density of 10 mA cm⁻² and a Tafel slope of 78 mV dec⁻¹. The cycling stability of CoFe₂O₄/NF is remarkable, and it only increased by 5 mV at a current density of 100 mA cm⁻² after 3000 cycles. Therefore, this simple method to prepare CoFe₂O₄/NF can enhance the OER properties of electrocatalysts, which makes CoFe₂O₄/NF a promising material to replace noble metal-based catalysts for the oxygen evolution reaction.

The effect of the oxygen evolution reaction (OER) is important in water splitting.     

Free-standing TiO2 nanotubes decorated with spherical nickel nanoparticles as a cost-efficient electrocatalyst for oxygen evolution reaction

Here, we report significant activity towards the oxygen evolution reaction (OER) of spherical nickel nanoparticles (NPs) electrodeposited onto free-standing TiO₂ nanotubes (TNT) via cyclic voltammetry. It has been shown that simple manipulation of processing parameters, including scan rate and number of cycles, allows for formation of the NPs in various diameters and amounts. The polarization data with respect to transmission electron microscopy (TEM) allowed for determination of the diameter and propagation depth of the Ni NPs leading to the highest activity towards the OER with an overpotential of 540 mV at +10 mA cm⁻² and Tafel slope of 52 mV per decade. X-ray photoelectron spectroscopy (XPS) indicates the presence of structure defects within Ni NPs whereas Mott–Schottky analysis provides information on the anodically shifted flat band potential and highly increased donor density. The obtained results along with literature studies allowed a proposal of the origin of the enhancement towards the OER. We believe that combination of transition metal-based NPs and TNT provides valuable insight on efficient and low-cost electrocatalysts.

In this work, we show the electrocatalytic activity towards the oxygen evolution reaction (OER) of spherical nickel nanoparticles (NPs) electrodeposited onto free-standing TiO₂ nanotubes (TNT) via cyclic voltammetry.     

A three-dimensional flower-like NiCo-layered double hydroxide grown on nickel foam with an MXene coating for enhanced oxygen evolution reaction electrocatalysis

Electrolysis of water is currently one of the cleanest and most efficient ways to produce high-purity hydrogen. The oxygen evolution reaction (OER) at the anode of electrolysis is the key factor affecting the reaction efficiency, which involves the transfer of four electrons and can slow down the overall reaction process. In this work, using nickel foam coated with MXene (Ti₃C₂T_x) as the carrier, a three-dimensional flower-shaped layered double hydroxide (NiCo-LDH) is grown on Ti₃C₂T_x by a hydrothermal method to fabricate a NiCo-LDH/Ti₃C₂T_x/NF hybrid electrocatalyst for enhanced OER performance. The results reveal that the hybrid electrocatalyst has excellent OER activity in alkaline solution, in which a low overpotential of 223 mV and a small Tafel slope of 47.2 mV dec⁻¹ can be achieved at a current density of 100 mA cm⁻². The interface interaction and charge transfer between Ti₃C₂T_x and NiCo-LDH can accelerate the electron transfer rate during the redox process and improve the catalytic activity of the overall reaction. This NiCo-LDH/Ti₃C₂T_x/NF hybrid electrocatalyst may have important research significance and great application potential in catalytic electrolysis of water.

A three-dimensional flower-shaped layered double hydroxide is grown on MXene to fabricate a NiCo-LDH/MXene/NF hybrid electrocatalyst to enhance the OER performance.     

Constructing NiSe2@MoS2 nano-heterostructures on a carbon fiber paper for electrocatalytic oxygen evolution

Although MoS₂ has shown its potential as an electro-catalyst for the oxygen evolution reaction (OER), its research is still insufficient. In this study, as a novel MoS₂-based heterostructure electro-catalyst for OER, namely NiSe₂@MoS₂ nano-heterostructure, was constructed on a carbon fiber paper (CFP) substrate by a simple approach, which includes electrochemical deposition of NiSe₂ film and hydrothermal processing of MoS₂ film. In addition to a series of observations on the material structure, electrocatalytic OER performance of NiSe₂@MoS₂ was fully evaluated and further compared with other MoS₂-based OER electro-catalysts. It exhibits an outstanding catalytic performance with an overpotential η₁₀ of 267 mV and a Tafel slope of 85 mV dec⁻¹. Only 6% loss of current density before and after 10 h indicates its excellent durability. The results indicate that the obtained NiSe₂@MoS₂ is an excellent OER electro-catalyst and worth exploring as a substitute for noble metal-based materials.

Although MoS₂ has shown its potential as an electro-catalyst for the oxygen evolution reaction (OER), its research is still insufficient.     

NaBH4 induces a high ratio of Ni3+/Ni2+ boosting OER activity of the NiFe LDH electrocatalyst

Electrochemical water splitting is a promising way to produce hydrogen gas, but the sluggish kinetics of the oxygen evolution reaction (OER) extremely restrict the overall conversion efficiency of water splitting. Transition metal based LDHs (TM LDHs) are one of the most effective non-noble metal OER catalysts and have attracted wide interest, especially the nickel–iron LDH (NiFe LDH). The high valence Ni³⁺ species with a large coordination number play a vital role in OER catalysis. Herein, we report on a surprising discovery that reaction between NiFe LDH and NaBH₄ with multi-hydrides induces vacancy formation around Fe³⁺ and enrichment in Ni³⁺, crucially activating the OER performance. The ratio of Ni³⁺/Ni²⁺ is found to be closely tied to the OER performance, nicely accounting for the leading role of Ni³⁺ ions in octahedral sites in electrocatalysis. Significantly, the NaBH₄ treated NiFe LDH directly on nickel foam (NF), denoted as NaBH₄–NiFe LDH@NF exhibited an outstanding OER performance with an overpotential of only 310 mV at 100 mA cm⁻², and a Tafel slope of 47 mV dec⁻¹. For the series of TM LDHs we studied with different metal combinations, the high valence metal ion is found to be positively related to OER performance.

Reaction between NiFe LDH and NaBH₄ induces vacancies around Fe³⁺ and enrichment in Ni³⁺, crucially activating the OER catalyst leading to high performance.     

Boosting oxygen evolution reaction activity by tailoring MOF-derived hierarchical Co–Ni alloy nanoparticles encapsulated in nitrogen-doped carbon frameworks

The growing demand for sustainable energy has led to in-depth research on hydrogen production from electrolyzed water, where the development of electrocatalysts is a top priority. We here report a controllable strategy for preparing the cobalt–nickel alloy nanoparticles encapsulated in nitrogen-doped porous carbon by annealing a bimetal–organic framework. The delicately tailored hierarchical Co₂Ni@NC nanoparticles effectively realize abundant synergistic active sites and fast mass transfer for the oxygen evolution reaction (OER). Remarkably, the optimized Co₂Ni@NC exhibits a small overpotential of 310 mV to achieve a current density of 10 mA cm⁻² and an excellent long-term stability in alkaline electrolyte. Furthermore, the underlying synergistic effect mechanism of the Co–Ni model has been pioneeringly elucidated by density functional theory calculations.

The hierarchical Co₂Ni@NC nanoparticles realize fast mass transfer for the oxygen evolution reaction (OER). The synergistic effect between Co and Ni can effectively adjust the binding energy tending to an optimal value, further improving the energetics for the OER.     

Enhancing the water splitting performance via decorating Co3O4 nanoarrays with ruthenium doping and phosphorization

Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for its ultrahigh energy density, abundance and environmental friendliness. Generating hydrogen by water splitting with highly efficient electrocatalysts is a feasible route to meet current and future energy demand. Herein, the effects of Ru doping and phosphorization treatment on Co₃O₄ nanoarrays for water splitting are systemically investigated. The results show that a small amount of phosphorus can accelerate hydrogen evolution reaction (HER) and the trace of Ru dopant can significantly enhance the catalytic activities for HER and oxygen evolution reaction (OER). Ru-doped cobalt phosphorous oxide/nickel foam (CoRuPO/NF) nanoarrays exhibit highly efficient catalytic performance with an overpotential of 26 mV at 10 mA cm⁻² for HER and 342 mV at 50 mA cm⁻² for OER in 1 M KOH solution, indicating superior water splitting performance. Furthermore, the CoRuPO/NF also exhibits eminent and durable activities for alkaline seawater electrolysis. This work significantly advances the development of seawater splitting for hydrogen generation.

CoRuPO/NF shows low overpotentials in HER and OER.     

Controlled phase evolution from Cu0.33Co0.67S2 to Cu3Co6S8 hexagonal nanosheets as oxygen evolution reaction catalysts

Developing cheap and efficient transition metal-based catalysts for the oxygen evolution reaction (OER) plays the key role in large-scale implementation of hydrogen production. However, there is still a lack of effective ways to tune the catalysts performance for the OER reaction from the aspect of structure design and element modulation simultaneously. Herein, a novel Cu_0.33Co_0.67S₂ hexagonal nanosheet has been synthesized through the coprecipitation reaction followed by subsequent vapor sulfidation. Simply mixed with carbon nanotubes (CNTs) during electrode preparation, this Cu_0.33Co_0.67S₂ exhibits an overpotential of 284 mV vs. RHE at a current density of 10 mA cm⁻² in 1.0 M KOH. The improved OER performance of the Cu_0.33Co_0.67S₂ electrode can be attributed to the electrocatalytically active sites involved in octahedral coordination structures and further activated by Cu substitution. The encouraging results provide insight into further rational design of transition metal-based electrochemical catalysts towards OER applications.

Developing cheap and efficient transition metal-based catalysts for the oxygen evolution reaction (OER) plays the key role in large-scale implementation of hydrogen production.     

Nickel foam and stainless steel mesh as electrocatalysts for hydrogen evolution reaction,oxygen evolution reaction and overall water splitting in alkaline media

In this work, several commonly used conductive substrates as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions were studied, including nickel foam (Ni foam), copper foam (Cu foam), nickel mesh (Ni mesh) and stainless steel mesh (SS mesh). Ni foam and SS mesh are demonstrated as high-performance and stable electrocatalysts for HER and OER, respectively. For HER, Ni foam exhibited an overpotential of 0.217 V at a current density of 10 mA cm⁻² with a Tafel slope of 130 mV dec⁻¹, which were larger than that of the commercial Pt/C catalyst, but smaller than that of the other conductive substrates. Meanwhile, the SS mesh showed the best electrocatalytic performance for OER with an overpotential of 0.277 V at a current density of 10 mA cm⁻² and a Tafel slope of 51 mV dec⁻¹. Its electrocatalytic performance not only exceeded those of the other conductive substrates but also the commercial RuO₂ catalyst. Moreover, both Ni foam and SS mesh exhibited high stability during HER and OER, respectively. Furthermore, in the two-electrode system with Ni foam used as the cathode and SS mesh used as the anode, they enable a current density of 10 mA cm⁻² at a small cell voltage of 1.74 V. This value is comparable to or exceeding the values of previously reported electrocatalysts for overall water splitting. In addition, NiO on the surface of Ni foam may be the real active species for HER, NiO and FeO_x on the surface of SS mesh may be the active species for OER. The abundant and commercial availability, long-term stability and low-cost property of nickel foam and stainless steel mesh enable their large-scale practical application in water splitting.

Efficient electrocatalytic overall water splitting is achieved with commercially-available and low-cost nickel foam and stainless steel mesh as cathode and anode electrodes.     

An advanced and efficient Co3O4/C nanocomposite for the oxygen evolution reaction in alkaline media

The design of efficient nonprecious catalysts for the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) is a necessary, but very challenging task to uplift the water-based economy. In this study, we developed a facile approach to produce porous carbon from the dehydration of sucrose and use it for the preparation of nanocomposites with cobalt oxide (Co₃O₄). The nanocomposites were studied by the powder X-ray diffraction and scanning electron microscopy techniques, and they exhibited the cubic phase of cobalt oxide and porous structure of carbon. The nanocomposites showed significant OER activity in alkaline media, and the current densities of 10 and 20 mA cm⁻² could be obtained at 1.49 and 1.51 V versus reversible hydrogen electrode (RHE), respectively. The impedance study confirms favorable OER activity on the surface of the prepared nanocomposites. The nanocomposite is cost-effective and can be capitalized in various energy storage technologies.

The design of efficient nonprecious catalysts for the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) is a necessary, but very challenging task to uplift the water-based economy.     

Electrochemical oxidation of boron-doped nickel–iron layered double hydroxide for facile charge transfer in oxygen evolution electrocatalysts

The oxygen evolution reaction (OER) is the key reaction in water splitting systems, but compared with the hydrogen evolution reaction (HER), the OER exhibits slow reaction kinetics. In this work, boron doping into nickel–iron layered double hydroxide (NiFe LDH) was evaluated for the enhancement of OER electrocatalytic activity. To fabricate boron-doped NiFe LDH (B:NiFe LDH), gaseous boronization, a gas–solid reaction between boron gas and NiFe LDH, was conducted at a relatively low temperature. Subsequently, catalyst activation was performed through electrochemical oxidation for maximization of boron doping and improved OER performance. As a result, it was possible to obtain a remarkably reduced overpotential of 229 mV at 10 mA cm⁻² compared to that of pristine NiFe LDH (315 mV) due to the effect of facile charge-transfer resistance by boron doping and improved active sites by electrochemical oxidation.

An electrochemically oxidized boron-doped NiFe LDH electrocatalyst was prepared and the electrocatalyst showed improved water oxidation performance.     

Preparation of Co–N carbon nanosheet oxygen electrode catalyst by controlled crystallization of cobalt salt precursors for all-solid-state Al–air battery

Production of bifunctional catalysts for catalyzing both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly advisable but challenging with respect to the applications of these catalysts in renewable energy conversion and storage technologies. Herein, we prepared highly reactive and stable cobalt-embedded nitrogen-rich carbon nanosheets (Co–N/CNs). Based on density functional theory (DFT) calculations and experiments, the as-prepared Co–N/CNs showed outstanding catalytic activities toward both OER and ORR. The optimized Co–N/CNs-800 catalyst revealed outstanding bifunctional catalytic activities for both ORR and OER with high catalytic efficiency and long-term durability, which were even comparable with those of the state-of-the-art Pt/C and RuO₂ catalysts. Furthermore, we observed that different cobalt salt precursors affected the size of Co nanoparticles, and both ORR and OER catalytic activities displayed completely consistent variations (sulfate < acetate < chloride < nitrate). An all-solid-state Al–air battery device comprising this hybrid catalyst showed superior performance when compared with the device containing the Pt/C catalyst.

Production of bifunctional catalysts for catalyzing both ORR and OER is highly advisable but challenging with respect to the applications of these catalysts in renewable energy conversion and storage technologies.     

Ni foam electrode solution impregnated with Ni-FeX(OH)Y catalysts for efficient oxygen evolution reaction in alkaline electrolyzers

Oxygen evolution reaction (OER) is a demanding step within the water splitting process for its requirement of a high overpotential. Thus, to overcome this unfavourable kinetics, an efficient catalyst is required to expedite the process. In this context, we report on Ni foam functionalised with low cost iron (Fe) and iron hydroxide (Fe(OH)_X), wet chemically synthesized as OER catalysts. The prepared catalyst based on iron hydroxide precipitate shows a promising performance, exhibiting an overpotential of 270 mV (at a current density of 10 mA cm⁻² in 1 M KOH solution), an efficient Tafel slope of ∼50 mV dec⁻¹ and stable chronopotentiometry. The promising performance of the anode was further reproduced in the overall water splitting reaction with a two electrode cell. The overall reaction requires a lower potential of 1.508 V to afford 10 mA cm⁻², corresponding to 81.5% electrical to fuel efficiency.

Modification of Ni foam electrode by FeCl₃·6H₂O and HCl, towards superior oxygen-evolving electrocatalyst for water splitting process.     

Well-dispersed Pt/RuO2-decorated mesoporous N-doped carbon as a hybrid electrocatalyst for Li–O2 batteries

Despite their high energy density, the poor cycling performance of lithium–oxygen (Li–O₂) batteries limits their practical application. Therefore, to improve cycling performance, considerable attention has been paid to the development of an efficient electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Catalysts that can more effectively reduce the overpotential and improve the cycling performance for the OER during charging are of particular interest. In this study, porous carbon derived from protein-based tofu was investigated as a catalyst support for the oxygen electrode (O₂-electrode) of Li–O₂ batteries, wherein ORR and OER occur. The porous carbon was synthesized using carbonization and KOH activation, and RuO₂ and Pt electrocatalysts were introduced to improve the electrical conductivity and catalytic performance. The well-dispersed Pt/RuO₂ electrocatalysts on the porous N-doped carbon support (Pt/RuO₂@ACT) showed excellent ORR and OER catalytic activity. When incorporated into a Li–O₂ battery, the Pt/RuO₂@ACT O₂-electrode exhibited a high specific discharge capacity (5724.1 mA h g⁻¹ at 100 mA g⁻¹), a low discharge–charge voltage gap (0.64 V at 2000 mA h g⁻¹), and excellent cycling stability (43 cycles with a limit capacity of 1000 mA h g⁻¹). We believe that the excellent performance of the Pt/RuO₂@ACT electrocatalyst is promising for accelerating the commercialization of Li–O₂ batteries.

The excellent performance of the Pt/RuO₂@ACT electrocatalyst is promising for accelerating the commercialization of Li–O₂ batteries.     

A high-efficiency oxygen evolution electrode material of a carbon material containing a NiCo bimetal

The preparation of highly efficient, stable, and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is still a challenge for the development of new energy systems. In this work, a NiCo bimetal loaded on porous carbon (NiCo-C/NF) grown on nickel foam (NF) was obtained via the pyrolysis of a NiCo bimetal MOF (NiCo-MOF/NF) under a nitrogen atmosphere at 500 °C. Compared with NiCo-MOF/NF, NiCo-C/NF had a larger specific surface and uniform mesoporous structure. As an electrocatalyst in the OER, this new type of electrode operated with better stability in an alkaline solution (1.0 mol L⁻¹ KOH), the overpotential when the current density reached 10 mA cm⁻² was only 260 mV, and the electrode also exhibited long-term durability in a stability test for 10 h without significant changes. The excellent activity and stability toward the OER can be attributed to the synergistic effect of the NiCo bimetal and the abundant active sites exposed after the carbonization of NiCo-MOF, which compensated for the defect of the insufficient conductivity of the material and promoted the evolution of oxygen in the catalytic process.

The preparation of highly efficient, stable, and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is still a challenge for the development of new energy systems.     

Highly active postspinel-structured catalysts for oxygen evolution reaction

The rational design principle of highly active catalysts for the oxygen evolution reaction (OER) is desired because of its versatility for energy-conversion applications. Postspinel-structured oxides, CaB₂O₄ (B = Cr³⁺, Mn³⁺, and Fe³⁺), have exhibited higher OER activities than nominally isoelectronic conventional counterparts of perovskite oxides LaBO₃ and spinel oxides ZnB₂O₄. Electrochemical impedance spectroscopy reveals that the higher OER activities for CaB₂O₄ series are attributed to the lower charge-transfer resistances. A density-functional-theory calculation proposes a novel mechanism associated with lattice oxygen pairing with adsorbed oxygen, demonstrating the lowest theoretical OER overpotential than other mechanisms examined in this study. This finding proposes a structure-driven design of electrocatalysts associated with a novel OER mechanism.

Postspinel-structured oxides, CaB₂O₄ (B = Cr³⁺, Mn³⁺, and Fe³⁺), have exhibited systematically higher catalytic activities in the oxygen evolution reaction (OER) than nominally conventional counterparts of perovskite LaBO₃ and spinel ZnB₂O₄.     

One-step chemical vapor deposition fabrication of Ni@NiO@graphite nanoparticles for the oxygen evolution reaction of water splitting

NiO combined with conductive materials is a practicable way to improve its catalytic property for the oxygen evolution reaction (OER) by enhancing its electrical conductivity. Herein, Ni@NiO@graphite nanoparticles less than 20 nm in average diameter were synthesized by a one-step chemical vapor deposition process. Due to the deliberately controlled lack of oxygen, Ni particles and carbon clusters decomposed from NiCp₂ precursors were oxidized incompletely and formed Ni@NiO core–shell nanoparticles coated by a graphite layer. The thickness of the graphite layer and the content of Ni were controlled by varying deposition temperature. The electrochemical activity towards the oxygen evolution reaction was assessed within alkaline media. Compared with commercial NiO powder, the Ni@NiO@graphite nanoparticles with the unique core–shell microstructure exhibit excellent OER performance, i.e., an overpotential of 330 mV (vs. RHE) at 10 mA cm⁻² and a Tafel slope of 49 mV dec⁻¹, due to the improved electrical conductivity and more active sites. This work provides a facile and rapid strategy to produce nanoparticles with unique microstructures as highly active electrocatalysts for the OER.

Ni@NiO@graphite nanoparticles with excellent OER performance were synthesized by a one-step chemical vapor deposition process.