Co–NiFe layered double hydroxide nanosheets as an efficient electrocatalyst for the electrochemical evolution of oxygen

The development of non-precious metal catalysts for the electrochemical oxygen evolution reaction (OER) is especially important for the water electrolysis process. Herein, a two-dimensional (2D) ultrathin hybrid Co–NiFe layered double hydroxide (LDH) is synthesized via a facile hydrothermal method. In 1.0 M KOH electrolyte, Co–NiFe LDH exhibits remarkable activities for OER. At the current density of 10 mA cm⁻², it only needs an overpotential of 278 mV, which is ca. 50 mV and 20 mV lower than those for NiFe LDH (328 mV) and RuO₂ catalysts (298 mV), respectively. In addition, Co–NiFe LDH also shows impressive long-term stability for OER. Besides the stable morphology and crystal structure, the potential is always kept at 1.50 V and shows almost no attenuation during the 20 h of durability test. Changes in the electronic structure of LDH due to introduction of Co ions, as well as the large specific surface area facilitate the mass/electron transfer and the oxygen bubbles release, and thus lead to the enhanced catalytic properties for OER. This work can be informative not only for understanding the role of physical and electronic structures on OER but also for designing high-performance non-precious metal OER electrocatalysts.     

Advanced Co3O4–CuO nano-composite based electrocatalyst for efficient hydrogen evolution reaction in alkaline media

In this study, we incorporate a copper impurity into (Co₃O₄) nanowires precursor that turn them into an active catalyst for the hydrogen evolution reaction in 1M KOH. The XRD and XPS results are in good agreement and confirmed the formation of Co₃O₄–CuO nano-composite by wet chemical method. To date, the performance of hydrogen evolution reaction in alkaline for the composite catalyst is comparable or superior to cobalt oxide based HER electro-catalysts. The HER catalyst exhibits the lowest Tafel slope of 65 mVdec⁻¹ for the cobalt-based catalysts in alkaline media. A current density of 10 mA/cm² is achieved at a potential of 0.288 V vs reversible hydrogen electrode (RHE). The mixed transition metal oxide Co₃O₄–CuO based HER electro-catalyst is highly stable and durable. The EIS results demonstrates that HER is highly favorable on the Co₃O₄–CuO due to the relatively small charge transfer resistance (173.20 Ohm) and higher capacitance values (1.97 mF).     

Cu–Co–P electrodeposited on carbon paper as an efficient electrocatalyst for hydrogen evolution reaction in anion exchange membrane water electrolyzers

To solve the issues of energy shortage and environmental pollution, it is essential to develop highly effective catalysts for hydrogen evolution reaction (HER) in water electrolysis. Herein, we report a facile and rapid fabrication of a Cu–Co–P catalyst on a carbon paper (CP) substrate using electrodeposition. First, the deposition conditions for Co–P/CP were optimized. The prepared Co–P consisted of numerous spheres and exhibited acceptable catalytic activity towards HER in an alkaline medium with an overpotential of 72 mV at current density of ?10 mA/cm². Further performance enhancement was achieved by the incorporation of Cu to modify the electronic structure of the Co–P catalyst. In a half-cell test, the optimized Cu–Co–P/CP exhibits remarkable performance, achieving ?10 mA/cm² at an overpotential of 59 mV, and the Tafel slope is 38 mV/dec. In a single-cell test, an anion exchange membrane water electrolyzer with a Cu–Co–P/CP cathode and commercial IrO₂/CP anode exhibited high current density of 0.70 A/cm² at 1.9 V_cell.     

One-step electrodeposition of cauliflower-like Ni–Fe–Sn particles as a highly-efficient electrocatalyst for the hydrogen evolution reaction

Herein, a Ni–Fe–Sn coating was synthesized in-situ on Ni mesh by one-step electrodeposition at different durations. The Ni–Fe–Sn60 electrode obtained after 1 h deposition exhibits cauliflower-like morphology and the best electrocatalytic properties for the hydrogen evolution reaction (HER) compared to other electrodes. The electrode requires an overpotential of 43 mV at a current density of 10 mA cm⁻² and a small Tafel slope of 70 mV dec⁻¹ in a 1 M KOH solution. Moreover, the electrode shows outstanding stability in prolonged electrolysis and overall water splitting performance, generating a current density of 93 mA cm⁻² at 1.8 V, which is thrice that of an industry electrode. This electrocatalytic activity is ascribed to the high active surface area produced by the cauliflower-like Ni–Fe–Sn particles and the synergistic interaction of Ni, Fe and Sn. The simple synthesis method and excellent performance endow this electrode with great potential for large-scale applications.     

Facile one-step fabrication of bimetallic Co–Ni–P hollow nanospheres anchored on reduced graphene oxide as highly efficient electrocatalyst for hydrogen evolution reaction

It is significant but challenging to develop noble-metal-free electrocatalysts exhibiting high activity and long-term stability toward hydrogen evolution reaction (HER) to satisfy the ever-increasing demand for clean and renewable energy. Herein, an environment-friendly and low-temperature electroless deposition method is developed for the synthesis of Co–Ni–P hollow nanospheres anchored on reduced graphene oxide nanosheets (Co–Ni–P/RGO). By optimizing the molar ratio of Ni/Co precursor, composition dependent electrocatalytic performances toward HER of nanostructured Co–Ni–P/RGO electrocatalyst are investigated in 1.0 M KOH solution. The results suggest that when the molar ratio of Ni/Co precursor is 3/7, as-prepared ternary Co–Ni–P/RGO electrocatalyst exhibits a remarkably enhanced HER activity in comparison to binary Ni–P/RGO and Co–P/RGO electrocatalysts, delivering a current density of 10 mA cm⁻² at the overpotential of only 207 mV. The value of Tafel slope for nanostructured Co–Ni–P/RGO electrocatalyst reveals that HER process undergoes Volmer-Heyrovsky mechanism. Besides, nanostructured Co–Ni–P/RGO electrocatalyst features superior stability under alkaline condition. The results suggest that nanostructured composite of Co–Ni–P hollow nanospheres/RGO is a potential candidate for hydrogen production through water splitting.     

MXene boosted metal-organic framework-derived Fe–N–C as an efficient electrocatalyst for oxygen reduction reactions

Iron-nitrogen-carbon (Fe–N–C) electrocatalysts offer great promise to replace their noble metal-based counterparts for oxygen reduction reactions (ORR). However, the practical applications of this type of catalyst are hindered by insufficient accessible active sies, low electrical conductivity, and poor durability. Here, we report a Ti₃C₂ MXene supported metal-organic framework (MOF)-derived Fe–N–C (Fe-N_x/N/Ti₃C₂) catalyst to simultaneously address the issues. Owing to the negatively charged characteristics, NH₂-MIL-53(Fe) is firmly anchored on Ti₃C₂ MXene, which not only serves as a conductive substrate to alleviate the collapse and agglomeration of MOFs during the pyrolysis, but also modulates the electronic properties of active FeN_x sites to improve the electrocatalytic activity and stability. As a result, the as-prepared Fe-N_x/N/Ti₃C₂ catalyst exhibits superb ORR activity and long-term stability in both alkaline and acidic electrolytes.     

NiCoP–CoP heterostructural nanowires grown on hierarchical Ni foam as a novel electrocatalyst for efficient hydrogen evolution reaction

The design and manufacture of effective non-noble metal catalysts for the H₂ evolution reaction (HER) are urgent for realizing a cost-effective hydrogen production. We report herein on flower-like structures consisting of NiCoP–CoP heterostructural nanowires grown directly on the hierarchically porous nickel framework (NiCoP–CoP/Ni/NF) to achieve a highly efficient HER in alkaline solution (1.0 M KOH). The NiCoP–CoP/Ni/NF is synthesized by electrodeposition of porous Ni layers on Ni foam, followed by simple hydrothermal reaction and phosphorization. For HER, the binder-free NiCoP–CoP/Ni/NF electrode can reach 10 mA cm^?2 current density at a quite low overpotential of 49 mV, because of the combination of porous Ni layers and highly active NiCoP–CoP nanowires. In addition, the NiCoP/CoP heterostructures exhibited remarkable stability under the long-term durability test. This work provides a new strategy that combines electrodeposition and hydrothermal reaction to synthesize effective HER catalysts.     

Novel MoSe2–Ni(OH)2 nanocomposite as an electrocatalyst for high efficient hydrogen evolution reaction

Nowadays, there is a great demand for low-cost and highly active electrocatalyst for the production of clean renewable energy. However, most of the electrocatalysts are noble metal-based which are very costly and unstable. To counter this, electrochemical water splitting in energy storage systems is been widely applied, using non-noble metal-based nanostructured electrocatalysts. In this work, a novel noble metal-free MoSe₂–Ni(OH)₂ nanocomposite electrocatalyst is synthesized using a multi-step hydrothermal technique for efficient hydrogen evolution reaction (HER). The morphology, structural, chemical composition, and functional features of the synthesized nanomaterials were characterized using different techniques that include scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), and Raman analysis. The new developed MoSe₂–Ni(OH)₂ nanocomposite combines a high active surface area with a high chemical stability, generating a novel material with a synergistic effect that enhances water splitting process performance. Thus, an outstanding low Tafel slope of 54 mV dec⁻¹ is accomplished in the hydrogen evolution reaction.     

Synthesis and optimization of Mo–Ni–Se@NiSe core-shell nanostructures as efficient and durable electrocatalyst for hydrogen evolution reaction in alkaline media

Synthesis conditions are among the most influential factors in the electrocatalytic properties of the samples studied for the hydrogen evolution reaction (HER). In this study, conditions of NiSe synthesis over a Mo–Ni–Se layer were optimized to create core-shell nanostructures with excellent electrocatalytic properties. To optimize the synthesis conditions, first, two electrodeposition techniques in constant potential and pulse potential conditions were investigated and then the optimal temperature for electrodeposition between 5, 25, 40, and 60 °C was found. The electrocatalytic activity of the synthesized samples was investigated using linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry tests in a 1 M KOH solution. Preliminary results showed that pulsed electrodeposition of NiSe could improve the electrocatalytic activity of Mo–Ni–Se by forming durable and suitable nanostructures, while electrodeposited NiSe at constant potential could reduce the electrocatalytic activity of the electrode by forming a dense structure. Then, to determine the appropriate temperature, electrodeposition at the optimal pulse potential at four temperatures of 5, 25, 40, and 60 °C was used to synthesize NiSe on Mo–Ni–Se. The final results showed that the sample synthesized at 60 °C with an electrochemically active surface area of 2870 cm² had the highest hydrogen production sites and required only an overpotential of 77 mV to achieve a current density of 10 mA cm^?2.     

Self-supported cobalt–molybdenum oxide nanosheet clusters as efficient electrocatalysts for hydrogen evolution reaction

In this paper, we report the three-dimensional self-supported CoMoO₄ nanosheet clusters on the nickel foam (denoted as CoMoO₄/NF) by a facile hydrothermal-calcination method for efficient hydrogen generation. As a result, the freestanding CoMoO₄ electrode exhibits an efficient electrochemical activity towards hydrogen evolution reaction, showing overpotentials as low as 68 and 178 mV at current densities of 10 and 100 mA cm⁻² in the alkaline condition (1 M KOH), respectively, a Tafel slope value of 82 mV per decade. Moreover, the electrode exhibits remarkable electrochemical durability for 1000 cycles. Significantly, the water splitting electrolyzer assembled with CoMoO₄/NF || NiFe LDH/NF (the nickel iron layered double hydroxide supported on the nickel foam) system achieved 20 mA cm⁻² at 1.63 V, showing the CoMoO₄/NF is promising for practical water splitting applications.     

Self-assembled nanocotton-like Co–B–P/bacterial cellulose based carbon nanofiber as highly efficient electrocatalyst for oxygen evolution reaction

It is urgent and challenging to exploit highly efficient oxygen evolution reaction (OER) catalysts for water splitting. Bacterial cellulose based carbon nanofiber (BCCNF) is highlighted for its 3D network structure, abundant surface functional groups and good conductivity. Herein, based on the different molar ratio of P/B precursor, a series of nanocotton-like Co–B–P/BCCNF electrocatalysts have been designed and prepared via a simple electroless deposition. When the molar ratio of P/B precursor is 3/7, nanocotton-like Co–B–P/BCCNF catalyst exhibits prominent catalytic performances, delivering the current density of 10 and 50 mA cm^?2 at low overpotentials of only 262 and 391 mV, respectively. Besides, it exhibits long-term stability for durative OER in alkaline solution. This result indicates that nanocotton-like Co–B–P/BCCNF catalyst has great potential as OER catalysts for large-scale hydrogen production via water splitting.     

Bimetallic palladium–iridium alloy nanoparticles as highly efficient and stable catalyst for the hydrogen evolution reaction

Addressed herein, a highly efficient, durable and uniformly dispersed activated carbon supported palladium–iridium nanomaterials (3.42 ± 0.34 nm) were reported for the first time as a catalyst in dimethylamine-borane dehydrogenation reaction at the room temperature. The activated carbon supported palladium-iridium nanosheet (Pd–Ir NPs) is obtained by a simple ultrasonic reduction method, and the fabricated nanocatalyst have been defined by Ultra-Violet-Visible (UV–VIS), Raman spectroscopy, X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HR-TEM). These newly prepared Pd–Ir nanocomposites were found to be highly efficient and stable for dehydrocoupling of dimethylamine borane. The catalytic activity of the Pd–Ir NPs was excellent by showing the one of the best catalytic activity with a very high turnover frequency (295.1 h^?1) and low E_a value of 36.6 ± 2 kJ/mol for DMAB dehydrocoupling. Another important fact about the prepared catalyst is the reusability of the catalyst was very high and easily reused five times without any significant decrease in their catalytic performance. In the current work, the synthesize, characterization and the catalytic performance of the Pd–Ir nanoparticles for the dehydrogenation of the DMAB reaction will be discussed in detail.     

Partial phosphorization of porous Co–Ni–B for efficient hydrogen evolution electrocatalysis

Design of cost-effective and high-efficient electrocatalysts for hydrogen evolution reaction (HER) is of vital significance for the current renewable energy devices — fuel cells. Herein, we report a facile strategy to prepare partial phosphorization of Co–Ni–B material with porous structure via a water-bath boronizing and subsequent phosphorization process at moderate temperature. The optimal atomic proportion of Co to Ni is investigated via physical and electrochemical characterization. As a result, Co₉–Ni₁–B–P exhibits the best HER activity, which require an lower overpotential of ~192 mV to deliver a current density value of 10 mA cm⁻² and a smaller Tafel slope of 94 mV dec⁻¹ in alkaline media, relative to P-free Co–Ni–B catalysts, Co₉–Ni₁–B–P with other Co: Ni proportion and mono metallic borides The excellent electrocatalytic performance of Co₉–Ni₁–B–P is mainly ascribed to the three-dimensional (3D) porous structure and the coordinate functionalization between the borides and phosphides. This work provides a promising strategy for the exploration of quaternary composites as efficient and cost-effective electrocatalysts for HER.     

Potentiostatic electrodeposited of Ni–Fe–Sn on Ni foam served as an excellent electrocatalyst for hydrogen evolution reaction

Ni–Fe–Sn electrocatalyst supported on nickel foam (Ni–Fe–Sn/NF) with high efficiency of hydrogen evolution reaction (HER) has been successfully fabricated through one-step potentiostatic electrodeposition route. The optimized Ni–Fe–Sn/NF displayed an extremely low overpotential of, respectively, 144 and 180 mV at 50 and 100 mA cm^?2 for HER in alkaline condition. Moreover, it could retain its superior stability for at least 12 h. The remarkable electrocatalytic activity of our electrocatalyst is ascribed to the high conductivity originated from synergistic effects between Ni, Fe, and Sn during HER process.     

Electrodeposition of Ni–Fe–Mn ternary nanosheets as affordable and efficient electrocatalyst for both hydrogen and oxygen evolution reactions

The synthesis of high performance and economical electrocatalysts in the process of overall water splitting is very important for the production of hydrogen energy and has become one of the most important challenges. Here, various Ni, Ni–Fe, Ni–Mn nanosheets and Ni–Fe–Mn ternary nanosheets were created using cost-effective, versatile and binder-free electrochemical deposition methods, and the electrocatalytic activity of various electrodes for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were investigated in an alkaline environment. Due to the high electrochemical active surface area due to the fabrication of nanosheets, the synergistic effect between different elements on the electronic structure, the high wettability due to the formation of nanosheets and the quick detachment of formed gasses from the electrode, the Ni–Fe–Mn nanosheets electrode showed excellent electrocatalytic activity. In order to deliver the 10 mA cm⁻² current density in HER and OER processes, this electrode required values of 64 mV and 230 mV overpotential, respectively. Also, the stability test showed that after 10 h of electrolysis at a current density of 100 mA cm⁻², the overpotential changes was very small (less than 4%), indicating that the electrode was excellent electrostatic stability. Also, when using as a bi-functional electrode in the full water splitting system, it only needed a cell voltage of 1528 V to deliver a current of 10 mA cm⁻². The results of this study indicate a new strategy for the synthesis of active and stable electrocatalysts.     

Tuning of electrocatalytic activity of Mn–O–Co composite for alkaline hydrogen evolution reaction

We report the enhancement in electrocatalytic activity of Mn–O–Co composite electrode developed through chemical reduction method. The Mn–O–Co composite electrode exhibits high catalytic activity with a low Tafel slope of 123 mV dec⁻¹ and a low overpotential of 117 mV at a current density of 10 mA cm⁻². The enhancement in electrocatalytic activity of Mn–O–Co composite electrode is due to the synergistic activity of MnO and CoO with the NiP matrix. The intermetallic interaction among the half-filled orbitals of manganese with the fully occupied orbitals of cobalt and nickel leads to an effective electron delocalization in the catalytic system which enhances the HER performance of the coating. The C_dl value of the composite electrode is in the order of 254 μF, which is approximately ten fold higher than the bare NiP coating, due to the enhancement in interaction between the Mn–O–Co composite electrode and the reactive species in the HER medium. The Mn–O–Co composite electrode shows promising characteristics as an electrocatalyst with long term stability and remarkable competency with the commercially available electrodes.     

Three-dimensional Ni2P–MoP2 mesoporous nanorods array as self-standing electrocatalyst for highly efficient hydrogen evolution

Electrochemical hydrogen evolution reaction (HER) via the splitting of water has required electrocatalysts with cost-effectiveness, environmentally friendliness, high catalytic activity, and superior stability to meet the hydrogen economy in future. In this context, we report the successful synthesis of self-standing mesoporous Ni₂P–MoP₂ nanorod arrays on nickel foam (Ni₂P–MoP₂ NRs/3D-NF) through an effective phosphidization of the corresponding NiMoO₄ NRs/3D-NF. The as-synthesis Ni₂P–MoP₂ NRs/3D-NF, as an efficient HER electrocatalyst, exhibits small overpotential of 82.2 and 124.7 mV to reach current density of 10 and 50 mA cm⁻², a low Tafel slope of 52.9 mV dec⁻¹ and it retains its catalytic performance for at least 20 h in alkaline condition. Our work also offers a new strategy in designing and using transition metal phosphide-based 3D nanoarrays catalysts with enhanced catalytic efficiency for mass production of hydrogen fuels.     

In situ activation with Mo of Ni–Co alloys for hydrogen evolution reaction

In this study Ni–Co alloys have been activated during hydrogen electrochemical production by adding Mo ions into the alkaline electrolyte. After dissolving different amounts of sodium molybdate in the Na(OH) electrolyte, Ni–Co alloys were used as cathodes for hydrogen evolution reaction. Afterwards a comparison between hydrogen overvoltage measured on Ni–Co alloys with and without in situ activation has been made. The in situ activation clearly shows an improvement of electrocatalytic properties of Ni–Co alloys for hydrogen evolution reaction. Depending on the alloy the best conditions are reached with different amounts of sodium molybdate in the electrolyte. The values of exchange current density for Ni–Co alloys without Mo, are an average of about 4.1 10⁻⁶ A/cm², while by using in situ activation, these values are about 3.5·10⁻⁴ A/cm². Therefore, exchange current density presents a value nearly one hundred-fold higher when molybdate ions are present in solution. Moreover, two Tafel slope values have been determined for HER on Ni–Co alloys with and without Mo in situ activation. Those Tafel slope values are different, so as their range of both overvoltage and current density, probably highlighting a different kinetic mechanism.     

Novel 3-D urchin-like Ni– Co–W porous nanostructure as efficient bifunctional superhydrophilic electrocatalyst for both hydrogen and oxygen evolution reactions

Fabrication of an electrocatalyst with remarkable electrocatalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is important for the production of hydrogen energy. In this study, Ni–Co–W alloy urchin-like nanostructures were fabricated by binder-free and cost-effective electrochemical deposition method at different applied current densities and HER and OER electrocatalytic activity was studied. The results of this study showed that the microstructure and morphology are strongly influenced by the electrochemical deposition parameters and the best electrocatalytic properties are obtained at the electrode created at the 20 mA.cm⁻²applied current density. The optimum electrode requires −66 mV and 264 mV, respectively, for OER and HER reactions for delivering the 10 mA cm⁻² current density. The optimum electrode also showed negligible potential change after 10 h electrolysis at 100 mA cm⁻², which means remarkable electrocatalytic stability. In addition, when this electrode used as a for full water splitting, it required only 1.58 V to create a current density of 10 mA cm⁻². Such excellent electrocatalytic activity and stability can be related to the high electrochemical active surface area, being binder-free, high intrinsic electrocatalytic activity and hydrophilicity. This study introduces a simple and cost-effective method for fabricating of effective electrodes with high electrocatalytic activity.     

Porous carbon incorporated β-Mo2C hollow sphere: An efficient electrocatalyst for hydrogen evolution reaction

Hydrogen is undoubtedly considered as the cleanest energy source and hence the urgency for production of H₂ is a concern to the scientific community. The major bottleneck for electrocatalytic hydrogen production is still exists as the reported catalysts, mainly noble metal based, are extremely costly. Thus the fabrication of cheap and noble metal free electrocatalyst for Hydrogen Evolution Reaction (HER) is still seeking. Here, a simplistic method is developed for the synthesis of carbon assimilated molybdenum carbide (β-Mo₂C) hollow sphere which showed effective electrocatalysis for HER. The synthesis of desired β-Mo₂CC hollow sphere is based on high temperature carbothermal reduction (800 °C in 10%-H₂/N₂ atmosphere) of carbon incorporated MoO₂ spheres. The synthesized β-Mo₂C with an optimal carbon loading reaches 10 mA/cm^?2 current density at a low overpotential of 146 mV with a small tafel slope of 90 mV dec^?1 for the electrochemical hydrogen evolution (HER) in 0.5 M H₂SO₄. The improved catalytic performance, long-term stability make β-Mo₂CC hollow sphere an auspicious HER electrocatalyst.