Hairy sphere-like Ni9S8/CuS/Cu2O composites grown on nickel foam as bifunctional electrocatalysts for hydrogen evolution and urea electrooxidation

The urea solution electrolysis has become more attractive than water splitting, because it not only produces clean H₂ via the cathodic hydrogen evolution reaction (HER) with lower cell voltage, but also treats sewage containing urea through anodic urea oxidation reaction (UOR). However, lack of efficient electrocatalysts for HER and UOR has limited its development. Herein, hairy sphere -like Ni₉S₈/CuS/Cu₂O composites were synthesized on nickel foam (NF) in situ by a two-step hydrothermal method. The Ni₉S₈/CuS/Cu₂O/NF exhibited good electrocatalytic activity for both HER (?0.146 V vs. RHE to achieve 10 mA cm^?2) and UOR (1.357 V vs. RHE to achieve 10 mA cm^?2). Based on the bifunctional properties of Ni₉S₈/CuS/Cu₂O/NF, a dual-electrode urea solution electrolytic cell was constructed, which only needed a low voltage of 1.47 V to reach a current density of 10 mA cm^?2, and displayed a good stability during a 20-h test. In addition, the reason for the good catalytic activity of Ni₉S₈/CuS/Cu₂O/NF was analyzed and the UOR mechanism was discussed in detail. Our research shows that Ni₉S₈/CuS/Cu₂O/NF is a very promising low-cost dual-function electrocatalyst, which can be used for high-efficiency electrolysis of urea solution to produce hydrogen and treat wastewater.     

Ni3Mo3N coupled with nitrogen-rich carbon microspheres as an efficient hydrogen evolution reaction catalyst and electrochemical sensor for H2O2 detection

Hydrogen evolution reaction (HER) and electrochemical analysis are two important fields of electrochemical research at present. We found that both HER and some electrochemical analytical reactions relied on the concentration of hydrogen ions (H⁺) in solution, so we intended to develop an electrode material that is sensitive to H⁺ and can be used for both HER and some electrochemical analyses. In this work, we synthesized Ni₃Mo₃N coupled with nitrogen-rich carbon microspheres (Ni₃Mo₃N@NC MSs) as highly efficient electrode material for HER and detection of Hydrogen peroxide (H₂O₂), which plays an important role in physiological processes. Here the aniline was used as the nitrogen and carbon sources to synthesize Ni₃Mo₃N@NC. The Ni₃Mo₃N@NC MSs showed high performance for HER in 1 M KOH solution with a small overpotential of 51 mV at 10 mA cm^?2 and superior stability. For H₂O₂ detection, a detection limit of 1 μM (S/N = 3), sensitivity of 120.3 μA·mM^?1 cm^?2 and linear range of 5 μM–40 mM can be achieved, respectively. This work will open up a low-cost and easy avenue to synthesize transition metal nitrides coupled with N-doped carbon as bifunctional electrode material for HER and electrochemical detection.     

Novel peapod-like Ni2P@N-doped carbon nanorods array on carbon fiber for efficient electrocatalytic urea oxidation and hydrogen evolution reaction

Designing and optimizing structure is an effective method to enhance electrocatalytic performance of transition metal-based catalysts. In this work, an innovative nanostructured electrode, consisted of peapod-like Ni₂P@N-doped carbon nanorods array coating on carbon fiber (CF@p-Ni₂P@NC), is devised and synthesized. The N-doped carbon layer is crucial for maintaining the peapod-like nanostructure, which allows for multi-channel electrolyte transport and gas product release. And the carbon layer coating Ni₂P nanoparticles also enhance electrical conductivity and stability, thus ensuring fast electron transport from/to active sites and the long-term stability of catalyst during urea oxidation reaction (UOR)/hydrogen evolution reaction (HER). Benefit from the reasonable structure, CF@p-Ni₂P@NC present perfect performance with getting 100 mA cm^?2 at potential/overpotential of 1.417/0.194 V for UOR/HER in 1.0 M KOH containing 0.5 M urea. In addition, the overall urea-electrolysis system using CF@p-Ni₂P@NC bifunctional electrode only requires 1.590 V to obtain 100 mA cm^?2.     

Electro-synthesis of tungsten carbide containing catalysts in molten salt for efficiently electrolytic hydrogen generation assisted by urea oxidation

Energy-efficient production of hydrogen through urea electrolysis is still challenging due to the lack of satisfactory catalysts for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) in urea containing solution. In this study, Ni–W_xC/C (x = 1,2) composite with high activity for urea electrocatalysis was prepared by direct electro-reduction of affordable feedstock of NiO–CaWO₄–C in molten CaCl₂–NaCl at 873–973 K. The addition of graphite in precursor decreases the particle size of Ni. Introducing W_xC into Ni particles can reduce the overpotential for UOR. As a result, the obtained Ni-W_xC/graphite composite exhibits high current density for urea oxidation, which is about 11-folds and 52-folds higher than that of Ni/graphite and Ni (@1.53 V vs. RHE), respectively. After changing the carbon source from graphite to CNTs, the anodic current density was further increased by 43%, reaching 50.31 mA cm^?2. Moreover, the cathodic catalyst W_xC/CNTs obtained by the same preparation process exhibits high performance towards HER, with a low onset potential of 131.5 mV and a Tafel slope of 69.5 mV dec^?1. Assembling an electrolyzer using Ni-W_xC/CNTs as anode and W_xC/CNTs as cathode can yield a current density of 10 mA cm^?2 at merely 1.65 V in 1 M KOH/0.33 M urea aqueous solution, with excellent long-term electrochemical durability. The environmental-friendly production process uses affordable feedstocks for the synthesis of efficient catalysts toward urea electrolysis, promising an energy-saving hydrogen production as well as waste treatment.     

Hollow hexagonal NiSe–Ni3Se2 anchored onto reduced graphene oxide as efficient electrocatalysts for hydrogen evolution in wide-pH range

Integrating transition metal complexes with carbon-based materials, especially graphene, is a useful strategy for synthesizing effective hydrogen evolution catalysts. Herein, we report a design of hollow hexagonal NiSe–Ni₃Se₂ nanosheets grown on reduced graphene oxide (NiSe–Ni₃Se₂/rGO) by a simple hydrothermal method as an effective catalyst for hydrogen evolution reaction (HER) in the full pH range. In 0.5 M H₂SO₄, the NiSe–Ni₃Se₂/rGO possesses 112 mV to achieve 10 mA cm^?2 and a small Tafel slope (61 mV dec^?1). In 1.0 M PBS and 1.0 M KOH, the overpotentials are 261 and 188 mV at 10 mA cm^?2, and Tafel slopes are 103 and 92 mV dec^?1, respectively. Meanwhile, it owns good cycle stability and durability over 20 h in the whole pH range (0-14). In all solutions, the HER performance of NiSe–Ni₃Se₂/rGO is better than that of NiSe–Ni₃Se₂. This is because the rGO substrate accelerates the electron transfer and improves the electrical conductivity, increasing HER activity of catalyst.     

Pulse-reverse electrodeposition of Ni–Mo–S nanosheets for energy saving electrochemical hydrogen production assisted by urea oxidation

Electrochemical hydrogen production from water splitting is one of the effective methods for hydrogen production that has recently attracted particular attention. One of the limitations of the electrochemical water splitting method is the slow oxygen evolution reaction (OER), which leads to an increase in overpotential and a decrease in hydrogen production efficiency. Here, Ni–Mo–S ultra-thin nanosheets were synthesized using the pulse reverse electrochemical deposition technique, and then this electrode was used as an electrode material for accelerating hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). Remarkably, the optimized electrode needs only 74 mV to attain the 10 mA cm⁻² current density in HER and require only 1.3 V vs RHE potential in the UOR process. Also, results showed that the replacement of the UOR with the OER process resulted in a significant improvement in the electrochemical production of hydrogen in which for delivering the current density of 10 mA cm⁻² in overall urea electrolysis, only 1.384 V is needed. In addition, outstanding catalytic stability was obtained, after 50 h electrolysis, the voltage variation was negligible. Such outstanding catalytic activity and stability was due to 3-D ultrathin nanosheets, the synergistic effect between elements, and the superhydrophilic/superaerophobic nature of fabricated electrode.     

Fe7Se8@Fe2O3 heterostructure nanosheets as bifunctional electrocatalyst for urea electrolysis

Water electrolysis for producing hydrogen is considered to be the most feasible means to develop new green energy. Compared with above, urea electrolysis can improve energy conversion efficiency by introducing urea, and can also be used for purification of wastewater rich in urea. In this paper, a bifunctional electrocatalyst with heterostructure, namely Fe₇Se₈@Fe₂O₃ nanosheets supported on nickel foam, were synthesized for the first time through typical hydrothermal and partial oxidation processes. Iron cation promotes electron transfer and adjusts electron structure under the synergistic action of selenium and oxygen anion, thus achieving excellent catalytic activity of urea electrolysis. In an alkaline solution of 1 M KOH with 0.5 M urea, the Fe₇Se₈@Fe₂O₃/NF catalyst can drive the current density of 10 mA cm^?2 with requiring only potential of 1.313 V and overpotential of 141 mV for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER), respectively. What is noteworthy is that Fe₇Se₈@Fe₂O₃/NF heterostructure is used as bifunctional electrocatalyst to form urea electrolyzer device, which only needs potential of 1.55 V to drive current density of 10 mA cm^?2, which is one of the best catalytic activities reported so far, and the electrode couple showed remarkable stability for 15 h. Density functional theory shows that the Fe₇Se₈@Fe₂O₃/NF material exhibits the minimum Gibbs free energy for the adsorption of hydrogen. This work provides a new method for exploring novel and environmentally friendly bifunctional electrocatalysts for urea electrolysis.     

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.     

Interlaced rosette-like MoS2/Ni3S2/NiFe-LDH grown on nickel foam: A bifunctional electrocatalyst for hydrogen production by urea-assisted electrolysis

In targeting the most important energy and environmental issues in current society, the development of low-cost, bifunctional electrocatalysts for urea-assisted electrocatalytic hydrogen (H₂) production is an urgent and challenging task. In this work, interlaced rosette-like MoS₂/Ni₃S₂/NiFe-layered double hydroxide/nickel foam (LDH/NF) is successfully synthesized by a two-step hydrothermal reaction. Due to its unique interlaced heterostructure, MoS₂/Ni₃S₂/NiFe-LDH/NF exhibits excellent bifunctional catalytic activity towards the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER) in 1.0 M KOH with 0.5 M urea. In a concurrent two-electrode electrolyser (MoS₂/Ni₃S₂/NiFe-LDH/NF(+,-)), only voltage of 1.343 V is required to reach 50 mA cm⁻², which is 216 mV lower than for pure water splitting. Furthermore, after 16 h of urea electrolysis in 1.0 M KOH with 0.5 M urea, the current density remains at 98% of the original value. Thus, the catalyst is not only favorable for H₂ production, but also has great significance for the problem of urea-rich wastewater treatment.     

Ru–MoS2@PPy hollow nanowire as an ultra-stable catalyst for alkaline hydrogen evolution reaction

Electrocatalytic hydrogen evolution reaction (HER) is one of the green and effective method to produce clean hydrogen energy. However, the development of non-Pt HER catalysts with excellent catalytic activity and long-term stability still remains a great challenge. Herein, a vertically aligned core-shell structure material with hollow polypyrrole (PPy) nanowire as a core and Ru-doped MoS₂ (Ru–MoS₂) nanosheets as a shell is firstly reported as a highly efficient and ultra-stable catalyst for HER in alkaline solutions. Results indicate that Ru–MoS₂@PPy catalyst demands a low overpotential of 37 mV at 10 mA cm^?2. In addition, the overpotential at 100 mA cm^?2 is 157 mV and it is almost unchanged after 40,000 cyclic voltammetry cycles. The existence of PPy core not only ensures the vertical growth of MoS₂ nanosheets to expose more edge sites, but also promotes the rapid transfer of electrons, contributing to the improvement of catalytic activity. More importantly, the strong interface interaction between MoS₂ and PPy prevents the collapse of the vertical structure of MoS₂ sheets in the electrocatalytic process and greatly enhances the stability of catalysts, which offers an effective strategy to design and synthesize the HER catalysts with superior catalytic stability.     

Superhydrophilic 3D peony flower-like Mo-doped Ni2S3@NiFe LDH heterostructure electrocatalyst for accelerating water splitting

Constructing highly efficient nonprecious electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential to improve the efficiency of overall water splitting, but still remains lots of obstacles. Herein, a novel 3D peony flower-like electrocatalyst was synthesized by employing Mo–Ni₂S₃/NF nanorod arrays as scaffolds to in situ growth ultrathin NiFe LDH nanosheets (Mo-Ni₂S₃@NiFe LDH). As expected, the novel peony flower-like Mo–Ni₂S₃@NiFe LDH displays superior electrocatalytic activity and stability for both OER and HER in alkaline media. Low overpotentials of only 228 mV and 109 mV are required to achieve the current densities of 50 mA cm^?2 and 10 mA cm^?2 for OER and HER, respectively. Additionally, the material remarkably accelerates water splitting with a low voltage of 1.54 V at 10 mA cm^?2, which outperforms most transition metal electrodes. The outstanding electrocatalytic activity benefits from the following these features: 3D peony flower-like structure with rough surface provides more accessible active sites; superhydrophilic surfaces lead to the tight affinity between electrode with electrolyte; metallic Ni substrate and highly conductive Mo–Ni₂S₃ nanorods scaffold together with offer fast electron transfer; the nanorod arrays and porous Ni foam accelerate gas bubble release and ions transmission; the strong interfacial effect between Mo-doped Ni₃S₂ and NiFe LDH shortens transport pathway, which are benefit for electrocatalytic performance enhancement. This work paves a new avenue for construction and fabrication the 3D porous structure to boost the intrinsic catalytic activities for energy conversion and storage applications.     

Constructing rod-shaped Co2C/MoN as efficient bifunctional electrocatalyst towards overall urea-water electrolysis

In this paper, Co₂C/MoN/NF at different calcination temperatures (T = 500, 550, 600, 650, 700 °C) was prepared in situ on 3D foam nickel (NF) by hydrothermal treatment and high-temperature calcination. The experimental results show that the sample synthesized at 600 °C (Co₂C/MoN-600/NF) has the best catalytic capacity and the maximum electrochemical active area. For the hydrogen evolution reaction (HER), the potential is only ?176 mV at 100 mA cm^?2, meanwhile, only 1.42 V is needed for urea oxidation reaction (UOR). Furthermore, a two-electrode electrolyze cell of Co₂C/MoN-600/NF6Co₂C/MoN-600/NF was constructed. And the voltage required for overall urea splitting (OUS) is 1.507 V at 50 mA cm^?2, which is 171 mV lower than that of overall water splitting (OWS, 1.678 V). Moreover, the prepared catalyst not only can treat urea in wastewater but also catalyze the production of hydrogen. Therefore, it will be a promising green electrocatalyst.     

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.     

Porous flower-like nickel nitride as highly efficient bifunctional electrocatalysts for less energy-intensive hydrogen evolution and urea oxidation

Finding a suitable replacement for the high potential of anodic water electrolysis (oxygen evolution reaction (OER)) is significant for hydrogen energy storage and conversion. In this work, a simple and scalable method synthesizes a structurally unique Ni₃N nanoarray on Ni foam, Ni₃N-350/NF, that provides efficient electrocatalysis for the urea oxidation reaction (UOR) that transports 10 mA cm⁻² at a low potential of 1.34 V. In addition, Ni₃N-350/NF exhibits electro-defense electrocatalytic performance for hydrogen evolution reaction, which provides a low overpotential of 128 mV at 10 mA cm⁻². As proof of concept, all-water-urea electrolysis measurement is carried out in 1 M KOH with 0.5 M Urea with Ni₃N-350/NF as cathode and anode respectively. Ni₃N-350/NF||Ni₃N-350/NF electrode can provide 100 mA cm⁻² at a voltage of only 1.51 V, 160 mV less than that of water electrolysis, which proves its commercial viability in energy-saving hydrogen production.     

Anion-modulation in CoMoO4 electrocatalyst for urea-assisted energy-saving hydrogen production

The anode oxygen evolution reaction (OER) is a delayed half-reaction of water splitting that requires a relatively high overpotential. Therefore, a more easily oxidized urea oxidation reaction (UOR) has been implemented to replace OER. Co–Mo-based bimetallic oxides have been recognized as interesting candidates for electrocatalytic water splitting due to their unique d electron configurations, but the low conductivity and limited active sites still hinder their development. Herein, we demonstrated that anion-modulation in CoMoO₄ nanoplates as coupled hydrogen evolution reaction (HER) and UOR for convenient and efficient urea-assisted hydrogen-production system are demonstrated. The findings of the experiments show that nitrogen doping and phosphorus doping exhibit excellent activity toward alkaline HER and UOR, respectively. As a result, the N–CoMoO₄ and P–CoMoO₄ electrode exhibit low potentials of ?0.062 V and 1.251 V (vs. RHE) to reach a current of 10 mA cm^?2 for HER and UOR. The full urea electrolysis is driven by N–CoMoO₄||P–CoMoO₄ executes stably for 24 h at a low potential of 1.41 V. This is a unique anion-modulation method in electrocatalysts to combine hydrogen generation and sewage treatment, which could pave the way for the creation of long-term energy conversion systems.     

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.     

Co3Mo3N nanosheets arrays on nickel foam as highly efficient bifunctional electrocatalysts for overall urea electrolysis

Replacing dynamics-restricted oxygen evolution reaction (OER) with smart urea oxidation reaction (UOR) is very important for reducing the power consumption for hydrogen production. Here, the Co₃Mo₃N-400/NF is prepared using a facial way, which exhibits remarkable catalytic performances for UOR, hydrogen evolution reaction (HER) and overall urea electrolysis (OUE) because of the more exposed active sites and high electrical conductivity. At 100 mA/cm², the Co₃Mo₃N-400/NF shows a small potential of 1.356 V vs. RHE (reversible hydrogen electrode) for UOR, which is much lower than that for OER. Furthermore, for HER, to reach to 100 mA/cm², a low overpotential of 299 mV is required, and the urea has negligible influence on the HER process. For OUE, the Co₃Mo₃N-400/NF||Co₃Mo₃N-400/NF shows a small cell potential of 1.481 V at 100 mA/cm² along with a good durability. Our work provides more choice for future OUE to generate hydrogen.     

Controlled synthesis of CrxPy-a/ComPn-b nanoarray on nickel foam as efficient electrocatalyst for overall urea splitting

Developing highly efficient bifunctional urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) catalysts for urea splitting to hydrogen are one of the strategies to cope with the energy crisis. Here, a series of Cr_xP_y-a/Co_mP_n-b composites were synthesized on Ni foam through hydrothermal and low-temperature phosphorization process for the first time. It is worth noting that Cr_xP_y-1/Co_mP_n-3@NF exhibited excellent UOR performance (1.331 V at 100 mA cm^?2) and HER performance (0.299 V at 100 mA cm^?2) in an electrolyte of 1 M KOH and 0.5 M urea due to the synergistic effect of Cr–Co. The Cr_xP_y-1/Co_mP_n-3@NF||Cr_xP_y-1/Co_mP_n-3@NF two-electrode system call for only 1.52 V to provide current density of 10 mA cm^?2, which is one of the best electrochemistry performances reported up to now. Experimental analysis show that the promoted electrochemistry performances is assigned to faster charge transfer rate, the exposure of more reaction site and better properties of metals. Density Functional theory (DFT) results demonstrate that the presence of the Co_mP_n material accelerates the kinetics of hydrogen production and the Cr_xP_y material improves the properties of metals for the electrode. The work provides a new idea to develop the environmentally friendly and low cost overall urea splitting catalyst with transition metals instead of noble metals.     

Super-hydrophilic/super-aerophobic Ni2P/Co(PO3)2 heterostructure for high-efficiency and durable hydrogen evolution electrocatalysis at large current density in alkaline fresh water,alkaline seawater and industrial wastewater

Seawater electrolysis has become an efficient method which makes full use of natural resources to produce hydrogen. However, it suffers high energy cost and chloride corrosion. Herein, we first present a Ni₂P/Co(PO₃)₂/NF heterostructure in which Co(PO₃)₂ with the nano-rose morphology in-situ grown on the rough Ni₂P/NF. The unique 3D nano-rose structure and the optimized electronic structure of the heterostructure enable Ni₂P/Co(PO₃)₂/NF super-hydrophilic and super-aerophobic characteristics, and highly facilitate hydrogen evolution reaction (HER) kinetics in alkaline fresh water, alkaline seawater and even industrial wastewater at large current density, which is rarely reported. Significantly, at large current densities, Ni₂P/Co(PO₃)₂/NF only requires overpotentials of 217 and 307 mV for HER to achieve 1000 mA cm⁻² in alkaline fresh water and alkaline seawater, respectively, and requires an overpotential of 469 mV for HER to deliver 500 mA cm⁻² in industrial wastewater. Furthermore, the overall seawater splitting system in the two-electrode electrolyzer only requires voltage of 1.98 V to drive 1000 mA cm⁻², which also demonstrates significant durability to keep 600 mA cm⁻² for at least 60 h. This study opens a new avenue of designing high efficiency electrocatalysts for hydrogen production at large current densities in alkaline seawater and industrial wastewater.     

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.