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.     

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.     

The 3D ultra-thin Cu1-xNixS/NF nanosheet as a highly efficient and stable electrocatalyst for overall water splitting

In recent years, the exploration of efficient and stable noble-metal-free electrocatalysts is becoming increasingly important, used mainly for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In this work, a new ultrathin porous Cu_1-xNi_xS/NF nanosheets array was constructed on the 3D nickel skeleton by two-step method: hydrothermal method and vulcanization method. Through these two processes, Cu_1-xNi_xS/NF has a larger specific surface area than that of foamed nickel (NF) and Cu_1-xNi_xO/NF. The Cu_1-xNi_xS/NF materials show excellent catalytic activity by accelerating the electron transfer rate and increase the amount of H₂ and O₂ produced. The lower overpotential was obtained only 350 mV at 20 mA cm⁻² for OER, not only that, but also the same phenomenon is pointed out in HER, optimal Cu_1-xNi_xS/NF presents low overpotentials of 189 mV to reach a current density of 10 mA cm⁻² in 1.0 M KOH for HER. Both OER and HER shows a lower Tafel slope: 51.2 mV dec⁻¹ and 127.2 mV dec⁻¹, subsequently, the overall water splitting activity of Cu_1-xNi_xS/NF was investigated, and the low cell voltage was 1.64 V (current density 10 mA cm⁻²). It can be stable for 14 h during the overall water splitting reaction. These results fully demonstrate that Cu_1-xNi_xS/NF non-precious metal materials can be invoked become one of the effective catalysts for overall water splitting, providing a richer resource for energy storage.     

Ni/NiO@rGO as an efficient bifunctional electrocatalyst for enhanced overall water splitting reactions

Herein, we fabricated bifunctional, noble metal-free, highly efficient nickel/nickel oxide on reduced graphene oxide (Ni/NiO@rGO) by chemical synthesis approach for electrochemical water splitting reaction. Its structural and morphological characterization using thermogravimetric analysis (TGA), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), energy dispersive analysis of X-ray (EDAX) and X-ray diffraction (XRD) represents, Ni/NiO@rGO is having Ni/NiO NPs ∼10 nm (±2 nm) on graphene oxide with face-centered cubic (FCC) crystal structure. Moreover, the presence of Ni/NiO (2.26%), O (6.56%), N (0.74%) and C (90.44%) from EDAX analysis further confirms the formation of Ni/NiO@rGO and it also supported by FTIR studies. This nanocatalyst is examined further for electrocatalytic water splitting reactions (HER and OER). It demonstrated low overpotential 582 mV to achieve current density at 10 mA cm⁻² and smaller Tafel slope of 63 mV dec⁻¹ obtained in 0.5 M H₂SO₄ towards HER. Also, at the other end at onset potential of 1.6 V vs. RHE towards OER. It demonstrated low overpotential 480 mV to achieve current density at 10 mA cm⁻² and smaller Tafel slope of 41 mV dec⁻¹ in 0.5 M KOH towards OER observed. Hydrogen fuel is eco-friendly to the environment and noteworthy performance of earth-saving reactions.     

Novel 13X Zeolite/PANI electrocatalyst for hydrogen and oxygen evolution reaction

In this work, first 13X zeolite was prepared by the hydrothermal method. Then, the composite electrode was fabricated by using 13X zeolite and aniline monomer in nickel foam by electropolymerization technique in an acidic medium (13X/PANI). The synthesized 13X zeolite was characterized by physicochemical characterization techniques such as Fourier transform infra-red (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) pattern and nitrogen sorption isotherm. 13X/PANI composite was further analyzed by XRD, XPS and FE-SEM techniques. Furthermore, the catalyst activity of the synthesized 13X, PANI and 13X/PANI composite electrodes was evaluated in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by using linear square voltammetry (LSV) and Tafel slope method. The Tafel slopes of HER were found to be 203 mV dec⁻¹, 440 mV dec⁻¹ and 282 mV dec⁻¹ for 13X, PANI and 13X/PANI-15 electrodes respectively. While the OER Tafel slopes were found to be 423 mV dec⁻¹, 310 mV dec⁻¹ and 168 mV dec⁻¹ for 13X, PANI and 13X/PANI-15, respectively. 13X/PANI-15 electrodes show excellent catalytic performance about the overpotential at 10 mA cm⁻² for HER and the overpotential at 20 mA cm⁻² for OER. The obtained results suggest fabricated novel electrodes are a potential candidate for HER and OER reaction and can be open new avenue for other electrochemical reactions.     

Engineering bimetallic cactus-like NiFeOOH/CoNiSe2 heterostructure nanosheets for efficient oxygen evolution and overall water splitting

The development of structural stable, high-performance, inexpensive electrocatalysts for oxygen evolution reactions (OER) is essential to alleviate the energy crisis. Herein, cactus-like CoNiSe₂ was synthesized on nickel foam and NiFeOOH was electrodeposited on surface of CoNiSe₂ to form a core-shell structural electrode. The obtained NiFeOOH/CoNiSe₂/NF exhibited ultra-low overpotentials of 204 mV and 234 mV at 10 and 100 mA cm⁻², with a Tafel slope of 26.2 mV dec⁻¹ in 1 M KOH alkaline solution. Furthermore, the current density only decreased by 5% after a 100 h durability test at 200 mA cm⁻², showing excellent robust stability. A two-electrode system with NiFeOOH/CoNiSe₂/NF as anode and Ni/NiO@MoO_3-x/NF as cathode (NiFeOOH/CoNiSe₂/NF||Ni/NiO@MoO_3-x/NF) showed a low voltage of 1.47/1.56 V to deliver 10/100 mA cm⁻². According to the experimental and density functional theory (DFT) results, the strong electronic interactions at the NiFeOOH/CoNiSe₂/NF interface leads to an increase in the valence state of Fe and an optimisation of the adsorption free energy, which are favourable to reduce the energy consumption of the OER. This work obtained high performance OER electrocatalysts by engineering amorphous and crystalline heterointerfaces and structural design, which will provide some inspiration for similar work.     

Enriched oxygen vacancy promoted heteroatoms (B,P, N,and S) doped CeO2: Challenging electrocatalysts for oxygen evolution reaction (OER) in alkaline medium

Increasing worldwide energy consumption has prompted considerable study into energy generation and energy storage systems in recent years. Chemical fuels may be produced efficiently via electrocatalytic water splitting, which uses electric and solar power. The development of efficient anodic electrocatalysts for efficient oxygen evolution reaction (OER) is a greater concern of present energy research. Cerium oxide (CeO₂) are promising electrocatalysts that exhibit outstanding OER but their reduced stability obstructs the practical application. A novel strategy was established to construct an effective catalyst of heteroatom (N, B, P and S) doped CeO₂ matrix were prepared. Moreover, the doping of heteroatoms into the CeO₂ matrix processes the improved electronic conductivity, reactive sites, increases the electrochemical catalytic activity, which enhances the water oxidation reaction. Consequently, well-suited alkaline electrolysers were brought together for water oxidation to ideal OER electrocatalytic activity. The OER activity of the electrocatalysts follows the order of S–CeO₂ (190 mV@10 mA cm⁻²), N– CeO₂ (220 mV @10 mA cm⁻²), P– CeO₂ (230 mV @10 mA cm⁻²), B–CeO₂ (250 mV @10 mA cm⁻²) and CeO₂ (260 mV @10 mA cm⁻²) in 1 M of KOH. From the kinetics analysis, Tafel slope value achieved for catalysts CeO₂, B–CeO_2, P–CeO₂, N–CeO₂ and S–CeO₂ are 142 mV dec⁻¹,121 mV dec⁻¹, 102 mV dec⁻¹, 98 mV dec⁻¹ and 83 mV dec⁻¹ respectively. These results validate that the S–CeO₂ electrode is prominent for OER performance with the requirement of cell voltage of 1.42 V at 10 mA cm⁻² current density. In addition, sulphur doped CeO₂ relatively have excellent stability through chrono-potentiometric analysis lasting for 20 h. Although the heteroatoms doped CeO₂ is acts as anode material, the preparation method is widespread, which will reduce the synthesis cost and streamline the preparation of electrode for OER. This research effort delivers a complete advantage for the development of robust, environmentally friendly and highly dynamic electrocatalysts for OER activity.     

Multi-shelled CoS2–MoS2 hollow spheres as efficient bifunctional electrocatalysts for overall water splitting

The exploration of highly efficient non-precious electrocatalysts is essential for water splitting devices. Herein, we synthesized CoS₂–MoS₂ multi-shelled hollow spheres (MSHSs) as efficient electrocatalysts both for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) using a Schiff base coordination polymer (CP). Co-CP solid spheres were converted to Co₃O₄ MSHSs by sintering in air. CoS₂–MoS₂ MSHSs were obtained by a solvothermal reaction of Co₃O₄ MSHSs and MoS₄²⁻ anions. CoS₂–MoS₂ MSHSs have a high specific surface area of 73.5 m²g^-1. Due to the synergistic effect between the CoS₂ and MoS₂, the electrode of CoS₂–MoS₂ MSHSs shows low overpotential of 109 mV with Tafel slope of 52.0 mV dec⁻¹ for HER, as well as a low overpotential of 288 mV with Tafel slope of 62.1 mV dec⁻¹ for OER at a current density of 10 mA cm⁻² in alkaline solution. The corresponding two-electrode system needs a potential of 1.61 V (vs. RHE) to obtain anodic current density of 10 mA cm⁻² for OER and maintains excellent stability for 10 h.     

Bio-derived nanoporous activated carbon sheets as electrocatalyst for enhanced electrochemical water splitting

Designing highly efficient and durable metal-free electro-catalysts replacing the precious (non)noble metals is crucial to the future hydrogen economy and various renewable energy conversion and storage devices. Herein, we report an efficient low-cost nanoporous activated carbon sheets (NACS) with hierarchical pore architecture from Indian Ooty Varkey (IOV) food waste for oxygen evolution (OER) and hydrogen evolution reactions (HER) by following “waste to wealth creation” strategy. Characterization of NACS carbo-catalyst reveals the presence of pyridinic-nitrogen inherited by self-doping of N from the biomass with high BET surface area (1478.0 m² g^-1). As an electrocatalyst in alkaline medium, it exhibits low-onset potential (1.36 V vs. RHE), an overpotential (η₁₀) of 0.34 V at 10.0 mA cm⁻² with a small Tafel value (43 mV dec⁻¹), and good stability towards OER compared to Pt or Ir commercial catalysts. Tested as HER catalyst, it displays an impressive HER activity with a low-onset potential of −0.085 V (vs. RHE), and overpotential (η₁₀) of 0.38 V at 10.0 mA cm⁻² with a small Tafel slope of 85 mV dec⁻¹.     

MoS2/NiFeS2 heterostructure as a highly efficient electrocatalyst for overall water splitting at high current densities

Searching for efficient, stable and low-cost nonprecious catalysts for oxygen and hydrogen evolution reactions (OER and HER) is highly desired in overall water splitting (OWS). Herein, presented is a nickel foam (NF)-supported MoS₂/NiFeS₂ heterostructure, as an efficient electrocatalyst for OER, HER and OWS. The MoS₂/NiFeS₂/NF catalyst achieves a 500 mA cm⁻² current density at a small overpotential of 303 mV for OER, and 228 mV for HER. Assembled as an electrolyzer for OWS, such a MoS₂/NiFeS₂/NF heterostructure catalyst shows a quite low cell voltage (≈1.79 V) at 500 mA cm⁻², which is among the best values of current non-noble metal electrocatalysts. Even at the extremely large current density of 1000 mA cm⁻², the MoS₂/NiFeS₂/NF catalyst presents low overpotentials of 314 and 253 mV for OER and HER, respectively. Furthermore, MoS₂/NiFeS₂/NF shows a ceaseless durability over 25 h with almost no change in the cell voltage. The superior catalytic activity and stability at large current densities (>500 mA cm⁻²) far exceed the benchmark RuO₂ and Pt/C catalysts. This work sheds a new light on the development of highly active and stable nonprecious electrocatalysts for industrial water electrolysis.     

Preparation of ultrathin molybdenum disulfide dispersed on graphene via cobalt doping: A bifunctional catalyst for hydrogen and oxygen evolution reaction

The development of highly active and low-cost catalysts for hydrogen evolution reaction (HER) is significant for the development of clean and renewable energy research. Owing to the low H adsorption free energy, molybdenum disulfide (MoS₂) is regarded as a promising candidate for HER, but it shows low activity for oxygen evolution reaction (OER). Herein, graphene-supported cobalt-doped ultrathin molybdenum disulfide (Co–MoS₂/rGO) was synthesized via a one-pot hydrothermal method. The obtained hybrids modified electrode exhibits a high HER catalytic activity with a low overpotential of 147 mV at the current density of 10 mA cm⁻², a small Tafel slope of 49.5 mV dec⁻¹, as well as good electrochemical stability in acidic electrolyte. Meanwhile, the catalyst shows remarkable OER activity with a low overpotential of 347 mV at 10 mA cm⁻². The superior activity is ascribed not only to the high conductivity originated from the reduced graphene, but also to the synergistic effect between MoS₂ and cobalt.     

An alkaline-acid asymmetric electrolyzer using NiCoP/CoP/Co3O4 multi-shell hollow nanoflakes as cathode and Ag as anode to realizing energy efficient production of hydrogen and shape controllable silver oxide

Large scale hydrogen generation by water electrolysis is severely impeded by the high cost of noble metal electrode materials and the kinetic-sluggish anodic oxygen evolution reaction (OER). Here we design a MOF-derived NiCoP/CoP/Co₃O₄ multi-shell hollow nanoflakes as a low-cost cathode electrocatalyst for hydrogen evolution reaction (HER), and replace the OER with more favorable silver oxidation reaction (AOR). The NiCoP/CoP/Co₃O₄ supported on carbon cloth (CC@NiCoP/CoP/Co₃O₄) endows an impressive low overpotential (η) of 90 mV at 10 mA cm⁻² and a low Tafel slope of 81.7 mV dec⁻¹ for HER in 0.5 M H₂SO₄ electrolyte. Coupling it with Ag electrode to forming an asymmetric alkali-acid electrolyzer exhibits superior performance with the requirement of a cell voltage of only 1.16 V to attain 10 mA cm⁻² with nearly 100% of Faradaic efficiencies for both H₂ and Ag₂O generation, showing dramatically lower voltage than that previously reported for conventional water splitting systems. In addition, the size and shape of Ag₂O can be controlled by manipulating current density. Our electrolyzer design provides not only an economical approach to produce H₂ and Ag₂O but also shows great promise for expansion into the electrosynthesis of other value-added chemicals.     

Vertical Nickel–Iron layered double hydroxide nanosheets grown on hills-like nickel framework for efficient water oxidation and splitting

Herein, the vertical thin nickel–iron layered double hydroxide nanosheets grown on the hills-like nickel framework (NiFe LDH/Ni@NF) are employed for the oxygen evolution reaction (OER), securing at the low overpotentials of 197 and 270 mV to obtain the current densities of 20 and 100 mA cm⁻², respectively, with a Tafel slope of 73.34 mV dec⁻¹. The electrodeposited nickel film induces the NiFe LDH nanosheets grow vertically and thinly. As well, the nickel abundant interfaces and inner space makes this catalyst effective for OER. It was further served as the OER electrode in a water splitting system coupled the Pt/C cathode, and a cell voltage was at 1.52 and 1.67 V to achieve the current density of 10 mA cm⁻² and 50 mA cm⁻². In addition, the water electrolyzer can suffer a long time of 24 h at 50 mA cm⁻², showing the feasibility in a practical unbiased alkaline water splitting system.     

CoO/NF nanowires promote hydrogen and oxygen production for overall water splitting in alkaline media

The exploration of catalysts with high activity and low cost for water splitting is still necessary. Herein, a nanowire-like morphology CoO/NF electrode is synthesized using facile hydrothermal reaction and calcination treatment. The urea can regulate its morphology during the synthetic process of CoO/NF. Electrochemical studies reveal that the as-obtained CoO/NF exhibits excellent electrocatalytic performance with overpotential of 307 mV at current density of 10 mA cm⁻² and Tafel slope of 72 mV dec⁻¹ for oxygen evolution reaction, and CoO/NF delivers current density of 10 mA cm⁻² at overpotential of 224 mV for hydrogen evolution reaction. The results of the oxygen evolution reaction stability show that the overpotential of CoO/NF electrode is only increased by 4 mV at current density of 10 mA cm⁻². The two-electrode water splitting with CoO/NF electrodes as both anode and cathode needs a cell potential of 1.76 V to reach 10 mA cm⁻². Therefore, this simple method to prepare CoO/NF electrode can enhance the properties of electrocatalysts, which makes CoO/NF a promising material to replace noble metal-based catalysts.     

Carbon nanorod supported metal alloy nanocubes using polydopamine as location reagent for water splitting

Transition metal catalysts were supposed to be the most likely substitute for commercial noble metal catalysts, and the development of highly active and long-term catalyst for water splitting are the future trend. Herein, Ni rectangular nitrogen doped carbon nanorods@Fe–Co nanocubes (Ni-CNRs@Fe–Co cubes) were fabricated via a facile template-free method. This simple strategy not only realizes the structure tailoring, but also achieves high-quality nitrogen-doping. Specifically, nickel dimethylglyoxime [Ni(dmg)₂] with rectangular rodlike structure was firstly synthesized by solution method, then metal-organic frameworks Fe–Co nanocube with different contents were loaded on rectangular carbon nanorods with polydopamine as the locating and the connecting agent, and finally Ni-CNRs@xFe-Co cubes were obtained by a one-step calcination. A series of electrochemical tests were researched on materials with different metal contents in the 1 M KOH solution. The Ni-CNRs@Fe–Co cubes show excellent electrocatalytic activity in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). For HER and OER, the Tafel slopes were 83.3 mV dec⁻¹ and 71 mV dec⁻¹, the onset potential were −167 mV and 1.62 V, and reached the current densities of 10 mA cm⁻², the overpotential just needed 196 mV and 433 mV, respectively. This novel synthetic strategy will provide a template-free way for cheap electrocatalysts of non-precious metal for OER and HER.     

Cobalt phosphide nanoparticles embedded in 3D N-doped porous carbon for efficient hydrogen and oxygen evolution reactions

An electrocatalyst based on a unique three-dimensional (3D) N-doped porous carbon sheet networks embedded with CoP₂ nanoparticles (CoP₂@3D-NPC) was synthesized by a facile pyrolysis process as well as an in-situ phosphatization method. The improved CoP₂@3D-NPC hybrid materials show excellent electrocatalytic activity toward HER and OER. This material provides a low overpotential of 126 mV at 10 mA cm⁻² in 0.5 M H₂SO₄ and 167 mV at 20 mA cm⁻² in 1.0 M KOH for HER with a small Tafel slope value of 59 mV dec⁻¹, respectively. Besides, it is also active for the OER under alkaline conditions. Such a prominent property of the CoP₂@3D-NPC electrocatalyst could be attributed to its excellent electrical conductivity of 3D carbon substrate, strong synergistic effect between CoP₂ nanoparticles and carbon nanosheet as well as extra active sites created by the N-doped structure.     

Facile galvanic replacement method for porous Pd@Pt nanoparticles as an efficient HER electrocatalyst

In realm of renewable energy, development of an efficient and durable electrocatalyst for H₂ production through electrochemical hydrogen evolution reaction (HER) is indispensable. Herein, we demonstrate a simple preparation of carbon-supported nanoporous Pd with surface coated Pt (CS–PdPt) by a simple galvanic replacement reaction (GRR). The phase purity and porosity have been confirmed by XRD, HRTEM, and N₂ sorption techniques. As HER electrocatalyst, CS-PdPt showed a low overpotential of 26 mV in 0.5 M H₂SO₄ at current density of 10 mA cm⁻², which is lower than the commercial Pt/C electrode. The CS-PdPt catalyst exhibits an overpotential of 46 mV in 1 M KOH, and 50 mV in neutral buffer (1 M PBS) at 10 mA cm⁻². The CS-PdPt furnished with small Tafel values of 33, 88, and 107 mV dec⁻¹ in acidic, alkaline, and neutral medium, respectively. Accelerated durability test at 100 mV s⁻¹ for 1000 cycles demonstrated a negligible change in HER activity.     

Facile and scalable synthesis of heterostructural NiSe2/FeSe2 nanoparticles as efficient and stable binder-free electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) is a rate-limiting step in electrocatalytic water splitting due to its sluggish reaction kinetics. Therefore, it is still challengeable to develop an inexpensive and efficient OER catalyst via a facile and scalable synthesis method. To address such issues, herein, we present a facile and scalable approach to prepare ultrathin NiSe₂/FeSe₂ heterostructural nanoparticles in-situ grown on NiFe foam (NFS/NFF), which can be employed as a self-supported non-noble metal-based catalyst for OER. The NFS/NFF catalyst delivers outstanding OER performance with a small Tafel slope of 57.07 mV dec⁻¹ and a low overpotential of 274 mV at 40 mA cm⁻² and displays terrific long-term stability, surpassing the performance of commercial RuO₂ and single component NiSe₂/NF catalyst. The results of XPS manifest that there is a strong heterointerface interaction between NiSe₂ and FeSe₂. In addition, combined with density functional theory (DFT) calculations, we further confirmed that the synergistic interface effect between NiSe₂ and FeSe₂ reduces the value of the Gibbs free energy of oxygen-containing intermediates as determining step (RDS) from 3.15 eV (NiSe₂) to 2.41 eV (NiSe₂/FeSe₂ heterostructures), leading to excellent OER performance. This work provides a novel strategy to rationally design and fabricate selenide-based heterostructural nanoparticles via a facile method, which can extend to prepare other non-precious OER catalysts with high efficiency and long-term stability.     

Mesoporous nickel-sulfide/nickel/N-doped carbon as HER and OER bifunctional electrocatalyst for water electrolysis

The development of non-precious metal-based highly active bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical factor for making water electrolysis a viable process for large-scale industrial applications. In this study, bi-functional water splitting electrocatalysts in the form of nickel-sulfide/nickel nanoparticles integrated into a three-dimensional N-doped porous carbon matrix, are prepared using NaCl as a porous structure-forming template. Microstructures of the catalytic materials are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N₂ adsorption-desorption analysis. The most active catalyst synthesized in this study exhibits a low HER overpotential of 70 mV at 10 mA cm⁻² and a low Tafel slope of 45 mV dec⁻¹. In OER, the optimized sample performs better than a state-of-the-art RuO₂ catalyst and produces an overpotential of 337 mV at 10 mA cm⁻², lower than that of RuO₂. The newly obtained materials are also used as HER/OER electrocatalysts in a specially assembled two-electrode water splitting cell. The cell demonstrates high activity and good stability in overall water splitting.     

Efficient bifunctional hydrogen and oxygen evolution reaction electrocatalyst based on the NU-1000/CuCo2S4 heterojunction

One of the current necessities to produce clean energy is the logical design of inexpensive noble-metal free electrocatalysts with developed structure and composition for electrochemical water splitting. In this study, we introduce a new core-shell-structured bifunctional electrocatalyst of NU-1000/CuCo₂S₄ for oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and overall water splitting for the first time. Own to unique structure with rich porosity, high electrical conductivity, high stability and larger density of active sites, this nanocomposite can produce water electrolysis in a 1 M KOH solution. The electrochemical measurements show overpotentials of 335 mV for OER and 93 mV for HER at a current density of 10 mAcm⁻². Also, the NU-1000/CuCo₂S₄ nanocomposite exhibits Tafel slope values of 110 mV dec⁻¹ and 103 mV dec⁻¹ for HER and OER, respectively. Besides, NU-1000/CuCo₂S₄ presents a significant long-term stability in a 72 h run. Additionally, NU-1000/CuCo₂S₄ requires 1.55 V to deliver 10 mA cm⁻² current density in overall water splitting. According to these results, we hope to use this electrocatalyst in producing oxygen and hydrogen from water.