Electrodeposited Ni-Co-Sn alloy as a highly efficient electrocatalyst for water splitting

Water splitting to produce hydrogen and oxygen is considered as a feasible solution to solve the current energy crisis. It is highly desirable to develop inexpensive and efficient electrocatalyst for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this paper, nanostructured Ni-Co-Sn alloys were electrodeposited on copper foil and the excellent electrocatalytic performances for both HER and OER in alkaline media were achieved. The optimized Ni-Co-Sn electrode shows a low onset overpotential of −18 mV and a small Tafel slope of 63 mV/dec for the HER, comparable to many state-of-the-art non-precious metal HER catalysts. For the OER, it produces an overpotential of 270 mV (1.50 V vs. RHE) at current density of 10 mA/cm², which is better than that of the commercial Ir/C catalyst. In addition to high electrocatalytic activities, it exhibits good stability for both HER and OER. This is the first report that Ni-Co-Sn is served as a cost-effective and highly efficient bifunctional catalyst for water splitting and it will be of great practical value.     

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.     

NiFe single atom catalysts anchored on carbon for oxygen evolution reaction

Single atom catalysts (SACs) can improve the efficiency of oxygen evolution reaction (OER). However, metal SACs anchored on carbon materials are relatively uncommon for the OER. In this paper, using carbon black as carrier, NiFe SACs are fabricated by one step pyrolysis method. When the weight ratio of Ni/Fe is lower than 5:3, NiFe@C exibits highly-dispersed SACs over carbon in addition to some Ni₃Fe alloy. The prepared NiFe@C 5:3 SACs showed excellent OER performance with an overpotential of 322 mV and 438 mV for current density of 10 mA/cm² and 100 mA/cm², respectively. The Tafel slope of NiFe@C 5:3 was as small as 87.6 mV/dec, indicating fast charge transfer of NiFe@C 5:3 during OER process, which was also confirmed by electrochemical impedance spectra with R_ct = 18.07 Ωcm². Meanwhile, NiFe@C 5:3 had the highest specific capacitance of 5 mF/cm² with good stability. This work provides a reference for designing electocatalyst material for efficient, stable and economical OER process.     

Nitrogen-doped cobalt sulfide as an efficient electrocatalyst for hydrogen evolution reaction in alkaline and acidic media

The enhancement in intrinsic catalytic activity and material conductivity of an electrocatalyst can leads to promoting HER activity. Herein, a successful nitrogenation of CoS₂ (N–CoS₂) catalyst has been investigated through the facile hydrothermal process followed by N₂ annealing treatment. An optimized N–CoS₂ catalyst reveals an outstanding hydrogen evolution reaction (HER) performance in alkaline as well as acidic electrolyte media, exhibiting an infinitesimal overpotential of ?0.137 and ?0.097 V at a current density of ?10 mA/cm² (?0.309 and ?0.275 V at ?300 mA/cm²), corresponding respectively, with a modest Tafel slope of 117 and 101 mV/dec. Moreover, a static voltage response was observed at low and high current rates (?10 to ?100 mA/cm²) along with an excellent endurance up to 50 h even at ?100 mA/cm². The excellent catalytic HER performance is ascribed to improved electronic conductivity and enhanced electrochemically active sites, which is aroused from the synergy and mutual interaction between heteroatoms that might have varied the surface chemistry of an active catalyst.     

Boosting the kinetics of oxygen and hydrogen evolution in alkaline water splitting using nickel ferrite /N-graphene nanocomposite as a bifunctional electrocatalyst

Design, synthesize and application of metal-oxide based bifunctional electrocatalysts with sustainability and efficient activity in water splitting is significant among the wide spread researches in energy applications. Herein, bifunctional electrocatalysts composed of NiFe₂O₄ dispersed on N-doped graphene has been prepared by in-situ polymerization and characterized for further bifunctional catalytic performances. The electrocatalyst exhibited bespoken performances as cathode in HER as well as anode in OER at alkaline electrolyte. The nanocomposite N-doped graphene/NiFe₂O₄ (NGNF) exhibited low overpotential of 184 mV in HER and 340 mV in OER for attaining the current density of 10 mA/cm² which is far better than their pristine counterparts. Similarly its Tafel slopes were found to be 82.9 mV/dec and 93.2 mV/dec for HER and OER. As an electrocatalyst NGNF outperformed pure nickel ferrite and graphene/NiFe₂O₄ (GNF) as bifunctional electrocatalyst with low overpotential and Tafel slopes. This indicates the impact of graphene and N-doping on graphene in the activity of pure NF. The graphene in the composite and the N-dopants provoked the catalytic activity and tuned the electron transfer and interaction with the electrolyte. Thus, herein we endow with strategies of preparing highly efficient bifunctional electrocatalysts by coupling spinel oxides and N-doped graphene for HER and OER.     

Electroless deposition synthesis of composite catalysts Ni-Fe-P-WO3/NF with superior oxygen evolution performance

The proper construction of high efficiency, low-cost, earth-abundant oxygen evolution reaction (OER) catalyst is essential for hydrogen formation by water splitting. A novel electrocatalyst with highly active OER performance was manufactured by a simple electroless deposition method of Ni-Fe-P-WO₃ on nickel foam (NF). Benefiting from outstanding mass transfer capability of Ni-Fe-P-WO₃/NF heterogeneous structure, abundance of active sites in the amorphous architecture and etc., the Ni-Fe-P-WO₃/NF shows extremely superb electrocatalytic properties compare to noble metal catalyst IrO₂/NF for OER, which needs an overpotential of only 218 mV in 1.0 M KOH solution to achieve the current density of 10 mA cm^?2. It also has remarkable OER activity at high current density that only needs 298 mV to attain 100 mA cm^?2 current density. Moreover, the Ni-Fe-P-WO₃/NF has low Tafel slope of 42 mV dec^?1. This study offers a novel approach to the production of OER multiphase electrocatalysts from oxides and alloys.     

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.     

Platinum nanoparticles decorated Nb2CTx MXene as an efficient dual functional catalyst for hydrogen evolution and oxygen reduction reaction

Here, a dual functional Nb₂CT_x@Pt nanocomposite has been synthesized by in situ reduction method. The Pt loading in the composite has been optimized to get minimum overpotential (141 mV at 10 mA/cm²) for hydrogen evolution reaction (HER) along with a promising Tafel slope of 46.3 mV/dec, while Pt/C shows an overpotential and Tafel slope of 104 mV and 32.4 mV/dec, respectively. The Pt mass activity for Nb₂CT_x@Pt3.8 composite at 100 mV overpotential was 3.44 A g^?1 while the Pt mass activity for conventional Pt/C was 0.7 A g^?1, which shows that the activity of Nb₂CT_x@Pt3.8 composite is approximately 5 times higher than Pt/C. In addition, the catalyst was found to be stable for continuous 500 cycles without any binder molecules. The oxygen reduction reaction (ORR) capability of the material was also evaluated and found that the catalyst exhibited a current density of ?4.28 mA/cm² in the diffusion limiting region in comparison with the current density of ?5.82 mA/cm² for Pt/C at 2600 revolutions per minute (RPM). The Pt mass activity of Nb₂CT_x@Pt3.8 composite for ORR is approximately 10 times higher than Pt/C. The Nb₂CT_x@Pt3.8 composite was able to reduce O₂ completely using the 4-electron pathway with very little peroxide production. From these results, the dual functionality of the Nb₂CT_x@Pt3.8 composite for both HER and ORR has been established.     

Optimized performance of nickel in crystal-layered arrangement of NiFe2O4/rGO hybrid for high-performance oxygen evolution reaction

To rescue the future from the global energy crisis and to ensure it with clean and economical hydrogen energy, it is an urgency to develop an efficient OER catalyst, which intensely sluggish the kinetic process of hydrogen production. Herein, we have precisely synthesized an efficient, stable, earth-abundant metal-based NiFe₂O₄/rGO hybrid OER electrocatalysts by a simple solvothermal method. The measurements including XRD, FTIR, XPS, EDS, SEM, and TEM revealed the prominent structural integrity of catalyst with crystal-layered structure. The rich oxidation chemistry of transition metals and substantially active carbon substrate allows tuning of their electronic properties concerning their concentration, composition, and morphology. The effect of different Ni wt.% (0%, 2%, 4%, and 6%) on the morphology of hybrid as well as on electrochemical performance investigated. The protocols like overpotential required to achieve a current density of 10 mA/cm², Tafel slope, ECSA, RF, EIS, stability was utilized to examine the overall abilities of electrocatalyst in alkaline 1 M KOH solution. The optimized NiFe₂O₄/rGO hybrid with 2 wt % Ni exhibited the excellent OER performance, which delivers a current density of 10 mA/cm² at an overpotential of only 302 mV with a small Tafel slope of 63 mV/dec. The high activity of the catalyst is attributed to the synergistic effect of the crystal-layered structure as well as rapid mass-charge transfer. Such, rational design concept of anchoring non-precious metal on carbon in a controlled manner, offering splendid flexibility to tailor electrochemical OER performance. The optimized variations in metal concentration and morphologies, providing a promising route to develop a cost-effective catalyst for advanced energy conversion applications.     

Phase pure synthesis of iron-nickel nitride nanoparticles: A low cost electrocatalyst for oxygen evolution reaction

Synthesis of mixed transition metal nitrides often leads to the formation of more than one phases in the final product. A control over molar ratio of metals (Fe:Ni) along with synthetic strategy is used to form phase pure product (Fe₃Ni₇N@C). The synthesized material is used as an efficient and cost-effective electrocatalyst for oxygen evolution reaction (OER). Fe₃Ni₇N@C requires a low overpotential of 290 mV to achieve a catalytic current density of 10 mA cm⁻² which holds Tafel slope of 40 mV dec⁻¹ superior to the noble metal benchmark catalysts. The physicochemical integrity of Fe₃Ni₇N@C is maintained up to 12 h activity as evident from post catalytic characterization.     

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.     

Engineering the semiconducting CdS nanostructures by N-doped rGO for enhancing the adsorption sites: Promising electrocatalyst for hydrogen evolution reaction

The development of non-noble electrocatalysts for hydrogen production from water is of immense interest as it is clean and eco-friendly. The present work explores the electrocatalytic performance of morphologically varied CdS NPs synthesized using different sulphur source and ionic liquids via hydrothermal treatment, in catalyzing hydrogen evolution reaction (HER). The hierarchical flower shaped morphology denoted as CdS–N3 outperformed other prepared electrocatalysts with a Tafel slope value of 118 mV dec^?1 and a low overpotential 344 mV @ a current density of 10 mA/cm². However, the outperformed CdS–N3 catalyst when blended with N doped rGO, it showed a superior activity with a low overpotential of 201 mV at 10 mA/cm². The catalyst disclosed a small Tafel slope of 70 mV dec^?1 corroborating that the catalyst contains more electroactive sites and oxygen vacancy voids for the adsorption-desorption of charge carriers generated from the heteroatom doping. The CdS/N-rGO catalyst also revealed a higher TOF value of 5.18 × 10^?3 s^?1, which further proves that catalyst is more efficient in releasing H₂ molecules and this findings affirms that CdS/N-rGO catalyst can be an efficient candidate for initiating HER kinetics with endurable stability in acidic medium for high purity hydrogen production.     

A highly active oxygen evolution electrocatalyst: Ni-Fe-layered double hydroxide intercalated with the Molybdate and Vanadate anions

Efficient low-cost electrocatalysts in the oxygen evolution reaction (OER) are important components of renewable energy technologies, e.g. solar fuel synthesis and water splitting for powering fuel cells. A great deal of attention has been attracted toward LDHs due to their electrical power and they are potentially applied in the field of electrocatalysts. The present paper reports synthesis of the Ni-Fe-Molybdate and Ni-Fe-Vanadate layered double hydroxides (LDHs) using a simple co-precipitation method. Powder X-ray diffraction, Fourier transform infrared spectra, Transmission electron microscopy, and X-ray energy dispersive spectroscopy spectrum provide successful intercalation of the Vanadate and Molybdate anions. Compared to the bare glassy carbon electrode, in alkaline media, the as-obtained Ni-Fe-MoO₄-LDH represents superior electrocatalytic activity toward water oxidation with the overpotential of 491 mV at10 mA/cm² and a low Tafel slope of 23 mV/dec. Ni–Fe-MoO₄-LDH exhibits good OER activity, which is stated as low onset overpotential, small Tafel slope, and large exchange current density. The current density of the Ni–Fe-MoO₄-LDH nanosheets is about 10 mA cm⁻² at the overpotential of 0.491 (V vs SCE). This value is much larger than that of the Ni–Fe-NO₃-LDH and Ni–Fe-VO₃-LDH nanoparticles.     

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.     

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.     

Construction of two-dimensional CoPS3@defective N-doped carbon composites for enhanced oxygen evolution reaction

The rational design of highly efficient, economical and environment-friendly electrocatalysts is currently an important goal of research on renewable energy conversion and storage. Herein, a facile metod was developed to construct two-dimensional composites, which consist of exfoliated CoPS₃ nanosheets grafted onto defective N-doped carbon (DNC) derived from spent tea leaves. The CoPS₃@DNC composites demonstrate remarkable oxygen evolution reaction (OER) performance in an alkaline medium, with an overpotential of 297 mV at 10 mA cm^{? 2} and a small Tafel slope of 51.8 mV dec^?1, which is better than that of commercial IrO₂ catalysts. Our experimental evidence reveals that the enhanced OER performance of this hybrid catalyst can be attributed to the interfacial effect of exfoliated CoPS₃ and N-doped carbon defects (electron transfer from the CoPS₃ layer to DNC). This work suggests a promising interface engineering technique for developing highly efficient and non-precious OER catalysts based on layered transition-metal trichalcogenides.     

Co0.85Se on three-dimensional hierarchical porous graphene-like carbon for highly effective oxygen evolution reaction

Designing an efficient, cheap and abundant catalyst for oxygen evolution reaction (OER) is crucial for the development of sustainable energy sources. A novel catalyst which could be a promising candidate for such electrocatalysts is described. Co_0.85Se supported on three-dimensional hierarchical porous graphene-like carbon (HPG) exhibits outstanding catalytic performances for OER in alkaline medium. It is found that the onset overpotential is 311 mV on the Co_0.85Se/HPG electrode, which is more 28 and 41 mV negative than that on the Co/HPG and Co₃O₄/HPG electrodes. What's more, the value of Tafel slope is 61.7 mV dec⁻¹ and the overpotential at the current density of 10 mA cm⁻² is 385 mV on this electrode. The Co_0.85Se/HPG of this work is an appealing electrocatalyst for OER in basic electrolyte.     

Bimetallic-MOF derived nickel-iron phosphide nanosheets on carbon cloth for efficacious oxygen evolution reaction

It is of momentously realistic significance to exploit highly efficacious and cost-effective non-noble metal electrocatalysts for oxygen evolution reaction (OER), considering its promising renewable energy application. Herein, a self-supporting electrocatalyst composed of nickel-iron phosphide nanosheets on carbon cloth (NiFeP@CC) is proposed for OER, which are derived from the phosphating treatment of two-dimensional NiFe-MOF nanosheets. The NiFeP@CC composite possesses the synergistic effect of bimetallic NiFe phosphides in promoting the OER, the fully exposed active sites of the nano-sheet structure and the fast charge/mass transfer from the hierarchical porous structure. Owing to the above structural features, the optimized NiFeP@CC presents an impressive OER performance in alkaline solution. The overpotential and Tafel slope are as low as 229 mV and 36.4 mV dec^?1 under a current density of 10 mA cm^?2, respectively, much superior to those for the commercial IrO₂ catalyst. More excitingly, this self-supporting electrocatalyst also possesses an exceptionally high durability, showing no activity degradation for 25 h. This work offers a simple and feasible strategy for developing practically available OER catalysts with a high activity and stability.     

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.     

Bifunctional nanoporous ruthenium-nickel alloy nanowire electrocatalysts towards oxygen/hydrogen evolution reaction

A class of ruthenium-nickel alloy catalysts featured with nanoporous nanowires (NPNWs) were synthesized by a strategy combining rapid solidification with two-step dealloying. RuNi NPNWs exhibit excellent electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in which the RuNi-2500 NPNWs catalyst shows an OER overpotential of 327 mV to deliver a current density of 10 mA cm^?2 and the RuNi-0 NPNWs catalyst requires the overpotential of 69 mV at 10 mA cm^?2 showing the best HER activity in alkaline media. Moreover, the RuNi-1500 NPNWs catalyst was used as the bifunctional electrocatalyst in a two-electrode alkaline electrolyzer for water splitting, which exhibits a low cell voltage of 1.553 V and a long-term stability of 24 h at 10 mA cm^?2, demonstrating that the RuNi NPNWs catalysts can be considered as promising bifunctional alkaline electrocatalysts.