Cobalt Sulfide Nanoparticles Grown on Nitrogen and Sulfur Codoped Graphene Oxide: An Efficient Electrocatalyst for Oxygen Reduction and Evolution Reactions

Heterojunction-Assisted Co3 S4 @Co3 O4 Core-Shell Octahedrons for Supercapacitors and Both Oxygen and Carbon Dioxide Reduction Reactions

Expedition of electron transfer efficiency and optimization of surface reactant adsorption products desorption processes are two main challenges for developing non-noble catalysts in the oxygen reduction reaction (ORR) and CO₂ reduction reaction (CRR). A heterojunction prototype on Co₃ S₄ @Co₃ O₄ core-shell octahedron structure is established via hydrothermal lattice anion exchange protocol to implement the electroreduction of oxygen and carbon dioxide with high performance. The synergistic bifunctional catalyst consists of p-type Co₃ O₄ core and n-type Co₃ S₄ shell, which afford high surface electron density along with high capacitance without sacrificing mechanical robustness. A four electron ORR process, identical to the Pt catalyzed ORR, is validated using the core-shell octahedron catalyst. The synergistic interaction between cobalt sulfide and cobalt oxide bicatalyst reduces the activation energy to convert CO₂ into adsorbed intermediates and hereby enables CRR to run at a low overpotential, with formate as the highly selective main product at a high faraday efficiency of 85.3%. The remarkable performance can be ascribed to the synergistic coupling effect of the structured co-catalysts; heterojunction structure expedites the electron transfer efficiency and optimizes surface reactant adsorption product desorption processes, which also provide theoretical and pragmatic guideline for catalyst development and mechanism explorations.

Hexagonal-Phase Cobalt Monophosphosulfide for Highly Efficient Overall Water Splitting

The rational design and synthesis of nonprecious, efficient, and stable electrocatalysts to replace precious noble metals are crucial to the future of hydrogen economy. Herein, a partial sulfurization/phosphorization strategy is proposed to synthesize a nonstoichiometric pyrrhotite-type cobalt monophosphosulfide material (Co_0.9S_0.58P_0.42) with a hexagonal close-packed phase for electrocatalytic water splitting. By regulating the degree of sulfurization, the P/S atomic ratio in the cobalt monophosphosulfide can be tuned to activate the Co³⁺/Co²⁺ couples. The synergy between the nonstoichiometric nature and the tunable P/S ratio results in the strengthened Co³⁺/Co²⁺ couples and tunable electronic structure and thus efficiently promotes the oxygen/hydrogen evolution reaction (OER/HER) processes toward overall water splitting. Especially for OER, the Co_0.9S_0.58P_0.42 material, featured with a uniform yolk-shell spherical morphology, shows a low overpotential of 266 mV at 10 mA cm^-2 (η₁₀) with a low Tafel slope of 48 mV dec^-1 as well as high stability, which is comparable to that of the reported promising OER electrocatalysts. Coupled with the high HER activity of Co_0.9S_0.58P_0.42, the overall water splitting is demonstrated with a low η₁₀ at 1.59 V and good stability. This study shows that phase engineering and composition control can be the elegant strategy to realize the Co³⁺/Co²⁺ couple activation and electronic structure tuning to promote the electrocatalytic process. The proposed strategy and approaches allow the rational design and synthesis of transition metal monophosphosulfides toward advanced electrochemical applications.

A Ni(OH)2-CoS2 hybrid nanowire array: a superior non-noble-metal catalyst toward the hydrogen evolution reaction in alkaline media

The rising H₂ economy urgently demands active, durable and cost-effective catalysts for the electrochemical hydrogen evolution reaction (HER). However, improving the HER performance of electrocatalysts in alkaline media is still challenging. Herein, we report the development of a nickel hydroxide-cobalt disulfide nanowire array on a carbon cloth (Ni(OH)₂-CoS₂/CC) as a hybrid catalyst to significantly enhance the HER activity in alkaline solutions. Benefitting from heterogeneous interfaces in this 3D hybrid electrocatalyst, Ni(OH)₂-CoS₂/CC shows superior HER activity with only 99 mV overpotential to drive a current density of 20 mA cm^-2 in 1.0 M KOH, which is 100 mV less than that of CoS₂/CC. Moreover, Ni(OH)₂-CoS₂/CC exhibits long-term electrochemical durability with the maintenance of its catalytic activity for 30 h. Density functional theory calculations are performed to gain further insight into the effect of Ni(OH)₂-CoS₂ interfaces, revealing that Ni(OH)₂ plays a key role in water dissociation to hydrogen intermediates and CoS₂ facilitates the adsorption of hydrogen intermediates and H₂ generation. This work not only develops a promising electrocatalyst for the alkaline HER, but also paves a way to enhance the alkaline HER activity of CoS₂via the interface engineering strategy.

Mo doped Ni2P nanowire arrays: an efficient electrocatalyst for the hydrogen evolution reaction with enhanced activity at all pH values

We report the successful synthesis of Mo doped Ni₂P nanowires (NWs) on a Ni foam (NF) substrate by a two-step strategy, which could be used as an efficient and stable hydrogen evolution reaction (HER) electrocatalyst over the whole pH range (0-14). Electrochemical investigations demonstrated that Mo doping made the catalytic activity of Ni₂P significantly enhanced. To achieve a current density of 10 mA cm^-2, Mo-Ni₂P NWs/NF required an overpotential of 67 mV in acidic solution, 78 mV in alkaline solution and 84 mV in neutral solution. It also showed superior stability with negligible activity decay after its use in the HER under different pH conditions for 24 h. Such excellent HER activity might originate from the synergistic effect between molybdenum (Mo) and nickel (Ni) atoms. The present work provides a valuable route for the design and synthesis of inexpensive and efficient all-pH HER electrocatalysts.

Two-Dimensional N,S-Codoped Carbon/Co9S8 Catalysts Derived from Co(OH)2 Nanosheets for Oxygen Reduction Reaction

The development of highly active and cost-efficient electrocatalysts for the oxygen reduction reaction (ORR) is of great importance in a wide range of clean energy devices, including fuel cells and metal-air batteries. Herein, the simultaneous formation of Co₉S₈ and N,S-codoped carbon with high ORR catalytic activity was achieved in an efficient strategy with a dual templates system. First, Co(OH)₂ nanosheets and tetraethyl orthosilicate were utilized to direct the formation of two-dimensional carbon precursors, which were then dispersed into thiourea solution. After subsequent pyrolysis and template removal, N,S-codoped porous carbon-sheet-confined Co₉S₈ catalysts (Co₉S₈/NSC) were obtained. Owing to the morphological and compositional advantages as well as the synergistic effects, the resultant Co₉S₈/NSC catalysts with a modified doping level and pyrolysis degree exhibit superior ORR catalytic activity and long-term stability compared with the state-of-the-art Pt/C catalysts in alkaline media. Remarkably, the as-prepared carbon composites also reveal exceptional tolerance of methanol, indicating their potential applications in fuel cells.

Architecting a Mesoporous N-Doped Graphitic Carbon Framework Encapsulating CoTe2 as an Efficient Oxygen Evolution Electrocatalyst

To improve the efficiency of cobalt-based catalysts for water electrolysis, tremendous efforts have been dedicated to tuning the composition, morphology, size, and structure of the materials. We report here a facile preparation of orthorhombic CoTe₂ nanocrystals embedded in an N-doped graphitic carbon matrix to form a 3D architecture with a size of ∼500 nm and abundant mesopores of ∼4 nm for the oxygen evolution reaction (OER). The hybrid electrocatalyst delivers a small overpotential of 300 mV at 10 mA cm^-2, which is much lower than that for pristine CoTe₂ powder. After cycling for 2000 cycles or driving continual OER for 20 h, only a slight loss is observed. The mesoporous 3D architecture and the strong interaction between N-doped graphitic carbon and CoTe₂ are responsible for the enhancement of the electrocatalytic performance.

High-Efficiency Co/CoxSy@S,N-Codoped Porous Carbon Electrocatalysts Fabricated from Controllably Grown Sulfur- and Nitrogen-Including Cobalt-Based MOFs for Rechargeable Zinc-Air Batteries

Developing bifunctional oxygen electrocatalysts with superior catalytic activities of oxygen reduction reaction (ORR) and oxygen revolution reaction (OER) is crucial to their practical energy storage and conversion applications. In this work, we report the fabrication of Co/Co_xS_y@S,N-codoped porous carbon structures with various morphologies, specific surface areas, and pore structures, derived from controllably grown Co-based metal-organic frameworks with S- and N-containing organic ligands (thiophene-2,5-dicarboxylate, Tdc; and 4,4'-bipyridine, bpy) utilizing solvent effect (e.g., water and methanol) under room temperature and hydrothermal conditions. The results demonstrate that Co/Co_xS_y@S,N-codoped carbon fibers fabricated at a pyrolytic temperature of 800 °C (Co/Co_xS_y@SNCF-800) from Co-MOFs fibers fabricated in methanol under hydrothermal conditions as electrocatalysts exhibit superior bifunctional ORR and OER activities in alkaline media, endowing them as air cathodic catalysts in rechargeable zinc-air batteries with high power density and good durability.

Bifunctional Transition Metal Hydroxysulfides: Room-Temperature Sulfurization and Their Applications in Zn-Air Batteries

Bifunctional electrocatalysis for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) constitutes the bottleneck of various sustainable energy devices and systems like rechargeable metal-air batteries. Emerging catalyst materials are strongly requested toward superior electrocatalytic activities and practical applications. In this study, transition metal hydroxysulfides are presented as bifunctional OER/ORR electrocatalysts for Zn-air batteries. By simply immersing Co-based hydroxide precursor into solution with high-concentration S^2- , transition metal hydroxides convert to hydroxysulfides with excellent morphology preservation at room temperature. The as-obtained Co-based metal hydroxysulfides are with high intrinsic reactivity and electrical conductivity. The electron structure of the active sites is adjusted by anion modulation. The potential for 10 mA cm^-2 OER current density is 1.588 V versus reversible hydrogen electrode (RHE), and the ORR half-wave potential is 0.721 V versus RHE, with a potential gap of 0.867 V for bifunctional oxygen electrocatalysis. The Co₃ FeS_1.5 (OH)₆ hydroxysulfides are employed in the air electrode for a rechargeable Zn-air battery with a small overpotential of 0.86 V at 20.0 mA cm^-2 , a high specific capacity of 898 mAh g^-1 , and a long cycling life, which is much better than Pt and Ir-based electrocatalyst in Zn-air batteries.

Graphene Composites with Cobalt Sulfide: Efficient Trifunctional Electrocatalysts for Oxygen Reversible Catalysis and Hydrogen Production in the Same Electrolyte

Nitrogen and sulfur-codoped graphene composites with Co₉ S₈ (NS/rGO-Co) are synthesized by facile thermal annealing of graphene oxides with cobalt nitrate and thiourea in an ammonium atmosphere. Significantly, in 0.1 m KOH aqueous solution the best sample exhibits an oxygen evolution reaction (OER) activity that is superior to that of benchmark RuO₂ catalysts, an oxygen reduction reaction (ORR) activity that is comparable to that of commercial Pt/C, and an overpotential of only -0.193 V to reach 10 mA cm^-2 for hydrogen evolution reaction (HER). With this single catalyst for oxygen reversible electrocatalysis, a potential difference of only 0.700 V is observed in 0.1 m KOH solution between the half-wave potential in ORR and the potential to reach 10 mA cm^-2 in OER; in addition, an overpotential of only 450 mV is needed to reach 10 mA cm^-2 for full water splitting in the same electrolyte. The present trifunctional catalytic activities are markedly better than leading results reported in recent literature, where the remarkable trifunctional activity is attributed to the synergetic effects between N,S-codoped rGO, and Co₉ S₈ nanoparticles. These results highlight the significance of deliberate structural engineering in the preparation of multifunctional electrocatalysts for versatile electrochemical reactions.

Co9S8 nanoparticles anchored on nitrogen and sulfur dual-doped carbon nanosheets as highly efficient bifunctional electrocatalyst for oxygen evolution and reduction reactions

To promote the practical application of electrochemical energy storage and conversion systems, nonprecious electrocatalysts of low cost and with highly efficient performance in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desired. In this work, a cubic sodium chloride (NaCl) crystal-templated strategy is proposed for coupling Co₉S₈ nanoparticles to nitrogen- and sulfur-doped carbon nanosheets (Co₉S₈/N,S-CNS) by facile pyrolysis. The nitrogen and sulfur dual-doped carbon nanosheets can effectively prevent the aggregation of Co₉S₈ nanoparticles and greatly improve the conductivity of the hybrid structure. The well-dispersed Co₉S₈ nanoparticles could provide more active sites. When evaluated as a bifunctional electrocatalyst, an overpotential of 350 mV could yield 10 mA cm^-2 current density for OER and a high onset potential around 0.90 V vs. RHE was obtained with a four-electron pathway for ORR, which is comparable to that of a Pt/C catalyst. The remarkable electrochemical performance can be attributed to the synergistic catalytic effect of Co₉S₈ nanoparticles and the N,S-doped carbon nanosheets. Considering the simplicity, low cost and scalability of the approach, the strategy presented here can be extendable to the preparation of other nanoparticles/carbon hybrid nanosheets, which may potentially be applied in the fields of high-performance supercapacitors, lithium-ion batteries, catalysts, sensors, adsorbents and so on.

Ni-Fe Nitride Nanoplates on Nitrogen-Doped Graphene as a Synergistic Catalyst for Reversible Oxygen Evolution Reaction and Rechargeable Zn-Air Battery

Obtaining bifunctional electrocatalysts with high activity for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is a main hurdle in the application of rechargeable metal-air batteries. Earth-abundant 3d transition metal-based catalysts have been developed for the OER and ORR; however, most of these are based on oxides, whose insulating nature strongly restricts their catalytic performance. This study describes a metallic Ni-Fe nitride/nitrogen-doped graphene hybrid in which 2D Ni-Fe nitride nanoplates are strongly coupled with the graphene support. Electronic structure of the Ni-Fe nitride is changed by hybridizing with the nitrogen-doped graphene. The unique heterostructure of this hybrid catalyst results in very high OER activity with the lowest onset overpotential (150 mV) reported, and good ORR activity comparable to that for commercial Pt/C. The high activity and durability of this bifunctional catalyst are also confirmed in rechargeable zinc-air batteries that are stable for 180 cycles with an overall overpotential of only 0.77 V at 10 mA^-2 .

In-situ Electrodeposition of Highly Active Silver Catalyst on Carbon Fiber Papers as Binder Free Cathodes for Aluminum-air Battery

Carbon fiber papers supported Ag catalysts (Ag/CFP) with different coverage of electro-active site are prepared by electrochemical deposition and used as binder free cathodes in primary aluminum-air (Al-air) battery. Scanning Electron Microscopy and X-ray Diffraction studies are carried out to characterize the as-prepared Ag/CFP air cathodes. Oxygen reduction reaction (ORR) activities on these air cathodes in alkaline solutions are systematic studied. A newly designed aluminum-air cell is used to further determine the cathodes performance under real operation condition and during the test, the Ag/CFP electrodes show outstanding catalytic activity for ORR in concentrated alkaline electrolyte, and no obvious activity degradation is observed after long-time discharge. The electrochemical test results display the dependence of coverage of the electro-active Ag on the catalytic performance of the air cathodes. The resulting primary Al-air battery made from the best-performing cathode shows an impressive discharge peak power density, outperforming that of using commercial nano-manganese catalyst air electrodes.

Highly efficient oxygen evolution from CoS2/CNT nanocomposites via a one-step electrochemical deposition and dissolution method

The oxygen evolution reaction (OER) has been viewed as a critical step in electrochemical energy conversion and storage devices. However, searching for cheap and efficient OER electrocatalysts still remains an urgent task. Herein, we develop a new strategy involving a one-step electrochemical deposition and dissolution method to fabricate hydrophilic porous CoS₂/carbon nanotube (CNT) composites (CNT-CoS₂). X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy measurements confirm the formation of hydrophilic groups on the surface of the porous CoS₂ during electrochemical oxidation. Our design holds several advantages. The electricity conductivity of CoS₂ is increased by introducing CNTs as a conductive substrate. The porous nanostructures of CoS₂ increase its surface area, and provide paths to promote charge and reactant transfer. The active edge sites modified with hydrophilic groups can increase the content of electrolyte-electrode contact points, increasing the intrinsic catalytic performance of CoS₂. These factors allow CNT-CoS₂ to achieve a low onset potential of 1.33 V vs. RHE, a stable current density (j) of 10 mA cm^-2 at an overpotential of 290 mV, and excellent stability under alkaline conditions compared to that of IrO₂. The comprehensive performance of the CNT-CoS₂ electrocatalyst is comparable to or better than that of any reported noble metal-free OER catalyst, even RuO₂ and IrO₂. This facile synthesis strategy involving synchronous electrochemical deposition and dissolution should be easily adapted for large-scale water electrolysis.

Amorphous nickel-cobalt complexes hybridized with 1T-phase molybdenum disulfide via hydrazine-induced phase transformation for water splitting

Highly active and robust eletcrocatalysts based on earth-abundant elements are desirable to generate hydrogen and oxygen as fuels from water sustainably to replace noble metal materials. Here we report an approach to synthesize porous hybrid nanostructures combining amorphous nickel-cobalt complexes with 1T phase molybdenum disulfide (MoS₂) via hydrazine-induced phase transformation for water splitting. The hybrid nanostructures exhibit overpotentials of 70 mV for hydrogen evolution and 235 mV for oxygen evolution at 10 mA cm⁻² with long-term stability, which have superior kinetics for hydrogen- and oxygen-evolution with Tafel slope values of 38.1 and 45.7 mV dec⁻¹. Moreover, we achieve 10 mA cm⁻² at a low voltage of 1.44 V for 48 h in basic media for overall water splitting. We propose that such performance is likely due to the complete transformation of MoS₂ to metallic 1T phase, high porosity and stabilization effect of nickel-cobalt complexes on 1T phase MoS₂.

Electrocatalysts based on earth-abundant elements have emerged as promising candidates to replace noble metal materials. Here, the authors develop porous hybrid nanostructures combining amorphous Ni-Co complexes with 1T phase MoS₂ for enhanced electrocatalytic activity for overall water splitting.

Nanostructured Nickel-Cobalt-Titanium Alloy Grown on Titanium Substrate as Efficient Electrocatalyst for Alkaline Water Electrolysis

One of the important challenges in alkaline water electrolysis is to utilize a bifunctional catalyst for both hydrogen evolution (HER) and oxygen evolution (OER) reactions to increase the efficiency of water splitting devices for the long durable operations. Herein, nickel-cobalt-titanium (NCT) alloy is directly grown on a high corrosion resistance titanium foil by a simple, single, and rapid electrochemical deposition at room temperature. The electrocatalytic activity of NCT alloy electrodes is evaluated for both HER and OER in aqueous electrolyte. Our NCT electrocatalyst exhibits low overpotentials around 125 and 331 mV for HER and OER, respectively, in 1 M KOH. In addition to this outstanding activity, the bifunctional catalyst also exhibits excellent OER and HER electrode stability up to 150 h of continuous operation with a minimal loss in activity. Further, the NCT alloy directly grown on titanium foil is used to directly construct membrane electrode assembly (MEA) for alkaline electrolyte membrane (AEM) water electrolyzer, which make the practical applicability. This single-step electrodeposition reveals NCT on titanium foil with high activity and excellent electrode stability suitable for replacing alternative commercial viable catalyst for the alkaline water splitting.

Morphology-Controllable Synthesis of Zn-Co-Mixed Sulfide Nanostructures on Carbon Fiber Paper Toward Efficient Rechargeable Zinc-Air Batteries and Water Electrolysis

It remains an ongoing challenge to develop cheap, highly active, and stable electrocatalysts to promote the sluggish electrocatalytic oxygen evolution, oxygen reduction, and hydrogen evolution reactions for rechargeable metal-air batteries and water-splitting systems. In this work, we report the morphology-controllable synthesis of zinc cobalt mixed sulfide (Zn-Co-S) nanoarchitectures, including nanosheets, nanoplates, and nanoneedles, grown on conductive carbon fiber paper (CFP) and the micronanostructure dependent electrochemical efficacy for catalyzing hydrogen and oxygen in zinc-air batteries and water electrolysis. The formation of different Zn-Co-S morphologies was attributed to the synergistic effect of decomposed urea products and the corrosion of NH₄F. Among synthesized Zn-Co-S nanostructures, the nanoneedle arrays supported on CFP exhibit superior trifunctional activity for oxygen reduction, oxygen evolution, and hydrogen evolution reactions than its nanosheet and nanoplate counterparts through half reaction testing. It also exhibited better catalytic durability than Pt/C and RuO₂. Furthermore, the Zn-Co-S nanoneedle/CFP electrode enables rechargeable Zn-air batteries with low overpotential (0.85 V), high efficiency (58.1%), and long cycling lifetimes (200 cycles) at 10 mA cm^-2 as well as considerable performance for water splitting. The superior performance is contributed to the integrated nanoneedle/CFP nanostructure, which not only provides enhanced electrochemical active area, but also facilitates ion and gas transfer between the catalyst surface and electrolyte, thus maintaining an effective solid-liquid-gas interface necessary for electrocatalysis. These results indicate that the Zn-Co-S nanoneedle/CFP system is a low cost, highly active, and durable electrode for highly efficient rechargeable zinc-air batteries and water electrolysis in alkaline solution.

Highly Crumpled Hybrids of Nitrogen/Sulfur Dual-Doped Graphene and Co9S8 Nanoplates as Efficient Bifunctional Oxygen Electrocatalysts

A bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly attractive for the manufacture of clean energy conversion devices. In this work, highly crumpled hybrid of nitrogen and sulfur dual-doped graphene and quasi-hexagonal Co₉S₈ nanoplates (Co₉S₈/NSG_g-C3N4) is fabricated via a facile ionic assembly approach. The unique structure of Co₉S₈/NSG_g-C3N4 renders it high specific surface area (288.3 m² g^-1) and large pore volume (1.32 cm³ g^-1). As the electrocatalyst for ORR, Co₉S₈/NSG_g-C3N4 demonstrates excellent performance with the onset potential of -0.02 V vs Ag/AgCl and the limited current density of 6.05 mA cm^-2 at -0.9 V vs Ag/AgCl. Co₉S₈/NSG_g-C3N4 also presents outstanding catalytic activity toward OER by delivering a limited current density of 48 mA cm^-2 at 1 V vs Ag/AgCl. The bifunctional catalytic behaviors of Co₉S₈/NSG_g-C3N4 enable the assembly of a rechargeable Zn-air battery with it as the cathode catalyst, which exhibits stable discharge/charge voltage plateaus upon long time cycling over 50 h.

Sulfurizing-Induced Hollowing of Co9S8 Microplates with Nanosheet Units for Highly Efficient Water Oxidation

Transition metal-based compounds are promising alternative nonprecious electrocatalysts for oxygen evolution to noble metals-based materials. Nanosheet-constructed hollow structures can efficiently promote the electrocatalystic activity, mainly because of their largely exposed active sites. Herein, hierarchical Co₉S₈ hollow microplates with nanosheet building units are fabricated via sulfurization and subsequent calcination of preformed Co-glycolate microplates. Benefiting from the advantages of a hollow structure, nanosheet units and high Co³⁺ content, Co₉S₈ hollow microplates exhibit remarkable catalytic property for oxygen evolution reaction (OER) with low overpotential of 278 mV to reach a current density of 10 mA cm^-2, a low Tafel slope of 53 mV dec^-1, and satisfied stability. This construction method of Co₉S₈ hierarchical hollow microplates composed of a nanosheet structure is an effective tactic for promoting OER performance of water splitting electrocatalysts.

Morphology controlled synthesis of 2-D Ni–Ni3S2 and Ni3S2 nanostructures on Ni foam towards oxygen evolution reaction

Catalysts for oxygen evolution reactions (OER) are at the heart of key renewable energy technologies, and development of non-precious metal catalysts with high activity and stability remain a great challenge in this field. Among various material candidates, metal sulfides are receiving increasing attention. While morphology-dependent catalytic performances are well established in noble metal-based catalysts, relatively little is known for the morphology‒catalytic performance relationship in metal sulfide catalysts. In this study, uniform spider web-like Ni nanosheets–Ni₃S₂ and honeycomb-like Ni₃S₂ structures are deposited on nickel foam (Ni₃S₂/NF) by a facile one-step hydrothermal synthetic route. When used as an oxygen evolution electrode, the spider web-like Ni–Ni₃S₂/NF with the large exposed surface area shown excellent catalytic activity and stability with an overpotential of ~310 mV to achieve at 10 mA/cm² and a Tafel slope of 63 mV/dec in alkaline media, which is superior to the honeycomb-like structure without Ni nanosheet. The low Tafel slope of the spider web-like Ni–Ni₃S₂/NF represents one of the best OER kinetics among nickel sulfide-based OER catalysts. The results point to the fact that performance of the metal sulfide electrocatalysts might be fine-tuned and optimized with morphological controls.

Atomic-layer-deposited ultrafine MoS2 nanocrystals on cobalt foam for efficient and stable electrochemical oxygen evolution

Ultrafine molybdenum sulfide (MoS₂) nanocrystals are grown on a porous cobalt (Co) foam current collector by atomic layer deposition (ALD) using molybdenum hexacarbonyl and hydrogen sulfide as precursors. When used to catalyze the oxygen evolution reaction (OER), the optimal Co@MoS₂ electrode, even with a MoS₂ loading as small as 0.06 mg cm^-2, exhibits a large cathodic shift of ca. 200 mV in the onset potential (the potential at which the current density is 5 mA cm^-2), a low overpotential of only 270 mV to attain an anodic current density of 10 mA cm^-2, much smaller charge transfer resistance and substantially improved long-term stability at both low and high current densities, with respect to the bare Co foam electrode, showing substantial promise for use as an efficient, low-cost and durable anode in water electrolyzers.

Cu(OH)2 @CoCO3 (OH)2 ·nH2 O Core-Shell Heterostructure Nanowire Array: An Efficient 3D Anodic Catalyst for Oxygen Evolution and Methanol Electrooxidation

A Cu(OH)₂ @CoCO₃ (OH)₂ ·nH₂ O (CCHH) core-shell heterostructure nanowire array acts as robust 3D oxygen evolution reaction catalyst. It needs an overpotential of 270 mV to drive 50 mA cm^-2 in 1.0 m KOH, outperforming CCHH nanowire arrays on copper foam and most reported Co-based oxygen evolution reaction catalysts in alkaline media. It is also efficient for methanol electrooxidation.

S,N-Containing Co-MOF derived Co9S8@S,N-doped carbon materials as efficient oxygen electrocatalysts and supercapacitor electrode materials

Co₉S₈@S,N-doped carbon materials derived from S,N-containing Co-MOFs exhibited superior performance as bifunctional oxygen electrocatalysts and supercapacitor electrode materials.

Bifunctional electro-catalytic performances of CoWO4 nanocubes for water redox reactions (OER/ORR)

In this paper, we report the synthesis of cube shaped nanoparticles of CoWO₄ (∼30 nm) by molten salts and their bifunctional electro-catalytic activities in water redox reactions for oxygen evolution and oxygen reduction reactions (OER and ORR).

Fe9S10-decorated N, S co-doped graphene as a new and efficient electrocatalyst for oxygen reduction and oxygen evolution reactions

An advanced Fe₉S₁₀(700)/N,S-G catalyst for the oxygen reduction and evolution reactions was prepared via the combination of solvothermal and pyrolysis procedures.

Cobalt sulfide supported on nitrogen and sulfur dual-doped reduced graphene oxide for highly active oxygen reduction reaction

An efficient composite catalyst of Co–S/NS-rGO has been successfully prepared by a facile one-step annealing approach, which demonstrates excellent catalytic activity and good durability in alkaline solution.

Cobalt disulfide/graphite foam composite films as self-standing electrocatalytic electrodes for overall water splitting

A unique inter-layer porous 3D cobalt disulfide/graphite foam (CoS₂/GF) electrocatalytic electrode exhibits superior performance for overall water splitting.

Electrocatalysis for the oxygen evolution reaction: recent development and future perspectives

We review the fundamental aspects of metal oxides, metal chalcogenides and metal pnictides as effective electrocatalysts for the oxygen evolution reaction.

A bifunctional two dimensional TM3(HHTP)2 monolayer and its variations for oxygen electrode reactions

To achieve renewable energy technologies, low-cost electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are required to replace Pt and IrO₂/RuO₂ catalysts.

A controllable honeycomb-like amorphous cobalt sulfide architecture directly grown on the reduced graphene oxide–poly(3,4-ethylenedioxythiophene) composite through electrodeposition for non-enzyme glucose sensing

A facile, controllable two-step electrodeposition route was developed, whereby a honeycomb-like amorphous Co_xS_y architecture was obtained via direct growth on rGO–PEDOT/GCE as an electrode for glucose detection.