Nickel–cobalt bimetallic sulfide NiCo2S4 nanostructures for a robust hydrogen evolution reaction in acidic media

There are many challenges associated with the fabrication of efficient, inexpensive, durable and very stable nonprecious metal catalysts for the hydrogen evolution reaction (HER). In this study, we have designed a facile strategy by tailoring the concentration of precursors to successfully obtain nickel–cobalt bimetallic sulfide (NiCo₂S₄) using a simple hydrothermal method. The morphology of the newly prepared NiCo₂S₄ comprised a mixture of microparticles and nanorods, which were few microns in dimension. The crystallinity of the composite sample was found to be excellent with a cubic phase. The sample that contained a higher amount of cobalt compared to nickel and produced single-phase NiCo₂S₄ exhibited considerably improved HER performance. The variation in the salt precursor concentration during the synthesis of a material is a simple methodology to produce a scalable platinum-free catalyst for HER. The advantageous features of the multiple active sites of cobalt in the CN-21 sample as compared to that for pristine CoS and NiS laid the foundation for the provision of abundant active edges for HER. The composite sample produced a current density of 10 mA cm⁻² at an overpotential of 345 mV. Also, it exhibited a Tafel value of 60 mV dec⁻¹, which predominantly ensured rapid charge transfer kinetics during HER. CN-21 was highly durable and stable for 30 hours. Electrochemical impedance spectroscopy showed that the charge transfer resistance was 21.88 ohms, which further validated the HER polarization curves and Tafel results. CN-21 exhibited a double layer capacitance of 4.69 μF cm⁻² and a significant electrochemically active surface area of 134.0 cm², which again supported the robust efficiency for HER. The obtained results reveal that our developed NiCo₂S₄ catalyst has a high density of active edges, and it is a non-noble metal catalyst for the hydrogen evolution reaction. The present findings provide an alternative strategy and an active nonprecious material for the development of energy-related applications.

There are many challenges associated with the fabrication of efficient, inexpensive, durable and very stable nonprecious metal catalysts for the hydrogen evolution reaction (HER).     

Genomic DNA-mediated formation of a porous Cu2(OH)PO4/Co3(PO4)2·8H2O rolling pin shape bifunctional electrocatalyst for water splitting reactions

Among the accessible techniques, the production of hydrogen by electrocatalytic water oxidation is the most established process, which comprises oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Here, we synthesized a genomic DNA-guided porous Cu₂(OH)PO₄/Co₃(PO₄)₂·8H₂O rolling pin shape composite structure in one pot. The nucleation and development of the porous rolling pin shape Cu₂(OH)PO₄/Co₃(PO₄)₂·8H₂O composite was controlled and stabilized by the DNA biomolecules. This porous rolling pin shape composite was explored towards electrocatalytic water oxidation for both OER and HER as a bi-functional catalyst. The as-prepared catalyst exhibited a very high OER and HER activity compared to its various counterparts in the absence of an external binder (such as Nafion). The synergistic effects between Cu and Co metals together with the porous structure of the composite greatly helped in enhancing the catalytic activity. These outcomes undoubtedly demonstrated the beneficial utilization of the genomic DNA-stabilised porous electrocatalyst for OER and HER, which has never been observed.

Among the accessible techniques, the production of hydrogen by electrocatalytic water oxidation is the most established process, which comprises oxygen evolution reaction (OER) and hydrogen evolution reaction (HER).     

Controlled assembly of cobalt embedded N-doped graphene nanosheets (Co@NGr) by pyrolysis of a mixed ligand Co(ii) MOF as a sacrificial template for high-performance electrocatalysts

The development of high-efficiency and durable bifunctional electrocatalysts is an important and challenging topic in the area of energy storage/conversion. Herein, we prepared metallic cobalt nanoparticle decorated N-doped graphitic sheets (Co@NGr) by adopting facile pyrolysis of a mixed ligand cobalt-based MOF (CoMOF-2) as a sacrificial template displaying good OER and HER activity. The catalytic material harvested at three different pyrolytic temperatures was characterized by various analytical methods such as PXRD, SEM, TEM, Raman, and XPS analyses. The catalytic activity of the obtained hybrid composite materials towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was studied. Co@NGr-900 was found to be an efficient bifunctional electrocatalyst and 10 mA cm⁻² current density was afforded at an overpotential of 390 mV for OER and 340 mV for HER respectively. This study provides insight for the development of cost-effective nonprecious element-based electrocatalysts for water splitting which has relevance in energy storage and conversion. Catalytic performance is governed by the synergistic compositional effect of metallic cobalt/nitrogen-doping in the graphitic carbon increasing the electrical conductivity/active sites of the composite material.

Synthesis, characterization and application of monodispersed cobalt embedded nitrogen-doped graphene derived from a cobalt-based mixed ligand MOF by pyrolysis as a bifunctional electrocatalyst for water splitting have been investigated.     

Hollow waxberry-like cobalt–nickel oxide/S,N-codoped carbon nanospheres as a trifunctional electrocatalyst for OER,ORR, and HER

With the aggravation of the energy crisis, increasing attention has been paid to electrocatalytic technology for renewable energy devices. In particular, the research on catalysts towards the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) has become more urgent, and the development of multifunctional electrocatalysts has become a research trend. Here we report the synthesis of waxberry-like cobalt–nickel oxide/S,N-codoped carbon hollow nanocomposites as trifunctional catalysts. Uniform cobalt–nickel glycerate solid spheres are first synthesized as the precursor and subsequently chemically transformed into cobalt–nickel oxide/S,N-codoped carbon hollow nanospheres. Benefiting from the synergistic coupling of cobalt–nickel oxide and S,N-codoped carbon nanocomposites, hierarchical porosity and hollow structure, the cobalt–nickel oxide/S,N-codoped carbon nanohybrids exhibit superior trifunctional electrocatalytic activity and durability towards OER, ORR, and HER in alkaline media.

The catalyst is assembled from small nanoparticles in the shape of a bayberry, and exhibits superior trifunctional electrocatalytic activity.     

Efficient tri-metallic oxides NiCo2O4/CuO for the oxygen evolution reaction

In this study, a simple approach was used to produce nonprecious, earth abundant, stable and environmentally friendly NiCo₂O₄/CuO composites for the oxygen evolution reaction (OER) in alkaline media. The nanocomposites were prepared by a low temperature aqueous chemical growth method. The morphology of the nanostructures was changed from nanowires to porous structures with the addition of CuO. The NiCo₂O₄/CuO composite was loaded onto a glassy carbon electrode by the drop casting method. The addition of CuO into NiCo₂O₄ led to reduction in the onset potential of the OER. Among the composites, 0.5 grams of CuO anchored with NiCo₂O₄ (sample 2) demonstrated a low onset potential of 1.46 V vs. a reversible hydrogen electrode (RHE). A current density of 10 mA cm⁻² was achieved at an over-potential of 230 mV and sample 2 was found to be durable for 35 hours in alkaline media. Electrochemical impedance spectroscopy (EIS) indicated a small charge transfer resistance of 77.46 ohms for sample 2, which further strengthened the OER polarization curves and indicates the favorable OER kinetics. All of the obtained results could encourage the application of sample 2 in water splitting batteries and other energy related applications.

In this study, a simple approach was used to produce nonprecious, earth abundant, stable and environmentally friendly NiCo₂O₄/CuO composites for the oxygen evolution reaction (OER) in alkaline media.     

Enhancing the water splitting performance via decorating Co3O4 nanoarrays with ruthenium doping and phosphorization

Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for its ultrahigh energy density, abundance and environmental friendliness. Generating hydrogen by water splitting with highly efficient electrocatalysts is a feasible route to meet current and future energy demand. Herein, the effects of Ru doping and phosphorization treatment on Co₃O₄ nanoarrays for water splitting are systemically investigated. The results show that a small amount of phosphorus can accelerate hydrogen evolution reaction (HER) and the trace of Ru dopant can significantly enhance the catalytic activities for HER and oxygen evolution reaction (OER). Ru-doped cobalt phosphorous oxide/nickel foam (CoRuPO/NF) nanoarrays exhibit highly efficient catalytic performance with an overpotential of 26 mV at 10 mA cm⁻² for HER and 342 mV at 50 mA cm⁻² for OER in 1 M KOH solution, indicating superior water splitting performance. Furthermore, the CoRuPO/NF also exhibits eminent and durable activities for alkaline seawater electrolysis. This work significantly advances the development of seawater splitting for hydrogen generation.

CoRuPO/NF shows low overpotentials in HER and OER.     

Electrochemical fabrication of FeSx films with high catalytic activity for oxygen evolution

Electrochemical decomposition of water to produce oxygen (O₂) and hydrogen (H₂) through an anodic oxygen evolution reaction (OER) and a cathodic hydrogen evolution reaction (HER) is a promising green method for sustainable energy supply. Here, we demonstrate that cauliflower-like S-doped iron microsphere films are materials that can efficiently decompose water as an electrocatalyst for the oxygen evolution reaction. FeS_x films are prepared by a simple one-step electrodeposition method and directly grow on copper foam from a deep eutectic solvent, ethaline (mixture of choline chloride and ethylene glycol), as a durable and highly efficient catalyst for the OER in 1.0 M KOH. The prepared FeS_x/CF, as an oxygen-evolving anode, shows remarkable catalytic performance toward the OER with a moderate Tafel slope of 105 mV dec⁻¹, and require an overpotential of only 340 mV to drive a geometrical catalytic current density of 10 mA cm⁻². In addition, this catalyst also demonstrates strong long-term electrochemical durability. This study provides a simple synthesis route for practical applications of limited transition metal nano catalysts.

Electrochemical decomposition of water to produce oxygen (O₂) and hydrogen (H₂) through an anodic oxygen evolution reaction (OER) and a cathodic hydrogen evolution reaction (HER) is a promising green method for sustainable energy supply.     

First-principles study of vanadium carbides as electrocatalysts for hydrogen and oxygen evolution reactions

Vanadium carbides have attracted much attention as highly active catalysts in both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), while a satisfactory understanding of the underlying mechanisms still remains a challenge. Herein we apply first-principles calculations to systematically analyze the crystal structures, electronic properties, free energies during the HER and OER processes, surface energies and crystal formation energies of the three types of vanadium carbides, i.e., V₄C₃, V₈C₇ and VC. We show that all these vanadium carbides are metallic, which enables efficient electron transport from the bulk to the surface of the catalysts. All these vanadium carbides exhibit excellent HER performance but show poor OER catalytic activity. In particular, the V₈C₇ (110) surface shows the best catalytic performance for its relatively small |ΔG(H*)| value (−0.114 eV) for HER. Emergence of natural carbon vacancies gives rise to large surface energy, proper hydrogen adsorption energy, low crystal formation energy and weak bond strength in V₈V₇, which guarantees its leading position among the three vanadium carbides. In addition, a remarkable resemblance between VC/V₈C₇ and Pt in their electronic structures on (110) and (111) surfaces are found, which indicates a Pt-like HER mechanism in these vanadium carbides. Our results thus bring new insights to the theoretical understanding of the excellent HER performance of vanadium carbides.

The origin of excellent performance of vanadium carbides (VC and V₈V₇) in hydrogen and oxygen evolution reactions (HER and OER) is revealed by first-principles calculations. It is found that the underlying mechanisms in HER/OER processes are Pt-like.     

Enhanced electrochemical properties of cellular CoPS@C nanocomposites for HER,OER and Li-ion batteries

Cellular CoPS@C nanocomposites were successfully synthesized via a facile two-steps route. The performances of the CoPS@C electrode as a non-noble metal electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) show good activity. On the other hand, the electrochemical investigation of CoPS systems for lithium ion batteries (LIBs) is reported for the first time. The CoPS@C nanocomposite as a novel anode can maintain a capacity of about 713 mA h g⁻¹ after 50 cycles at a current density of 0.2 A g⁻¹, indicating its potential applications in lithium storage. Test results also demonstrate that the CoPS@C nanocomposite exhibit more excellent HER, OER and Li storage performances compared to the bulk CoPS sample.

A novel porous CoPS@C nanocomposite show excellent electrochemical properties for HER, OER, Li-storage.     

Electrochemical deposition of amorphous cobalt oxides for oxygen evolution catalysis

The oxygen evolution reaction (OER) is crucial in water splitting for hydrogen production. However, its high over-potential and sluggish kinetics cause an additional energy loss and hinder its practical application. The cobalt spinel oxide Co₃O₄ exhibits a high catalytic activity for the OER in alkaline solutions. However, the activity requires further enhancement to meet the industrial demand for hydrogen production. This paper presents an electrochemical deposition method to obtain cobalt oxides with a controllable crystallinity on carbon paper (CP). Usually, cobalt oxides grown on CP have a Co₃O₄ spinel oxide structure. The self-supported Co₃O₄/CP exhibited a considerable catalytic activity for the OER. When a VS₂ layer grown on the CP beforehand by a hydrothermal method was used as substrate, the deposited cobalt oxides were in an amorphous state, denoted as CoO_x/VS₂/CP, which exhibited a higher OER activity and better stability than those of Co₃O₄/CP. The enhancement in the catalytic activity was attributed to the mixture formation of different types of cobalt species, including Co₃O₄, CoO, Co(OH)₂, and metallic Co, because of the reduction by VS₂. We also clarify the significance of the crystallinity of cobalt oxides in the improvement in the OER activity. This process can also be applied to the direct formation of other types of self-supported oxide electrodes for OER catalysis.

Amorphous cobalt oxides electrodeposited on VS₂ grown on carbon paper show better catalytic activity for the oxygen evolution reaction than crystalline Co₃O₄ on carbon paper.     

Cobalt/nitrogen codoped carbon nanosheets derived from catkins as a high performance non-noble metal electrocatalyst for oxygen reduction reaction and hydrogen evolution reaction

Novel energy devices which are capable of alleviating and/or solving the energy dilemma such as overall water splitting and fuel cells require the development of highly efficient catalysts, especially cheap high performance non-precious metal (NPM) catalysts. Here, we prepare highly efficient NPM catalysts of cobalt and nitrogen codoped carbon nanosheets (Co/N–CNSs) for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) using harmful environment-polluting waste of biomass catkins as carbon precursors via a mild mechanical exfoliation and chemical process which is facile, low-cost, environmentally friendly and up-scalable. Compared with a commercial platinum-based catalyst (commercial 20% Pt/C), the Co/N–CNS electrocatalysts show outstanding ORR activity, acceptable HER activity and long term stability with an onset potential of 0.92 V versus the reversible hydrogen electrode (vs. RHE) and a half-wave potential of 0.83 V vs. the RHE in alkaline electrolytes. The excellent performance is closely related to the presence of abundant CoN_x active sites. This work offers a novel and effective approach for preparing highly efficient ORR and HER NPM electrocatalysts from waste biomass materials.

We prepare highly efficient NPM catalysts of cobalt and nitrogen co-doped carbon nanosheets for oxygen reduction and hydrogen evolution reactions using catkin biomass.     

Mesoporous K-doped NiCo2O4 derived from a Prussian blue analog: high-yielding synthesis and assessment as oxygen evolution reaction catalyst

The conversion and storage of clean renewable energy can be achieved using water splitting. However, water splitting exhibits sluggish kinetics because of the high overpotentials of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) and should therefore be promoted by OER and/or HER electrocatalysts. As the kinetic barrier of the former reaction exceeds that of the latter, high-performance OER catalysts are highly sought after. Herein, K-doped NiCo₂O₄ (HK-NCO) was hydrothermally prepared from a Prussian blue analog with a metal–organic framework structure and assessed as an OER catalyst. Extensive K doping increased the number of active oxygen vacancies and changed their intrinsic properties (e.g., binding energy), thus increasing conductivity. As a result, HK-NCO exhibited a Tafel slope of 49.9 mV dec⁻¹ and a low overpotential of 292 mV at 10 mA cm⁻², outperforming a commercial OER catalyst (Ir) and thus holding great promise as a component of high-performance electrode materials for metal-oxide batteries and supercapacitors.

OER characteristics of K-doped NiCo₂O₄ catalyst and K doping control through simple hydrothermal synthesis.     

Nearly spherical CoP nanoparticle/carbon nanosheet hybrids: a high-performance trifunctional electrocatalyst for oxygen reduction and water splitting

Developing active multifunctional electrocatalysts composed of earth-abundant and cheap elements is an urgent demand in energy conversion applications. This study presents a facile approach for the scalable synthesis of nanostructured cobalt phosphide embedded in carbon nanosheets (CoP NPs/CNSs). The hybrid structures show highly efficient trifunctional electrocatalytic activities toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) under alkaline condition. The catalytic performances, which are remarkably superior to those of the previously reported CoP nanostructures enclosed by single or a few low index facets, can be attributed to the nearly spherical shape of the CoP nanoparticles with many more exposed crystal planes. Density functional theory (DFT) computations are performed to investigate the facet effects of CoP on electrocatalytic activity, and they reveal the relatively low overpotentials of (101) facets towards the OER and the free energy of water dissociation (ΔG_H2O) and adsorbed H intermediates (ΔG_H*) of (311) toward the HER being close to thermoneutral. This work is expected to inspire the design and fabrication of multifunctional and high-efficiency electrocatalysts by selectively exposing specific crystal planes.

The CoP nanoparticles/carbon sheets hybrid structures are highly efficient trifunctional electrocatalytic activities toward the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction under alkaline condition.     

MWCNT-modified MXene as cost-effective efficient bifunctional catalyst for overall water splitting

Utilization of cost-effective, bifunctional, and efficient electrocatalysts for complete water splitting is desirable for sustainable clean hydrogen energy. In last decade, MXenes, a family of emerging two-dimensional (2D) materials with unique physiochemical properties, enticed scientists because of their use in different applications. However, insufficient electron transport, lower intrinsic chemical activity and limited active site densities are the factors inhibiting their use in electrocatalytic cells for hydrogen production. Here, we have presented material design to address this issue and introduced carbon nanotubes (CNTs) on V₂CT_x MXene sheets for conductive network channels that enhance the ion diffusion for enhanced electrochemical activity. The SEM reveals the uniform dispersion of the MWCNTs over the MXene surface that resulted in the formation of conductive network channels and enhances reaction kinetics. The as-synthesized electrocatalyst was subjected to linear sweep voltammetry (LSV) measurements for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The hybrid catalyst M2 exhibited an enhanced HER activity with a lower over-potential of 27 mV which is comparable to commercially available Pt-based catalysts (32 mV). Similarly, an enhanced OER activity was observed with a lower over-potential of 469 mV as compared to pristine V₂CT_x MXene. The electrocatalyst was subjected to a durability test through chronoamperometry and was observed to be stable for 16 hours. Hence, this study opens a new avenue for future cost-effective efficient catalysts for overall water splitting as a solution to produce clean hydrogen.

Utilization of cost-effective, bifunctional, and efficient electrocatalysts for complete water splitting is desirable for sustainable clean hydrogen energy.     

Preparation of Co–N carbon nanosheet oxygen electrode catalyst by controlled crystallization of cobalt salt precursors for all-solid-state Al–air battery

Production of bifunctional catalysts for catalyzing both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly advisable but challenging with respect to the applications of these catalysts in renewable energy conversion and storage technologies. Herein, we prepared highly reactive and stable cobalt-embedded nitrogen-rich carbon nanosheets (Co–N/CNs). Based on density functional theory (DFT) calculations and experiments, the as-prepared Co–N/CNs showed outstanding catalytic activities toward both OER and ORR. The optimized Co–N/CNs-800 catalyst revealed outstanding bifunctional catalytic activities for both ORR and OER with high catalytic efficiency and long-term durability, which were even comparable with those of the state-of-the-art Pt/C and RuO₂ catalysts. Furthermore, we observed that different cobalt salt precursors affected the size of Co nanoparticles, and both ORR and OER catalytic activities displayed completely consistent variations (sulfate < acetate < chloride < nitrate). An all-solid-state Al–air battery device comprising this hybrid catalyst showed superior performance when compared with the device containing the Pt/C catalyst.

Production of bifunctional catalysts for catalyzing both ORR and OER is highly advisable but challenging with respect to the applications of these catalysts in renewable energy conversion and storage technologies.     

Controlled phase evolution from Cu0.33Co0.67S2 to Cu3Co6S8 hexagonal nanosheets as oxygen evolution reaction catalysts

Developing cheap and efficient transition metal-based catalysts for the oxygen evolution reaction (OER) plays the key role in large-scale implementation of hydrogen production. However, there is still a lack of effective ways to tune the catalysts performance for the OER reaction from the aspect of structure design and element modulation simultaneously. Herein, a novel Cu_0.33Co_0.67S₂ hexagonal nanosheet has been synthesized through the coprecipitation reaction followed by subsequent vapor sulfidation. Simply mixed with carbon nanotubes (CNTs) during electrode preparation, this Cu_0.33Co_0.67S₂ exhibits an overpotential of 284 mV vs. RHE at a current density of 10 mA cm⁻² in 1.0 M KOH. The improved OER performance of the Cu_0.33Co_0.67S₂ electrode can be attributed to the electrocatalytically active sites involved in octahedral coordination structures and further activated by Cu substitution. The encouraging results provide insight into further rational design of transition metal-based electrochemical catalysts towards OER applications.

Developing cheap and efficient transition metal-based catalysts for the oxygen evolution reaction (OER) plays the key role in large-scale implementation of hydrogen production.     

One-step electrodeposition of cerium-doped nickel hydroxide nanosheets for effective oxygen generation

Efficient electrocatalysts catalyzing oxygen evolution reaction (OER) in alkaline media is highly desirable for large-scale hydrogen production from water splitting. Here we report the direct electrodeposition of cerium-doped nickel hydroxide nanosheets on carbon fiber paper and its prominent performance in catalyzing the OER. The composite generates a current density of 100 mA cm⁻² at an overpotential of 320 mV, rivaling the performance of most reported OER catalysts and commercially available RuO₂. X-ray photoelectron spectroscopy analysis shows strong electronic interaction between Ni(OH)₂ and CeO₂, making a great contribution to the OER enhancement.

Cerium doping is effective approach to promoting performance of nickel hydroxide in oxygen evolution reaction.     

Computational screening of transition-metal doped boron nanotubes as efficient electrocatalysts for water splitting

The search for efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is of utmost importance for the production of hydrogen and oxygen via water splitting. In this work, the catalytic performance of the OER and HER on transition metal doped boron nanotubes (BNTs) was investigated using density functional theory. It was found that the doped transition metal atoms determine the catalytic activity of the BNTs. Rhodium-doped BNTs exhibited excellent OER activity, while cobalt-doped BNTs displayed great catalytic activity toward the HER. Volcano relationships were found between the catalytic activity and the adsorption strength of reaction intermediates. Rhodium- and cobalt-doped BNTs exhibited great OER and HER catalytic activity due to the favorable adsorption strength of reaction intermediates. This work sheds light on the design of novel electrocatalysts for water splitting and provides helpful guidelines for the future development of advanced electrocatalysts.

Rhodium-doped BNTs demonstrated excellent OER activity, while cobalt-doped BNTs exhibited the best catalytic activity toward the HER among 12 different transition metal-doped BNTs.     

Highly cost-effective platinum-free anion exchange membrane electrolysis for large scale energy storage and hydrogen production

Anion exchange membrane (AEM) electrolysis eradicates platinum group metal electrocatalysts and diaphragms and is used in conventional proton exchange membrane (PEM) electrolysis and alkaline electrolysis. It can produce pressurised hydrogen by using low cost non-noble metal catalysts. However, the performances are still lower than that of the conventional PEM electrolysis technology. In this study, we addressed the performance issue by using a novel combination of Ni–Fe–O_x for oxygen evolution reaction (OER) and Ni–Fe–Co hydrogen evolution reaction (HER) electrodes with a PBI anion exchange membrane. The Ni–Fe–O_x and Ni–Fe–Co electrodes exhibit exceptionally high catalytic activity, requiring over potentials that are as low as 236 and 84 mV dec⁻¹, respectively, for OER and HER to occur. These electrocatalysts exhibits excellent durability which can be used as oxygen evolution and hydrogen evolution catalysts for long term electrolysis. The high rate capability of 1000 mA cm⁻² at 1.9 V and 60 °C demonstrates the potential of the combined membrane electrode assembly. The best performance, which is comparable to those of commercial PEM electrolysis systems, is thus an affordable alternative to this technology. In addition to that, the AEM electrolysis is promising on a multi-scale level for long-term hydrogen production.

Anion exchange membrane (AEM) electrolysis eradicates platinum group metal electrocatalysts and diaphragms and is used in conventional proton exchange membrane (PEM) electrolysis and alkaline electrolysis.     

Hierarchical Co–FeS2/CoS2 heterostructures as a superior bifunctional electrocatalyst

The traditional method of preparing hydrogen and oxygen as efficient clean energy sources mainly relies on the use of platinum, palladium, and other precious metals. However, the high cost and low abundance limit wide application of such metals. As such, one challenging issue is the development of low-cost and high-efficiency electrocatalysts for such purposes. In this study, we synthesized Co–FeS₂/CoS₂ heterostructures via a hydrothermal method for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Benefitting from their unique three-dimensional hierarchical nanostructures, Co-doped FeS₂, and CoS₂ formed heterostructures on Co–FeS₂ petals, which bestowed remarkable electrocatalytic properties upon Co–FeS₂/CoS₂ nanostructures. Co–FeS₂/CoS₂ effectively catalyzed the OER with an overpotential of 278 mV at a current density of 10 mA cm⁻² in 1 M KOH solution, and also is capable of driving a current density −10 mA cm⁻² at an overpotential of −103 mV in 0.5 M H₂SO₄ solution. The overpotential of the OER and HER only decreased by 5 mV and 3 mV after 1000 cycles. Our Co–FeS₂/CoS₂ materials may offer a promising alternative to noble metal-based electrocatalysts for water splitting.

Here we report a facile solvothermal synthesis of Co–FeS₂/CoS₂ heterostructures with remarkable electrocatalytic properties.