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.     

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.     

Steps towards highly-efficient water splitting and oxygen reduction using nanostructured β-Ni(OH)2

β-Ni(OH)₂ nanoplatelets are prepared by a hydrothermal procedure and characterized by scanning and transmission electron microscopy, X-ray diffraction analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. The material is demonstrated to be an efficient electrocatalyst for oxygen reduction, oxygen evolution, and hydrogen evolution reactions in alkaline media. β-Ni(OH)₂ shows an overpotential of 498 mV to reach 10 mA cm⁻² towards oxygen evolution, with a Tafel slope of 149 mV dec⁻¹ (decreasing to 99 mV dec⁻¹ at 75 °C), along with superior stability as evidenced by chronoamperometric measurements. Similarly, a low overpotential of −333 mV to reach 10 mA cm⁻² (decreasing to only −65 mV at 75 °C) toward hydrogen evolution with a Tafel slope of −230 mV dec⁻¹ is observed. Finally, β-Ni(OH)₂ exhibits a noteworthy performance for the ORR, as evidenced by a low Tafel slope of −78 mV dec⁻¹ and a number of exchanged electrons of 4.01 (indicating direct 4e⁻-oxygen reduction), whereas there are only a few previous reports on modest ORR activity of pure Ni(OH)₂.

β-Ni(OH)₂ nanoplatelets produced via a hydrothermal method exhibit good performance as trifunctional electrocatalysts for the ORR, OER, and HER in alkaline media along with excellent stability under cathodic/anodic polarisation conditions.     

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.     

Nickel foam and stainless steel mesh as electrocatalysts for hydrogen evolution reaction,oxygen evolution reaction and overall water splitting in alkaline media

In this work, several commonly used conductive substrates as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions were studied, including nickel foam (Ni foam), copper foam (Cu foam), nickel mesh (Ni mesh) and stainless steel mesh (SS mesh). Ni foam and SS mesh are demonstrated as high-performance and stable electrocatalysts for HER and OER, respectively. For HER, Ni foam exhibited an overpotential of 0.217 V at a current density of 10 mA cm⁻² with a Tafel slope of 130 mV dec⁻¹, which were larger than that of the commercial Pt/C catalyst, but smaller than that of the other conductive substrates. Meanwhile, the SS mesh showed the best electrocatalytic performance for OER with an overpotential of 0.277 V at a current density of 10 mA cm⁻² and a Tafel slope of 51 mV dec⁻¹. Its electrocatalytic performance not only exceeded those of the other conductive substrates but also the commercial RuO₂ catalyst. Moreover, both Ni foam and SS mesh exhibited high stability during HER and OER, respectively. Furthermore, in the two-electrode system with Ni foam used as the cathode and SS mesh used as the anode, they enable a current density of 10 mA cm⁻² at a small cell voltage of 1.74 V. This value is comparable to or exceeding the values of previously reported electrocatalysts for overall water splitting. In addition, NiO on the surface of Ni foam may be the real active species for HER, NiO and FeO_x on the surface of SS mesh may be the active species for OER. The abundant and commercial availability, long-term stability and low-cost property of nickel foam and stainless steel mesh enable their large-scale practical application in water splitting.

Efficient electrocatalytic overall water splitting is achieved with commercially-available and low-cost nickel foam and stainless steel mesh as cathode and anode electrodes.     

Microflower-like Co9S8@MoS2 heterostructure as an efficient bifunctional catalyst for overall water splitting

The development of a distinguished and high-performance catalyst for H₂ and O₂ generation is a rational strategy for producing hydrogen fuel via electrochemical water splitting. Herein, a flower-like Co₉S₈@MoS₂ heterostructure with effective bifunctional activity was achieved using a one-pot approach via the hydrothermal treatment of metal-coordinated species followed by pyrolysis under an N₂ atmosphere. The heterostructures exhibited a 3D interconnected network with a large electrochemical active surface area and a junctional complex with hydrogen evolution reaction (HER) catalytic activity of MoS₂ and oxygen evolution reaction (OER) catalytic activity of Co₉S₈, exhibiting low overpotentials of 295 and 103 mV for OER and HER at 10 mA cm⁻² current density, respectively. Additionally, the catalyst-assembled electrolyser provided favourable catalytic activity and strong durability for overall water splitting in 1 M KOH electrolyte. The results of the study highlight the importance of structural engineering for the design and preparation of cost-effective and efficient bifunctional electrocatalysts.

A flower-like Co₉S₈@MoS₂ heterostructure was prepared as efficient bifunctional electrocatalyst for overall water splitting by a sample one-pot approach.     

Enhanced oxygen evolution reaction on amine functionalized graphene oxide in alkaline medium

Development of highly efficient oxygen evolution reaction (OER) electrocatalysts is a critical challenge in the cost-effective generation of clean fuels. Here, a metal-free tyramine functionalized graphene oxide (T-GO) electrocatalyst is proposed to use in alkaline electrolytes for enhanced OER. Moreover, the T-GO and GO nanomaterials are well characterized by SEM, XRD, FTIR, XPS and Raman spectroscopy. T-GO exhibits an electrocatalytic OER with a current density of 2 mA cm⁻² at a low onset potential of ∼1.39 V and a small Tafel slope of about 69 mV dec⁻¹ and GO exhibits an onset potential of 1.51 V and Tafel slope of about 92 mV dec⁻¹. Additionally, the current stability and RRDE based diffusion controlled response of the T-GO electrocatalyst are outstanding compared to GO. This study establishes metal free T-GO as an efficient electrocatalyst for the OER and used for cathodic production of hydrogen as a counter reaction in the field of water splitting.

Metal free tyramine functionalized graphene oxide (T-GO) is a promising electrocatalyst for oxygen evolution reaction (OER) in alkaline medium having high activity and stability, resulting from the tyramine active sites.     

Nanostructured RuO2–Co3O4@RuCo-EO with low Ru loading as a high-efficiency electrochemical oxygen evolution catalyst

Electrochemical water splitting technology is considered to be the most reliable method for converting renewable energy such as wind and solar energy into hydrogen. Here, a nanostructured RuO₂/Co₃O₄–RuCo-EO electrode is designed via magnetron sputtering combined with electrochemical oxidation for the oxygen evolution reaction (OER) in an alkaline medium. The optimized RuO₂/Co₃O₄–RuCo-EO electrode with a Ru loading of 0.064 mg cm⁻² exhibits excellent electrocatalytic performance with a low overpotential of 220 mV at the current density of 10 mA cm⁻² and a low Tafel slope of 59.9 mV dec⁻¹ for the OER. Compared with RuO₂ prepared by thermal decomposition, its overpotential is reduced by 82 mV. Meanwhile, compared with RuO₂ prepared by magnetron sputtering, the overpotential is also reduced by 74 mV. Furthermore, compared with the RuO₂/Ru with core–shell structure (η = 244 mV), the overpotential is still decreased by 24 mV. Therefore, the RuO₂/Co₃O₄–RuCo-EO electrode has excellent OER activity. There are two reasons for the improvement of the OER activity. On the one hand, the core–shell structure is conducive to electron transport, and on the other hand, the addition of Co adjusts the electronic structure of Ru.

The optimized RuO₂/Co₃O₄–RuCo-EO electrode with Ru loading of 0.064 mg cm⁻² exhibits the excellent oxygen evolution activity with an overpotential of 220 mV at the current density of 10 mA cm⁻² and a Tafel slope of 59.9 mV dec⁻¹.     

Low temperature scalable synthetic approach enabling high bifunctional electrocatalytic performance of NiCo2S4 and CuCo2S4 thiospinels

Ternary metal sulfides are currently in the spotlight as promising electroactive materials for high-performance energy storage and/or conversion technologies. Extensive research on metal sulfides has indicated that, amongst other factors, the electrochemical properties of the materials are strongly influenced by the synthetic protocol employed. Herein, we report the electrochemical performance of uncapped NiCo₂S₄ and CuCo₂S₄ ternary systems prepared via solventless thermolysis of the respective metal ethyl xanthate precursors at 200 and 300 °C. The structural, morphological and compositional properties of the synthesized nanoparticles were examined by powder X-ray diffraction (p-XRD), transmission electron microscopy (TEM), high-resolution TEM, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) techniques. Electrochemical studies indicate that NiCo₂S₄ nanoparticles synthesized at 300 °C exhibit superior energy storage characteristics with a high specific capacitance of ca. 2650 F g⁻¹ at 1 mV s⁻¹, as compared to CuCo₂S₄ nanoparticles, which showcased a specific capacitance of ca. 1700 F g⁻¹ at the same scan rate. At a current density of 0.5 A g⁻¹, NiCo₂S₄ and CuCo₂S₄ nanoparticles displayed specific capacitances of 1201 and 475 F g⁻¹, respectively. In contrast, CuCo₂S₄ nanoparticles presented a higher electrocatalytic activity with low overpotentials of 269 mV for oxygen evolution reaction (OER), and 224 mV for the hydrogen evolution reaction (HER), at 10 mA cm⁻². The stability of the catalysts was examined for 2000 cycles in which a negligible change in both OER and HER activities was observed.

A scalable solventless approach is employed to prepare NiCo₂S₄ and CuCo₂S₄ with bare surface for enhanced supercapacitance and water splitting. The particles exhibit good energy storage and electrocatalytic activity as well as stability.     

Ultradispersed IrxNi clusters as bifunctional electrocatalysts for high-efficiency water splitting in acid electrolytes

Design and synthesis of electrocatalysts with high activity and low cost is an important challenge for water splitting. We report a rapid and facile synthetic route to obtain Ir_xNi clusters via polyol reduction. The Ir_xNi clusters show excellent activity for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic electrolytes. The optimized Ir₂Ni/C clusters exhibit an electrochemical active area of 18.27 mF cm⁻², with the overpotential of OER being 292 mV and HER being 30 mV at 10 mA cm⁻², respectively. In addition, the Ir₂Ni/C used as the cathode and anode for the H-type hydrolysis tank only needs 1.597 V cell voltages. The excellent electrocatalytic performance is mainly attributed to the synergistic effect between the metals and the ultra-fine particle size. This study provides a novel strategy that has a broad application for water splitting.

A method of preparing Ir_xNi/C clusters by polyol reduction using a XC-72R support was proposed. Due to the 2 nm size of the catalyst particles, more active sites are exposed. This is a promising route for the development of efficient water splitting electrocatalysts.     

An advanced and efficient Co3O4/C nanocomposite for the oxygen evolution reaction in alkaline media

The design of efficient nonprecious catalysts for the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) is a necessary, but very challenging task to uplift the water-based economy. In this study, we developed a facile approach to produce porous carbon from the dehydration of sucrose and use it for the preparation of nanocomposites with cobalt oxide (Co₃O₄). The nanocomposites were studied by the powder X-ray diffraction and scanning electron microscopy techniques, and they exhibited the cubic phase of cobalt oxide and porous structure of carbon. The nanocomposites showed significant OER activity in alkaline media, and the current densities of 10 and 20 mA cm⁻² could be obtained at 1.49 and 1.51 V versus reversible hydrogen electrode (RHE), respectively. The impedance study confirms favorable OER activity on the surface of the prepared nanocomposites. The nanocomposite is cost-effective and can be capitalized in various energy storage technologies.

The design of efficient nonprecious catalysts for the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER) is a necessary, but very challenging task to uplift the water-based economy.     

Phyto-inspired and scalable approach for the synthesis of PdO–2Mn2O3: a nano-material for application in water splitting electro-catalysis

A modified co-precipitation method has been used for the synthesis of a PdO–2Mn₂O₃ nanocomposite as an efficient electrode material for the electro-catalytic oxygen evolution (OER) and hydrogen evolution reaction (HER). Palladium acetate and manganese acetate in molar ratio 1 : 4 were dissolved in water, and 10 ml of an aqueous solution of phyto-compounds was slowly added until completion of precipitation. The filtered and dried precipitates were then calcined at 450 °C to obtain a blackish brown colored mixture of PdO–2Mn₂O₃ nanocomposite. These particles were analyzed by ultra violet visible spectrophotometry (UV-vis), infrared spectroscopy (FTIR), powder X-ray diffractometry (XRD), scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) for crystallinity, optical properties, and compositional and morphological makeup. Using Tauc''s plot, the direct band gap (3.18 eV) was calculated from the absorption spectra. The average crystallite sizes, as calculated from the XRD, were found to be 15 and 14.55 nm for PdO and Mn₂O₃, respectively. A slurry of the phyto-fabricated PdO–2Mn₂O₃ powder was deposited on Ni-foam and tested for electro-catalytic water splitting studies in 1 M KOH solution. The electrode showed excellent OER and HER performance with low over-potential (0.35 V and 121 mV) and Tafel slopes of 115 mV dec⁻¹ and 219 mV dec⁻¹, respectively. The outcomes obtained from this study provide a direction for the fabrication of a cost-effective mixed metal oxide based electro-catalyst via an environmentally benign synthesis approach for the generation of clean energy.

A modified co-precipitation method has been used for the synthesis of PdO–2Mn₂O₃ nanocomposite as an efficient electrode material for the electro-catalytic oxygen evolution (OER) and hydrogen evolution reaction (HER).     

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.     

Alkaline water-splitting reactions over Pd/Co-MOF-derived carbon obtained via microwave-assisted synthesis

Cobalt-based metal–organic framework-derived carbon (MOFDC) has been studied as a new carbon-based support for a Pd catalyst for electrochemical water-splitting; i.e., the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline medium. The study shows a high increase in the HER activity, in terms of low onset overpotential (onset η = 35 mV vs. RHE), high exchange current density (j_o,s ≈ 0.22 mA cm⁻²), high mass activity (j_o,m ≈ 59 mA mg⁻¹), high kinetic current (j_K ≈ 5–8 mA cm⁻²) and heterogeneous rate constant (k⁰ ≈ 4 × 10⁻⁴ cm s⁻¹), which are attributed to the high porosity of MOFDC and contribution from residual Co, while the large Tafel slope (b_c = 261 mV dec⁻¹) is ascribed to the high degree of hydrogen adsorption onto polycrystalline Pd as a supplementary reaction step to the suggested Volmer–Heyrovsky mechanism. These values for the catalyst are comparable to or better than many recent reports that adopted nano-carbon materials and/or use bi- or ternary Pd-based electrocatalysts for the HER. The improved HER activity of Pd/MOFDC is associated with the positive impact of MOFDC and residual Co on the Pd catalyst (i.e., low activation energy, E_A ≈ 12 kJ mol⁻¹) which allows for easy desorption of the H_ads to generate hydrogen. Moreover, Pd/MOFDC displays better OER activity than its analogue, with lower onset η (1.29 V vs. RHE) and b_a (≈78 mV dec⁻¹), and higher current response (ca. 18 mA cm⁻²). Indeed, this study provides a new strategy of designing and synthesizing MOFDC with physico-chemical features for Pd-based electrocatalysts that will allow for efficient electrochemical water-splitting processes.

Palladium nanoparticles supported on MOF-derived carbon serve as an efficient bifunctional electrocatalyst for alkaline water-splitting reactions.     

In situ addition of graphitic carbon into a NiCo2O4/CoO composite: enhanced catalysis toward the oxygen evolution reaction

We present a rapid, environmentally benign one-pot synthesis technique for the production of a NiCo₂O₄/CoO and graphite composite that demonstrates efficient electrocatalysis towards the Oxygen Evolution Reaction (OER), in 1.0 M KOH. The NiCo₂O₄/CoO/graphitic carbon composite that displayed optimal OER catalysis was synthesized by nitrate decomposition in the presence of citric acid (synthesized glycine and sucrose variants displayed inferior electro kinetics towards the OER). Screen-printed electrodes modified with ca. 530 μg cm⁻² of the citric acid NiCo₂O₄/CoO/graphite variant displayed remarkable OER catalysis with an overpotential (η) of +323 mV (vs. RHE) (recorded at 10 mA cm⁻²), which is superior to that of IrO₂ (340 mV) and RuO₂ (350 mV). The composite also exhibited a large achievable current density of 77 mA cm⁻² (at +1.5 V (vs. RHE)), a high O₂ turnover frequency of 1.53 × 10⁻² s⁻¹ and good stability over the course of 500 repeat cycles. Clearly, the NiCo₂O₄/CoO composite has the potential to replace precious metal based catalysts as the anodic material within electrolysers, thereby providing a reduction in the associated costs of hydrogen production via water splitting.

A facile synthesis technique for the production of NiCo₂O₄/CoO and graphite composites that demonstrate efficient electrocatalysis towards the oxygen evolution reaction.     

Coordination environment evolution of Co(ii) during dehydration and re-crystallization processes of KCoPO4·H2O towards enhanced electrocatalytic oxygen evolution reaction

Development of efficient and stable electrodes for electrocatalytic oxygen evolution reaction (OER) is essential for energy storage and conversion applications, such as hydrogen generation from water splitting, rechargeable metal–air batteries and renewable fuel cells. Alkali metal cobalt phosphates show great potential as OER electrocatalysts. Herein, an original electrode design strategy is reported to realize an efficient OER electrocatalyst through engineering the coordination geometry of Co(ii) in KCoPO₄·H₂O by a facile dehydration process. Experimental result indicated that the dehydration treatment is accompanied by a structural transformation from orthorhombic KCoPO₄·H₂O to hexagonal KCoPO₄, involving a concomitant coordination geometry evolution of Co(ii) from octahedral to tetrahedral configuration. More significantly, the local structural evolution leads to an advantageous electronic effect, i.e. increased Co–O covalency, resulting in an enhanced intrinsic OER activity. To be specific, the as-produced KCoPO₄ can deliver a current density of 10 mA cm⁻² at a low overpotential of 319 mV with a small Tafel slope of 61.8 mV dec⁻¹ in alkaline electrolyte. Thus, this present research provides a new way of developing alkali metal transition-metal phosphates for efficient and stable electrocatalytic oxygen evolution reaction.

Coordination environment evolution of potassium cobalt phosphate towards enhanced electrocatalytic oxygen evolution reaction.     

N-doped mixed Co,Ni-oxides with petal structure as effective catalysts for hydrogen and oxygen evolution by water splitting

Developing electrocatalytic nanomaterials for green H₂ energy is inseparable from the exploration of novel materials and internal mechanisms for catalytic enhancement. In this work, nano-petal N-doped bi-metal (Ni, Co) and bi-valence (+2, +3) (Ni_1−xCo_x)²⁺Co₂³⁺O₄ compounds have been in situ grown on the surface of Ni foam. The N³⁻ atoms originate from the amino group in urea and doped in the compound during annealing. The as-synthesized N-doped (Ni_1−xCo_x)²⁺Co₂³⁺O₄ nano-petals demonstrate commendable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) bi-functional catalytic efficiency and stability. Electrochemical measurements confirm that the nitrogen doping significantly improves the catalytic kinetics and the surface area. Density functional theory calculations reveal that the improved HER and OER kinetics is not only due to the synergistic effect of bi-metal and bi-valence, as well as the introduction of defects such as oxygen vacancies, but also it more depends on the shortened bond length between the nitrogen N³⁻ atoms and the metal atoms, and the increased electron density of the metal atoms attached to the N³⁻ atoms. In other words, the change of lattice parameters caused by nitrogen doping is more conducive to the catalytic enhancement than the synergistic effect brought by bi-metal. This study provides an experimental and theoretical reference for the design of bi-functional electrocatalytic nanomaterials.

Developing electrocatalytic nanomaterials for green H₂ energy is inseparable from the exploration of novel materials and internal mechanisms for catalytic enhancement.     

A high-efficiency oxygen evolution electrode material of a carbon material containing a NiCo bimetal

The preparation of highly efficient, stable, and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is still a challenge for the development of new energy systems. In this work, a NiCo bimetal loaded on porous carbon (NiCo-C/NF) grown on nickel foam (NF) was obtained via the pyrolysis of a NiCo bimetal MOF (NiCo-MOF/NF) under a nitrogen atmosphere at 500 °C. Compared with NiCo-MOF/NF, NiCo-C/NF had a larger specific surface and uniform mesoporous structure. As an electrocatalyst in the OER, this new type of electrode operated with better stability in an alkaline solution (1.0 mol L⁻¹ KOH), the overpotential when the current density reached 10 mA cm⁻² was only 260 mV, and the electrode also exhibited long-term durability in a stability test for 10 h without significant changes. The excellent activity and stability toward the OER can be attributed to the synergistic effect of the NiCo bimetal and the abundant active sites exposed after the carbonization of NiCo-MOF, which compensated for the defect of the insufficient conductivity of the material and promoted the evolution of oxygen in the catalytic process.

The preparation of highly efficient, stable, and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is still a challenge for the development of new energy systems.     

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).     

Enhancing oxygen and hydrogen evolution activities of perovskite oxide LaCoO3via effective doping of platinum

In this study, a series of perovskite oxides LaCo_1−xPt_xO_3−δ (x = 0, 0.02, 0.04, 0.06, and 0.08) were prepared by the citric acid–ethylenediaminetetraacetic acid (CA–EDTA) complexing sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Then, the samples were investigated as OER and HER bifunctional electrocatalysts in alkaline media. Compared with other catalysts, LaCo_0.94Pt_0.06O_3−δ had good stability and presented more activity at a lower overpotential of 454 mV (at 10 mA cm⁻²), a lower Tafel slope value of 86 mV dec⁻¹ and a higher mass activity of 44.4 A g⁻¹ for OER; it displayed a lower overpotential of 294 mV (at −10 mA cm⁻²), a lower Tafel slope value of 148 mV dec⁻¹ and a higher mass activity of −34.5 A g⁻¹ for HER. The improved performance might depend on a larger ECSA, faster charge transfer rate and higher ratio of the highly oxidative oxygen species (O₂²⁻/O⁻). Furthermore, the e_g orbital filling of Co approaching 1.2 in the B site might play a leading role.

Among the perovskite LaCo_1−xPt_xO_3−δ catalysts, LaCo_0.94Pt_0.06O_3−δ proved best for catalyzing OER/HER, with η = 454/294 mV, which might be attributed to LCP6 having the e_g orbital filling of Co closest to 1.2.