Controlled Synthesis of Ni-Doped MoS2 Hybrid Electrode for Synergistically Enhanced Water-Splitting Process

The development of high-efficiency, low-cost, and earth-abundant electrocatalysts for overall water splitting remains a challenge. In this work, Ni-modified MoS₂ hybrid catalysts are grown on carbon cloth (Ni-Mo-S@CC) through a one-step hydrothermal treatment. The optimized Ni-Mo-S@CC catalyst shows excellent hydrogen evolution reaction (HER) activity with a low overpotential of 168 mV at a current density of 10 mA cm⁻² in 1.0 m KOH, which is lower than those of Ni-Mo-S@CC (1:1), Ni-Mo-S@CC (3:1), and pure MoS₂. Significantly, the Ni-Mo-S@CC hybrid catalyst also displays outstanding oxygen evolution reaction (OER) activity with a low overpotential of 320 mV at a current density of 10 mA cm⁻², and remarkable long-term stability for 30 h at a constant current density of 10 mA cm⁻². Experimental results and theoretical analysis based on density functional theory demonstrate that the excellent electrocatalytic performance can be attributed mainly to the remarkable conductivity, abundant active sites, and synergistic effect of the Ni-doped MoS₂. This work sheds light on a unique strategy for the design of high-performance and stable electrocatalysts for water-splitting electrolyzers.     

Optimizing Electronic and Geometrical Structure of Vanadium Doped Cobalt Phosphides for Enhanced Electrocatalytic Hydrogen Evolution

Despite the expectation on transition-metal phosphides as precious-metal-free electrocatalysts, the reported performance of these materials still necessitates further improvement. Ingenious regulations of both geometric and electronic structure have been proposed as an effective approach to boost their electrocatalytic properties. In this regard, the self-supported V doped CoP nanowires on nickel foam are prepared to accommodate both optimized electronic structure and desired nanostructure, which enable large surface area, abundant active sites exposure, low charge transfer resistance, as well as favorable H* adsorption. As for the alkaline hydrogen evolution, it only requires a lower potential of 79 mV and 125 mV to drive 10 mA ⋅ cm⁻² and 100 mA ⋅ cm⁻² current with a Tafel slope of 47.41 mV ⋅ dec⁻¹, which prevails over commercial Pt/C catalysts. The catalyst also exhibits excellent durability to retain activity unchanged for more than 16 h. Such a simple and convenient strategy by electronic tuning and structure design provides a new avenue toward the exploration of efficient electrocatalysts.     

Flower-like Fe-Co-M (M=S,O, P and Se) Nanosheet Arrays Grown on Nickel Foam as High-efficiency Bifunctional Electrocatalysts

The development of highly efficient, inexpensive, abundant and non-precious metal electrocatalysts is the lifeblood of the hydrogen production industry, especially the hydrogen production industry by electrolysis of water. A Fe-Co-S/NF bifunctional electrocatalyst with nanoflower-like structure was synthesized on three-dimensional porous nickel foam through one-step hydrothermal and one-step high-temperature sulfuration operations, and the material displays high-efficiency electrocatalytic performance. As a catalyst for the hydrogen evolution reaction, Fe-Co-S/NF can drive a current density of 10 mA/cm² at an overpotential of 143 mV with a Tafel slope of 80.2 mV/dec. When it was used as an oxygen evolution reaction catalyst, it exhibits good OER reactivity with a low Tafel slope (82.6 mV/dec) and with requiring only 117 mV overpotential to drive current densities up to 50 mA/cm². In addition, the Fe-Co-S/NF//Fe-Co-S/NF electrolytic cell was assembled, an electrolysis voltage of 1.64 V is required to drive a current density of 50 mA/cm², which is one of the most active catalysts reported so far. This work indicates that the introduction of S, P and Se treating processes could effectively improve electrical conductivity of the material and enhance the catalytic activity of the material. This work offers an effective and convenient method for improving the morphology of the catalyst, increasing the surface area of the catalyst and developing high-efficiency and low-cost catalysts.     

Heterostructured Inter-Doped Ruthenium–Cobalt Oxide Hollow Nanosheet Arrays for Highly Efficient Overall Water Splitting

The development of transition-metal-oxides (TMOs)-based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. Herein, the rational design and controllable fabrication of unique heterostructured inter-doped ruthenium–cobalt oxide [(Ru–Co)O_x] hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)O_x nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm⁻² and a small Tafel slope of 23.5 mV dec⁻¹, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm⁻². As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm⁻² for alkaline overall water splitting.     

Atmospheric-Temperature Chain Reaction towards Ultrathin Non-Crystal-Phase Construction for Highly Efficient Water Splitting

Combining the self-sacrifice of a highly crystalline substance to design a multistep chain reaction towards ultrathin active-layer construction for high-performance water splitting with atmospheric-temperature conditions and an environmentally benign aqueous environment is extremely intriguing and full of challenges. Here, taking cobalt carbonate hydroxides (CCHs) as the initial crystalline material, we choose the Lewis acid metal salt of Fe(NO₃)₃ to induce an aqueous-phase chain reaction generating free CO₃²⁻ ions with subsequent instant FeCO₃ hydrolysis. The resultant ultrathin (∼5 nm) amorphous Fe-based hydroxide layer on CCH results in considerable activity in catalyzing the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), yielding 10/50 mA ⋅ cm⁻² at overpotentials of 230/266.5 mV for OER and 72.5/197.5 mV for HER. The catalysts can operate constantly in 1.0 M KOH over 48 and 45 h for the OER and HER, respectively. For bifunctional catalysis for alkaline electrolyzer assembly, a cell voltage as low as 1.53 V was necessary to yield 10 mA cm⁻² (1.7 V at 50 mA cm⁻²). This work rationally builds high-efficiency electrochemical bifunctional water-splitting catalysts and offers a trial in establishing a controllable nanolevel ultrathin lattice disorder layer through an atmospheric-temperature chemical route.     

Controlled Synthesis of 3D Flower‐like Ni2P Composed of Mesoporous Nanoplates for Overall Water Splitting

Developing efficient non‐noble metal and earth‐abundant electrocatalysts with tunable microstructures for overall water splitting is critical to promote clean energy technologies for a hydrogen economy. Herein, novel three‐dimensional (3D) flower‐like Ni₂P composed of mesoporous nanoplates with controllable morphology and high surface area was prepared by a hydrothermal method and low‐temperature phosphidation as efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Compared with the urchin‐like Ni_x P_y , the 3D flower‐like Ni₂P with a diameter of 5 μm presented an efficient and stable catalytic performance in 0.5 m H₂SO₄, with a small Tafel slope of 79 mV dec⁻¹ and an overpotential of about 240 mV at a current density of 10 mA cm⁻² with a mass loading density of 0.283 mg cm⁻². In addition, the catalyst also exhibited a remarkable performance for the OER in 1.0 m KOH electrolyte, with an overpotential of 320 mV to reach a current density of 10 mA cm⁻² and a small Tafel slope of 72 mV dec⁻¹. The excellent catalytic performance of the as‐prepared Ni₂P may be ascribed to its novel 3D morphology with unique mesoporous structure.     

Anodic Hydrazine Oxidation Assists Energy‐Efficient Hydrogen Evolution over a Bifunctional Cobalt Perselenide Nanosheet Electrode

Water electrolysis is a promising source of hydrogen; however, technological challenges remain. Intensive efforts have focused on developing highly efficient and earth‐abundant electrocatalysts for water splitting. An effective strategy is proposed, using a bifunctional tubular cobalt perselenide nanosheet electrode, in which the sluggish oxygen evolution reaction is substituted with anodic hydrazine oxidation so as to assist energy‐efficient hydrogen production. Specifically, this electrode produces a current density of 10 mA cm^?2 at ?84 mV for hydrogen evolution and ?17 mV for hydrazine oxidation in 1.0 m KOH and 0.5 m hydrazine electrolyte. An ultralow cell voltage of only 164 mV is required to generate a current density of 10 mA cm^?2 for 14 hours of stable water electrolysis.     

Hollow Nanotube Ru/Cu2+1O Supported on Copper Foam as a Bifunctional Catalyst for Overall Water Splitting

Hydrogen energy is considered as one of the ideal clean energies for solving the energy shortage and environmental issues, and developing highly efficient electrocatalysts for overall water splitting to produce hydrogen is still a huge challenge. Herein, for the first time, Ru-doped Cu₂₊₁O vertically arranged nanotube arrays in situ grown on Cu foam (Ru/Cu₂₊₁O NT/CuF) are reported and further investigated for their catalytic properties for overall water splitting. The Ru/Cu₂₊₁O NT/CuF presents ultrahigh catalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline conditions, and it exhibits a small overpotential of 32 mV at 10 mA cm⁻² in the HER, and only needs 210 mV overpotential to achieve a current density of 10 mA cm⁻² in the OER. Importantly, the alkaline electrolyzer using Ru/Cu₂₊₁O NT/CuF as a bifunctional electrocatalyst only needs 1.53 V voltage to deliver a current density of 10 mA cm⁻², which is much lower than the benchmark of IrO₂(+)/Pt(−) counterpart (1.64 V at 10 mA cm⁻²). The excellent performance of the Ru/Cu₂₊₁O NT/CuF catalyst is attributed to its high conductive substrate and special Ru-doped nanotube structure, which provides a high electrochemical active surface area and 3D gas diffusion channel.     

Ru-Doping Enhanced Electrocatalysis of Metal–Organic Framework Nanosheets toward Overall Water Splitting

An Ru-doping strategy is reported to substantially improve both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activity of Ni/Fe-based metal–organic framework (MOF) for overall water splitting. As-synthesized Ru-doped Ni/Fe MIL-53 MOF nanosheets grown on nickel foam (MIL-53(Ru-NiFe)@NF) afford HER and OER current density of 50 mA cm⁻² at an overpotential of 62 and 210 mV, respectively, in alkaline solution with a nominal Ru loading of ≈110 μg cm⁻². When using as both anodic and cathodic (pre-)catalyst, MIL-53(Ru-NiFe)@NF enables overall water splitting at a current density of 50 mA cm⁻² for a cell voltage of 1.6 V without iR compensation, which is much superior to state-of-the-art RuO₂-Pt/C-based electrolyzer. It is discovered that the Ru-doping considerably modulates the growth of MOF to form thin nanosheets, and enhances the intrinsic HER electrocatalytic activity by accelerating the sluggish Volmer step and improving the intermediate oxygen adsorption for increased OER catalytic activity.     

Carbon Nanotubes Decorated with CoP Nanocrystals: A Highly Active Non‐Noble‐Metal Nanohybrid Electrocatalyst for Hydrogen Evolution

The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. The strongly acidic conditions in proton exchange membranes create a need for acid‐stable HER catalysts. A nanohybrid that consists of carbon nanotubes decorated with CoP nanocrystals (CoP/CNT) was prepared by the low‐temperature phosphidation of a Co₃O₄/CNT precursor. As a novel non‐noble‐metal HER catalyst operating in acidic electrolytes, the nanohybrid exhibits an onset overpotential of as low as 40 mV, a Tafel slope of 54 mV dec^?1, an exchange current density of 0.13 mA cm^?2, and a Faradaic efficiency of nearly 100 %. This catalyst maintains its catalytic activity for at least 18 hours and only requires overpotentials of 70 and 122 mV to attain current densities of 2 and 10 mA cm^?2, respectively.     

Heterostructured Inter‐Doped Ruthenium–Cobalt Oxide Hollow Nanosheet Arrays for Highly Efficient Overall Water Splitting

The development of transition‐metal‐oxides (TMOs)‐based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. Herein, the rational design and controllable fabrication of unique heterostructured inter‐doped ruthenium–cobalt oxide [(Ru–Co)O_x] hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)O_x nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm^?2 and a small Tafel slope of 23.5 mV dec^?1, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm^?2. As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm^?2 for alkaline overall water splitting.     

Hollow Porous MnFe2O4 Sphere Grown on Elm-Money-Derived Biochar towards Energy-Saving Full Water Electrolysis

The development of inexpensive and efficient bifunctional electrocatalysts is significant for widespread practical applications of overall water splitting technology. Herein, a one-pot solvothermal method is used to prepare hollow porous MnFe₂O₄ spheres, which are grown on natural-abundant elm-money-derived biochar material to construct MnFe₂O₄/BC composite. When the overpotential is 156 mV for both the oxygen evolution reaction and the hydrogen evolution reaction, the current density reaches up to 10 mA cm⁻², and its duration is 10 h. At 1.51 V, the overall water decomposition current density of 10 mA cm⁻² can be obtained in 1 m KOH. This work proves that elm-money-derived biochar is a valid substrate for growing hollow porous spheres. MnFe₂O₄/BC give a promising general strategy for preparing the effective and stable bifunctional catalysis that can be expand to multiple transition metal oxide.     

Bifunctional Electrocatalyst with 0D/2D Heterostructure for Highly Efficient Hydrogen and Oxygen Generation

A novel MoS₂ quantum dots/CoSe₂ nanosheet (MoS₂ QDs/CoSe₂) hybrid with 0D/2D heterostructure has been developed. The CoSe₂ nanosheets (NSs) enable an excellent oxygen evolution reaction (OER) activity with increasing vacancy configuration on one hand, while the MoS₂ QDs serve as an eminent hydrogen evolution reaction (HER) catalyst on the other. By integrating MoS₂ QDs and CoSe₂ NSs, the hybrid exhibits excellent electrocatalytic performances in HER and OER. The unique 0D/2D hetero‐interface increases the exposed active sites and facilitates electron transfer, thereby boosting the electrocatalytic activity. Relatively low overpotentials of 82 mV and 280 mV are required to drive the current density of 10 mA/cm² for HER and OER, with corresponding Tafel slopes of 69 and 75 mV/dec, respectively. As such, this work provides an efficient yet simple approach to construct bifunctional electrocatalysts with enhanced activity and stability.     

Improving the Electrocatalytic Activity of a Nickel-Organic Framework toward the Oxygen Evolution Reaction through Vanadium Doping

Metal-organic frameworks (MOFs) have been considered as potential oxygen evolution reaction (OER) electrocatalysts owning to their ultra-thin structure, adjustable composition, high surface area, and high porosity. Here, we designed and fabricated a vanadium-doped nickel organic framework (V_1−x−Ni_xMOF) system by using a facile two-step solvothermal method on nickel foam (NF). The doping of vanadium remarkably elevates the OER activity of V_1−x−Ni_xMOF, thus demonstrating better performance than the corresponding single metallic Ni-MOF, NiV-MOF and RuO₂ catalysts at high current density (>400 mA cm⁻²). V_0.09−Ni_0.91MOF/NF provides a low overpotential of 235 mV and a small Tafel slope of 30.3 mV dec⁻¹ at a current density of 10 mA cm⁻². More importantly, a water-splitting device assembled with Pt/C/NF and V_0.09−Ni_0.91MOF/NF as cathode and anode yielded a cell voltage of 1.96 V@1000 mA cm⁻², thereby outperforming the-state-of-the-art RuO₂⁽⁺⁾||Pt/C⁽⁻⁾. Our work sheds new insight on preparing stable, efficient OER electrocatalysts and a promising method for designing various MOF-based materials.     

Hollow Chevrel‐Phase NiMo3S4 for Hydrogen Evolution in Alkaline Electrolytes

Electrochemical water splitting to generate molecular hydrogen requires catalysts that are cheap, active, and stable, particularly for alkaline electrolyzers, where the cathodic hydrogen evolution reaction is slower in base than in acid even on platinum. Herein, we describe the synthesis of new hollow Chevrel‐phase NiMo₃S₄ and its alkaline hydrogen evolution reaction (HER) performance: onset potential of ?59 mV, Tafel slope of 98 mV per decade, and exchange current density of 3.9×10^?2 mA cm^?2. This Chevrel‐phase chalcogenide also demonstrates outstanding long‐term stability under harsh HER cycling conditions. Chevrel‐phase nanomaterials show promise as efficient, low‐cost catalysts for alkaline electrolyzers.     

Facile and Large-Scale Fabrication of Sub-3 nm PtNi Nanoparticles Supported on Porous Carbon Sheet: A Bifunctional Material for the Hydrogen Evolution Reaction and Hydrogenation

Facile and large-scale preparation of materials with uniform distributions of ultrafine particles for catalysis is a challenging task, and it is even more difficult to obtain catalysts that excel in both the hydrogen evolution reaction (HER) and hydrogenation, which are the corresponding merging and splitting procedures of hydrogen, respectively. Herein, the fabrication of ultrafine bimetallic PtNi nanoparticles embedded in carbon nanosheets (CNS) by means of in situ self-polymerization and annealing is reported. This bifunctional catalyst shows excellent performance in the hydrogen evolution reaction (HER) and the hydrogenation of p-nitrophenol. Remarkably PtNi bimetallic catalyst with low metal loading (PtNi₂@CNS-600, 0.074 wt % Pt) exhibited outstanding HER activity with an overpotential as low as 68 mV at a current density of 10 mA cm⁻² with a platinum loading of only 0.612 μg_Pt cm⁻² and Tafel slope of 35.27 mV dec⁻¹ in a 0.5 m aqueous solution of H₂SO₄, which is comparable to that of the 20 % Pt/C catalyst (31 mV dec⁻¹). Moreover, it also shows superior long-term electrochemical durability for at least 30 h with negligible degradation compared with 20 % Pt/C. In addition, the material with increased loading (mPtNi₂@CNS-600, 2.88 % Pt) showed robust catalytic activity for hydrogenation of p-nitrophenol at ambient pressure and temperature. The catalytic activity towards hydrogen splitting is a circumstantial evidence that agrees with the Volmer–Tafel reaction path in the HER.     

PtNi Alloy Coated in Porous Nitrogen-Doped Carbon as Highly Efficient Catalysts for Hydrogen Evolution Reactions

The development of low platinum loading hydrogen evolution reaction (HER) catalysts with high activity and stability is of great significance to the practical application of hydrogen energy. This paper reports a simple method to synthesize a highly efficient HER catalyst through coating a highly dispersed PtNi alloy on porous nitrogen-doped carbon (MNC) derived from the zeolite imidazolate skeleton. The catalyst is characterized and analyzed by physical characterization methods, such as XRD, SEM, TEM, BET, XPS, and LSV, EIS, it, v-t, etc. The optimized sample exhibits an overpotential of only 26 mV at a current density of 10 mA cm⁻², outperforming commercial 20 wt% Pt/C (33 mV). The synthesized catalyst shows a relatively fast HER kinetics as evidenced by the small Tafel slope of 21.5 mV dec⁻¹ due to the small charge transfer resistance, the alloying effect between Pt and Ni, and the interaction between PtNi alloy and carrier.     

Rational Design and Controlled Synthesis of V-Doped Ni3S2/NixPy Heterostructured Nanosheets for the Hydrogen Evolution Reaction

Rational construction of high-efficiency and low-cost catalysts is one of the most promising ways to produce hydrogen but remains a huge challenge. Herein, interface engineering and heteroatom doping were used to synthesize V-doped sulfide/phosphide heterostructures on nickel foam (V-Ni₃S₂/Ni_xP_y/NF) by phosphating treatment at low temperature. The incorporation of V can adjust the electronic structure of Ni₃S₂, expose more active sites, and protect the 3D structure of Ni foam from damage. Meanwhile, the heterogeneous interface formed between Ni₃S₂ and Ni_xP_y can provide abundant active sites and accelerate electron transfer. As a result, the V-Ni₃S₂/Ni_xP_y/NF nanosheet catalyst exhibits outstanding activity in the hydrogen evolution reaction (HER) with an extremely low overpotential of 90 mV at a current density of 10 mA cm⁻² and stable durability in alkaline solution, which exceeds those most of the previously reported Ni-based materials. This work shows that rational design by interfacial engineering and metal-atom incorporation has a significant influence for efficient hydrogen evolution.     

A Surface-Oxide-Rich Activation Layer (SOAL) on Ni2Mo3N for a Rapid and Durable Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal–air batteries. However, the multiple steps associated with proton-coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni₂Mo₃N, is a highly active OER catalyst that outperforms the benchmark material RuO₂. Ni₂Mo₃N exhibits a current density of 10 mA cm⁻² at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface-oxide-rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen-containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.     

Magnetic Field-Enhanced Electrocatalytic Oxygen Evolution on a Mixed-Valent Cobalt-Modulated LaCoO3 Catalyst

Extensive efforts to enhance the oxygen evolution reaction (OER) catalytic performance of transition metal oxides mainly concentrate on the extrinsic morphology tailoring, lattice doping, and electrode interface optimizing. Nevertheless, little room is left for performance improvement using these methods and an obvious gap still exists compared to the precious metal catalysts. In this work, a novel “mixed-valent cobalt modulation” strategy is presented to enhance the electrocatalytic OER of perovskite LaCoO₃ (LCO) oxide. The valence transition of cobalt is realized by ethylenediamine post reduction procedure at room temperature, which further induces the variation of magnetic properties for LCO catalyst. The optimized LCO catalyst with Co²⁺/Co³⁺ of 1.98 % exhibits the best OER activity, and the overpotential at 10 mA cm⁻² current density is decreased by 170 mV compared pristine LCO. Impressively, the ferromagnetic LCO catalyst can perform magnetic OER enhancement. By application of an external magnetic field, the overpotential of LCO at 10 mA cm⁻² can be further decreased by 20 mV compared to that of under zero magnetic field, which arises from the enhanced energy states of electrons and accelerated electron transfer process driven by magnetic field. Our findings may provide a promising strategy to break the bottleneck for further enhancement of OER performance.