Unique Multi-Hetero-Interface Engineering of Fe-Doped Co-LDH@MoS2-Ni3S2 Nanoflower-Based Electrocatalyst for Overall Water-Splitting: An Experimental and Theoretical Investigation

Herein, a self-supported, robust, and noble-metal-free 3D hierarchical interface-rich Fe-doped Co-LDH@MoS2-Ni3S2/NF heterostructure electrocatalyst has been prepared through a controllable two-step hydrothermal process. The resultant electrode shows low overpotential of ~95 mV for hydrogen evolution reaction (HER), ~220 mV for the oxygen evolution reaction (OER), and the two-electrode system requires only a cell voltage of ~1.54 V at 10 mA cm-2 current density, respectively. Extensive ab initio calculations were carried out to find out the overpotential for HER, orbital interaction through the determination of electron density of states and quantification of charge transfer by Bader charge analysis. The computed overpotential matched closely with the experimental data. The superior HER performance of the tri-layer is enhanced due to the charge transfer (1.7444 e) to Fe-doped Co-LDH from Ni3S2-MoS2 hybrid. This research strategy paves an effective pathway for affordable green H2 production and future efficient non-precious bifunctional electrocatalyst design for overall water electrolysis.

Tin-doped NiFe2O4 nanoblocks grown on an iron foil for efficient and stable water splitting at large current densities

Developing low-cost and self-supported bifunctional catalysts for highly efficient water splitting devices is of great significance. Herein, different from previously reported NiFe2O4-based electrocatalysts, we have grown nano-NiFe2O4 directly onto the iron foil (IF) surface and in situ introduced Sn4+ into NiFe2O4. The resulting experimental phenomena confirmed that the as-synthesized Sn-NiFe2O4/IF can deliver large-current densities (>1000 mA cm-2) during oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes at a low overpotential. The needed overpotentials at the current density of 10 and 1000 mA cm-2 are 231 and 368 mV for OER and 57 and 439 mV for HER, respectively. Additionally, when applied for the two-electrode water splitting, the corresponding needed voltage for Sn-NiFe2O4/IF at the current density of 10 mA cm-2 was only 1.56 V, which was comparable to the commercial Pt/C-RuO2/IF electrode. Thus, the introduced Sn4+ greatly enhanced the electrocatalytic property of Sn-NiFe2O4/IF, resulting in a superior bifunctional catalyst that can be applied for large-scale hydrogen production.

Ni(OH)2-derived lamellar MoS2/Ni3S2/NF with Fe-doped heterojunction catalysts for efficient overall water splitting

Heterostructures formed by combining semiconductor materials with different band structures can provide work functions, d-band positions and electronic properties different from bulk materials and are considered as an effective strategy to improve the catalytic activity through electronic modification. In this study, an efficient MoS2/Fe-Ni3S2/NF heterojunction material was prepared by a two-step hydrothermal method. With the help of flake Ni(OH)2 synthesized in the first step, growth sites were provided for flake Ni3S2. The electronic structure of Ni3S2 was optimized by Fe doping, while the construction of the MoS2/Fe-Ni3S2 heterostructure allowed the catalyst to expose more active sites. MoS2/Fe-Ni3S2/NF exhibited a small charge transfer resistance and excellent electrocatalytic performance. At a current density of 10 mA cm-2, only low overpotentials of 148 mV and 118 mV were required for the oxygen precipitation reaction (OER) and hydrogen precipitation reaction (HER), respectively. Notably, when MoS2/Fe-Ni3S2/NF is used as the anode and cathode for overall hydrolysis, only 1.51 V is required to reach a current density of 10 mA cm-2, demonstrating its great potential for application in hydrolysis. This work provides a feasible idea for the rational construction of non-precious metal bifunctional electrocatalysts with excellent performance.

MoSe2-NiSe dual co-catalysts modified g-C3N4 for enhanced photocatalytic H2 generation

Solar energy conversion into hydrogen (H₂) energy has attracted much attention. However, the low light utilization rate and fast carrier recombination of photocatalysts extremely limit the practical application of photocatalytic H₂ production. In this paper, MoSe₂-NiSe with abundant active sites and interfacial electronic structures as dual co-catalysts were assembled on g-C₃N₄ nanosheets (NSs) vis a solvothermal reaction process. MoSe₂-NiSe/g-C₃N₄ NSs composite exhibited improved light absorption and photoelectrochemical properties. The photocatalytic H₂ production rate of MoSe₂-NiSe/g-C₃N₄ composite achieved 2379.04 μmol·h^-1·g^-1, which is 99.25, 1.44, and 3.67 times those of pure g-C₃N₄ nanosheets (23.97 μmol·h^-1·g^-1), MoSe₂/C₃N₄ (1654.57 μmol·h^-1·g^-1), and NiSe/C₃N₄ (649.08 μmol·h^-1·g^-1), respectively. The apparent quantum efficiency (AQE) value of MoSe₂-NiSe/g-C₃N₄ achieved 4.07 % under light at λ = 370 nm. The corresponding characterization and experiments proved that 2D ultrathin g-C₃N₄ NSs with a large surface area and short charge-transfer distance could facilitate light scattering and the transport of photoexcited electrons. MoSe₂-NiSe, as a dual co-catalyst, showed strong electronic synergistic interaction between the interfaces, thus improving the conductivity and promoting the electron transfer process.

Synergistic Effect of P Doping and Mo-Ni-Based Heterostructure Electrocatalyst for Overall Water Splitting

Heterostructure construction and heteroatom doping are powerful strategies for enhancing the electrolytic efficiency of electrocatalysts for overall water splitting. Herein, we present a P-doped MoS₂/Ni₃S₂ electrocatalyst on nickel foam (NF) prepared using a one-step hydrothermal method. The optimized P_[0.9mM]-MoS₂/Ni₃S₂@NF exhibits a cluster nanoflower-like morphology, which promotes the synergistic electrocatalytic effect of the heterostructures with abundant active centers, resulting in high catalytic activity for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolyte. The electrode exhibits low overpotentials and Tafel slopes for the HER and OER. In addition, the catalyst electrode used in a two-electrode system for overall water splitting requires an ultralow voltage of 1.42 V at 10 mA·cm^-2 and shows no obvious increase in current within 35 h, indicating excellent stability. Therefore, the combination of P doping and the heterostructure suggests a novel path to formulate high-performance electrocatalysts for overall water splitting.

Carbon-encapsulated Co2P/P-modified NiMoO4 hierarchical heterojunction as superior pH-universal electrocatalyst for hydrogen production

The development of hydrogen evolution reaction (HER) technology that operates stably in a wide potential of hydrogen (pH) range of electrolytes is particular important for large-scale hydrogen production. However, the rational design of low-cost and pH-universal electrocatalyst with high catalytic performance remains a huge challenge. Herein, Co₂P nanoparticles strongly coupled with P-modified NiMoO₄ nanorods are directly grown on nickel foam (NF) substrates through carbon layer encapsulation (denoted as C-Co₂P@P-NiMoO₄/NF) by hydrothermal, deposition, and phosphating processes. This novel kind of hierarchical heterojunction has abundant heterogeneous interfaces, strong electronic interactions, and optimized reaction kinetics, representing the highly-active pH-universal electrodes for HER. Remarkably, the C-Co₂P@P-NiMoO₄/NF catalyst shows excellent HER properties in acidic and basic electrolytes, where the overpotentials of 105 mV and 107 mV are applied to drive the current density of 100 mA cm^-2. In addition, a low overpotential of 177 mV at 100 mA cm^-2 along with high stability is realized in 1 M phosphate buffer solution (PBS), which is close to the state-of-the-art non-precious metal electrocatalysts. Our work not only provides a class of robust pH-universal electrocatalyst but also offers a novel way for the rational design of other heterogeneous materials bythe interface regulation strategy.

An electrochemical modification strategy to fabricate NiFeCuPt polymetallic carbon matrices on nickel foam as stable electrocatalysts for water splitting

Electrochemical modification is a mild and economical way to prepare electrocatalytic materials with abundant active sites and high atom efficiency. In this work, a stable NiFeCuPt carbon matrix deposited on nickel foam (NFFeCuPt) was fabricated with an extremely low Pt load (∼28 μg cm⁻²) using one-step electrochemical co-deposition modification, and it serves as a bifunctional catalyst for overall water splitting and achieves 100 mA cm⁻² current density at a low cell voltage of 1.54 V in acidic solution and 1.63 V in alkaline solution, respectively. In addition, a novel electrolyte was developed to stabilize the catalyst under acidic conditions, which provides inspiration for the development of highly efficient, highly stable, and cost-effective ways to synthesize electrocatalysts.

Multiple metal elements immobilized into a carbon matrix to fabricate an ultra-stable water splitting electrocatalyst by one-step electrochemical modification.

Ni2P nanowire arrays grown on Ni foam as an efficient monolithic cocatalyst for visible light dye-sensitized H2 evolution

Nanostructured H2 evolution cocatalysts are able to promote charge separation and thus enhance the efficiency of the photocatalytic H2 evolution reaction (HER). However, the nanosized cocatalyst particles are easily detached...

Electronically modulated nickel boron by CeOx doping as a highly efficient electrocatalyst towards overall water splitting

Exploiting economic, efficient and durable non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is promising, but still faces enormous challenges. Herein, the strategy of doping a metal boride with a rare earth metal oxide has been explored to develop a highly efficient bifunctional electrocatalyst. The novel electrocatalyst CeO_x-NiB consists of CeO_x-doped NiB supported on nickel foam, and was fabricated by a one-step mild electroless plating reaction. Remarkably, the CeO_x-NiB@NF electrode delivers a current density of 10 mA cm^-2 at overpotentials of only 19 mV and 274 mV for the HER and OER, respectively. Two-electrode electrolyzers with the CeO_x-NiB@NF electrode require only 1.424 V to deliver 10 mA cm^-2 for overall water splitting in 1.0 M KOH, outperforming the Pt-C/NF∥IrO₂/NF electrolyzer. Meanwhile, the electrode also has good stability (can work for 100 hours at 10 mA cm^-2) and industrial-grade current density. This work provides a new idea for the development of efficient and durable non-precious metal catalysts.

Sulfur doped FeOx nanosheet arrays supported on nickel foam for efficient alkaline seawater splitting

Developing economical, efficient and stable bifunctional catalysts for hydrogen production from seawater is of great significance for hydrogen utilization. Herein, sulfur doped iron oxide nanosheet arrays supported on nickel foam (FeO_x-Ni₃S₂@NF) are prepared by a one-pot solvothermal reaction. Owing to the high intrinsic activity of FeO_x-Ni₃S₂, the large catalytic specific surface area of nanosheet arrays and the fast charge transportation capability achieved by the self-supporting configuration, the FeO_x-Ni₃S₂@NF electrode delivers excellent catalytic performance in alkaline simulated seawater (1 M KOH + 0.5 M NaCl). Impressively, a low overpotential of 120 mV at 50 mA cm^-2 with a Tafel slope of 57 mV dec^-1 for the hydrogen evolution reaction and an overpotential of 470 mV at 200 mA cm^-2 with a Tafel slope of 62 mV dec^-1 for the oxygen evolution reaction are achieved. More importantly, the voltage is only 1.5 V at 50 mA cm^-2 for continuous overall water splitting for 100 h at 200 mA cm^-2 with negligible decay in alkaline simulated seawater with almost 100% Faraday efficiency. This work provides a simple and universal strategy to prepare highly efficient bifunctional catalytic materials, promoting the development of Earth-abundant materials to catalyse seawater splitting to produce high-purity hydrogen.

Hierarchical ultrathin layered MoS2@NiFe2O4 nanohybrids as a bifunctional catalyst for highly efficient oxygen evolution and organic pollutant degradation

Rational design and highly efficient dual-functional catalyst are still difficult to develop for electrocatalytic oxygen evolution reaction and degradation of RhB dye pollutant. Herein, we report a highly efficient "bandgap matching and interfacial coupling" strategy to synthesize nano-assembled ultrathin layered MoS₂@NiFe₂O₄ (MS@NiFeO) bifunctional catalyst constructed by the hydrothermal route and subsequently amine-hydrolysis. The OER performance of the prepared MS@NiFeO catalyst delivers a low overpotential of 290 mV at 10 mA/cm² and Tafel slope is 69.2 mV dec^-1 in an alkaline solution. In addition, the nano-assembled ultrathin layered structure of MS@NiFeO showed a highly efficient (96.37%) RhB dye degradation performance than that of MoS₂ nanosheets and NiFe₂O₄ nanostructures. Unique nanostructure of ultrathin layered MS@NiFeO with suitable band matching, interfacial charge transfer, high surface area and more active sites favored for the enhancement of the catalytic activity. This work presents an unpretentious construction and low-cost production strategy to synthesize bifunctional hybrid catalyst for oxygen evolution reaction as well as degradation of organic pollutant with superior efficiency and longer stability.

Superior Electrocatalytic Activity of MoS2-Graphene as Superlattice

Evidence by selected area diffraction patterns shows the successful preparation of large area (cm × cm) MoS2/graphene heterojunctions in coincidence of the MoS2 and graphene hexagons (superlattice). The electrodes of MoS2/graphene in superlattice configuration show improved catalytic activity for H2 and O2 evolution with smaller overpotential of +0.34 V for the overall water splitting when compared with analogous MoS2/graphene heterojunction with random stacking.

Recent advances in pristine tri-metallic metal-organic frameworks toward the oxygen evolution reaction

Pristine metal-organic frameworks (MOFs) have received much attention in recent years due to their high specific surface areas, large porosity, excellent pore size distributions, flexible structure, and remarkable catalytic properties. The design of functional MOFs that can function as efficient HER and OER catalysts is significant in solving the energy crisis but remains a big challenge. Tri-metallic metal-organic frameworks show a good application prospect in water oxidation. In this review, we are going to focus on the latest progress and future trends in the development of pristine trimetallic MOFs with respect to the OER. The synergistic effect between multi-metal active sites is effective at improving the intrinsic activity of MOFs toward the OER. By summarizing the synthesis method of tri-metallic MOFs and observing their performance toward the oxygen evolution reaction, we hope that this review will trigger new developments in coordination chemistry, electrochemistry, nanomaterials and energy materials.

Synthesis of Ni3S2 catalysts using various sulphur sources and their HER and OER performances

The performance of nickel sulfur catalyst for HER and OER was affected by its structure resulted from the different sulfur sources.