Flower-like NiCo2S4/NiFeP/NF composite material as an effective electrocatalyst with high overall water splitting performance

CeO2-Modified Ni2P/Fe2P as Efficient Bifunctional Electrocatalyst for Water Splitting

Developing efficient bifunctional electrocatalysts with excellent stability at high current densities for overall water splitting is a challenging yet essential objective. However, transition metal phosphides encounter issues such as poor dispersibility, low specific surface area, and limited electronic conductivity, which hinder the achievement of satisfactory performance. Therefore, this study presents the highly efficient bifunctional electrocatalyst of CeO2-modified NiFe phosphide on nickel foam (CeO2/Ni2P/Fe2P/NF). Ni2P/Fe2P coupled with CeO2 was deposited on nickel foam through hydrothermal synthesis and sequential calcination processes. The electrocatalytic performance of the catalyst was evaluated in an alkaline solution, and it exhibited an HER overpotential of 87 mV at the current density of 10 mA cm-2 and an OER overpotential of 228 mV at the current density of 150 mA cm-2. Furthermore, the catalyst demonstrated good stability, with a retention rate of 91.2% for the HER and 97.3% for the OER after 160 h of stability tests. The excellent electrochemical performance can be attributed to the following factors: (1) The interface between Ni2P/Fe2P and CeO2 facilitates electron transfer and reactant adsorption, thereby improving catalytic activity. (2) The three-dimensional porous structure of nickel foam provides an ideal substrate for the uniform distribution of Ni2P, Fe2P, and CeO2 nanoparticles, while its high conductivity facilitates electron transport. (3) The incorporation of larger Ce3⁺ ions in place of smaller Fe3⁺ ions leads to lattice distortion and an increase in defects within the NiFe-layered double hydroxide structure, significantly enhancing its catalytic performance. This research finding offers an effective strategy for the design and synthesis of low-cost, high-potential catalysts for water electrolysis.

Polyoxometalate superlattices derived bimetallic sulfides to accelerate acidic and alkaline hydrogen evolution reaction

Over the years, polyoxometalates (POMs) have been advocated as one of the most promising classes of molecular preassembly platform for the fabrication of highly efficient metal sulfide electrocatalysts. However, designing POMs-derived metal sulfides with high intrinsic activity, good site accessibility and structural stability for both acidic and alkaline hydrogen evolution reaction (HER) remains a great challenge because of the self-aggregation and random distribution of traditional POM precursors. Herein, we have designed a bimetallic sulfide eventually encapsulated by C3N4 walls (CoMoS@CN) for efficient HER based on a simple hydrothermal and subsequent high-temperature vulcanization using the well-designed POM superlattice assembly as precursor. The organized superlattice structure with long-range ordered arrangements of POM units provide chance to prevent the agglomeration of metal sites. The in-situ formed exterior C3N4 protective wall can accelerate the electron transfer and protect catalyst from chemical corrosion in different electrolyte. The merits combining with a large specific surface area enable CoMoS@CN with remarked HER performance of low overpotentials of 164 and 95 mV at 10 mA cm-2 in acidic and alkaline conditions. Such results are better than that of p-CoMoS@CN synthesized by pyrolysis of the corresponding physical mixtures and other comparative single metal sulfides.

Synergistic dual built-in electric fields in 1T-MoS2/Ni3S2/LDH for efficient electrocatalytic overall water splitting reactions

Designing cost-effective electrocatalysts for water decomposition is crucial for achieving environmental-friendly hydrogen production. A transition metal sulfide/hydroxide electrocatalyst (1T-MoS2/Ni3S2/LDH) with double heterogeneous interfaces was developed through a two-step hydrothermal assisted electrodeposition method. The presence of the two built-in electric fields not only accelerated the charge transfer at the interface, but also enhanced the adsorption of the reactants and intermediate groups, and therefore improved the reaction rate and overall catalytic performance. The results suggest that the 1T-MoS2/Ni3S2/LDH catalysts display exceptional electrocatalytic reactivity. Under alkaline conditions, the overpotential of the electrocatalyst was 187 (η50) mV for OER and 104 (η10) mV for HER. Furthermore, the two-electrode system assembled by the electrocatalyst needs only a voltage of 1.55 V to deliver a current density of 10 mA cm-2. Our result provides a simple and effective methodical approach to the design of dual heterogeneous interfacial electrocatalysts.

Ultrasmall Ru nanoparticles-decorated nickel/nickel oxide three phase heterojunctions to boost alkaline hydrogen evolution

The rational design and optimization of heterogeneous interface for low loading noble metal HER eletrocatalysts to facilitate the upscaling of alkaline water/seawater electrolysis is highly challenging. Herein, we present a facile deep corrosion strategy induced by NaBH4 to precisely construct an ultrasmall Ru nanoparticle-decorated Ni/NiO hybrid (r-Ru-Ni/NiO) with highly dispersed triple-phase heterostructures. Remarkably, it exhibits superior activity with only 53 mV and 70 mV at 100 mA cm-2 for hydrogen evolution reaction (HER) in alkaline water and seawater, respectively, surpassing the performance of Pt/C (109.7 mV, 100 mA cm-2, 1 M KOH). It is attributed to collaborative optimization of electroactive interfaces between well-distributed ultrasmall Ru nanoparticles and Ni/NiO hybrid. Moreover, the assembled r-Ru-Ni/NiO system just require 2.03 V at 1000 mA cm-2 in anion exchange membrane (AEM) electrolyzer, outperforming a RuO2/NF || Pt/C system, while exhibiting outstanding stability at high current densities. This study offers a logical design for accurate construction of interfacial engineering, showing promise for large-scale hydrogen production via electrochemical water splitting.

Hierarchical Sea Urchin-like Fe-doped Heazlewoodite for High-Efficient Oxygen Evolution

Electrochemical water-splitting to produce hydrogen is potential to substitute the traditional industrial coal gasification, but the oxygen evolution kinetics at the anode remains sluggish. In this paper, sea urchin-like Fe doped Ni3S2 catalyst growing on nickel foam (NF) substrate is constructed via a simple two-step strategy, including surface iron activation and post sulfuration process. The NF-Fe-Ni3S2 obtains at temperature of 130 °C (NF-Fe-Ni3S2-130) features nanoneedle-like arrays which are vertically grown on the particles to form sea urchin-like morphology, features high electrochemical surface area. As oxygen evolution catalyst, NF-Fe-Ni3S2-130 exhibits excellent oxygen evolution activities, fast reaction kinetics, and superior reaction stability. The excellent OER performance of sea urchin-like NF-Fe-Ni3S2-130 is mainly ascribed to the high-vertically dispersive of nanoneedles and the existing Fe dopants, which obviously improved the reaction kinetics and the intrinsic catalytic properties. The simple preparation strategy is conducive to establish high-electrochemical-interface catalysts, which shows great potential in renewable energy conversion.

Design and multilevel regulation of transition metal phosphides for efficient and industrial water electrolysis

Renewable energy electrolysis of water to produce hydrogen is an effective measure to break the energy dilemma. However, achieving activity and stability at a high current density is still a key problem in water electrolyzers. Transition metal phosphides (TMPs), with high activity and relative inexpensiveness, have become excellent candidates for the production of highly pure green hydrogen for industrial applications. In this mini-review, multilevel regulation strategies including nanoscale control, surface composition and interface structure design of high-performance TMPs for hydrogen evolution are systematically summarized. On this basis, in order to achieve large-scale hydrogen production in industry, the hydrogen evolution performance and stability of TMPs at a high current density are also discussed. Peculiarly, the practical application and requirements in proton exchange membrane (PEM) or anion exchange membrane (AEM) electrolyzers can guide the advanced design of regulatory strategies of TMPs for green hydrogen production from renewable energy. Finally, the challenges and prospects in the future development trend of TMPs for efficient and industrial water electrolysis are given.

Mo-Ni-based Heterojunction with Fine-customized d-Band Centers for Hydrogen Production Coupled with Benzylamine Electrooxidation in Low Alkaline Medium

Benzylamine electrooxidation reaction (BAOR) is a promising route to produce value-added, easy-separated benzonitrile, and effectively hoist H2 production. However, achieving excellent performance in low alkaline medium is a huge challenge. The performance is intimately correlated with effective coupling of HER and BAOR, which can be achieved by manipulating the d-electron structure of catalyst to regulate the active species from water. Herein, we constructed a biphasic Mo0.8 Ni0.2 N-Ni3 N heterojunction for enhanced bifunctional performance toward HER coupled with BAOR by customizing the d-band centers. Experimental and theoretical calculations indicate that charge transfer in the heterojunction causes the upshift of the d-band centers, which one side facilitates to decrease water activation energy and optimize H* adsorption on Mo0.8 Ni0.2 N for promoting HER activity, the other side favors to more easily produce and adsorb OH* from water for forming NiOOH on Ni3 N and optimizing adsorption energy of benzylamine, thus catalyzing BAOR effectively. Accordingly, it shows an industrial current density of 220 mA cm-2 at 1.59 V and high Faradaic efficiencies (>99 %) for H2 production and converting benzylamine to benzonitrile in 0.1 M KOH/0.5 M Na2 SO4 . This work guides the design of excellent bifunctional electrocatalysts for the scalable production of green hydrogen and value-added products.

Rational Design of Goethite-Sulfide Nanowire Heterojunctions for High Current Density Water Splitting

The preparation of efficient and stable bifunctional electrocatalysts for electrochemical overall water splitting (OWS) to scale up commercial hydrogen production remains a great challenge. Here, we synthesized heterojunction structures consisting of Co₉S₈/Ni₃S₂ nanowire arrays and amorphous goethite (FeOOH, α-phase) particles as efficient OWS catalysts using an interface engineering strategy. The interfacial charge inhomogeneity caused by the heterojunction contact leads to the generation of a built-in electric field, which makes the electron-deficient FeOOH and electron-rich Co₉S₈/Ni₃S₂ favorable for hydrogen/oxygen evolution reaction, respectively, thus ensuring the excellent activity of FeOOH/Co₉S₈/Ni₃S₂ as a bifunctional catalyst. FeOOH/Co₉S₈/Ni₃S₂ exhibits impressive catalytic activity for the oxygen evolution reaction, achieving an ultralarge current density of 1000 mA cm^-2 needed as low as 265 mV overpotential, and its stability was tested up to 1440 h. Furthermore, an excellent OWS output (1.55 V to generate 10 mA cm^-2) is achieved by the bifunctional FeOOH/Co₉S₈/Ni₃S₂ catalysts.

Hybrid Heterostructure Ni3 N|NiFeP/FF Self-Supporting Electrode for High-Current-Density Alkaline Water Electrolysis

Exploring earth-abundant and efficient electrocatalysts for oxygen evolution reaction (OER) is an urgent need and significant to water electrolysis. Although great achievements have been made, it is still challenging to achieve industrial current density and stability. Herein, a hybrid heterostructure electrode based on Ni₃ N and NiFeP over Fe foam substrate (Ni₃ N|NiFeP/FF) is reported, along with 3D-interconnected hierarchical porous architecture, achieving the low overpotentials of 287, 178, and 290 mV at 500 mA cm^-2 in 1 m KOH, 30 wt% KOH, and alkaline simulated seawater, respectively, with excellent durability at 800 mA cm^-2 over 120 h, which can satisfy the requirements of industrial water electrolysis. Here, the hybrid heterostructure can ensure the low energy barrier of the catalytic active sites, the 3D-interconnected hierarchical porous architecture can facilitate the fast mass/ions/electrons transformation, which contributes together to boost the superb water splitting performance. Furthermore, the COMSOL simulations confirm the multiple merits of the designed electrode during the water electrocatalysis. The present work provides a new strategy in the design and engineering of high-performance electrodes for industrial water electrolysis.

Crystalline-Amorphous Interface Coupling of Ni3S2/NiPx/NF with Enhanced Activity and Stability for Electrocatalytic Oxygen Evolution

The rational design of highly efficient and stable electrocatalysts for the oxygen evolution reaction (OER) is an urgent need but remains challenging for various sustainable energy systems. How to adjust the atomic structure and electronic structure of the active center is a key bottleneck problem. Accelerating the electron transfer process and the deep self-reconstruction of active sites could be a cost-effective strategy toward electrocatalytic OER catalyst development. Here, a crystalline-amorphous (c-a) coupled Ni₃S₂/NiP_x electrocatalyst self-supported on nickel foam with an intimate interface was developed via a feasible solvothermal-electrochemistry method. The coupling interface of the crystalline structure with high conductivity and amorphous structure with numerous potential active sites could regulate the electronic structure and optimize the adsorption/desorption of O-containing species, ultimately resulting in high OER catalytic performance. The obtained Ni₃S₂/NiP_x/NF presents a low OER overpotential of 265 mV to obtain 10 mA·cm^-2 and a small Tafel slope of 51.6 mV·dec^-1. Also, the catalyst with the coupled interface exhibited significantly enhanced long-term stability compared to the other two catalysts, with <5% decay in OER activity over 20 h of continuous operation, while that of Ni₃S₂/NF and NiP_x/NF decreased by about 30 and 50%, respectively. This study provides inspiration for other energy conversion reactions in optimizing the performance of catalysts by coupling crystalline-amorphous structures.

Rational design of S-scheme AgI/ZrTiO4-x heterojunctions for remarkably boosted norfloxacin degradation

Emerging S-scheme heterojunction photocatalysts endowed with efficient charge separation and strong redox capacity have stimulated wide interests in dealing with environmental issues nowadays. In this work, we firstly fabricated the oxygen vacancy modified ZrTiO_4-x nanocrystals, which was further combined with AgI to build the defective S-scheme AgI/ZrTiO_4-x heterojunctions for visible-light photocatalytic norfloxacin degradation. The synthesized ZrTiO_4-x nanocrystals and AgI/ZrTiO_4-x heterojunctions displayed remarkably boosted norfloxacin degradation performance under visible-light irradiation. The reaction rate constant of the optimized AgI/ZrTiO_4-x-5% heterojunction is as high as 0.01419 min^-1, which is approximately 43.35 times that of AgI and 7.93 times that of ZrTiO_4-x nanocrystals, and far superior to those of commercial TiO₂ and commercial ZrO₂. The high-performance photocatalytic norfloxacin degradation could be mainly attributed to the formation of S-scheme charge transfer pathways and oxygen vacancy defects. More significantly, AgI/ZrTiO_4-x could also realize the effective photo-decomposition of other emerging pollutants. Finally, the visible-light photocatalytic performance and photocatalysis mechanism were investigated.

Facile synthesis of ZIF-67 derived dodecahedral C/NiCO2S4 with broadband microwave absorption performance

The increasing hazard of electromagnetic radiation prompts people to pursue absorbing materials with better performance. However, absorbing materials with a single loss mechanism usually is unable to obtain better absorbing performance due to low impedance matching or high filling ratio. Therefore, this work proposes a C/NiCo₂S₄ (CNCS) material with both dielectric loss/magnetic loss to achieve efficient absorption of electromagnetic waves. The simple preparation of CNCS materials was achieved through the etching of the ZIF-67 template by nickel nitrate and the subsequent hydrothermal vulcanization process. Its unique prismatic dodecahedron hollow structure promotes multiple scattering of electromagnetic waves. The attachment of the magnetic NiCo₂S₄ particles on the surface of the carbon template further promotes the interface polarization and dipole polarization, which is equivalent to the formation of a resistance-rich microcircuit and enhances the effect of the conductance loss on electromagnetic waves. At 2-18 GHz, the CNCS-2 with 30% paraffin addition achieves an effective bandwidth of 5.54 GHz at a matching thickness of 1.7 mm, and has a maximum reflection loss of -36.44 dB at 1.5 mm. By adjusting the thickness of the material matching layer (1-3 mm), an effective bandwidth of up to 13.48 GHz can be achieved, perfectly covering the X-band and Ku-band. Based on the simple preparation process of the material, the special hollow structure and the multiple loss mechanisms for electromagnetic waves, we believe that CNCS can become a strong competitor for high-efficiency broadband absorbers.