Overall Water Splitting Research Articles

Efficient Hydrogen Evolution on Antiperovskite CuNCo3 Nanowires by Mo Incorporation and its Trifunctionality for Zn Air Batteries and Overall Water Splitting.

The current development of single electrocatalyst with multifunctional applications in overall water splitting (OWS) and zinc-air batteries (ZABs) is crucial for sustainable energy conversion and storage systems. However, exploring new and efficient low-cost trifunctional electrocatalysts is still a significant challenge. Herein, the antiperovskite CuNCo3 prototype, that is proved to be highly efficient in oxygen evolution reaction but severe hydrogen evolution reaction (HER) performance, is endowed with optimum HER catalytic properties by in situ-derived interfacial engineering via incorporation of molybdenum (Mo). The as-prepared Mo-CuNCo3 @CoN nanowires achieve a low HER overpotential of 58 mV@10mA cm-2 , which is significantly higher than the pristine CuNCo3 . The assembled CuNCo3 -antiperovskite-based OWS not only entails a low overall voltage of 1.56 V@10mA cm-2 , comparable to most recently reported metal-nitride-based OWS, but also exhibits excellent ZAB cyclic stability up to 310h, specific capacity of 819.2 mAh g-1 , and maximum power density of 102mW cm-2 . The as-designed antiperovskite-based ZAB could self-power the OWS system generating a high hydrogen rate, and creating opportunity for developing integrated portable multifunctional energy devices.

Interfacial and Electronic Modulation of W Bridging Heterostructure Between WS2 and Cobalt-Based Compounds for Efficient Overall Water Splitting.

The development of high performance electrocatalysts for effective hydrogen production is urgently needed. Herein, three hybrid catalysts formed by WS2 and Co-based metal-organic frameworks (MOFs) derivatives are constructed, in which the small amount of W in the MOFs derivatives acts as a bridge to provide the charge transfer channel and enhance the stability. In addition, the effects of the surface charge distribution on the catalytic performance are fully investigated. Due to the optimal interfacial electron coupling and rearrangement as well as its unique porous morphology, WS2 @W-CoPx exhibits superior bifunctional performance in alkaline media with low overpotentials in hydrogen evolution reaction (HER) (62mV at 10mA cm-2 ) and oxygen evolution reaction (OER) (278mV at 100mA cm-2 ). For overall water splitting (OWS), WS2 @W-CoPx only requires a cell voltage of 1.78V at 50mA cm-2 and maintains good stability within 72 h. Density functional theory calculations verify that the combination of W-CoPx with WS2 can effectively enhance the activity of OER and HER with weakened OH (or O) adsorption and enhanced H atom adsorption. This work provides a feasible idea for the design and practical application of WS2 or phosphide-based catalysts in OWS.

Lattice Strain and Charge Redistribution of Pt Cluster/Ir Metallene Heterostructure for Ethylene Glycol to Glycolic Acid Conversion Coupled with Hydrogen Production.

Upgrading overall water splitting (OWS) system and developing high-performance electrocatalysts is an attractive way to the improve efficiency and reduce the consumption of hydrogen (H2 ) production from electrolyzed water. Here, a Pt cluster/Ir metallene heterojunction structure (Pt/Ir hetero-metallene) with a unique Pt/Ir interface is reported for the conversion of ethylene glycol (EG) to glycolic acid (GA) coupled with H2 production. With the assistance of ethylene glycol oxidation (EGOR), the Pt/Ir||Pt/Ir hetero-metallene two-electrode water electrolysis system exhibits a lower cell voltage of 0.36V at 10mA cm-2 . Furthermore, the Faradaic efficiency of EG to GA is as high as 87%. The excellent performance of this new heterostructure arise from the charge redistribution and strain effects induced by Pt-Ir interactions between the heterogeneous interfaces, as well as the larger specific surface area and more active sites due to the metallene structure.

In situ fabrication of sporoid-like flexible electrodes via Fe-regulated electron density for highly efficient and ultra-stable overall seawater splitting

Construction of ultra-stable, flexible, efficient and economical catalytic electrodes is of great significance for the seawater electrolysis for hydrogen production. This work is grounded in a one-step mild electroless plating method to construct industrial-grade super-stable overall water splitting (OWS) catalytic electrodes (Fe1-Ni1P@GF) by growing loose and porous spore-like Fe1-Ni1P conductive catalysts in situ on flexible glass fibre (GF) insulating substrates with precise elemental regulation. Cost-effective Fe regulation boosts the electronic conductivity and charge transfer ability to achieve the construction of high intrinsic activity and strong electron density electrodes. Fe1-Ni1P@GF exhibits remarkable catalytic performance in hydrogen and oxygen evolution reaction (HER and OER), providing current densities of 10 mA cm−2 for HER and 100 mA cm−2 for OER at overpotentials of 51 and 216 mV, respectively. Moreover, it achieves 10 mA cm−2 at 1.42 V for OWS, and exhibits stable operation for over 1440 h at 1000 mA cm−2 in quasi-industrial environment of 6.0 M KOH + 0.5 M NaCl, without any performance degradation. This strategy enables the preparation of universally applicable P-based electrodes (ternary, quaternary, etc.) and large-area flexible electrodes (paper or cotton), significantly expands the practicality of the electrodes and demonstrating promising potential for industrial applications.

Realizing Photocatalytic Overall Water Splitting by Modulating the Thickness-Induced Reaction Energy Barrier of Fluorenone-Based Covalent Organic Frameworks.

Direct photocatalytic hydrogen and oxygen evolution from water splitting is an attractive approach for producing chemical fuels. In this work, a novel fluorenone-based covalent organic framework (COF-SCAU-2) is successfully exfoliated into ultrathin three-layer nanosheets (UCOF-SCAU-2) for photocatalytic overall water splitting (OWS) under visible light. The ultrathin structures of UCOF-SCAU-2 greatly enhance carrier separation, utilization efficiency, and the exposure of active surface sites. Surprisingly, UCOF-SCAU-2 exhibits efficient photocatalytic OWS performance, with hydrogen and oxygen evolution rates reaching 0.046 and 0.021 mmol h-1 g-1 , respectively,under visible-light irradiation, whereas bulk COF-SCAU-2 shows no activity for photocatalytic OWS. Charge-carrier kinetic analysis and DFT calculations confirm that reducing the thickness of the COF nanosheets increasesthe number ofaccessible active sites, reduces the distance for charge migration, prolongs the lifetimes of photogenerated carriers, and decreases the Gibbs free energy of the rate-limiting step compared to nonexfoliated COFs. This work offers new insights into the effect of the layer thickness of COFs on photocatalytic OWS.

One-pot synthesized Li, V co-doped Ni3S2 nanorod arrays as a bifunctional electrocatalyst for industrialization-facile hydrogen production via alkaline exchange membrane water electrolysis

The design of a bifunctional electrocatalyst with excellent performance in water electrolysis under high current densities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with non-noble metals-based catalysts has been challenging. A novel bifunctional electrocatalyst constituted as the lithium and vanadium (Li, V) co-doped nickel sulfide (Ni3S2) nanorod arrays (LVN-0.1) is designed and investigated to take this challenge. The overall water splitting (OWS) electrolyzer constructed with our LVN-0.1 catalyst exhibited low cell voltages of 1.44 and 1.95 V to achieve 10 and 1000 mA/cm2, respectively, with excellent durability, which is almost the best Ni3S2-based electrocatalyst reported to date. The practical scale-up LVN-0.1 stack cell of 2 × 2 cm2 required 1.92 and 2.02 V to achieve high current densities at the industrial level at 500 and 1000 mA/cm2, respectively. Notably, our alkaline stack cell achieved a cell-efficiency of 61.9% and cell stability for 200 h at 1000 mA/cm2, while commercial alkaline cells have kept operating below 500 mA/cm2 to avoid the drop-off of binder-coated electrocatalysts. This study provides a facile way to design bifunctional electrocatalysts for realizing high efficient and stable hydrogen production by alkaline water splitting.

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.

Mo-doped Ni3S4 nanosheets grown on carbonized wood as highly efficient and durable electrocatalysts for water splitting

Rational design and fabrication of nonprecious metal-based electrocatalysts with high activity and excellent stability for overall water splitting (OWS) is still a grand challenge. Here we report a novel electrocatalyst constructed by incorporating molybdenum into the Ni3S4 lattices grown on carbonized wood (denoted as Mo-Ni3S4/CW). Experimental results and density functional theory (DFT)-based calculations demonstrate that lattice expansion of Ni3S4 caused by Mo doping optimizes adsorption energy of hydrogen/oxygen species and regulates local charge density of active sites, which promote the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Also, a nickel (oxy)hydroxide (Ni-OOH) layer generated via surface reconstruction of Ni3S4 nanosheets improves the intrinsic activity for OER. Moreover, the 3D low-tortuosity porous CW substrate increases the exposure of active specific surface, accelerates the rates of electron transfer, electrolyte diffusion, and gas products escaping. Accordingly, an optimized electrocatalyst (Mo-Ni3S4/CW-0.4) exhibits ultralow overpotentials of 17 and 240 mV for HER and OER at 10 mA cm−2, respectively. Besides, an electrolyzer composed of Mo-Ni3S4/CW-0.4 electrodes as both the anode and cathode shows a low cell voltage of 1.46 V at 10 mA cm−2 while maintaining superior durability over 50 h for OWS. Further, it requires only 0.19 V to achieve 10 mA cm−2 for hydrazine oxidation-assisted water electrolysis, indicating highly attractive potential for economical hydrogen production coupling with pollutants treatment.

In Situ Synthesis of Chemically Bonded 2D/2D Covalent Organic Frameworks/O-Vacancy WO3 Z-Scheme Heterostructure for Photocatalytic Overall Water Splitting.

Covalent organic frameworks (COFs) have shown great promise for photocatalytic hydrogen evolution via water splitting. However, the four-electron oxidation of water remains elusive toward oxygen evolution. Enabling this water oxidation pathway is critical to improve the yield and maximize atom utilization efficiency. A Z-scheme heterojunction is proposed for overcoming fundamental issues in COF-based photocatalytic overall water splitting (OWS), such as inefficient light absorption, charge recombination, and poor water oxidation ability. It is shown that the construction of a novel 2D/2D Z-scheme heterojunction through in situ growth of COFs on the O-vacancy WO3 nanosheets (Ov-WO3 ) via the WOC chemical bond can remarkably promote photocatalytic OWS. Benefiting from the synergistic effect between the enhanced built-in electric field by the interfacial WOC bond, the strong water oxidation ability of Ov-WO3, and the ultrathin structure of TSCOF, both separation and utilization efficiency of photogenerated electron-hole pairs can be significantly enhanced. An impressive photocatalytic hydrogen evolution half-rection rate of 593mmol h-1 g-1 and overall water splitting rate of 146 (hydrogen) and 68 (oxygen) µmol h-1 g-1 are achieved on the COF-WO3 (TSCOFW) composite. This 2D/2D Z-scheme heterojunction with two-step excitation and precisely cascaded charge-transfer pathway makes it responsible for the efficient solar-driven OWS without a sacrificial agent.

750 nm visible light-driven overall water splitting to H2 and O2 over Boron-doped Zn3As2 photocatalyst

Visible and NIR light count about 95% of solar irradiation on the earth, which has not well utilized in photocatalytic overall water splitting (OWS) since the available catalysts under visible-NIR irradiation are either low-effective or unstable. This obstacle may be overcome by the development of a new semiconductor catalyst with well absorption in the visible region and excellent charge transfer properties and photocatalytic activities for OWS. Here, we report a new catalyst B-doped Zn3As2 (B-Zn3As2) catalyst with well light response up to 750 nm, and achieves a record apparent quantum efficiency (AQE) of 4.09% at 750 nm for photocatalytic OWS without noble metal and sacrificial reagent addition. 14 times higher HER performance than bare Zn3As2, excellent light absorption in the visible region, and the excellent separation of photogenerated charges were obtained over B-Zn3As2. B-doping on Zn3As2 leads to easier H adsorption and desorption and thereafter results in promoted surface dynamics for OWS.

Manifolding surface sites of compositional CoPd alloys via pulsed laser for hydrazine oxidation-assisted energy-saving electrolyzer: Activity origin and mechanism discovery

Energy-driven overall water splitting (OWS) for renewable hydrogen generation is critical for carbon neutrality. However, the OWS electrolyzer efficiency is significantly affected by the kinetically sluggish anodic oxygen evolution reaction (OER). An efficient approach is proposed to promote energy-saving hydrogen production by using a composition-dependent multifunctional CoPd alloy via pulsed laser ablation in liquids, where the OER is replaced with the hydrazine oxidation reaction (HzOR). The CoPd alloy improves N2H4 chemisorption onto the surface via dative bonding between the lone pair electrons of N and the empty 5 s orbital of Pd and 3d of low spin Co. The optimal Co1Pd9 alloy sample demonstrates excellent hydrogen evolution reaction and HzOR with the lowest overpotentials of 0.224 and 0.329 V at 10 mA/cm2 in 1.0-M KOH and 1.0-M KOH/0.5-M N2H4, correspondingly. An in situ/operando Raman study reveals that metal active site and structural transformation occurred during the oxidation (M*-O) and reduction (M*-H) reactions under an alkaline medium. Besides, the overall hydrazine splitting performed using the Co1Pd9 ‖ Co1Pd9 electrolyzer requires a cell voltage of ∼ 0.228 V only at 10 mA/cm2 with remarkable electrochemical and structural stability over 10 h, which is significantly lower than that of the traditional OWS electrolyzer (∼1.837 V). This study demonstrates the practical use of CoPd alloys in direct N2H4 fuel cells to produce both H2 fuel and electrical energy.

An ultrafast H* migration channel and oxidation activity driven by multifunctional Co atoms on twin Co0.01Mn0.29Cd0.7S homojunction surface for photocatalytic overall water splitting

Low kinetics of water dissociation, unfavorable hydrogen adsorption, and high water-oxidation barriers restrict the photocatalytic overall water splitting (OWS) efficiency over sulfides. Herein, multifunctional Co atoms are doped on the twin Mn0.3Cd0.7S homojunction surface for efficient photocatalytic hydrogen (H2) and oxygen (O2) evolution. An ultrafast hydrogen atom (H*) migration channel bridging the water dissociation/H2 evolution step is established between cubic-S and hexagonal-S sites by introducing Co atoms, facilitating the HER kinetics. Specifically, Co atoms regulate the electron properties of neighboring S atoms and weaken their charge accumulation, which promotes cubic-S sites to capture sufficient H* from the water dissociation zone and accelerates hexagonal-S sites to release H2 through the H* migration channel. Meanwhile, unsaturated Co atoms on the cubic phase as oxygen evolution reaction (OER) sites promote water deprotonation and optimize the kinetics of the rate-determining step to form OOH* intermediate, enhancing water oxidation activity. Co atoms strengthen the internal electric field of the homojunction and local polarized electric field by increasing the work function difference between the two phases and introducing the high spin polarization, inhibiting the bulk and surface recombination of photogenerated carriers. The Co0.01Mn0.29Cd0.7S exhibits visible-light-driven H2 and O2 evolution rates of 443.12 and 219.67 μmol g−1 h−1, about 50 times that of the Mn0.3Cd0.7S. This work provides some guidance for the design of homojunction photocatalysts with efficient OWS performance.

Dynamic Electrodeposition on Bubbles: An Effective Strategy toward Porous Electrocatalysts for Green Hydrogen Cycling.

ConspectusClosed-loop cycling of green hydrogen is a promising alternative to the current hydrocarbon economy for mitigating the energy crisis and environmental pollution. It stores energy from renewable energy sources like solar, wind, and hydropower into the chemical bond of dihydrogen (H2) via (photo)electrochemical water splitting, and then the stored energy can be released on demand through the reverse reactions in H2-O2 fuel cells. The sluggish kinetics of the involved half-reactions like hydrogen evolution reaction (HER), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), and oxygen reduction reaction (ORR) limit its realization. Moreover, considering the local gas-liquid-solid triphase microenvironments during H2 generation and utilization, rapid mass transport and gas diffusion are critical as well. Accordingly, developing cost-effective and active electrocatalysts featuring three-dimensional hierarchically porous structures are highly desirable to promote the energy conversion efficiency. Traditionally, the synthetic approaches of porous materials include soft/hard templating, sol-gel, 3D printing, dealloying, and freeze-drying, which often need tedious procedures, high temperature, expensive equipment, and/or harsh physiochemical conditions. In contrast, dynamic electrodeposition on bubbles using the in situ formed bubbles as templates can be conducted at ambient conditions with an electrochemical workstation. Moreover, the whole preparation process can be finished within minutes/hours, and the resulting porous materials can be employed as catalytic electrodes directly, avoiding the use of polymeric binders like Nafion and the consequent issues like limited catalyst loading, reduced conductivity, and inhibited mass transport.In this Account, we summarize our contributions to the dynamic electrodeposition on bubbles toward advanced porous electrocatalysts for green hydrogen cycling. These dynamic electrosynthesis strategies include potentiodynamic electrodeposition that linearly scans the applied potentials, galvanostatic electrodeposition that fixes the applied currents, and electroshock which quickly switches the applied potentials. The resulting porous electrocatalysts range from transition metals to alloys, nitrides, sulfides, phosphides, and their hybrids. We mainly focus on the 3D porosity design of the electrocatalysts by tuning the electrosynthesis parameters to tailor the behaviors of bubble co-generation and thus the reaction interface. Then, their electrocatalytic applications for HER, OER, overall water splitting (OWS), biomass oxidation (to replace OER), and HOR are introduced, with a special emphasis on the porosity-promoted activity. Finally, the remaining challenges and future perspective are also discussed. We hope this Account will encourage more efforts into this attractive research field of dynamic electrodeposition on bubbles for various energy catalytic reactions like carbon dioxide/monoxide reduction, nitrate reduction, methane oxidation, chlorine evolution, and others.

Mechanistic insights into ZIF-67-derived Ir-doped Co3O4@N-doped carbon hybrids as efficient electrocatalysts for overall water splitting using in situ Raman spectroscopy

Developing highly active bifunctional electrocatalytic nanomaterials toward overall water splitting (OWS) is required to address the energy crisis via manufacturing clean hydrogen (H2) fuel. Herein, we demonstrate the rational synthesis of a bifunctional electrocatalyst based on an Ir-doped Co3O4-anchored N-doped carbon (Ir-Co3O4@NC) hybrid for the OWS. Zeolitic imidazolate framework-67 (ZIF-67) polyhedrons was synthesized by a novel pulsed laser ablation in liquid (PLAL) technique. Subsequently, ZIF-67 polyhedrons were employed as a self-template and cobalt precursor to develop the Ir-Co3O4@NC hybrid using ion exchange and calcination approaches. Owing to the availability of more active metal sites, effective charge transport, huge surface area, and good conductivity, the Ir-Co3O4@NC hybrid displayed excellent bifunctional catalytic activity toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The in situ Raman spectroscopy results demonstrated the creation of Co(OH)2 species for the HER and CoOOH and Ir-O species for the OER as active intermediates at the electrode–electrolyte interfaces. As a result, the fabricated alkaline water electrolyzer with the Ir-Co3O4@NC∥Ir-Co3O4@NC exhibited a low cell potential of 1.62 V at 10 mA cm−2 and superior catalytic durability. Our work paves the way for the practical applications of effective bifunctional electrocatalysts for hydrogen production.

CoMoO4-CoP/NC heterostructure anchored on hollow polyhedral N-doped carbon skeleton for efficient water splitting

We report the synthesis and electrocatalytic properties of a CoMoO4-CoP heterostructure anchored on a hollow polyhedral N-doped carbon skeleton (CoMoO4-CoP/NC) for water-splitting applications. The preparation involved the anion exchange of MoO42- to the organic ligand of ZIF-67, the self-hydrolysis of MoO42-, and NaH2PO2 phosphating annealing. CoMoO4 was found to enhance thermal stability and prevent active site agglomeration during annealing, while the hollow structure of CoMoO4-CoP/NC provided a large specific surface area and high porosity that facilitated mass transport and charge transfer. The interfacial electron transfer from Co to Mo and P sites promoted the generation of electron-deficient Co sites and electron-enriched P sites, which accelerated water dissociation. CoMoO4-CoP/NC exhibited excellent electrocatalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH solution, with overpotentials of 122 mV and 280 mV at 10 mA cm−2, respectively. The CoMoO4-CoP/NC‖CoMoO4-CoP/NC two-electrode system only required an overall water splitting (OWS) cell voltage of 1.62 V to achieve 10 mA cm−2 in an alkaline electrolytic cell. In addition, the material showed comparable activity to 20% Pt/C‖RuO2 in a pure water home-made membrane electrode device, demonstrating potential for practical applications in proton exchange membrane (PEM) electrolyzers. Our results suggest that CoMoO4-CoP/NC is a promising electrocatalyst for efficient and cost-effective water splitting.

Synergistic Coupling of CoFe-LDH Nanosheets with Cu3P Nanoarrays for Efficient Water Splitting

A crucial requirement for overall water splitting (OWS) is the creation of highly active bifunctional electrocatalysts. In this study, a CoFe-LDH (LDH = layered double hydroxide) nanosheet is integrated on a Cu3P nanowire to form heterogeneous structure Cu3P@CoFe-LDH/CF. Studies prove that the formation of a p–n heterojunction between Cu3P and CoFe-LDH promotes the charge-transfer reaction. Due to the synergistic contribution of the heterogeneous structure, Cu3P@CoFe-LDH/CF displays promising electrocatalytic activity. The overpotentials of 293 mV at 100 mA cm–2 for oxygen evolution reaction and 181 mV at 100 mA cm–2 for hydrogen evolution reaction are achieved in 1 M KOH. In addition, the alkaline electrolyzer of Cu3P@CoFe-LDH/CF||Cu3P@CoFe-LDH/CF shows a low cell voltage of 1.45 V at 10 mA cm–2 as well as great stability for OWS. This work provides a facile method to enhance the electrocatalytic activity by constructing heterogeneous structures with p–n heterojunctions, which holds significant promise for application in renewable energy technology.

Efficient Self-Powered Overall Water Splitting by Ni4 Mo/MoO2 Heterogeneous Nanorods Trifunctional Electrocatalysts.

The exploration of cost-effective multifunctional electrodes with high activity toward energy storage and conversion systems, such as self-powered alkaline water electrolysis, is very meaningful, although studies remain quite limited. Herein, a heterogeneous nickel-molybdenum (NiMo)-based electrode is fabricated for the first time as a trifunctional electrode for asymmetric supercapacitor (ASC), hydrogen evolution reaction, and oxygen evolution reaction. The trifunctional electrode consists of Ni4 Mo and MoO2 (denoted Ni4 Mo/MoO2 ) with hierarchical nanorod heterostructure and abundant heterogeneous nanointerfaces creating sufficient active sites and efficient charge transfer for achieving high performance self-power electrochemical devices. The ASC consists of the as-prepared Ni4 Mo/MoO2 positive electrode, showing a broad potential window of 1.6V, and a maximum energy density of 115.6Whkg-1 , while the alkaline overall water splitting (OWS) assembled using the as-prepared Ni4 Mo/MoO2 as bifunctional catalysts only requires a low cell voltage of 1.48V to achieve a current density of 10mAcm-2 in aqueous alkaline electrolyte. Finally, by integrating the Ni4 Mo/MoO2 -based ASC and OWS devices, an aqueous self-powered OWS is assembled, which self-power the OWS to generate hydrogen gas and oxygen gas, verifying great potential of the as-prepared Ni4 Mo/MoO2 for sustainable and renewable energy storage and conversion system.

Self-supporting electrocatalyst constructed from in-situ transformation of Co(OH)2 to metal-organic framework to Co/CoP/NC nanosheets for high-current-density water splitting

Transition metal phosphide (TMP) emerges as a promising electrocatalyst for overall water splitting (OWS). However, conventional TMP materials require exogenous metal ions to participate in coordination reactions, which usually suffer from active site blocking, pronounced intrinsic impedance, and inevitable catalyst shedding at high current density. Herein, a novel in-situ construction strategy has been developed to grow N-doped carbon (NC) enwrapped Co/CoP nanosheets directly onto Co foam (abbreviated as CoF) through a three-step transformation of Co to Co(OH)2 to Co-Metal-Organic Framework (Co-MOF) to Co/CoP/NC. In the entire preparation process, Co metal is only provided by the CoF substrate without external metal sources. Such in-situ construction yields tight contact at the interface of the heterogeneous catalyst, leading to much-reduced impedance and boundary vacancy, while the porous nitrogen-doped carbon backbone further endows the catalyst with the exposure of massive active sites, promotes mass transfer, and possesses high electrical conductivity. The Co/CoP/NC/CoF requires overpotentials of only 64 mV/263 mV@10 mA cm−2 and 414 mV/481 mV@400 mA cm−2 for both HER/OER in 1.0 M KOH, respectively. Remarkably, it reveals excellent OWS catalytic activity with a cell voltage of 1.56 V@10 mA cm−2 and 1.88 V@200 mA cm−2. This strategy of in-situ interface engineering transformation provides new ideas for direct device processing and construction of highly-efficient transition-metal-based OWS electrode materials.

Construction of an Advanced NiFe-LDH/MoS2-Ni3S2/NF Heterostructure Catalyst toward Efficient Electrocatalytic Overall Water Splitting.

Developing high-efficiency, low-cost, and earth-abundant electrocatalysts toward the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is highly desirable for boosting the energy efficiency of water splitting. Herein, we adopted an interfacial engineering strategy to enhance the overall water splitting (OWS) activity via constructing a bifunctional OER/HER electrocatalyst combining MoS2-Ni3S2 with NiFe layered double hydroxide (NiFe-LDH) on a nickel foam substrate. The NiFe-LDH/MoS2-Ni3S2/NF electrocatalyst delivers superior OER/HER activity and stability, such as low overpotentials (220 and 79 mV for OER and HER at current densities of 50 and 10 mA cm-2, respectively) and a low Tafel slope. This excellent electrocatalytic performance mainly benefits from the electronic structure modulation and synergistic effects between NiFe-LDH and MoS2-Ni3S2, which provides a high electrochemical activity area, more active sites, and strong electron interaction. Furthermore, the assembly of NiFe-LDH/MoS2-Ni3S2/NF into a two-electrode system only requires an ultra-low cell voltage of 1.50 V at a current density of 10 mA cm-2 and exhibits outstanding stability with a decay of current density of only 2.11% @50 mA cm-2 after 50 h, which is far superior to numerous other reported transition metal NiFe-LDH and MoS2-Ni3S2-based as well as RuO2||Pt-C electrocatalysts. This research highlights the rational design of heterostructures to efficiently advance electrocatalysis for water splitting applications.

Green electrosynthesis of CuN3 energetic materials coupled with energy-saving hydrogen production reaction

Oxygen evolution reaction (OER) is central to efficient hydrogen production. Replacing OER with thermodynamically more favorable anodic oxidation reaction can effectively improve the energy conversion efficiency in overall water splitting (OWS). Here, a new coupling system of green electro-oxidation synthesis of CuN3 primary explosive energetic materials and energy-saving hydrogen production is introduced. The cathodic catalyst is prepared by a two-step hydrothermal reaction to load ruthenium nanoparticles (Ru NPs) on the surface of three-dimensional (3D) molybdenum sulfide nanosheets (MoS2-NSs), and shows superior alkaline hydrogen production (HER) activity. Theoretical calculations reveal that the introduction of Ru NPs would induce local electron redistribution of in-plane MoS2 and optimize the adsorption capacity of the intermediates. The electro-oxidation synthesis of CuN3 energetic materials coupled with cathodic HER significantly reduce the cell voltage to only 1.07 V with current density of 10 mA cm−2, allowing low-energy-consumption hydrogen production. Meanwhile, the green electrosynthesis of CuN3 avoids generation of high-risk HN3 gas, high temperature, and long reaction time in the traditional method. This study demonstrates a new strategy of green electrosynthesis of primary explosive and energy-saving hydrogen production.