Nanoneedle Arrays Research Articles

Boosting the electrocatalytic performance of Co2P/Ni3S2 heterostructure for efficient water splitting

The development of a catalyst exhibiting outstanding catalytic activity and robust stability for both the oxygen evolution reaction and hydrogen evolution reaction in alkaline media represents a substantial challenge. In this work, a NF/Ni@NiCoSP heterostructure bifunctional catalyst was developed via a sequent process of electrodeposition-hydrothermal-low temperature thermal pyrolysis sulphuration/phosphorization. The physical characterizations reveal that the as-prepared sample of NF/Ni@NiCoSP exhibits a porous nano-needles array structure and consists of both Ni3S2 and Co2P phases with considerable boundaries. As a consequence, the NF/Ni@NiCoSP presents an ultralow overpotential of 47 mV and 260 mV at 10 mA cm−2 for hydrogen evolution reaction and oxygen evolution reaction, respectively. When assembled to a two-electrode system, it only requires 1.53 V to reach 10 mA cm−2, which surpasses the commercial RuO2‖Pt/C (1.61 V). The methanol oxidation reaction probing experiment suggests the easy desorption of ∗OH from active sites due to the decreased binding strength between ∗OH and the catalyst, thus optimizing the kinetics condition. Moreover, the in-situ Raman spectra reveal that NiOOH and CoOOH serve as active sites for OER while the metal sites for HER. Therefore, this work introduces a feasible strategy to design cost-effective and robust catalysts with excellent catalytic properties, thereby paving the way for water splitting.

In Situ Growth of Well-Aligned MOF Nanoneedle Arrays into Composite Photothermal Membranes for Solar Desalination.

The solar-driven interfacial evaporation (SDIE) technology serves as a clean and facile approach combining seawater desalination to address water shortage and energy crisis. Recently, porous organic framework materials have aroused great attention, and the development of MOF-based composites with significant performance in photothermal conversion and water activation has become one of the important focuses in this field. In this work, an MOF-based composite photothermal membrane (PON@MOF) was prepared via the in situ growth of metal-organic framework (MOF) nanoneedle arrays induced by a pyridine-based organic polymer nanowire network (PON). The PON@MOF membrane possessed an MOF array layer, a PON-induced layer, and a porous support layer. The PON is rich in coordinated nitrogen atoms for anchoring the metal-ion source, and the main role of the PON layer is to provide favorable nucleation sites and orient in situ growth of well-aligned MOF nanoneedle arrays. With the highly conjugated framework of PON@MOF and the light trapping of the nanoarrays strengthening the photothermal conversion as well as the hydrophilic chemical structure facilitating the decrease of the water evaporation enthalpy, the PON@MOF membrane realizes highly efficient thermal vapor conversion. Under solar irradiation (1.0 kW m-2), PON@MOF demonstrated an evaporation rate of 2.14 kg m-2 h-1 and a solar-to-vapor conversion efficiency of 98.5%. Meanwhile, the PON@MOF membrane has excellent salt resistance and stability, highlighting its potential application in desalination. Overall, this work provides a special idea for the structural design of photothermal composites for solar desalination and freshwater production.

Solar-driven chloride activation via 3D oxygen-vacancy-rich TiO2 network photoanode for ultrafast and durable purification of saline wastewater

Photoelectrochemical chloride activation (PEC-Cl) is a promising and reagent-free strategy to treat saline organic wastewater by activation of chloride (Cl–) using sunlight. However, the low efficiency and Cl– corrosion of photoelectrode, and the limited mass transfer of pollutant hinder its application. Herein we successfully solve these challenges by developing porous oxygen-vacancy-rich TiO2 nanoneedle arrays (TiO2 NNs-r400) photoanode. Under illumination, the photoinduced holes in TiO2 NNs-r400 oxidize Cl– to reactive species (e.g., HOCl, Cl•, Cl2•− and ClO•), resulting in the degradation rate of tetracycline hydrochloride (HTC, 0.861 min−1) by TiO2 NNs-r400/PEC-Cl system is 2–3 orders of magnitude higher than the state-of-the-art. Experiments and computational analysis indicate that oxygen vacancies (Ovs) on TiO2 NNs-r400 promote the photocarriers separation efficiency and more importantly, facilitate Cl– adsorption with intermediary strength and reduce the energy barriers of Cl– oxidation. Furthermore, we design a continuous flow-through PEC reactor for TiO2 NNs-r400/PEC-Cl technology. The process exhibits 100% HTC degradation (TOC = 60.23%) for over 2000 h flow-through operation, which maintains high activity in the treatment marine aquaculture wastewater with nearly zero energy consumption by directly utilize natural sunlight. In the final effluent, the toxicity of almost all degradation intermediates is decreased, and the formation of total organic chlorine is low (17.2 µg L–1). This work provides insights into Cl– activation on Ov-rich photoanode and strategy for practical application of solar energy in efficient, sustainable and eco-friendly wastewater decontamination.

Interfacial coupling of Ce-CoSe2 nanoneedle arrays with MXene for efficient overall water splitting

Designing highly effective, low-cost bifunctional electrocatalysts without noble metals for overall water splitting remains a significant challenge. In this work, interfacial coupling of Ce-doped CoSe2 nanoneedle arrays with MXene (Ce-CoSe2/MXene) is developed via the facile hydrothermal and selenization methods. The extensive specific surface area and favorable hydrophilicity of Ti3AlC2, combined with the optimized electronic structure and abundant active sites from Ce-doping and selenization, contribute to the exceptional bifunctional electrocatalytic performance of the Ce-CoSe2/MXene electrode. Specifically, this heterostructure achieves a low hydrogen evolution reaction (HER) overpotential of 34 mV at 10 mA cm−2, an oxygen evolution reaction (OER) overpotential of 279 mV at 100 mA cm−2, and an overall water splitting (OWS) potential as low as 1.45 V at 10 mA cm−2. In-situ Raman spectroscopy reveals that surface reconstruction would improve catalytic activity and stability. Theoretical calculations indicate that the Ce-CoSe2/MXene can improve the adsorption of intermediates and facilitate HER/OER process by lowering the kinetic barrier, thereby enhancing electrocatalytic activity. This research marks a substantial advancement in the development of low-cost, efficient electrocatalysts for overall water splitting.

Inducing Intermolecular Oxygen Coupling by Introducing S and FeOOH on Co(OH)2 Nanoneedle Arrays for Industrial Water Oxidation.

The design of electrocatalysts for oxygen evolution reaction (OER) remains a limitation of industrial hydrogen production by electrolysis of water. Excellent and stable OER catalysts can be developed by activating lattice oxygen and changing the reaction path. Herein, S and FeOOH on the Co(OH)2 nanoneedle arrays are introduced to construct a heterostructure (S-FeOOH/Co(OH)2/NF) as a proof of concept. Theoretical calculations and experimental suggest that the Co-O-Fe motif formed at the heterogeneous interface with the introduction of FeOOH, inducing electron transfer from Co to Fe, enhancing Co─O covalency and reducing intramolecular charge transfer energy, thereby stimulating direct intramolecular lattice oxygen coupling. Doping of S in FeOOH further accelerates electron transfer, improves lattice oxygen activity, and prevents dissolution of FeOOH. Consequently, the overpotential of S-FeOOH/Co(OH)2/NF is only 199mV at 10mA cm-2, and coupled with the Pt/C electrode can be up to 1 A cm-2 under 1.79V and remain stable for over 120h in an anion exchange membrane water electrolyzer (AEMWE). This work proposes a strategy for the design of efficient and stable electrocatalysts for industrial water electrolysis and promotes the commercialization of AEMWE.

Deciphering the Temporal-Spatial Interactive Heterogeneity of Long Non-Coding RNAs and RNA-Binding Proteins in Living Cells at Single-Cell Resolution.

The investigation of long noncoding RNAs (lncRNAs) and RNA binding proteins (RBPs) interactions in living cell holds great significance for elucidating their critical roles in a variety of biological activities, but limited techniques are available to profile the temporal-spatial dynamic heterogeneity. Here, we introduced a molecular beacon-functionalized nanoneedle array designed for spatially resolved profiling of lncRNA-RBP interactions (Nano-SpatiaLR). A nanoneedle array modified with a molecular beacon is employed to selectively isolate specific intracellular lncRNAs and their associated RBPs without affecting cell viability. The RBPs are then in situ analyzed with a fluorescent labeled antibody and colocalized with lncRNA signals to get a quantitative measurement of their dynamic interactions. Additionally, leveraging the spatial distribution and nanoscale modality of the nanoneedle array, this technique provides the spatial heterogeneity information on cellular lncRNA-RBPs interaction at single cell resolution. In this study, we tracked the temporal-spatial interactive heterogeneity dynamics of lncRNA-RBPs interaction within living cells across different biological progresses. Our findings demonstrated that the interactions between lncRNA HOTAIR and RBPs EZH2 and LSD1 undergo significant changes in response to drug treatments, particularly in tumor cells. Moreover, these interactions become more intensified as tumor cells aggregate during the proliferation process.

Facile Fabrication of Lilac-Like Multiple Self-Supporting WO3 Nanoneedle Arrays with Cubic/Hexagonal Phase Junctions for Highly Sensitive Ethylene Glycol Gas Sensors.

Metal oxides with nanoarray structures have been demonstrated to be prospective materials for the design of gas sensors with high sensitivity. In this work, the WO3 nanoneedle array structures were synthesized by a one-step hydrothermal method and subsequent calcination. It was demonstrated that the calcination of the sample at 400 °C facilitated the construction of lilac-like multiple self-supporting WO3 arrays, with appropriate c/h-WO3 heterophase junction and highly oriented nanoneedles. Sensors with this structure exhibited the highest sensitivity (2305) to 100 ppm ethylene glycol at 160 °C and outstanding selectivity. The enhanced ethylene glycol gas sensing can be attributed to the abundant transport channels and active sites provided by this unique structure. In addition, the more oxygen adsorption caused by the heterophase junction and the aggregation of reaction medium induced by tip effect are both in favor of the improvement on the gas sensing performance.

Phosphorization Engineering of CoP/NiCoP Nanoneedle Arrays for Energy Storage

Phosphorization Engineering of CoP/NiCoP Nanoneedle Arrays for Energy Storage

Zirconium doping facilitates a vertically aligned NiCoZr-layered hydroxide nanoneedle arrays electrode for hybrid supercapacitors exhibiting a 90,000 cycle durability

LDHs (Layered Double Hydroxides) are a kind of promising cathode material for high-performance hybrid supercapacitor. Nevertheless, it suffers quick capacitance decay after only thousands of cycles, which greatly prevents it from further application. In this contribution, zirconium (Zr) is introduced to the host layer of NiCo-LDH via a simple one-pot hydrothermal process. Owing to the strong bonding energy of ZrO (760 kJ mol−1) and special electronic structure (fully empty 4d orbits), the doped Zr could not only act as a structural stabilized element, but also change the mechanism of the energy storage process to alleviate the Jahn-Teller distortion of NiCo-LDH. Moreover, the introduction of Zr boosts an orderly growth of the LDHs, changing from disorder stack structure to vertically aligned nanoneedle arrays, which improve their structural stability. By controlling a varying level of Zr content, the electrode NiCoZr-LDH@CC with a Zr content ratio of 6.4 % delivers the best comprehensive electrochemical performance with a specific capacitance of 1758 F g−1 and good rate performance (73 % capacitance retention at 10 A g−1). The assembled asymmetric supercapacitor shows a highest energy density of 42.3 Wh kg−1 at 504 W kg−1 and an ultralong cycling lifespan beyond 90,000 cycles with a 97 % capacitance retention. The results exhibit the great potential of NiCoZr-LDH as a qualified candidate for high-performance hybrid supercapacitors.

A novel Janus composite membrane and its enhanced antifouling strategy for emulsion purification

The development of advanced membranes for the efficient separation of oil-water emulsions and the degradation of soluble pollutants is crucial for environmental protection. This study presents a Janus composite membrane with Co(CO3)0.5OH·0.11H2O nanoneedle arrays, fabricated through electrospinning, membrane assembly, surface hydrophobization, and chemical bath deposition (CBD). By controlling the amount of carbon nanofiber (CNF) and CBD time, the membrane's morphology can be optimized for improved performance. In dead-end filtration driven by gravity, the membrane effectively separates stabilized oil-in-water emulsions and demonstrates strong anti-fouling capabilities. Furthermore, the membrane exhibits significant catalytic activation for peroxymonosulfate (PMS), enabling complete restoration of water flux of polluted membranes and purifying emulsions with soluble organic pollutants. To further enhance anti-fouling performance, a novel separation strategy integrating pulse current is proposed. Under the influence of a pulsed electric field, the membrane achieves a permeate flux nearly twice as high as that observed without this external stimulus, while maintaining high separation efficiency. This research advances Janus nanofiber membrane development via electrospinning techniques and supports sustainable treatment of oily wastewater.

Solar-driven salt-free deposition evaporation for simultaneous desalination and electricity generation based on tip-effect and siphon-effect

Solar-driven desalination is a promising way to alleviate the freshwater shortage, while is facing challenges posed by low evaporation rates and severe salt accumulation. Herein, a high-performance two-dimensional (2D) solar absorber with Co3O4 nanoneedle arrays (Co3O4-NN) grown on the surface of reduced graphene oxide-coated pyrolyzed silk cloth (Co3O4-NN/rGO/PSC) was prepared, and a salt-free evaporator system was assembled based on the composite material and siphonage-the flowing water delivery. It is revealed that the evaporation enthalpy of water can be reduced over the 2D solar absorber grown with Co3O4-NN, enabling an evaporation rate of up to 2.35 kg m−2 h−1 in DI water under one solar irradiation. The desalination process can be carried out continuously even with salt concentration up to 20 wt%, due to the timely removal of concentrated brine from the interface with the assistance of directed flowing water. Moreover, the 2D structure and the flowing water also provide an opportunity to convert waste solar heat into electricity in the evaporator based on the seebeck effect, ensuring simultaneous freshwater production and power generation. It is believed that this work provides insights into designing hybrid systems with high evaporation rate, salt resistance, and electricity generation.

Copper silicate nanoneedle arrays on reduced graphene oxide like “shelter forest” guiding Zn gradient deposition

With the sustainable and efficient development of aqueous zinc ion batteries (AZIBs), the research on addressing the issues of the adaptability and durability of zinc anodes has been hot-topic and is still of great challenge. In this work, inspired by the sand treatment and afforestation of the Gobi Beach in Northwest China to ameliorate the problem of wind and sand encroachment, we propose a material with a morphology similar to that of a “shelter forest”, CuSiO3 nanoneedles arrays grown on both sides of reduced graphene oxide (rGO@CuSi), as a coating layer on the zinc metal surface to guide Zn gradient deposition. The presence of rGO improves the electrical conductivity of CuSiO3, and the finite element simulation of the electric field and Zn2+ concentration proves that the electric field distribution can be effectively homogenized and the local current density can be reduced for the rGO@CuSi-Zn electrode with the surface presenting the shape of a protective forest. This is due to the abundant pores between the nano-needle array structures on the surface of the electrode, which provides high electron and ion transport paths, and are conducive to achieve uniform Zn deposition, like the principle of wind-sand stabilization by protective forest. Both electrochemical experiments and density functional theory calculations show that the negatively charged surface of rGO@CuSi with good Zn affinity is more capable of guiding Zn2+ transport. Thanks to its inherent material and structural characteristics, the rGO@CuSi-Zn anode has a high specific capacity and good cycling stability. This study provides an insight for interface engineering like protective forest to accelerate the commercialization of high-performance Zn-based batteries.

Enhancing electrocatalytic nitrate reduction performance of Co3O4 nanoneedle arrays by La-doping

The excess emission of nitrate from human activities disturbs the global nitrogen cycle and thus needs to be remediated. In this work, we prepared a La-doped Co3O4 nanoneedle arrays catalyst for highly efficient electrocatalytic reduction of NO3− to NH3 at low concentration. The La-doped Co3O4 nanoneedle arrays exhibit remarkable activity with the highest Faradaic efficiency of 95.5% and an ammonia yield rate of 4.08 mg/(h·cm2) at −0.3 V versus RHE in 0.02 mol/L NO3−. Experiments and theoretical calculations show that the La doping not only facilitates the surface reconstruction to form active La-Co(OH)2, but also inhibits the hydrogen evolution reaction over Co sites, thus promoting the NH3 production. This work provides new insights into the promoting effect of the rare earth elements in transition metal-based electrocatalyst for nitrate reduction.

Interface Engineering via Ti3C2Tx MXene Enabled Highly Efficient Bifunctional NiCoP Array Catalysts for Alkaline Water Splitting.

Developing a non-noble metal-based bifunctional electrocatalyst with high efficiency and stability for overall water splitting is desirable for renewable energy systems. We developed a novel method to fabricate a heterostructured electrocatalyst, comprising a NiCoP nanoneedle array grown on Ti3C2Tx MXene-coated Ni foam (NCP-MX/NF) using a dip-coating hydrothermal method, followed by phosphorization. Due to the abundance of active sites, enhanced electronic kinetics, and sufficient electrolyte accessibility resulting from the synergistic effects of NCP and MXene, NCP-MX/NF bifunctional alkaline catalysts afford superb electrocatalytic performance, with a low overpotential (72 mV at 10 mA cm-2 for HER and 303 mV at 50 mA cm-2 for OER), a low Tafel slope (49.2 mV dec-1 for HER and 69.5 mV dec-1 for OER), and long-term stability. Moreover, the overall water splitting performance of NCP-MX/NF, which requires potentials as low as 1.54 and 1.76 V at a current density of 10 and 50 mA cm-2, respectively, exceeded the performance of the Pt/C∥IrO2 couple in terms of overall water splitting. Density functional theory (DFT) calculations for the NCP/Ti3C2O2 interface model predicted the catalytic contribution to interfacial formation by analyzing the electronic redistribution at the interface. This contribution was also evaluated by calculating the adsorption energetics of the descriptor molecules (H2O and the H and OER intermediates).

Engineering Internal and External Low-Coordination Atoms in Nickel-Organic Framework Nanoarrays to Promote the Electrochemical Oxygen Evolution Reaction.

Monometallic nickel-organic frameworks based on a carboxylated ligand [2,6-naphthalenedicarboxylic acid (Ni-NDC)] have abundant and uniformly distributed single-atom Ni sites, enabling superior oxygen evolution reaction (OER) activity. In theory, most of the Ni atoms inside Ni-NDC microcrystals are coordinatively saturated except for the surface. Therefore, there are no accessible low-coordination atoms (LCAs) as electrocatalytic sites for the OER. One effective way is to expose more LCAs by preparing self-supporting Ni-NDC nanoarrays (Ni-NDC NAs) with hierarchical secondary structural units. Another effective method is to create more internal LCAs by removing partial ligands or coordination atoms attached to the Ni atoms. Herein, by combining the two strategies, we engineered LCAs in the interior and exterior of Ni-NDC to synergistically accelerate the OER. In brief, ultrathick "brick-like" Ni-NDC NAs were first prepared with dissolution and coordination effects of NDC on self-sacrificial templates of "agaric-like" nickel hydroxide nanoarrays [Ni(OH)2 NAs]. Subsequently, dual-coordinated NDC was partially replaced by monocoordinated 2-naphthoic acid (NA). The Ni-NDC NAs were further tailed into ultrathin "liner leaf-like" nanoneedle arrays (LCAs-Ni-NDC NAs). As a consequence, the LCAs-Ni-NDC NAs have more internal and external LCAs, which can deliver an OER performance that is superior to that of Ni-NDC NAs.

Construction of structurally engineered NiCo2O4 nanostructures as a bifunctional electrocatalyst for high-performance overall water splitting

The development of low-cost and highly efficient bifunctional electrocatalysts for overall water splitting is a challenging but urgent goal. Herein, nickel cobaltite (NiCo2O4) with different morphologies was developed for electrocatalytic overall water splitting. Encouragingly, the NiCo2O4 nanoneedle arrays required competitive hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) overpotentials of 106 and 310 mV to achieve a density of 10 mA cm−2 (j10) in KOH media, respectively. Furthermore, the as-made nanoneedle electrocatalyst employed as both anode and cathode, which displayed a low voltage of 1.67 Vto attain j10, with satisfactory durability for 50 h. The nanoneedle morphology not only improves the electrochemical active surface area, but also helpful to boost the charge transfer ability of NiCo2O4 and control the adsorption of reaction intermediates in water splitting. These results demonstrate the feasibility of the NiCo2O4 nanostructure by altering the active sites using morphology to develop the electrocatalytic activity of the materials.

Boosting Electrochemical Ammonia Synthesis via NOx Reduction over Sulfur‐Doped Copper Oxide Nanoneedle Arrays

AbstractThe electrochemical NOx reduction reactions, involving nitrate and nitrite reduction reactions (NO3−RR and NO2−RR), have emerged as promising approaches for both NO3− and NO2− removal, and ammonium (NH3) synthesis under ambient conditions. However, the incorporation and stabilization of sulfur dopants in the catalysts for efficient NOx reduction are rarely explored, leading to an unclear effect of sulfur on the NOx reduction mechanism. Herein, sulfur‐doped Cu2O (S‐Cu2O) nanoneedle arrays via in situ electrochemical treatment are synthesized. The S‐Cu2O catalyst possesses excellent durability and selectivity for NH3 over a wide range of potentials in NO3−RR, attaining a maximum NH3 Faradaic efficiency of 94% at −0.6 VRHE and a maximum NH3 yield as high as 1.06 mmol h−1 cm−2. In NO3−RR, the sulfur dopant can accelerate the step from NO2− to NH3, contributing superior performance in NO2−RR and assembled Zn−NO2− battery device. Density functional theory (DFT) calculations reveal that the presence of sulfur can enhance the initial step of *NO3 adsorption, lower the reaction barriers for the formation of *NHO intermediate, and activate the H2O dissociation process. The work sheds light on the role of sulfur in enhancing electrocatalytic performance and provides a unique perspective for understanding the NOx reduction mechanism.

Three-dimensional NiO/Ni self-floating porous composite materials for efficient solar interfacial evaporation

The scarcity of freshwater resources and energy crisis are major challenges to the progress of human society. Recently, solar-driven interfacial water evaporation utilizes photothermal conversion materials to convert solar energy into thermal energy, which possesses great application potential in seawater desalination and sewage treatment. Here, we fabricated porous nickel sponge (NSP) composite photothermal material (NiO-NSP) containing abundant NiO nanoneedles array. This in situ-grown NiO with enhanced bonding between photothermal material and substrate can be used as a solar absorber directly without consuming additional photothermal material compared to conventional coating and cladding on the carrier surface. Due to the multi-scattering induced light trapping effect of the semiconductor NiO nanoneedles array on the surface of nickel fibers, resulting in light absorption up to 96.5 %. NiO-NSP evaporators have an abundance of interconnected porous channels for water supply, which results in strong capillary action to pump water to the evaporation interface efficiently. Moreover, the highly dispersed nanoneedles array expand the evaporation surface area. Consequently, the NiO-NSP evaporator delivers an excellent evaporation rate of 1.78 kg m−2 h−1 and a photothermal conversion efficiency of 84.7 % at one sun radiation. In addition, the micron-sized porous mesh structure of NiO-NSP dissolve salt crystals and diffuse them downward into the bulk brine, exhibiting excellent salt resistance and remarkable seawater desalination stability. Moreover, NiO-NSP solar evaporators has been demonstrated to possess excellent ability to purify dye and heavy metal ion wastewater. Therefore, the NiO-NSP high-performance evaporator produced by straightforward process proved to be suitable for solar seawater desalination and wastewater purification.

Ag nanopines over Al nanoneedle arrays enable high SERS sensitivity and reproducibility for molecular sensing

In this study, highly uniform 3D Al nanoneedle arrays (AlNNAs) decorated with Ag nanopines are synthesized by anodization of Al foil with prior nanoimprinting and subsequent electrodeposition method, demonstrating remarkable surface-enhanced Raman scattering (SERS) property. The AlNNAs possess a highly ordered periodicity of 1 μm and nanoneedle height of 800 nm, making it an optimal supporting matrix to host Ag-NPs as SERS substrate. Such well-ordered Ag@AlNNAs SERS substrate with precisely electrodeposited Ag nanopines generate high density SERS host spots and abundant sites to adsorb target molecules. As a result, Ag@AlNNAs exhibit high sensitivity for rhodamine 6 G down to 10–13 M and good signal reproducibility with a relative standard deviation of 7.2 %, as well as an average enhancement factor of 4.23 × 109. For practical detection of pollutants, 10–8 M adenine, 10–12 M bisphenol in water, and melamine (10–7 M) in opaque milk are clearly identified by using the Ag@AlNNAs sensor. This study opens a bright way to fabricate SERS substrate with a good balance of sensitivity, reproducibility and cost, indicating promising potential for environmental monitoring and food safety.

Two-step fabrication of hierarchical Ni(OH)2@NiCo2O4 core-shell nanoneedle array for highly efficient decoupled water splitting

The temporal and spatial segregation of the hydrogen and oxygen evolution reactions (HER and OER) are essential for advancing membrane-free electrolysis technology in H2 production through water splitting. This investigation employed a two-step fabrication approach to craft a three-dimensional self-supporting buffered electrode. This method involved utilizing a Ni(OH)2@NiCo2O4 core-shell nanoneedle array as the active material and nickel foam (NF) as the substrate. Remarkably, the H2 production at the cathode displayed remarkable efficiency, maintaining an uninterrupted operation duration of 1500 s at a current of 100 mA. Simultaneously, the Ni(OH)2@NiCo2O4 mediator on the anodic electrode underwent oxidation during this process, leading to the generation of its respective oxidized state, accompanied by a noteworthy operating voltage of 1.50 V. Afterwards, the second step of the OER involved the recovery of the buffered electrode and the generation of O2 at an operational voltage of 0.46 V, with the O2-production duration being equivalent to that of the first step in the HER process. Interestingly, the revival process of the buffered electrode in the second step can also be coupled with zinc sheets, thereby constructing a battery. During the discharge process of the battery, the regeneration of the buffered electrode was achieved, and this discharge process could also provide a power supply for the first step of H2-evolution. Therefore, this decoupled water electrolysis system presents a promising avenue for facilitating the effective transformation of renewable sources into hydrogen.