Engineering of Self-Supported Electrocatalysts on a Three-Dimensional Nickel Foam Platform for Efficient Water Electrolysis

Economical water electrolysis requires highly active non-noble electrocatalysts to overcome the sluggish kinetics of the two half-cell reactions,oxygen evolution reaction,and hydrogen evolution reaction.Although intensive efforts have been committed to achieve a hydrogen economy,the expensive noble metal-based catalysts remain under consideration.Therefore,the engineering of self-supported electrocatalysts prepared using a direct growth strategy on three-dimensional(3D)nickel foam(NF)as a conductive substrate has garnered significant interest.This is due to the large active surface area and 3D porous network offered by these electrocatalysts,which can enhance the synergistic eff ect between the catalyst and the substrate,as well as improve electrocatalytic performance.Hydrothermal-assisted growth,microwave heating,electrodeposition,and other physical methods(i.e.,chemical vapor deposition and plasma treatment)have been applied to NF to fabricate competitive electrocatalysts with low overpotential and high stability.In this review,recent advancements in the development of self-supported electrocatalysts on 3D NF are described.Finally,we provide future perspectives of self-supported electrode platforms in electrochemical water splitting.

Electrokinetic-mechanism of water and furfural oxidation on pulsed laser-interlaced Cu_(2)O and CoO on nickel foam

The electrocatalytic oxidation of biomass-derived furfural(FF)feedstocks into 2-furoic acid(FA)holds immense industrial potential in optics,cosmetics,polymers,and food.Herein,we fabricated Co O/Ni O/nickel foam(NF)and Cu_(2)O/Ni O/NF electrodes via in situ pulsed laser irradiation in liquids(PLIL)for the bifunctional electrocatalysis of oxygen evolution reaction(OER)and furfural oxidation reaction(FOR),respectively.Simultaneous oxidation of NF surface to NiO and deposition of CoO and/or Cu_(2)O on NF during PLIL offer distinct advantages for enhancing both the OER and FOR.CoO/NiO/NF electrocatalyst provides a consistently low overpotential of~359 m V(OER)at 10 m A/cm^(2),achieving the maximum FA yield(~16.37 m M)with 61.5%selectivity,79.5%carbon balance,and a remarkable Faradaic efficiency of~90.1%during 2 h of FOR at 1.43 V(vs.reversible hydrogen electrode).Mechanistic pathway via in situ electrochemical-Raman spectroscopy on CoO/NiO/NF reveals the involvement of phase transition intermediates(NiOOH and CoOOH)as surface-active centers during electrochemical oxidation.The carbonyl carbon in FF is attacked by hydroxyl groups to form unstable hydrates that subsequently undergo further oxidation to yield FA products.This method holds promise for large-scale applications,enabling simultaneous production of renewable building materials and fuel.

Bimetallic Single‑Atom Catalysts for Water Splitting

Green hydrogen from water splitting has emerged as a critical energy vector with the potential to spearhead the global transition to a fossil fuel-independent society.The field of catalysis has been revolutionized by single-atom catalysts(SACs),which exhibit unique and intricate interactions between atomically dispersed metal atoms and their supports.Recently,bimetallic SACs(bimSACs)have garnered significant attention for leveraging the synergistic functions of two metal ions coordinated on appropriately designed supports.BimSACs offer an avenue for rich metal–metal and metal–support cooperativity,potentially addressing current limitations of SACs in effectively furnishing transformations which involve synchronous proton–electron exchanges,substrate activation with reversible redox cycles,simultaneous multi-electron transfer,regulation of spin states,tuning of electronic properties,and cyclic transition states with low activation energies.This review aims to encapsulate the growing advancements in bimSACs,with an emphasis on their pivotal role in hydrogen generation via water splitting.We subsequently delve into advanced experimental methodologies for the elaborate characterization of SACs,elucidate their electronic properties,and discuss their local coordination environment.Overall,we present comprehensive discussion on the deployment of bimSACs in both hydrogen evolution reaction and oxygen evolution reaction,the two half-reactions of the water electrolysis process.

Self-supported Ni2P nanosheets on low-cost three-dimensional Fe foam as a novel electrocatalyst for efficient water oxidation

Electrochemical water splitting into hydrogen and oxygen is a promising strategy for future renewable energy conversion devices.The oxygen evolution reaction(OER)is considered as the bottleneck reaction in an overall water splitting system because it involves 4e- and 4H+ transfer processes.Currently,it is highly desirable to explore low-cost alternative catalysts for OER at ambient conditions.Herein,we report for the first time that nickel phosphide(Ni2P)nanosheets can be facilely grown on Fe foam(FF)as an efficient electrocatalyst for OER with excellent durability and catalytic activity under alkaline conditions.To reach a current density of 10 m A/cm2,the Ni2P-FF catalyst required a low overpotential of only 198 mV for OER.The catalyst’s high OER activity and durability were well maintained at a high current density.The required overpotentials were only 267 and 313 mV to achieve the current densities of 100 and 300 m A/cm2,respectively.The combination of low-cost Fe foam with Ni2P provides a promising low-cost catalyst for large-scale application of electrocatalytic water splitting.

Stability and water control of nitrogen foam in bulk phase and porous media

Foam is widely used in the petroleum industry thanks to its unique properties and performance. Its application to water control in oil wells has received more and more attention. The stability of nitrogen foam was investigated in pressurized equipment and sand pack. The result indicated that with increasing pressure （0-2 MPa） the stability of foam in the pressurized equipment increased linearly. Increased nitrogen injection pressure caused better dispersion of nitrogen-foaming solution in porous media. The initial residual resistance factor to gas was an exponential function of injection pressure, but the residual resistance factor （to gas and liquid） decreased exponentially with time. The halflife of foam in porous media （expressed in residual resistance factor） was much longer than that in bulk phase （expressed in foam height）. Pore model analysis indicated that good dispersion in porous media and the presence of thick liquid film during dispersion were the main reasons for high stability. Field test indicated that effective residence of foam in the formation not only resulted in much better heat insulation, but also improved steam stimulation by enhancing steam heating.

Tests on Alkali-Activated Slag Foamed Concrete with Various Water-Binder Ratios and Substitution Levels of Fly Ash

To provide basic data for the reasonable mixing design of the alkali-activated (AA) foamed concrete as a thermal insulation material for a floor heating system, 9 concrete mixes with a targeted dry density less than 400 kg/m3 were tested. Ground granulated blast-furnace slag (GGBS) as a source material was activated by the following two types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The main test parameters were water-to-binder (W/B) ratio and the substitution level (RFA) of fly ash (FA) for GGBS. Test results revealed that the dry density of AA GGBS foamed concrete was independent of the W/B ratio an RFA, whereas the compressive strength increased with the decrease in W/B ratio and with the increase in RFA up to 15%, beyond which it decreased. With the increase in the W/B ratio, the amount of macro capillaries and artificial air pores increased, which resulted in the decrease of compressive strength. The magnitude of the environmental loads of the AA GGBS foamed concrete is independent of the W/B ratio and RFA. The largest reduction percentage was found in the photochemical oxidation potential, being more than 99%. The reduction percentage was 87% - 93% for the global warming potential, 81% - 84% for abiotic depletion, 79% - 84% for acidification potential, 77% - 85% for eutrophication potential, and 73% - 83% for human toxicity potential. Ultimately, this study proved that the developed AA GGBS foamed concrete has a considerable promise as a sustainable construction material for nonstructural element.

Copper foam-derived electrodes as efficient electrocatalysts for conventional and hybrid water electrolysis

Electrochemical water splitting has been demonstrated as a promising technology for the renewable generation of green hydrogen from water.Despite the extensive progress in materials science,one particular challenge for further development towards industrial application lies in the rational design and exploitation of efficient and cost-effective materials,especially oxygen evolution reaction(OER)electrocatalysts at the anode.In addition,attempts to replace the OER with other more oxidizable anode reactions are being evaluated as a groundbreaking strategy for generating hydrogen at lower potentials and reducing overall energy costs while producing valuable chemicals simultaneously.Compared with Fe/Co/Ni-based compounds,Cu-based materials have not received extensive research attention for electrode designs despite their high conductivity and abundant earth reserves.In this review,combining with the advantages of a three-dimensional network structure of metal foams,we summarize recent progress on Cu foam(CF)-derived materials as efficient electrocatalysts towards pure water electrolysis and hybrid water electrolysis.The advantages of CF and design strategies to enhance the electrocatalytic activity and operational durability are presented first.Catalyst design and fabrication strategies are then highlighted and the structure-activity relationship is also discussed.Finally,we propose challenges and perspectives on self-supported electrodes beyond CF-derived materials.

Gas/water foams stabilized with a newly developed anionic surfactant for gas mobility control applications

Carbon dioxide(CO2) flooding is one of the most globally used EOR processes to enhance oil recovery.However,the low gas viscosity and density result in gas channeling and gravity override which lead to poor sweep efficiency.Foam application for mobility control is a promising technology to increase the gas viscosity,lower the mobility and improve the sweep efficiency in the reservoir.Foam is generated in the reservoir by co-injection of surfactant solutions and gas.Although there are many surfactants that can be used for such purpose,their performance with supercritical CO2(ScCO2) is weak causing poor or loss of mobility control.This experimental study evaluates a newly developed surfactant(CNF) that was introduced for ScCO2 mobility control in comparison with a common foaming agent,anionic alpha olefin sulfonate(AOS) surfactant.Experimental work was divided into three stages:foam static tests,interfacial tension measurements,and foam dynamic tests.Both surfactants were investigated at different conditions.In general,results show that both surfactants are good foaming agents to reduce the mobility of ScCO2 with better performance of CNF surfactant.Shaking tests in the presence of crude oil show that the foam life for CNF extends to more than 24 h but less than that for AOS.Moreover,CNF features lower critical micelle concentration(CMC),higher adsorption,and smaller area/molecule at the liquid-air interface.Furthermore,entering,spreading,and bridging coefficients indicate that CNF surfactant produces very stable foam with light crude oil in both deionized and saline water,whereas AOS was stable only in deionized water.At all conditions for mobility reduction evaluation,CNF exhibits stronger flow resistance,higher foam viscosity,and higher mobility reduction factor than that of AOS surfactant.In addition,CNF and ScCO2 simultaneous injection produced 8.83% higher oil recovery than that of the baseline experiment and 7.87% higher than that of AOS.Pressure drop profiles for foam flooding using CNF was slightly higher than that of AOS indicating that CNF is better in terms of foam-oil tolerance which resulted in higher oil recovery.

Integrated Ni2P nanosheet arrays on three-dimensional Ni foam for highly efficient water reduction and oxidation

The large-scale synthesis of efficient nonprecious bifunctional electrocatalysts for overall water splitting is a great challenge for future renewable energy conversion systems. Herein, Ni2P nanosheet arrays directly grown on three-dimensional(3 D) Ni foam(Ni P/NF) are fabricated by hydrothermal treatment of metallic Ni foam with H2O2solution and subsequent phosphidation with NaH2PO2. The Ni P/NF as electrocatalyst exhibits superior activities for both hydrogen evolution reaction(HER) and oxygen evolution reaction(OER). Most importantly, employing both as the cathode and anode for an alkaline water electrolyzer, Ni P/NF only requires a cell voltage of 1.63 V to reach a current density of 10 mV cm-2, together with stronger durability. Preliminary catalytic information suggests that the tailored 3 D superstructure and integrated electrode configurations afford improved active sties and enhanced electron/mass transfer,responding for the outstanding activity and stability.

Development and Performance Evaluation of Self-Generating Enhanced Foam Water Plugging System

For the waterflooding of late development on an offshore oilfield has become worse, and some wells group has entered into high water cut-off period, water plugging work becomes particularly important. Due to the limited construction of offshore oilfield, space water supply difficulties, and stability of plugging agent, self-generating enhanced foam has been designed as the aimed block plugging system. The formula is determined as: 23.25% of NH4Cl + 30% of NaNO2 + 0.1% of catalyst + 0.6% of COSL-3 foaming agent + 0.25% of HS-type HPAM foam stabilizer. Measurement point of pipe with permeability of 0.5 μm2 and 2 μm2 has been used in the plugging and EOR experiments. The experiments show that this system has the selective plugging effect for the heterogeneous formation, especially for middle and posterior part of high permeability formation, and the recovery rate of low permeability pipe is enhanced up to 32.15%.

Prompt Electrodeposition of Ni Nanodots on Ni Foam to Construct a High-Performance Water-Splitting Electrode:Efficient, Scalable,and Recyclable

In past decades,Ni-based catalytic materials and electrodes have been intensively explored as low-cost hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)catalysts for water splitting.With increasing demands for Ni worldwide,simplifying the fabrication process,increasing Ni recycling,and reducing waste are tangible sustainability goals.Here,binder-free,heteroatom-free,and recyclable Ni-based bifunctional catalytic electrodes were fabricated via a one-step quick electrodeposition method.Typically,active Ni nanodot(NiND)clusters are electrodeposited on Ni foam(NF)in Ni(NO3)2 acetonitrile solution.After drying in air,NiO/NiND composites are obtained,leading to a binder-free and heteroatom-free NiO/NiNDs@NF catalytic electrode.The electrode shows high efficiency and long-term stability for catalyzing hydrogen and oxygen evolution reactions at low overpotentials(10ηHER= 119 mV and 50ηOER=360 mV)and can promote water catalysis at 1.70 V@ 10mA cm-2.More importantly,the recovery of raw materials(NF and Ni(NO3)2)is quite easy because of the solubility of NiO/NiNDs composites in acid solution for recycling the electrodes.Additionally,a large-sized(S^70 cm2)NiO/NiNDs@NF catalytic electrode with high durability has also been constructed.This method provides a simple and fast technology to construct high-performance,low-cost,and environmentally friendly Ni-based bifunctional electrocatalytic electrodes for water splitting.

Synthesis of 3D Hexagram-Like Cobalt–Manganese Sulfides Nanosheets Grown on Nickel Foam: A Bifunctional Electrocatalyst for Overall Water Splitting

The exploration of low-cost and efficient bifunctional electrocatalysts for oxygen evolution reaction and hydrogen evolution reaction through tuning the chemical composition is strongly required for sustainable resources. Herein, we developed a bimetallic cobalt–manganese sulfide supported on Ni foam(CMS/Ni) via a solvothermal method. It has discovered that after combining with the pure Co_9S_8 and Mn S, the morphologies of CMS/Ni have modulated. The obtained three-dimensionally hexagram-like CMS/Ni nanosheets have a significant increase in electrochemical active surface area and charge transport ability. More than that, the synergetic effect of Co and Mn has also presented in this composite. Benefiting from these, the CMS/Ni electrode shows great performance toward hydrogen evolution reaction and oxygen evolution reaction in basic medium, comparing favorably to that ofthe pure Co_9S_8/Ni and Mn S/Ni. More importantly, this versatile CMS/Ni can catalyze the water splitting in a twoelectrode system at a potential of 1.47 V, and this electrolyzer can be efficiently driven by a 1.50 V commercial dry battery.

Effect of Post-Added Water Amount on Pre-Concentrated Bark Foaming Materials by Mechanical Stirring

In this study,pre-concentrated bark,furfuryl alcohol and other biomass raw materials were used to prepare foaming materials by high-speed mechanical stirring without using a foaming agent.We investigated the effect of the postadded water amount on the properties of foaming materials.In particular,we determined basic physical properties of these materials,including the limiting oxygen index(LOI),porosity,thermal conductivity,thermogravimetric analysis,pore size distribution,and microstructure.The results of scanning electron microscopy(SEM)indicated that the pore size distribution was uniform and the pore size increased with increasing water volume.Thermogravimetric analysis(TG/DTG)showed that when the temperature reached 410°C,the foam was easily decomposed,the final residual mass was only 2.8%,and water addition had little effect on it.Moreover,the amount of post-added water is 5–30 g,the density and compression strength of the foamed materials gradually decreased,while the degree of pulverization increased.LOI ranged from 26.1%to 30.79%,and porosity ranged from 81%to 83%.The change in water volume greatly affected the foam’s performance,the performance of foamed material deteriorated as the amount of added water increased,but the effect on thermal conductivity was not very obvious.The highest thermal conductivity was only 0.0179 W/(m·K),still providing excellent thermal insulation.

Properties of Water Blown Rigid Polyurethane Foams with Different Funetionality

Water blown rigid polyurethane foams with different functionality were prepared. The physical properties of rigid foams were measured with rotational viscometer （NDJ-1 ）, universal testing machine （Instron3365）, scanning electron microscope （SEM） and differential scanning calorimeter （DSC）. The results show that the viscosity of polyether polyol increases exponentially from 62 mPa s to 6 000 mPa s with the increase of functionality from 2 to 5.6, respectively. The overall density of foam increases slightly from 31.7 kg/m^3 to 37.4 kg/m^3 with increasing functionality while core density exhibited little difference. Compressive strength of foam shows the similar behavior with density except for 2-functional sample. At the same time, dimensional stability becomes better with increasing functionality except for 5.6-functional foam that has worse stability than 4.8-functional foam. From the SEM results, the functionality is not an important factor in determining distribution of cell size of foam. According to the results of thermal analysis, the glass transition temperature （T） shifts to a higher temperature from 128.9 ℃ to 166.3 ℃ for the 2 to 5.6 functional foam, respectively.

Visualization of Water Plugging Displacement with Foam/Gel Flooding in Internally Heterogeneous Reservoirs

During the displacement of water plugging with binary flooding in internally heterogeneous reservoirs,it is essential to understand the distributions of remaining oil as well as the oil displacement mechanisms at different stages.In this study,two types of internally heterogeneous systems,i.e.,vertical and horizontal wells are investigated experimentally through a microscopic approach.The results show that plugging agent types have a greater impact on oil recovery than well types,and foam injection can enhance oil recovery more effectively than gel injection.Additionally,the injection sequence of plugging agents significantly affects oil displacement efficiency.Injecting gel after foam is more beneficial.According to the present results,the main formation mechanisms of remaining oil in each displacement stage are influenced by:capillary force,viscous force,inertial force,shear force,microscopic fingering&channeling.

WATER-BLOWN POLYURETHANE RIGID FOAMS MODIFIED BY CHEMICAL PLASTICATION

Water-blown polyurethane rigid foams are getting more and more attention,because the traditional blowing agent HCFC141b has already been abolished to prevent the ozone layer from destruction.However,the polyurethane rigid foams blown by water have serious defects,i.e.friability and resulting lower adhesion strength.Thus,the purpose of this study is to resolve the problems by chemical plastication.The maleate was added to polyol-premix containing water or to polyisocyanate,with both of which maleate does not react.To prove the reaction when polyol-premix and polyisocyanate were mixed,the model composite was synthesized and analyzed by IR,NMR and ESI(MS).Furthermore,a series of water-blown polyurethane rigid foams added different amount maleate were successfully prepared.By testing impact strength and adhesion strength of the foams,the actual effect of adding maleate was obtained.

Coupled cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes supported on nickel foam as a binder-free electrode for overall water splitting

In an attempt to develop low-cost,non-noble-metal bifunctional electrocatalysts for water electrolysis in alkaline media,cobalt-doped molybdenum carbide@N-doped carbon nanosheets/nanotubes were fabricated by using C3N4 as the carbon source on a 3D porous nickel foam substrate.Benefiting from the optimized electronic structure and enhanced mass and charge transport,as well as the 3D conducting pathway,MoxCoy@N-CNSs/CNTs shows superior performance towards both the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in an alkaline medium.The optimal electrocatalyst is Mo2Co1@N-CNSs/CNTs,which reveals a current density of 10 mA cm^-2 at the low overpotentials of 99 mV and 300 mV for the HER and OER,respectively,and a relatively low cell voltage(1.63 V)for the overall water electrolysis.The method of optimizing the composition and nanostructure of a material provides a new avenue for the development and utilization of high-performance electrocatalysts.

In situ growth of minimal Ir-incorporated CoxNi1-xO nanowire arrays on Ni foam with improved electrocatalytic activity for overall water splitting

Exploration of cost-effective electrocatalysts for boosting the overall water-splitting efficiency is vitally important for obtaining renewable fuels such as hydrogen.Here,earth-abundant CoxNi1-xO nanowire arrays were used as a structural framework to dilute Ir incorporation for fabricating electrocatalysts for water splitting.Minimal Ir-incorporated CoxNi1-xO nanowire arrays were synthesized through the facile hydrothermal method with subsequent calcination by using Ni foam(NF)as both the substrate and source of Ni.The electrocatalytic water-splitting performance was found to crucially depend on the Ir content of the parent CoxNi1-xO nanowire arrays.As a result,for a minimal Ir content,as low as 0.57 wt%,the obtained Ir-CoxNi1-xO/NF electrodes exhibited optimal catalytic activity in terms of a low overpotential of 260 mV for the oxygen evolution reaction and 53 mV for the hydrogen evolution reaction at 10 mA cm?2 in 1 mol L–1 KOH.When used as bifunctional electrodes in water splitting,the current density of 10 mA cm–2 was obtained at a low cell voltage of 1.55 V.Density functional theory calculations revealed that the Ir-doped CoxNi1-xO arrays exhibited enhanced electrical conductivity and low Gibbs free energy,which contributed to the improved electrocatalytic activity.The present study presents a new strategy for the development of transition metal oxide electrocatalysts with low levels of Ir incorporation for efficient water splitting.

Ni3S2 nanorods growing directly on Ni foam for all-solid-state asymmetric supercapacitor and efficient overall water splitting

Transition metal compounds are attractive for their significant applications in supercapacitors and as non-noble metal catalysts for electrochemical water splitting.Herein,we develop Ni3 S2 nanorods growing directly on Ni foam,which act as multifunctional additive-free Ni3 S2@Ni electrode for supercapacitor and overall water splitting.Based on PVA-KOH gel electrolyte,the assembled all-solid-state Ni3 S2@Ni//AC asymmetric supercapacitor delivers a high areal energy density of 0.52 mWh cm^-2 at an areal power density of 9.02 MW cm^-2,and exhibits an excellent cycling stability with a capacitance retention ratio of 89%after 10000 GCD cycles at a current density of 30 mA cm^-2.For hydrogen evolution reaction and oxygen evolution reaction in 1 M KOH,Ni3 S2@Ni electrode achieves a benchmark of 10 mA cm^-2at overpotentials of 82 mV and 310 mV,respectively.Furthermore,the assembled Ni3 S2@Ni‖Ni3 S2@Ni electrolyzer for overall water splitting attains a current density of 10 mA cm^-2 at 1.61 V.The in-situ synthesis of Ni3 S2@Ni electrode enriches the applications of additive-free transition metal compounds in high-performance energy storage devices and efficient electrocatalysis.

A study on effects of ceramic foam filter on flow aspect through water modeling experiment

Casting defects that are closely related to entrapped air bubbles and metallic oxides occur very frequently in the sand mold casting process. Many researchers have shown that these defects can be reduced by adopting an appropriate gating system design. However, it is difficult for field engineers to identify a specific gating system that is more appropriate for their products. In this study, we tried to draw a comparison between two gating system designs with and without a ceramic foam filter. The ceramic foam filter was added to the horizontal runner just after the down sprue to prevent air bubble generation and reduce turbulence without a change of gating system design. The water modeling experiment was conducted with four different amounts of the initial volumes of water in the reservoir to verify the effects of initial pouring velocity. The results of the experiment applying the filter showed remarkably changed flow characteristics. The use of the filter was found to convert the flow pattern of water in the desired direction. The ceramic foam filter performed well to reduce flow velocity and stabilize the water stream.The flow pattern without a filter can be improved significantly even with the the use of just a 10 PPI irregular filter. Although the study confirmed that use of the filter may change the flow characteristics, it needs to be noted that the use of the ceramic filter alone cannot solve all the problems caused by a poorly designed gating system.