Oxyhydroxide Research Articles

Mineralogy and environmental geochemistry of copper slag from Butte, Montana

Herein we characterize the mineralogy, chemical composition, and environmental geochemistry of slag formed by historic (1880s to circa 1910) smelting of the copper-rich lodes of Butte, Montana. The air-cooled slag exists as monolithic “walls” that border Silver Bow Creek, the headwaters of the upper Clark Fork River Superfund site. The slag is mainly comprised of fayalite, hedenbergite, wollastonite, magnetite, and glass. Zinc is present at per cent levels in all of these phases. The overall high zinc content of the slag is partly due to the polymetallic character of the Butte ore bodies. Copper occurs mainly as tiny spheres, or “prills”, which are remnants of the molten Cu-sulfide matte that failed to separate from the slag during smelting. Minerals in the prills include bornite, chalcopyrite, chalcocite, pyrrhotite, pyrite, sphalerite, galena, elemental copper, and elemental silver. The prills are variably oxidized along shrinkage cracks that penetrate into the enclosing slag matrix. Secondary minerals, including hydrous ferric oxide and ferric clay, coat the cracks. Where the cracks meet the surface of the slag, secondary encrustations of calcite, FeMn oxyhydroxides, and mixed Ca-Cu-Zn-Mn-Al-Fe sulfates have locally accumulated. Acid-base accounting tests show that the unweathered slag is non-acid-generating, with the acid potential from FeCu sulfides offset by the neutralization potential of the CaFe silicates (olivine, pyroxene). Interaction of the slag with synthetic precipitation (SPLP tests) confirms the slag's ability to buffer pH to values >8. Nonetheless, the SPLP leachate solutions contain ppb levels of copper, arsenic, zinc, and lead that approach or exceed current regulatory standards for protection of aquatic life (Cu, Pb, Zn) and human health (As). Leaching experiments using Silver Bow Creek water show an increase in dissolved As and W, but variable results for Cu, Pb, and Zn. Leaching of the secondary sulfate-salt deposits produced much higher concentrations of dissolved metals and metalloids which could be a source of contamination to Silver Bow Creek during heavy rain events. Based on bulk analyses, some metals in the slag, including Fe, As, Co, Mn, Pb, Zn, and W, exceed USEPA screening levels for residential and/or urban soils. Leachates containing organic acids (TCLP tests) show Pb concentrations that approach levels for the slag to be classified as hazardous waste. Rather than removing the slag walls, which have value as a form of industrial architecture, an alternate remedy currently under evaluation is to divert Silver Bow Creek around the smelter site and preserve the slag as part of a non-motorized recreational trail system in the reclaimed Butte-Anaconda mine-scape.

SECONDARY MINERAL FORMATION IN PRODUCTIVE DEPOSITS OF THE PASHIYSKY HORIZON OF THE SOUTH TATAR ARCH (REPUBLIC OF BASHKORTOSTAN)

The article presents the results of studying the postsedimentary mineralization of productive terrigenous deposits of the Pashiysky horizon of the South Tatar arch. The authors' research was carried out on the basis of a large amount of core material from newly studied wells with the involvement of wells from the archival fund. The analytical work included the following methods: classical optical microscopy and scanning electron microscopy (SEM). Using these methods, the main types of secondary mineral formation, the form and nature of the allocation of authigenic minerals that form secondary cement were studied, and an assessment of the degree of their influence on the filtration-capacitive properties (FPP) was given. It is shown that sideritization is a fairly common phenomenon in the studied deposits, but it does not have a significant effect on the reduction of the reservoir properties of productive deposits. Detailed optical and mineralogical studies have shown that authigenic siderite in the studied rocks is presented in various forms (spherites, spherulites, oolites and granular grains) and is mostly found in silt varieties. In productive sandstones, an insignificant decrease in the reservoir properties can only be associated with expanding rims in siderite spherites. As shown by the study of the composition of these rims, they are composed mainly of ankerite, in places they contain mangano-siderite. In some samples of the Pashiysky horizon, partial replacement of siderite by iron hydroxides was observed; in isolated wells, thin layers of oolitic siderite-ferruginous rocks were encountered. It was shown that the main influence on the reduction of the filtration-capacity properties of the studied sediments is secondary silification and carbonatization. At the same time, secondary quartz is developed mainly in water-saturated sandstones and heterogeneous silt-sandstones, and, as a rule, is distributed mostly locally. Secondary silica is observed in the form of regeneration rims, xenomorphic grains and is deposited on the walls of pores and channels. A significant effect on the reduction of the porosity and permeability parameters of the productive sandstones of the Pashiysky horizon of the South Tatar arch is exerted by secondary crystalline calcite or dolomite island cement of the basal, basal-pore and poikillite type.

Further Results on the Effects of the Grinding Environment on the Flotation of Copper Sulphides

Grinding conditions affect the flotation of copper sulphide minerals as changes in the properties of the grinding media and their interactions with the sulphide minerals, and between sulphide minerals themselves, affect the chemical environment in the flotation pulp. Galvanic interactions between steel grinding media and sulphide minerals, and between sulphide minerals, can lower the pulp potential, decrease the dissolved oxygen concentration in the mineral slurry, and lead to the dissolution of iron and copper from the media and the minerals. As a result, the formation of hydrophilic iron hydroxides and their adsorption on the copper sulphide minerals can be deleterious to copper flotation while pyrite (when present) can be activated to flotation by dissolved copper lowering the grade of the copper concentrate. Electrochemically less active grinding media (e.g., chrome alloy balls rather than mild steel media) can have beneficial effects on flotation performance due to the lower oxidation of the grinding media and consequently the lower production of oxidised iron species in the pulp. Copper activation of pyrite can be decreased by chemical additions to the pulp. In this paper, relevant experimental data published in the last 15 years are discussed.

Morphogenetic varieties of iron oxyhydroxides in shimmering smokers-diffusers of the Rainbow hydrothermal field (36°13′ N, 33°54′ W, Mid-Atlantic Ridge): LA-ICP-MS data for the development of halmyrolysis theory

Research subject. Iron oxyhydroxides covering and replacing the chimneys of shimmering water smokers-diffusers of the Rainbow hydrothermal field (MAR). Aim. To identify features of the concentration and associations of chemical elements in varieties of iron oxyhydroxides to recognize patterns of geochemical differentiation under conditions of halmyrolysis of sulfide chimneys-diffusers. Materials and methods. Samples were collected during a dive to a depth of 2300 m using the manual manipulator of the Mir-2 manned vehicle (travel No. 50, research vessel Akademik Mstislav Keldysh, 2005). Varieties of iron ohyhydroxides were identified using electron microscopes (REMMA-202М with LZ-5 Link system, Tescan Vega 3 sbu with an Oxford Instruments X-act energy-dispersive analyzer, and Jeol Superprobe 733 with an EDA Oxford Instruments INCAx-sight) and a powder X-ray diffractometer (SHIMADZU XRD-6000, CuK-α radiation with monochromator). Further, a mass spectrometry with inductively coupled plasma and laser ablation (LA-ICP-MS) analysis was conducted at the South Urals Federal Scientific Center of Mineralogy and Geoecology, Ural Branch of the Russian Academy of Sciences. Results. Microlayered goethite aggregates containing admixtures of barite, calcite, aragonite, native sulfur, covellite, sphalerite, and an X-ray amophoric oxyhydroxide phase of iron cover the shimmering diffusers. Towards the inner parts of the chimney walls, they are replaced by pseudomorphs of lepidocrocite after pyrite and pyrrhotite, and then by radial and bacteriomorphic crustifications of lepidocrocite. The use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) showed that goethite varieties have the increased contents of Zn and Co associated with other elements of medium-temperature hydrothermal fluids (Cd, Mn, Ni, Ga, Sn, Pb and Sb) in the absence of significant concentrations of a high-temperature hydrothermal association (Se, Bi, Te). The role of elements of seawater association (Mg, Na, K, Sr, U, V, As, Mo, Ni, P, B, W, Cs, REE) decreases from the surface layered goethite aggregates to crustification varieties of lepidocrocite. Different scenarios of accumulation under conditions of sulfide halmyrolysis and precipitation on local reduction barriers are proposed for elements with different valences (U, V, Mo, As, Cr, Eu). It is assumed that some of the microelements (Sr, V, As, P, REE) found in goethite are products of sorption on iron hydroxides or are part of invisible Fe-Ca hydroxyphosphates. Conclusion. The influence of sulfide halmyrolysis on the differentiation of chemical elements has been revealed.

Evaluation of Ferric Ion Adsorption On The Surface Imprinting Adsorbent

<span lang="EN-AU">Rapidity in technological aspects encourages industrial sector to utilize and apply the latest technology to accelerate and optimize production in its field. Thus, waste from industry polluting various aspects of environment, such as water, gives rise to environmental impacts. Heavy metals, including iron, are one of the most common and dangerous pollutants often found in water environments. Therefore, consideration of methods for heavy metal separation from water becomes important. The adsorption method has been used for separating heavy metals because of its simplicity, thus effectively cuts energy consumption and costs in process. However, heavy metal characteristics in water can vary depending on the element. Consequently, understanding the heavy metal characteristics in water is important, hence capable of formulate appropriate and effective adsorption systems. This study, Fe(III)-IIPs was applied to adsorb and separate iron from water through repeated adsorption with parameter improvements. The pH parameter plays an important role, with ion competition happens at pH <2 and the formation of iron hydroxide species at pH >4.5, which results in adsorption inhibition. The modeling of adsorption kinetic equation was found that the adsorption system carries chemisorption characteristics, with adsorption capacity of 11.15 mg/g and reaction rate constant of 19 min<sup>-1</sup>.</span>

Synthesis, characterization and study of Sb(Ⅲ) adsorption from aqueous solution by iron-aluminum pillared attapulgite

In this study, a simple, environmentally friendly and inexpensive adsorbent for Sb(III) in aqueous solution was prepared by the copolymerization method using attapulgite as the matrix, FeCl3 and AlCl3 as the metal sources. The morphology and structure of iron-aluminum pillared attapulgite were analyzed through various characterization methods. The conditions and influencing factors of iron-aluminum pillared attapulgite preparation and Sb(III) adsorption were studied. The saturated adsorption capacity of Sb(III) could reach 60.44 mg·g−1 for 180 min at pH 7 and 298 K. The adsorption process is conformed to Langmuir isothermal model and pseudo-second-order kinetic model, and the thermodynamic investigation suggested a spontaneous and endothermic adsorption process. It was revealed by X-ray photoelectron spectroscopy analysis and Zeta potential analysis that Sb(III) was first electrostatically adsorbed by the adsorbent, part of Sb(III) was oxidized to Sb(V) by Fe(III) and then antimony was complexed with iron and aluminum hydroxides to form surface complexes. In addition, a small amount of antimony migrated through intra-particle diffusion into the internal micropores and reacted with hydroxyl groups. Most coexisting components under the chosen conditions had no influence on Sb(III) adsorption, and PO43−, AsO33−, C6H8O7 and H2C2O4 had a negligible effect. However, the adsorption capacity of over 90 % without interference showed that the material has a strong selectivity for Sb(III) adsorption. The findings of the desorption experiment showed that the adsorption product has a considerable degree of desorption at increased hydrochloric acid concentrations. It may be concluded that the adsorption product is more stable in the overall polluted water environment since the actual acidity of the polluted water environment is significantly lower than the desorption experiment acidity. Overall, iron-aluminum pillared attapulgite has great potential for application in removing Sb(III).

Silicate coprecipitation reduces green rust crystal size and limits dissolution-precipitation during air oxidation

Green rusts (GR) are mixed-valence iron (Fe) hydroxides which form in reducing redox environments like riparian and wetland soils and shallow groundwater. In these environments, silicon (Si) can influence Fe oxides’ chemical and physical properties but its role in GR formation and subsequent oxidative transformation have not been studied starting at initial nucleation. Green rust sulfate [GR(SO4)] and green rust carbonate [GR(CO3)] were both coprecipitated from salts by base titration in increasing % mol Si (0, 1, 10, and 50). The minerals were characterized before and after rapid (24 h) aqueous air-oxidation by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fe extended x-ray absorption fine structure spectroscopy (EXAFS), and N2-BET surface area. Results showed that only GR(SO4) or GR(CO3) was formed at every tested Si concentration. Increasing % mol Si caused decreased plate size and increased surface area in GR(CO3) but not GR(SO4). GR plate basal thickness was not changed at any condition indicating a lack of Si interlayering. Air oxidation of GR(SO4) at all % mol Si contents transformed by dissolution and reprecipitation into lepidocrocite and goethite, favoring ferrihydrite with higher % Si content. Air oxidation of GR(CO3) transformed into magnetite and goethite but increasing Si caused GR to oxidize while retaining its hexagonal plate structure via solid-state oxidation. Our results indicate that Si has the potential to cause GR to form in smaller particles and upon air oxidation, Si can either stabilize the plate structure or alter transformation to ferrihydrite.Graphical

Speciation Controls the Kinetics of Iron Hydroxide Precipitation and Transformation at Alkaline pH.

The formation of energetically favorable and metastable mineral phases within the Fe-H2O system controls the long-term mobility of iron complexes in natural aquifers and other environmentally and industrially relevant systems. The fundamental mechanism controlling the formation of these phases has remained enigmatic. We develop a general partial equilibrium model, leveraging recent synchrotron-based data on the time evolution of solid Fe(III) hydroxides along with aqueous complexes. We combine thermodynamic considerations and particle-morphology-dependent kinetic rate equations under full consideration of the aqueous phase in disequilibrium with one or more of the forming minerals. The new model predicts the rate of amorphous 2-line ferrihydrite precipitation, dissolution, and overall transformation to crystalline goethite. It is found that the precipitation of goethite (i) occurs from solution and (ii) is limited by the comparatively slow dissolution of the first forming amorphous phase 2-line ferrihydrite. A generalized transformation mechanism further illustrates that differences in the kinetics of Fe(III) precipitation are controlled by the coordination environment of the predominant Fe(III) hydrolysis product. The framework allows modeling of other iron(bearing) phases across a broad range of aqueous phase compositions.

Particle size analysis of iron hydroxide adipate tartrate (IHAT) in a food supplement: Interlaboratory testing of a dynamic light scattering method

Iron hydroxide adipate tartrate (IHAT) is a nano-scale material with a diameter of less than 5 nm intended for use as iron source in food supplements. It is the first engineered nanomaterial that was authorised as novel food in the European Union in 2022 (Commission Implementing Regulation (EU) 2022/1373) and subsequently added to the European Union list of novel foods. Official control laboratories of EU Member States are required to conduct compliance testing of novel foods, including IHAT, against approved specifications. In the case of IHAT, the authorised specifications include the constituent particle size, referred to in the implementing regulation as ‘primary particle size’. In this study, a method to determine the constituent particle size distribution of IHAT using the volume-based hydrodynamic diameter with dynamic light scattering is proposed and tested in an interlaboratory comparison study involving five experienced European food control and food research laboratories. Three test materials were examined, including an early batch of IHAT without the flow agent, a damaged material unintentionally exposed to water, and the final commercial product that included the flow agent. The results demonstrate that dynamic light scattering can reliably measure the particle size of particles in the low nanometre range if samples are prepared and measured following a robust, easy-to-reproduce, and standardised protocol. The results obtained for the commercial product met the compliance requirements specified in the annex of the Commission Implementing Regulation in all laboratories for the primary particle size distribution (Dv(10/50/90)). The method proposed in this study could represent an initial step towards the full validation of the method.

Oxyanions Enhancing Crystallinity of Reconstructed Phase for Oxygen Evolution Reaction.

The catalysts were always undergoing continuous amorphization and dissolution of active structure in operating condition, hindering the compatibility between stability and activity for oxygen evolution reaction (OER). Herein, we propose the selective adsorption of leached NO3- to strengthen the crystallinity and activity of surface reconstructed layer with amorphous and crystalline (a-c) heterojunction. Taking a-c Ni doped Fe2O(OH)3NO3·H2O (Ni-FeNH) as a model precatalyst, we uncover that the leached NO3- are readily adsorbs on the crystalline phase in the formed a-c Fe(Ni)OOH during OER, lowering the disorder degree and further activating Ni and Fe ion of the crystalline Fe(Ni)OOH on a-c heterojunctions. Accordingly, Ni-FeNH deliver a low overpotential of 303 mV and high durability of 500 hours at 500 mA cm-2 for OER. Particularly, constructing industrial water electrolysis equipment exhibits high stability of 100 hours under a high operating current of 8000 mA.

Oxyanions Enhancing Crystallinity of Reconstructed Phase for Oxygen Evolution Reaction

The catalysts were always undergoing continuous amorphization and dissolution of active structure in operating condition, hindering the compatibility between stability and activity for oxygen evolution reaction (OER). Herein, we propose the selective adsorption of leached NO3‐ to strengthen the crystallinity and activity of surface reconstructed layer with amorphous and crystalline (a‐c) heterojunction. Taking a‐c Ni doped Fe2O(OH)3NO3·H2O (Ni‐FeNH) as a model precatalyst, we uncover that the leached NO3‐ are readily adsorbs on the crystalline phase in the formed a‐c Fe(Ni)OOH during OER, lowering the disorder degree and further activating Ni and Fe ion of the crystalline Fe(Ni)OOH on a‐c heterojunctions. Accordingly, Ni‐FeNH deliver a low overpotential of 303 mV and high durability of 500 hours at 500 mA cm‐2 for OER. Particularly, constructing industrial water electrolysis equipment exhibits high stability of 100 hours under a high operating current of 8000 mA.

Effective elimination of internal phosphorus pollution with MgFe-LDHs hybrid material in eutrophic water: The chemical forms, transformation mechanism, and dynamic relationships

The internal phosphorus (P) pollution is a major cause of water eutrophication. Although the traditional powders materials, with good performance, were difficult to recycle due to its shape, and the reaction mechanism between materials and internal P was rarely elucidated. In this work, a hydrotalcite composite material (MgFe-LDHs hybrid gel microspheres) was prepared via chemical crosslinking to eliminate internal P pollution both in overlying water and sediments effectively. Benefiting from the strong coordination between iron hydroxide on the MgFe-LDHs surface and internal P, the P adsorption capacity was up to 1256.38 mg/kg under natural conditions, the IP (NaOH-P and HCl-P) and OP were 78 % and 22 %, respectively. During 40-days remediation experiment, with the addition of MgFe-LDHs hybrid gel microspheres, whatever in the mixed or the capped, promoted a conversion from stable P to soluble active P of NaOH-P in sediments, and thus contributing to an easy adsorption of NaOH-P by MgFe-LDHs hybrid gel microspheres (The NaOH-P in sediments decreased by 16 % and 22 %, respectively). Meanwhile, the excessive stable HCl-P (only a minor portion) that could not be adsorbed by MgFe-LDHs remained in the form of Ca-P in sediments. Additionally, the MgFe-LDHs hybrid gel microspheres improved the microbial community structure, and the microorganism was involved in the elimination of internal P simultaneously. In summary, this study proposed a promising remediation approach to resolve the problem of internal P pollution in eutrophic water with high efficiency, cost-effective, and environmentally friendly.

Sheet nanocomposites of sorghum stalk loaded with hydrated ferric oxide for Cu(Ⅱ) deep removal from water

Novel sheet porous nanocomposites were developed for Cu(II) deep removal form water utilizing waste crop stalks. Hydrated ferric oxide (HFO) was coated onto the surface of sorghum crop stalk (SCS) through a simple and cleaner impregnation-surface deposition method to fabricate the nanocomposite adsorbent SCS-HFO. BET, SEM-EDX, FTIR and XPS characterization proved that HFO with a particle size of 10–50 nm was successfully loaded on the sorghum stalk surface. High level of coexisting cations such as Na+, Mg2+ and Ca2+ in aqueous solution had little influence on the Cu2+ adsorption capacity, showing that SCS-HFO had excellent adsorption selectivity. The adsorption of Cu2+ onto SCS-HFO fitted to Langmuir isothermal model, and the adsorption process conformed to the quasi-secondary kinetics, which indicates that monolayer chemical adsorption is dominant. The fixed-bed column of SCS-HFO could effectively reduce the Cu2+ concentration in 6.8 L of simulated wastewater to less than 0.01 mg/L. The NaCl-NH3·H2O mixed solution can regenerate SCS-HFO, and the adsorption efficiency of SCS-HFO still reaches more than 90 % after multiple adsorption-desorption cycles, indicating good stability of the prepared material. This study successfully constructed and fabricated a green and cost-effective nanocomposite adsorbent based on agricultural waste.

Environmentally friendly, high near-infrared reflection green pigments for thermal insulation

In this paper, TiO2 and MgAl-LDHs were coated on yellow pigment hydroxyl iron oxide (FeOOH) with sol-gel and hydrothermal synthesis method respectively to prepare loaded yellow pigment (FT8M0.25). Then, phthalocyanine blue (CuPc) was combined with FT8M0.25 to prepare composite green pigment (FT8M0.25Px). The results indicate the FT8M0.25Px has the structural characteristics of hydrotalcites and CuPc. The surface of FeOOH pigment has a clear TiO2 coating layer and MgAl-LDHs flake structure. KPFM analysis indicate that there is electron transfer between the interfaces of pigments. According to the analysis of color performance and near-infrared reflectance (NIR), the FT8M0.25P0.13 (a*=-12.98) is greener than that of Cr2O3 (a*=-6.65). The NIR of FT8M0.25P0.13 is as high as 73.54 %. The visible light absorption spectrum characteristics determine the color of the pigments, and there is electron transfer between the interfaces of each group. The formation of multi-level interfaces and the resulting multiple light reflections increase the reflectivity of the pigment. The developed coating achieved a considerable temperature difference of 20 °C before and after the coating surface with excellent photostability and reusability, which makes it possible for pigments to replace chromium containing pigments and be used as energy-saving cold pigments.

Electronic structure engineering of NiFe hydroxide nanosheets via ion doping for efficient OER electrocatalysis

Nickel-iron layered double hydroxides (NiFe-LDH) with tunable catalytic properties have shown promise as an outstanding alternative to ruthenium iridium oxide for the oxygen evolution reaction (OER). However, the intrinsic activity of such electrocatalysts is suboptimal, and a considerable gap remains in understanding the working mechanism. To address this issue, we employ a convenient corrosion method to synthesize Mo-modified nickel–iron hydroxide (Mo-NiFeOxHy) ultrathin nanosheets. Mo-NiFeOxHy demonstrates excellent OER activity, requiring only 216 mV at a current density of 10 mA cm−2, with enhanced stability. Theoretical calculations reveal that the Mo doping induces material distortion, shifting the d-band center closer to the Fermi level, which accelerates the kinetic rate and catalytic activity. In situ Raman experiments show that doping with Mo promotes the rapid formation of high-oxidation-state transition metal hydroxide species, further enhancing the catalytic properties of Mo-NiFeOxHy in OER. This work provides a novel strategy to tailor the structure and composition of NiFe-based electrocatalysts, demonstrating a great potential to break barriers in OER.

Development of new cathode materials for all-iron redox flow batteries using hard carbon-based composites containing niobium pentoxide

We report in this study new cathodes for all-Fe RFBs synthesized using carbon flakes dispersed in plasticizing and hardening agents to obtain hard and dense carbon (HC) materials in the absence and presence (HC-Nb) of niobium pentoxide (Nb2O5). These cathode materials exhibited excellent resistance to wear in acidic solutions and larger potential intervals for water stability (e.g., 1200–1300 mV) compared to conventional graphite (e.g., 800 mV). These characteristics decreased the parasitic occurrence of hydrogen evolution reaction (HER) using a laboratory-made battery cell during the charging process. The latter was based on the Fe0/Fe2+ and Fe2+/Fe3+ redox couples present in the anode and cathode compartments, respectively. The different ex-situ and in-situ characterization studies evidenced that the presence of Nb2O5 in HCs substantially changed their physicochemical properties. The highest heterogenous kinetic rate constant (k0) representing the electrocatalytic activity for electron transfer was verified for the cathode containing 10 wt.% Nb2O5. An electromotive force (EMF) of 1.053 V was verified for the fully charged all-Fe RFB. Galvanostatic charge–discharge (GCD) studies revealed excellent coulombic efficiency (> 88 %) after 300 cycles. A pH control by acid addition as a function of the battery operation is necessary to avoid iron hydroxide formation on the anode’s surface.

Highly efficient oxygen carrier NiFeP (oxy) hydroxides nanoparticle embedded in N-doped porous carbon derived from bio-waste for bifunctional electrocatalysts

Developing cost-effective, readily available materials for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting is a crucial step toward enhancing the profitability and sustainability of energy conversion systems. This research introduces a novel synthesis method for NiFeP/NPC OHs from banana peel bio-waste, a method that could revolutionize the field of materials science and electrochemistry. The use of metallic phosphides, known for their excellent electrical conductivity and catalytic activity, as bifunctional catalysts, combined with the efficient synthesis of nanoporous carbons (NPC) from banana peel bio-waste (BPW), could pave the way for a new era of sustainable and cost-effective energy conversion. By chemically activating different porogens, such as nickel, iron, and phosphorus (NiFeP), to form (oxy) hydroxides (OHs), functional carbonaceous structures with a high density of pores and large specific surface areas can be achieved. The resulting materials, designated as NiFeP/NPC OHs, are characterized by their remarkable porosity, high conductivity, large surface area, and chemical stability. These properties make NiFeP/NPC OHs particularly suitable for electrocatalysis, where they exhibit outstanding activity in both HER and OER. The optimized NiFeP/NPC OHs material shows a very low overpotential of 93 mV for HER and 243 mV for OER at 10 mA cm⁻2 and high durability over 100 h. Moreover, the bifunctional NiFeP/NPC OHs electrode demonstrates exceptional catalytic activity and stability in alkaline solutions. This study not only highlights the innovative synthesis of NPC from BPW and the cost-effective fabrication of NiFeP/NPC OHs but also sparks curiosity about the potential of this novel synthesis method.

Facile synthesis and electrochemical properties of FeO/Fe(OH)3 nanosheets

Iron oxides and hydroxides, including Fe(OH)3 and Fe(OH)2, exhibit diverse morphologies and compositions. Nanostructures of Fe(OH)3 such as nanosheets are non-toxic and offer multiple active sites that are advantageous for catalysis. We synthesized iron oxide/iron hydroxide (FeO/Fe(OH)3) nanosheets using a surfactant-assisted method and analyzed their structure and composition. Their phase transition to iron oxyhydroxides/oxides via heat treatment were also analyzed. The formation of FeOOH, which catalyzes the oxygen evolution reaction, significantly affected the electrochemical properties. We report the morphological and crystallographic characteristics of the as-synthesized and annealed FeO/Fe(OH)3 nanosheets, highlighting the influence of specific species on their electrochemical behavior. The proposed approach is simple and efficient for the synthesis of highly crystalline transition metal oxide nanosheets using different cation precursors.

The interstitial Ru dopant induces abundant Ni(Fe)[sbnd]Ru cooperative sites to promote ampere-level current density for overall water splitting

Directionally induced interstitial Ru dopant rather than ordinary substitutional doping is a challenge. Furthermore, DFT calculations revealed that compared with the substituted Ru dopants, the interstitial Ru dopants induce abundant Ni(Fe)Ru cooperative sites, greatly expediting the reaction kinetics for HER and OER. Inspired by these, the interstitial Ru-doped NiFeP/NF electrode is constructed by the ’quenching doped Ru-phosphorization’ strategy. Relevant physical characterizations confirmed that interstitial Ru dopants promote electron reset in the Ni(Fe)Ru synergistic sites, effectively avoiding metal atom dissolution and encouraging more Ni (Fe)OOH active species. As expected, the Ru-NiFeP/NF||Ru-NiFeP/NF electrolyzer only need as low as 1.54 V to yield a current density of 1 A cm−2. In summary, this work innovatively constructs the phosphide electrode with ampere-level current density from the perspective of regulating the doping position of Ru. This provides a new design idea for optimizing the Ru doping strategy.

Amorphous/crystalline Ni-Fe based electrodes with rich oxygen vacancies enable highly active oxygen evolution in seawater electrolysis

To realize large-scale production of hydrogen through seawater electrolysis, it is highly crucial to engineer high-activity and robustly stable catalytic materials for oxygen evolution reaction (OER). Here, a facile etching growth strategy based on Ni foam (NF) is employed to fabricate an amorphous/crystalline Ni-Fe based electrode with rich oxygen vacancies as a promising OER electrocatalyst (a/c-NiFeOxHy@NF). Of note, the introduction of Fe induces the generation of plentiful Ni(Fe)OOH species, which can contribute to the remarkable OER behavior. Profiting from the favorable geometric microstructure of ultrathin nanosheets coupled with 3D open-pore architecture and regulated electronic state by increased oxygen vacancies and abundant crystalline-amorphous boundaries, the resulting a/c-NiFeOxHy@NF displays prominent electrocatalytic OER activity in pure alkaline solution and seawater, achieving impressive overpotentials of only 219 and 233 mV to reach 100 mA cm−2, respectively. More significantly, the electrode can keep stable operation without obvious attenuation for over 1200 h at 100 mA cm−2, demonstrating its exceptional corrosion resistance. Such robustness of this electrode surpasses those of almost all reported OER electrocatalysts. Furthermore, in a self-assembled seawater electrolyzer with a/c-NiFeOxHy@NF as the anode and l-RuP@NF as the cathode, a large current density of 500 mA cm−2 is easily achieved at the voltage of 1.795 V at 65 °C. The work offers a novel paradigm for constructing low-cost, high-efficiency, and ultra-stable OER catalysts, which shows huge promise for industrial seawater electrolysis applications.