Metal Oxyhydroxides Research Articles

A widely applicable method to stabilize nanoparticles comprising oxygen-rich functional groups

Colloidal stability of nanoparticle suspensions is fundamental to apply nanomaterials in functional devices and to develop new methodologies in nanoscience. Herein, a versatile method is described to disperse and stabilize various solids with technological applications in pharmaceutical industry, batteries and fuel cells, dye sensitized solar cells, pigments and coatings. The method is based on the use of Zr(IV) hydroxo-complexes that interact with carboxylic- and hydroxo- functional groups at the solid-liquid interfaces of active pharmaceutical ingredients (API), carbon black (CB) and Pt-CB, metal oxide and metal oxy-hydroxide nanoparticles. The colloidal stability is assessed via sedimentation analysis, electrophoretic measurements, ultraviolet-visible spectroscopy (UV–Vis), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and isothermal titration calorimetry (ITC). The effect of the anion and pH are studied in depth. Finally, the current work enables liquid phase length and diameter characterization of rod-like goethite (α-FeOOH) particles without relying on tedius counting the particles from electron micrographs.

S/Se dual-doping promotes the formation of active Ni/Fe oxyhydroxide for oxygen evolution reaction of (sea)water splitting

Surface reconstruction produces metal oxyhydroxide (∗OOH) active sites, and promoting surface reconstruction is essential for the design of OER electrocatalysts. In this paper, we reported that a large amount of active NiFeOOH was generated in-situ on the surface of nickel-iron sulfide selenide, thus exposing more active sites and efficiently catalyzing OER. In 1 M KOH solution, NiFeOOH(S,Se) achieves an ultra-low overpotential of 195 mV at the current density of 10 mA cm−2, and the Tafel slope is only 31.99 mV dec−1, showing excellent catalytic performance. When the current density is 100 mA cm−2, the over-potential of NiFeOOH(S,Se) in KOH + seawater solution is 239 mV, which is almost equivalent to 231 mV in KOH solution. The excellent OER stability of the NiFeOOH(S,Se) catalyst in alkaline electrolytes was confirmed, and the overpotential did not change significantly after 4 days of testing in KOH + seawater solution.

Effect of Thermal Treatment on Nickel‐Cobalt Electrocatalysts for Glycerol Oxidation

AbstractNickel‐cobalt electrocatalysts with atomic ratios of 2 : 1 and 1 : 2 were synthesized on nickel foam (NF) substrates by cathodic electrodeposition, further evaluating the performance of the pristine and thermally‐treated materials as anodes for glycerol oxidation in alkaline medium. The electrodes were characterized by cyclic and linear sweep voltammetry at alkaline pH, showing an indirect oxidation of glycerol mediated by the metal oxyhydroxides. Under the selected conditions, a favourable potential window of 0.2 V upon comparison of water and glycerol oxidation was found. In addition, the increase in nickel content and the thermal treatment enhanced the anode polarization. After galvanostatic electrolysis at 10 mA cm−2, the products were analysed by HPLC, formate ion being the primary product, with a faradaic efficiency (FE) higher than 70 % in most cases. Both the FE to formate and the glycerol conversion were substantially enhanced using the thermally‐treated anodes, whereas the effect of the Ni/Co ratio on these two parameters did not follow a clear trend.

Spectroelectrochemical Analysis of the Water Oxidation Mechanism on Doped Nickel Oxides.

Metal oxides and oxyhydroxides exhibit state-of-the-art activity for the oxygen evolution reaction (OER); however, their reaction mechanism, particularly the relationship between charging of the oxide and OER kinetics, remains elusive. Here, we investigate a series of Mn-, Co-, Fe-, and Zn-doped nickel oxides using operando UV–vis spectroscopy coupled with time-resolved stepped potential spectroelectrochemistry. The Ni2+/Ni3+ redox peak potential is found to shift anodically from Mn- < Co- < Fe- < Zn-doped samples, suggesting a decrease in oxygen binding energetics from Mn- to Zn-doped samples. At OER-relevant potentials, using optical absorption spectroscopy, we quantitatively detect the subsequent oxidation of these redox centers. The OER kinetics was found to have a second-order dependence on the density of these oxidized species, suggesting a chemical rate-determining step involving coupling of two oxo species. The intrinsic turnover frequency per oxidized species exhibits a volcano trend with the binding energy of oxygen on the Ni site, having a maximum activity of ∼0.05 s–1 at 300 mV overpotential for the Fe-doped sample. Consequently, we propose that for Ni centers that bind oxygen too strongly (Mn- and Co-doped oxides), OER kinetics is limited by O–O coupling and oxygen desorption, while for Ni centers that bind oxygen too weakly (Zn-doped oxides), OER kinetics is limited by the formation of oxo groups. This study not only experimentally demonstrates the relation between electroadsorption free energy and intrinsic kinetics for OER on this class of materials but also highlights the critical role of oxidized species in facilitating OER kinetics.

Synthesis of hierarchical transition metal oxyhydroxides in aqueous solution at ambient temperature and their application as OER electrocatalysts

First-row (3d) transition metal oxyhydroxides have attracted increasing attention due to their various advantages. Although investigating the oxidation mechanism and processing such materials into hierarchical architectures are greatly desired for their further development, it remains unclear how the oxidation state change occurs, and efforts to produce hierarchical oxyhydroxides in compliance with high ecological and economic standards have progressed slowly. Here, we describe a facile one-step coprecipitation route for the preparation of hierarchical CoOOH, NiOOH and MnOOH, which involves the diffusion of NH3 originating from ammonium hydroxide solution into an aqueous solution containing metal ion salts and K2S2O8. Comprehensive characterizations by scanning electron microscope, transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy and in situ pH measurement demonstrated that K2S2O8 induces the oxidation state change of metal ion species after the start of hydrolysis. Meanwhile, it was found that, benefiting from the OH– concentration gradient created by the NH3 diffusion method and the suitable growth environment provided by the presence of K2S2O8 (high nucleation rate and secondary nucleation), the formation of hierarchical oxyhydroxide structures can be realized in aqueous solution at ambient temperature without the use of heat energy and additional structure-directing agents. The hierarchical CoOOH structures are performed as the electrocatalysts for the oxygen evolution reaction in alkaline media, which exhibit good activity with an overpotential of 320 mV at 10 mA cm−2 and a low Tafel slope of 59.6 mV dec–1, outperforming many congeneric electrocatalysts. Overall, our study not only provides important insights to understand the formation mechanism of hierarchical oxyhydroxides, but also opens up new opportunities for the preparation of hierarchical oxyhydroxides via a facile, green and low-cost method.

A Facile Synthetic Strategy for Decavanadate and Transition Metal Based All‐Inorganic Coordination Polymers and Insights into Their Electrocatalytic OER Activity

AbstractThis study reports a facile synthetic strategy for decavanadate ([V10O28]6−) cluster‐based all inorganic coordination polymers (CPs) containing earth‐abundant and redox‐active transition metals and their electrocatalytic oxygen evolution reaction (OER) activity. The first series of such isomorphous compounds containing the transition metals Mn, Co, and Ni, {(H2O)2K‐μ‐(H2O)3Mn(H2O)3}2n[V10O28]n (1), {(H2O)2K‐μ‐(H2O)3Co(H2O)3}2n[V10O28]n (2) and {(H2O)2K‐μ‐(H2O)3Ni(H2O)3}2n[V10O28]n (3), have been synthesized and structurally characterized. In these polymeric compounds, the [V10O28]6− clusters are interlaced and inter‐connected by {(H2O)2K‐μ‐(H2O)3‐M(H2O)3}+3 units leading to a linear chain‐like arrangement. Each of such chains is further interconnected to adjacent chains by bonding K+ ions with a [V10O28]6− cluster of the adjacent chain leading to a two‐dimensional (2D) sheet‐like arrangement. Hydrogen bonding interactions between the coordinated water molecules and the cluster oxygens further interconnect the adjacent sheets. All these compounds 1–3 are shown to catalyze the oxygen evolution reaction (OER) under alkaline (0.1 M KOH) conditions. Among the three, the Ni‐based catalyst 3 exhibited the best OER activity with a moderate overpotential of 270 mV at onset, a low Tafel slope of 89 mV dec−1, and a turnover frequency (TOF) of 7.5 s−1, which is comparable to similar Keggin POM‐based systems reported so far. The CPs were not highly stable under the OER conditions employed. The post‐catalytic analyses indicated the ‘precatalyst’ nature of these compounds in alkaline media forming V‐doped metal oxyhydroxides as the OER active species under the turnover conditions. Thus, this study provides a new and facile strategy for synthesizing [V10O28]6−cluster and transition metal‐based all‐inorganic CPs and insights into their OER electrocatalytic activities for the first time.

Water-assisted controllable growth of atomically thin WTe2 nanoflakes by chemical vapor deposition based on precursor design and substrate engineering strategies

WTe2 nanostructures have intrigued much attention due to their unique properties, such as large non-saturating magnetoresistance, quantum spin Hall effect and topological surface state. However, the controllable growth of large-area atomically thin WTe2 nanostructures remains a significant challenge. In the present work, we demonstrate the controllable synthesis of 1T′ atomically thin WTe2 nanoflakes (NFs) by water-assisted ambient pressure chemical vapor deposition method based on precursor design and substrate engineering strategies. The introduction of water during the growth process can generate a new synthesized route by reacting with WO3 to form intermediate volatile metal oxyhydroxide. Using WO3 foil as the growth precursor can drastically enhance the uniformity of as-prepared large-area 1T′ WTe2 NFs compared to WO3 powders. Moreover, highly oriented WTe2 NFs with distinct orientations can be obtained by using a-plane and c-plane sapphire substrates, respectively. Corresponding precursor design and substrate engineering strategies are expected to be applicable to other low dimensional transition metal dichalcogenides, which are crucial for the design of novel electronic and optoelectronic devices.

Silicate minerals control the potential uses of phosphorus-laden mineral-engineered biochar as phosphorus fertilizers

Silicate minerals constitute the main components in silicon (Si)-rich biomass, affecting the phosphorus (P) adsorption and release competencies of mineral-engineered biochar; however, the mechanisms underlying their differences remain largely unresolved. To examine these interactions, we investigated the mineralogical compositions and quantified the P-adsorption capacities of Al-, Fe-, Mn-, Zn-, and Mg-engineered biochars from Si-rich rice husk material. The potential uses of P-laden mineral-engineered biochar for P fertilizers were assessed using citric acid extraction. The results from X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectrometry revealed that mixed metal (oxyhydr)oxides and metal-silicate compounds precipitated in the biochar structure and acted as the main P adsorbents. Micro-crystalline silicates derived from the biomass-induced metal-silicate precipitates in all engineered biochars, which effectively retained the aqueous P with varying excellent capacities (25.6–46.5 mg/g) but relatively slow kinetics (48 h). The suitability of the Zn-, Mg-, Mn-, and Fe-biochars as P-recycled fertilizers was confirmed by the high amounts of citric acid extractable P (19–69% of the total P). Varying amounts of Zn, Mg, and Mn (34–47% of the total host metals) were also released from the engineered biochar through ligand-promoted dissolution. Our data shed light on the novel potential utilization of Mn-, Mg- and Zn-biochars from Si-rich biomass for P retrieval and their use for P, Mg, and micronutrient (Mn and Zn) fertilizers. Regarding the P removal capacity, the mineral-engineered biochar needed a longer adsorption period than conventional metal-engineered biochar.Graphical

Metal oxyhydroxide nanosheet-assisted fabrication of ultrathin carbon molecular sieve membrane for hydrogen separation

An ultrathin carbon molecular sieve membrane with superior H2/CO2 separation performance was fabricated by using metal oxyhydroxide nanosheets as a scaffold.

Enhancement of oxygen evolution reaction by X-doped (X = Se, S, P) holey graphitic carbon shell encapsulating NiCoFe nanoparticles: a combined experimental and theoretical study

Among the two half-reactions of the electrochemical water splitting, the anodic oxygen evolution reaction (OER) is a kinetically sluggish process and usually requires noble metal oxide catalysts. Therefore, the development of highly active, noble metal-free, and durable catalysts for OER is an urgent need for sustainable applications. The encapsulation of transition-metal alloyed nanoparticles in graphitic carbon layers, with core-shell features, is a viable approach for establishing an undegradable and highly efficient catalyst toward OER. Furthermore, the reactivity of the carbon shell surface can be further improved by the electron transfers between the core alloy and carbon shell, through a control of the alloyed nanoparticle compositions, or through a chemical doping. Nevertheless, it is still not clear whether the incorporation of a chemical dopant directly into the carbon shells systematically promotes the catalytic activities toward OER. To clarify this point, we synthetize trimetallic (CoNiFe) nanoparticles encapsulated in graphitic carbon shells by pyrolysis of metal−organic frameworks. We then investigate the effect of a doped graphitic carbon shell by incorporating non-metallic elements such as sulfur, phosphorus, and selenium. The main finding is that all doped CoNiFe@C core-shell catalysts exhibit an enhanced catalytic activity toward OER in the alkaline electrolyte with a low overpotential, a small Tafel slope, and long stability, which are all being comparable to those of RuO2 benchmark. Electrochemical impedance spectroscopy, X-ray photoelectron spectroscopic, and Raman measurements collected at different applied potentials during the OER process indicate that the doping of graphitic carbon shell significantly improves the interfacial electron-transfer kinetics and facilitates the adsorption of OH− ion as well as promotes the formation of metal oxyhydroxide, which positively affect the OER performances. Moreover, this improvement in OER efficiency upon incorporating of a chemical doping is rationalized by the optimization of the Gibbs free energy of OER intermediates, thereby remarkably reducing the required energy input of rate-determining step, as elucidated by the density functional theory calculations.

Corrosion behavior of new rare-earth free Cu-based metallic glasses in NaCl solution of different molarity

The present study reports the glass-forming ability, density change on crystallization and corrosion behavior of newly developed rare-earth free Cu-based metallic glasses (CBMGs). The critical casting thickness of these new CBMGs increased from 15 mm at 8 at.% Hf to 22 mm at 12 at.% Hf, reaching a maximum value of 28.5 mm at 13.5 at.% Hf. It dropped to 24 mm and 15 mm thereafter, for 15 and 20 at.% Hf, respectively. The alloys showed a monotonic increase in density going from 8 at.% Hf to 20 at.% Hf, with the density of amorphous samples increasing from 7.83 g/cm3 to 8.84 g/cm3 and crystallized samples increasing from 7.92 g/cm3 to 8.91 g/cm3. Potentiodynamic polarization tests carried out in 0.1, 0.2 and 0.5 M NaCl solution at 25 °C showed a direct correlation between corrosion resistance and Hf content in the order: 8 at.% < 13.5 at.% < 20 at.% Hf. Increase in NaCl concentration also had a significant impact on the corrosion intensity due to the chaotropic effect. Scanning electron microscopy of corroded sample surfaces showed formation and eventual merging of individual micro cracks resulting in a mud-cracking pattern. Energy-dispersive X-ray spectroscopy maps of pitted regions revealed reduction in Zr and Al concentration with increase in Hf and Cu percentage for all compositions. An increase in the O concentration along with the appearance of new peaks in the X-ray photoelectron spectroscopy results, measured post corrosion, confirmed the formation of metal oxides and oxyhydroxides in the passive layer.

Assembling and Regulating of Transition Metal‐Based Heterophase Vanadates as Efficient Oxygen Evolution Catalysts

Developing efficient, durable, and low-cost earth-abundant elements-based oxygen evolution reaction (OER) catalysts by rapid and scalable strategies is of great importance for future sustainable electrochemical hydrogen production. The earth-abundant high-valency metals, especially vanadium, can modulate the electronic structure of 3d metal oxides and oxyhydroxides and offer the active sites near-optimal adsorption energies for OER intermediates. Here, the authors propose a facile assembling and regulating strategy to controllably synthesize a serial of transition metal (CoFe, NiFe, and NiCo)-based vanadates for efficient OER catalysis. By tuning the reaction concentrations, NiFe-based vanadates with different crystallinities can be facilely regulated, where the catalyst with moderate heterophase (mixed crystalline and amorphous structures) shows the best OER catalytic activity in terms of low overpotential (267mV at the current density of 10mA cm-2 ), low Tafel slope (38mV per decade), and excellent long-term durability in alkaline electrolyte, exceeding its noble metal-based counterparts (RuO2 ) and most current existing OER catalysts. This work not only reports a facile and controllable method to synthesize a series of vanadates-based catalysts with heterophase nanostructures for high-performance OER catalysis, but also may expand the scope of designing cost-effective transition metal-based electrocatalysts for water splitting.

Nano-on-micro approach for fabricating ternary metal oxy-hydroxide–based flexible supercapacitors

In the present work, we unveil a facile and effective method to directly grow Ni–Mo–Co oxy-hydroxide–based 3-dimensional hierarchical nanostructures on carbon microfibers (nano-on-micro) by using a facile hydrothermal synthesis route. Further, the electrochemical activity for directly grown fiber electrode as well as electrode formed by slurry coating of active material formed after hydrothermal reaction has been investigated. In this study, the metal ratios (nickel and cobalt) were selected to cover the wide spectrum of the concentration in order to obtain the optimum concentration for the best electrochemical performance. Electrochemical analysis of these ternary metal oxy-hydroxide–based active materials on the carbon microfiber shows significantly high electrochemical activity with a specific capacitance of 519 Fg−1 in hydrothermally activated sample and 890 Fg−1 in a slurry coated sample (at 1 Ag−1). This simple technique provides a novel method to fabricate high energy-storage devices with the advantage of being lighter and flexible and can be easily integrated for various flexible electronic applications potential applications including e-textiles, personal electronics, military apparel devices, and antimicrobial and biomedical textiles.

Desorption and Migration Behavior of Beryllium from Contaminated Soils: Insights for Risk-Based Management.

Factors influencing the desorption, distribution, and vertical migration behavior of Be in contaminated soils are not fully understood. This study examined the desorption and migration of Be in a soil profile from a legacy radioactive waste disposal site using different batch leaching [monofilled waste extraction procedure (MWEP); synthetic precipitation leaching procedure (SPLP); simulated acid rain solution (SARS); and toxicity characteristic leaching procedure] and sequential leaching [community bureau of reference (BCR)] methods for insights relevant to the application of risk-based management. The results showed that Be desorption was higher in the presence of organic than the inorganic leachate composition (MWEP < SPLP < SARS < TCLP < BCR first-step). The desorption followed three diffusion control mechanisms, which resulted in three desorption rate constant estimates of 157, 87.1, and 40.4 Be/kg.h0.5, and the estimated desorption maximum was 556 μg/kg. The desorption process was, spontaneous (ΔG > 0), enthalpically and entropically influenced. Increasing the incubation period and heat treatment resulted in a decrease of Be desorption and migration. The soil clay content and pH were the primary factors influencing Be desorption, and the results suggested that Be was desorbed from metal oxyhydroxides and surfaces of silicates (e.g., reactive surfaces of clay minerals), organic matters, and soil pores. Because of high Kd values, the mobility of Be was limited, and no exceedances of ecological or human health risk index or guidelines were determined for the current contamination levels at the site. However, Be released from the waste trenches has the ongoing potential to increase Be concentration in the soil.

Bioinspired engineering protein nanofibrils-based multilayered self-cleaning membranes for universal water purification

Proteinaceous materials are promising for membranes due to greater mechanical strength, in-built functionalities, amphiphilicity and high molecular loading capacity. Herein, a novel strategy of functionalization of silk nanofibrils with metal oxyhydroxide and fabrication of ultrafast permeable multi-layered and self-cleaning membrane was demonstrated. Typically, 1.9 µm thick multilayered membrane efficiently purifies macromolecules, dyes, pharmaceutical, surfactants and oil-water emulsion contaminated wastewater with rejection rate > 89% with the flux rate > 883 Lm2h−1. Further, the potential of the multilayered membrane was tested for series of different feed concentrations of fluoride and As (V) to validate the commercial applicability of the multilayered membranes for industry wastewater. Notably, even at higher concentration of 10–30 mgL−1, >96% for fluoride and >87% for As (V) rejection was obtained. Furthermore, the functionalized multilayered membrane exhibited outstanding performance for fluoride removal in real water streams, where, it purifies approximately 4710 L.m−2 in two consecutive cycles, before the quality of the effluents no longer meets WHO criteria. However, the remarkable separation efficiency principally attributed to adsorption sites on the surface of the membrane. Thus, various regeneration strategies were established based on the nature of pollutants. More importantly, photocatalytic Fenton-like reaction assisted self-cleaning property of the multilayered membrane is demonstrated for regeneration of organic fouled membrane. Overall, the present multilayered membrane exhibits superior performance in purifying organic, inorganic contaminated water and oil-water emulsion with excellent recyclability; hence, envisaged its application for Universal water purification.

Synthesis of highly water‐absorbing chromium oxyhydroxide as a dopant in a hybrid proton‐conducting membrane

Proton-conductive membranes restrict the energy conversion efficiency and operating performance of the proton exchange membrane fuel cells. In this work, we develop a simple and easy scale-up method to synthesise a new proton-conductive material, amorphous chromium oxyhydroxide (CrO(OH)·xH2O). The CrO(OH)·xH2O shows a high water-adsorption value of 450 mg g−1, contributing to the construction of continuous and ordered hydrogen-bonding network within the materials. An ultra-high proton conductivity of 0.31 S cm−1 is obtained in CrO(OH)·xH2O at 90°C and 98% relative humidity, with an activation energy of 0.39 eV, which indicates a proton hopping mechanism. To further study the application potential of CrO(OH)·xH2O in proton exchange membranes, CrO(OH)·xH2O is added to sulfonated poly(ether ether ketone) (SPEEK) as a dopant, forming a SPEEK-CrO(OH) proton exchange membrane. The composite membrane exhibits a proton conductivity comparable to Nafion, 0.17 S cm−1 at 80°C in water without decreasing in 36 hours. This research enlightens us the development of metal oxyhydroxide via a simple and feasible strategy as efficient proton conductors.

Vertical-crystalline Fe-doped β-Ni oxyhydroxides for highly active and stable oxygen evolution reaction

<h2>Summary</h2> The layered transition metal oxyhydroxides have received increasing interest owing to the efficient energy conversion performance and material stability during the oxygen evolution reaction (OER). In particular, Fe-doped NiOOH has shown record-high OER performance in alkaline media among various catalysts. Theoretically, undercoordinated facets including Ni⁴⁺, exposed at the edges of NiOOH, were predicted to perform highly active OER. Therefore, here we suggest a rational catalyst design, a vertical-crystalline β-Fe/NiOOH layer built on faceted Fe/Ni nanocrystals, which exposes Ni⁴⁺ sites and could improve the OER performance dramatically. Electrochemical OER tests recorded the overpotential of 210 mV at a current density of 10 mA cm⁻²_GEO and stable operation for 5 days. <i>In situ/operando</i> and density functional theory studies revealed that the Ni valence cycle between +2 and +4 assisted by Fe dopant is the key engine that greatly accelerates OER kinetics and that the vertical-crystalline β-Fe/NiOOH layers on Ni octahedra are stable under harsh OER conditions.

Structural and Interfacial Engineering of Ni2P/Fe3O4 Porous Nanosheet Arrays for Efficient Oxygen Evolution Reaction.

Rational design of transition-metal phosphide (TMPs)-based electrocatalysts can effectively promote oxygen evolution reaction (OER). Herein, the novel efficient Ni2P/Fe3O4 porous nanosheets arrays supported on Ni foam (Ni2P/Fe3O4/NF) as alkaline OER catalysts were synthesized using structural and interfacial engineering. The three-dimensional (3D) porous hierarchical structure of Ni2P/Fe3O4/NF provides abundant active sites for OER and facilitates the electrolyte diffusion of ions and O2 liberation. Furthermore, the strong interfacial coupling and synergistic effect between Ni2P and Fe3O4 modify the electronic structure, resulting in the enhanced intrinsic activity. Consequently, the optimized Ni2P/Fe3O4/NF exhibits excellent OER performance with low overpotentials of 213 and 240 mV at 60 and 100 mA cm-2 in 1.0 M KOH, respectively, better than the RuO2/NF and most Ni/Fe-based OER catalysts. Impressively, it can maintain its catalytic activity for at least 20 h at 60 mA cm-2. In addition, the relationship between the structure and performance is fully elucidated by the experimental characterizations, indicating that the metal oxyhydroxides in situ generated on the surface of catalysts are responsible for the high OER activity.

Selenization triggers deep reconstruction to produce ultrathin γ-NiOOH toward the efficient water oxidation

Transition metal chalcogenides will be in situ transformed into metal oxyhydroxides during oxygen evolution reaction (OER) process in alkaline medium. However, most of these compounds only undergo surface reconstruction under operating conditions, which contains a large percentage of inactive atoms in the core, thus limiting the exposure of the active sites. Here, we synthesize a Ni-Mo-Se precatalyst with three-dimensional hierarchical structure and develop a facile on-site electrochemical activation strategy for achieving deep reconstruction of the precatalyst. Using the combination of multiple spectroscopic characterizations and high resolution electron microscopy techniques, we unravel that the Ni-Mo-Se precatalyst is deeply reconstructed into γ-NiOOH with co-leaching of Mo and Se after the anodic oxidation. Such flower-like γ-NiOOH is constituted by distorted ultrathin nanosheets with a thickness of ∼ 4.5 nm and contains abundant intercalated species such as water and OH–/CO32–, thus offering a large quantity of accessible active sites. To reach the current density of 10 mA cm−2, the derived electrode requires an overpotential of only 244 mV, outperforming almost all the reported analogues. This work highlights the reconstruction chemistry and provides a simple method for the preparation of efficient OER electrocatalyst.

Crystal and Electronic Structure Modification of Synthetic Perryite Minerals: A Facile Phase Transformation Strategy to Boost the Oxygen Evolution Reaction.

Geometry effect and electronic effect are both essential for the rational design of a highly efficient electrocatalyst. In order to untangle the relationship between these effects and electrocatalytic activity, the perryite phase with a versatile chemical composition, (NixFe1-x)8(TyP1-y)3 (T = Si and Ge; 1 ≥ x, y ≥ 0), was selected as a platform to demonstrate the influence of geometry (e.g., atomic size and bond length) and electronic (e.g., bond strength and bonding scheme) factors toward the oxygen evolution reaction (OER). It was realized that the large Ge atom in the perryite phase can expand the unit cell parameters and interatomic distances (i.e., weaken bond strengths), which facilitates the phase transformation into active metal oxyhydroxide during OER. The quaternary perryite phase, Ni7FeGeP2, displays excellent OER activity and achieves current densities of 20 and 100 mA/cm2 at overpotentials of 239 and 273 mV, respectively. The oxidation state of Ni and Fe in the perryite phase before/after OER was analyzed and discussed. The result suggests that incorporating the Fe element in the system may increase the rate constant of OER (KOER) and therefore keeps the Ni element in a low valance state (i.e., Ni2+). This work indicates that the manipulation of geometry and electronic factors can promote phase transformation as well as OER activity, which exemplifies a strategy to design a promising "precatalyst" for OER.