Cobalt Hydroxide Research Articles

Mesoporous hydrogel electrodes with flexible frameworks exhibiting enhanced mass transport for the oxygen evolution reaction.

Mesoporous hydrogel electrodes with unique flexible mesopores surrounded by CoOOH nanosheets were prepared via the electrochemical deposition of hybrid cobalt hydroxide nanosheets, exhibiting high oxygen evolution reaction activity at a high current density owing to the enhanced mass transport of oxygen molecules.

Accelerated ammonia electrosynthesis of cobalt hydroxide through electronic modulation with ultralow noble metal doping.

This study introduces an innovative method to ammonia production through electrocatalytic reduction of nitrate using Ru-doped Co(OH)2. The incorporation of Ru into the Co(OH)2 was found to markedly enhance the catalytic activity by optimizing the electronic structure and increasing the number of active sites.

Enhancing the oxygen evolution reaction activity of CuCo based hydroxides with V2CT x MXene.

The oxygen evolution reaction (OER) is a key reaction in the production of green hydrogen by water electrolysis. In alkaline media, the current state of the art catalysts used for the OER are based on non-noble metal oxides. However, despite their huge potential as OER catalysts, these materials exhibit various disadvantages including lack of stability and conductivity that hinder the wide-spread utilization of these materials in alkaline electrolyzer devices. This study highlights the innovative chemical functionalization of a mixed copper cobalt hydroxide with the V2CT x MXene to enhance the OER efficiency, addressing the need for effective electrocatalytic interfaces for sustainable hydrogen production. The herein synthesized CuCo@V2CT x electrocatalysts demonstrate remarkable activity, outperforming the pure CuCo catalysts for the OER and moreover show increased efficiency after 12 hours of continuous operation. This strategic integration improved the water oxidation performance of the pure oxide material by improving the composite's hydrophilicity, charge transfer properties and ability to hinder Cu leaching. The materials were characterized using an array of materials characterization techniques to help decipher both structure of the composite materials after synthesis and to elucidate the reasoning for the OER enhancement for the composites. This work demonstrates the significant potential of TMO-based nanomaterials combined with V2CT x for advanced innovative electrocatalytic interfaces in energy conversion applications.

Silver-integrated cobalt hydroxide hybrid nanostructured materials for improved electrocatalytic oxygen evolution reaction

Synthesizing Co(OH)2 with coexisting amorphous and crystalline phases showed strong electrocatalytic OER activity in the alkaline medium. The OER activity of Co(OH)2 was further improved upon the integration of AgNPs.

Beyond the ordinary: exploring the synergistic effect of iodine and nickel doping in cobalt hydroxide for superior energy storage applications

Beyond the ordinary: exploring the synergistic effect of iodine and nickel doping in cobalt hydroxide for superior energy storage applications

Synthesis and study of some physicochemical features of Co-Pt nanostructured system

In the work by methods of XRD, TEM, SAED, XPS combined with mass-spectrometry of gaseous products, SAXS, and elemental analysis of samples the phase compositions and morphology of particles of nanostructured Co-Pt system synthesized by the method of reduction of hydrazine-hydrate aqueous solutions of precursors were studied (in the region rich in Pt for the first time). It was found that in the composition range up to ≈ 60 at. % Co. XRD-analysis of synthesized samples fixes as the only FCC phase of solid solution of Co in Pt, with the established upper limit of solubility %18±1 at. At the content of Co above the limit, along with it, the X-ray diffraction unregistered phases with the content of Co above the limit in solid solution are also formed. Their presence was confirmed by the SAXS method, and their metallic nature (not oxide-hydroxide) nature follows from the results of XRD, SAED. When FCC phase formed metal reduction process proceeded directly without cobalt hydroxides forming. According to results of XPS with the Ar-etching of samples there were internal platinum-rich sub-regions in Co-Pt nanoalloys.

Exploring the potential of cobalt hydroxide and its derivatives as a cost-effective and abundant alternative to noble metal electrocatalysts in oxygen evolution reactions: a review

Exploration of various cobalt-based hydroxides for oxygen evolution reaction applications.

Study on a direct hydrazine borane fuel cell based on an anion exchange membrane

The carbon-supported cobalt hydroxide (Co(OH)2–C–PPY) can catalyze N2H4BH3 to produce H2O and BO2−. Furthermore, the optimized anion exchange membrane-type direct hydrazine borane fuel cell achieves a high performance of 244 mW cm−2.

Designing few-layered graphitic carbons with atomic-sized cobalt hydroxide by harnessing hollow metal-organic frameworks.

Graphitic carbon exhibits distinctive characteristics that can be modulated by varying the number of carbon layers. Here, we developed a method to control the growth of graphitic carbon layers through pyrolysis of zeolitic imidazolate frameworks (ZIFs). The key is to pyrolyze hollow-structured ZIF-8 containing Co ions to simultaneously obtain an amorphous carbon source for graphitic carbons and Co metal nanoparticles for catalyzing graphitization of amorphous carbons. Owing to sparsely distributed Co ions within ZIF-8, Co nanoparticles are formed, which leads to localized graphitization. The graphitic carbon obtained contained two to five layers, unlike carbonized ZIF-67. The few-layered graphitic carbon was subjected to KOH activation and employed as a support for atomic-sized Co(OH)2 owing to the short routes for Co nanoparticle egress and OH- ion movement. Our strategy does not involve any highly corrosive process for catalyst leaching and can even be used to produce atomic-sized Co(OH)2 with few-layered graphitic carbons.

In situ evolution of bulk-active γ-CoOOH with immobilized Gd dopants enabling efficient oxygen evolution electrocatalysis.

Promoting the in situ reconstruction of transition metal (TM)-based precatalysts into low-crystalline and well-modified TM (oxy)hydroxides (TMOxHy) during the alkaline oxygen evolution reaction (OER) is crucial for enhancing their catalytic performances. In this study, we incorporated gadolinium (Gd) into a cobalt hydroxide precatalyst, achieving a deep reconstruction into cobalt oxyhydroxide (γ-CoOOH) while retaining the incorporated Gd during the activation process of the alkaline OER. The unconventional non-leaching Gd dopants endow γ-CoOOH with reduced crystallinity, increasing the exposure of electrolyte-accessible Co atoms and enhancing its bulk activity. Furthermore, the modulation of the electronic structure of γ-CoOOH substantially boosts the intrinsic activity of the active Co sites. As a result, when supported on nickel foam, the catalyst exhibits remarkable alkaline OER performance, achieving a current density of 100 mA cm-2 at a low overpotential of approximately 327 mV. Notably, an ultrahigh current density of 1000 mA cm-2 is robustly maintained for 5 days, highlighting its immense potential for practical applications in large-scale hydrogen production.

ZIF‐67‐Derived Antivirus Cobalt Hydroxide LDH Nanosheets Produced through High‐Concentration Cobalt Ion‐Assisted Hydration

AbstractIn this study, a novel strategy is developed for the first time, referred to as high‐concentration cobalt ion‐assisted hydration (HCCAH) utilizing zeolitic imidazolate framework‐67 (ZIF‐67) as a precursor, to produce independent and flat α‐cobalt hydroxide nanosheets (CHN). These nanosheets offer abundant contact sites for binding with virus surface proteins. The formation of CHN involves the in situ transformation from ZIF‐67, due to the matching of the hydrolysis rate of ZIF‐67 and in situ growth rate of cobalt hydroxide orchestrated by high concentration of cobalt ions. Notably, the CHN contains a higher proportion of trivalent cobalt, which is shown to enhance the binding with the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS‐CoV‐2) Spike protein and induce protein structural denaturation, as demonstrated by molecular dynamics (MD) simulation. Antiviral experiments using pseudovirus and authentic viruses have confirmed the promising antiviral performance of CHN. Furthermore, both in vitro and in vivo experiments have demonstrated the excellent biocompatibility of CHN. This research opens up new possibilities for the application of cobalt hydroxide nanosheets and serves as a valuable reference for the design of antiviral nanomaterials.

Activating Co sites activity in Co(OH)2via VN coupling to facilitate highly efficient oxygen evolution reaction

The quest for efficient electrocatalysts to drive the oxygen evolution reaction (OER) is paramount for renewable energy technologies such as water electrolysis. This study focuses on augmenting the catalytic activity of cobalt hydroxide (Co(OH)2) electrocatalysts by strategically coupling them with vanadium nitride (VN) heterostructures (Co(OH)2/VN@C). The synergistic effect between Co(OH)2 and VN is explored to achieve a remarkable improvement in the OER performance that the hybrid Co(OH)2/VN@C exhibits a low overpotential of 319 mV at a current density of 10 mA cm−2 and a small Tafel slope of 65 mV dec−1. Through characterization techniques and electrochemical measurements, we unveil the intricate interplay at the atomic level that triggers the activation of Co sites by V element, leading to an exceptional enhancement in catalytic activity and excellent stability. This work not only sheds light on the fundamental mechanisms involved in the Co(OH)2/VN heterostructure interaction but also presents a promising strategy for designing highly efficient OER electrocatalysts.

The Active Interface of Iron-Decorated Cobalt (Oxy)Hydroxide for Oxygen Evolution Reaction

Iron can significantly enhance the activity of Co (oxy)hydroxide. However, the nature of active sites is currently under debate for Fe-Co (oxy)hydroxide. Here, we use well-define crystalline cobalt hydroxide nanosheets and nanorods as model catalysts to investigate the role of Fe on different crystal planes. The electrochemical reactivity and morphology-dependent analysis suggest that the lateral facets of Co(OH)2 are active sites and the enhancement effect of iron incorporation only occurs on lateral facets rather than basal facets. Furthermore, by introducing tetramethylammonium cation (TMA+) as a chemical probe in KOH solution, we demonstrate the Fe species can interact strongly with the “active species” on the lateral facets and promote the improvement of OER activity. This work identifies the active site of cobalt hydroxides in the presence and absence of iron and elucidates the interaction of Fe species with “active oxygen” species on the lateral facets of cobalt hydroxide, which has a fundamental implication on the design of efficient OER catalysts.

Self-Repairing Ability of Hybrid Cobalt Hydroxide Nanosheets As Oxygen Evolution Catalysts in Alkaline Electrolytes

Introduction Water electrolysis is a key technology to produce H2 from renewable energy. Because proton exchange membrane water electrolyzers (PEMWE) require noble metals as catalysts, alkaline-type electrolyzers, such as alkaline water electrolyzers (AWE) and anion exchange membrane water electrolysis (AEMWE), have attracted much attention for the use of nonnoble-metal-based catalysts. One of the most important issues of AWE is the degradation of catalysts due to generation of reverse current upon shutdown and power fluctuation. Reverse current hardly generates in AEMWE in principle; however, it possibly generates if an electrolyte is supplied instead of pure water.We have previously reported the self-repairing anode catalysts for AWE [1, 2]. A hybrid cobalt hydroxide nanosheet (denoted as Co-ns, Figure 1a), a Brucite-type cobalt hydroxide modified with tripodal ligands (tris(hydroxymethyl)aminomethane), was dispersed in an alkaline electrolyte. Co-ns is deposited on the anode during the electrolysis at 800 mA/cm2 to form a catalyst layer. After the degradation of the catalyst by potential cycling, Co-ns is deposited to retain the catalytic activity. To develop catalysts with higher activity, durability, and repairing ability, the understanding of the electrochemical deposition of Co-ns is quite important. Here, we demonstrate the mechanism of the electrochemical deposition of Co-ns.ExperimentalCo-ns was synthesized according to our previous report [1]. The Co-ns was dispersed in 1 M KOH electrolyte at varied concentrations of Co-ns. Ni electrodes were used as both working and counter electrodes. Reversible hydrogen electrode (RHE) was used as a reference. Constant current electrolysis at 800 mA/cm2 was applied for 30 min, followed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to evaluate the oxygen evolution reaction (OER) activity and the amount of deposited Co. These processes ware repeated for several times to characterize the deposition behaviors. Similar experiments were performed, using Co(OH)2 or CoOOH instead of Co-ns.Results and DiscussionCo-ns was transformed into CoOOH by the decomposition of the tripodal ligand. The deposited amount of Co was evaluated by CV, in which the charge of the cathodic currents at 0.8–1.6 V vs. RHE (denoted as Q c) was proportional to the amount of Co measured by ICP-AES. Figure 1b shows the plots of Q c vs. duration of electrolysis. The amounts of deposited CoOOH depended on the concentration of Co-ns. The deposition rates (slope of the curves) gradually decreased along with the progress of the catalyst deposition. During the electrolysis, the electrode potential decreased because of the increased OER activity due to the catalyst deposition. Assuming that the deposition of CoOOH is a pseudo first-order reaction, its rate constant was calculated by dividing the deposition rate by the concentration of Co-ns. The rate constants are linearly correlated with the electrode potential (Figure 1c); thus, the deposition was confirmed to be an electrochemical process. The present results mean that the electrochemical deposition of CoOOH is accelerated when the electrode potential increases due to the degradation of catalysts. Therefore, the self-repairing process is automatically controlled by the condition of the electrode.The electrochemical deposition proceeds with Co(OH)2, whereas CoOOH hardly deposited at the same conditions, indicating that the oxidation of Co2+ to Co3+ is an essential step of the electrochemical deposition. The electrochemical deposition of Co(OH)2 was stopped after 60 min of electrolysis because of the autooxidation of Co(OH)2 by dissolving O2. It was shown that Co-ns is stable in an electrolyte saturated with O2 probably because the organic modification suppresses the autooxidation. Thus, it is shown that the organic modification of cobalt hydroxide is crucial to retain the self-repairing ability in an electrolyzer.ConclusionIn conclusion, the potential dependence of the rate constant and the essential step of electrochemical deposition of Co-ns were elucidated through systematic studies using Co-ns and related metal hydroxide catalysts. These findings lead to the design of self-repairing electrocatalysts with high activity, long lifetime, and high self-repairing ability using organic functionalization.Acknowledgement This work was supported by the JSPS KAKENHI (grant number 20H02821). Part of this study uses outcomes of the development of fundamental technology for the advancement of water electrolysis hydrogen production in the advancement of hydrogen technologies and utilization projects (grant number JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) in Japan.

Synthesis of amorphous cobalt hydroxide nanosheets and electrochemical performance according to phase transition into crystalline cobalt oxides

Ultrathin two-dimensional nanosheets have attracted attention as nanostructures that maximize the electrochemical performance in energy storage and conversion because of their unique advantages of large specific surface areas and large exposure to active sites. Herein, we synthesized cobalt hydroxide nanosheets with an amorphous phase and a thickness of <1.5 nm. Amorphous cobalt hydroxide nanosheets grown according to the surfactant concentration were converted into crystalline cobalt oxides through a simple heat treatment. The change in the electrochemical oxygen evolution reaction performance according to this process was investigated in detail by ex- and in-situ Raman spectroscopy, and the supercapacitor performance was confirmed. This study provides promising guidelines for developing phase-dependent catalysts from cobalt hydroxide and cobalt oxides and highlights the critical role of the crystal structure in facilitating electrocatalytic processes.

Effect of Pore Size on the Oxygen Evolution Reaction Activity of Hydrogel Electrodes Composed of Hybrid Cobalt Hydroxide Nanosheets

Introduction Alkaline water electrolysis (AWE) is a promising technology for large-scale production of hydrogen from renewable energy; however, the sluggish oxygen evolution reaction leads to a large overvoltage. Porous electrodes with a large specific surface area are useful to achieve high current densities in AWE, whereas mass transport in small pores often reduces the overall current density. We have reported that hydrogel electrodes, possessing a flexible framework composed of interconnected hybrid cobalt hydroxide nanosheets (Co-ns), exhibit enhanced mass transport at high current density.1 Hydrogel electrodes can be regarded as porous electrodes swollen by electrolytes. They are expected to repair cracked surfaces by recombination of microparticles and to optimize the framework structure suitable for mass transport. In this study, we demonstrate the relationship between the pore size of the hydrogel electrodes and the OER activity at high current density. Experiment Co-ns was synthesized by mixing aqueous solutions of 1.0 M tris(hydroxymethyl)aminomethane and 0.1 M CoCl2·6H2O, followed by heating at 90 °C.2 The heating time was varied as 1, 5 and 10 days in order to control the particle size.Electrochemical measurements were performed in a 1.0 M KOH, using a PFA three-electrode cell. Co-ns was dispersed in the electrolyte (200 ppm). Nickel plate, nickel coil, and reversible hydrogen electrode (RHE) were used as working, counter, and reference electrodes, respectively. Co-ns was deposited on the electrode by constant current electrolysis at 800 mA cm–2 for varied time (10 min–100 h). The OER activity was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy for iR correction. Result and Discussion TEM images of the synthesized Co-ns exhibited that the diameter (long axis) of Co-ns increased along with the heating time. Therefore, the samples were named as 1d_21, 5d_34 and 10d_42, based on the heating time (days) and average diameter (nm). The FESEM images of the hydrogels after drying showed that nanosheets were assembled into house-of-cards structures (Figure 1). The assembled structures of Co-ns with different diameters were analogous to each other.The charges of the cathodic peaks (Q c) at 0.8–1.5 V vs. RHE due to Co2+/3+ and Co3+/4+ in cyclic voltammograms were used as a measure of the amount of deposited Co-ns. The linear relationship between Q c and the thickness of catalyst layers exhibited that deposited Co-ns presented uniformly along the thickness of catalyst layers (Figure 2). The slope of this line corresponds to the porosity of the hydrogels. The porosity increased along with the diameter of Co-ns; therefore, the pore size is expected to depend on the diameter of Co-ns because of the analogy of the assembled structure.Polarization curves of representative hydrogels are shifted from the Tafel equation at high current densities, indicating the influence of mass transport (Figure 3). The OER current densities at 1.6 V vs. RHE (i geo-1.6 V) of relatively thin hydrogels were linearly correlated with their thicknesses (Figure 4), though they were saturated for hydrogels with larger thicknesses. In the thicker hydrogels, OER is limited by mass transport of generated O2 and OH– in pores. The order of the limiting current densities were 1d_21 < 5d_34 < 10d_42; thus, the influence of mass transport is lowered for hydrogels with larger pores.In conclusion, the size of Co-ns was used to control the porosity and pore size of hydrogel electrodes. Hydrogel electrodes with larger pore size exhibited better mass transport to achieve higher OER activity at high current density. These insights will contribute to designing an optimal hydrogel as an oxygen evolving electrode. Acknowledgement This work was supported partially by the JSPS KAKENHI from MEXT, Japan. References R. Nakajima, T. Taniguchi, Y. Sasaki, Y. Nishiki, A. Zaenal, T. Nakai, A. Kato, S. Mitsushima, and Y. Kuroda, Autumn Meeting of the Electrochemical Society of Japan, 1P15 (2022).Y. Kuroda, T. Koichi, K. Muramatsu, K. Yamaguchi, N. Mizuno, A. Shimojima, H. Wada, and K. Kuroda, Chem. Eur. J., 23 (2017) 5023. Figure 1

Design of Ni–Fe Hybrid Metal Hydroxide Nanomaterials As Self-Repairing Anode Catalysts For Alkaline Water Electrolysis

Introduction To use renewable energy efficiently, the conversion of renewable energy into hydrogen by alkaline water electrolysis has attracted much attention. When an alkaline water electrolyzer is powered by renewable energy, electrodes degrade due to reverse current generated on shutdown. To address this problem, we have reported the usefulness of a hybrid cobalt hydroxide nanosheet (Co-ns) as a self-repairing catalyst that keeps the oxygen evolution reaction (OER) ability under frequent potential fluctuations.[1] However, the OER activity of Co-ns is relatively lower than the state-of-the-art catalysts, such as Ni–Fe layered double hydroxides (LDHs). In this study, we synthesized hybrid Ni–Fe hydroxides with various compositions and structures, and their correlations with the OER activity. Experimental Hybrid Ni–Fe hydroxides were synthesized by mixing nickel chloride, iron chloride, and tris(hydroxymethyl)aminomethane (Tris-NH2) similar to the method to synthesize Co-ns.[2] Electrochemical measurements were performed in 1.0 M KOH, using a three-electrode cell made of PFA. A nickel plate, a nickel coil, and a reversible hydrogen electrode (RHE) were used as the working, counter, and reference electrodes, respectively. The chronoamperometry –0.5 V vs. RHE for 3 min was repeated to remove oxides from the Ni substrate surface. A dispersion of hybrid Ni–Fe hydroxide was added in the electrolyte to adjust the total metal concentration (Ni + Fe) at 40 ppm. Catalysts were deposited by repeating the constant current electrolysis at 800 mA cm- 2 for 30 min, cyclic voltammetries (CVs) and electrochemical impedance spectroscopy for the evaluation of OER activities for 8 times (total electrolysis time is 240 min). Results and discussion The synthesis of hybrid Ni–Fe hydroxides were confirmed by XRD, FTIR, elemental analyses, and XAFS. The structure of products were layered, amorphous, and tunnel structures, depending on the metal composition (represented by Ni/(Ni + Fe)) and the degree of modification (represented by Tris-NH2/(Ni + Fe)). Ni/(Ni + Fe) tends to be high when the concentration of metal salts was low and the concentration of Tris-NH2 was high in the preparation solution. The oxidation states of Ni and Fe in all samples were +2.1 and +3.0, respectively.The amount of catalyst deposited on the electrode by the electrolysis was confirmed by elemental analyses. The amount of deposited catalyst increased along with Ni/(Ni + Fe) (Fig. 1). The lowest deposition amount was 2.74 µg cm- 2 (Ni/(Ni + Fe)=0) and the highest one was 41.5 µg cm– 2 (Ni/(Ni + Fe)=0.82), whereas the values were still lower than that of Co-ns (88.7 µg cm– 2). In our previous study, the oxidation of Co2+ to Co3+ on an electrode surface is crucial for the electrochemical deposition of Co-ns.[3] Thus, it is reasonable that the content of divalent cation (Ni2+) is related with the deposition amount.From the OER measurements, the mass activity of catalysts was defined as the current at 1.53 V vs. RHE normalized by the amount of deposited catalyst (i m,1.53). i m,1.53 decreased along with the increase in Ni content (Fig. 2). The increase in Ni content is beneficial to the electrochemical deposition, though it is negatively correlated with the OER activity. Therefore, there is a trade-off between the amount of deposited catalyst and mass activity. The highest geometrical OER current density was obtained for Ni/(Ni+Fe) = 0.82 and i 1.53 = 296 mA cm–2 (Fig. 3). The deposited amount of catalyst significantly contributed to the highest activity of the electrode. Conclusion In this study, we synthesized Ni–Fe hybrid metal hydroxides and demonstrated that the Ni content of the catalysts affect both its deposition behavior and oxygen evolution reaction activity. The highest Ni content catalyst showed the highest activity, indicating a trade-off between the amount of catalyst deposited and mass activity. Acknowledgement A part of this study was supported by KAKENHI (Grant-in-Aid for Scientific Research 20H02821) from Japan Society for the Promotion of Science (JSPS) Reference [1] Y. Kuroda, T. Nishimoto, S. Mitsushima, Electrochim. Acta, 323, 134812, (2019).[2] Y. Kuroda, T. Koichi, K. Muramatsu, K. Yamaguchi, N. Mizuno, A. Shimojima, H. Wada, K. Kuroda, Chem. Eur. J., 23, 5023, (2017).[3] R. Nakajima, T. Taniguchi, Y. Sasaki, Y. Nishiki, Z. Awaludin, T. Nakai, A. Kato, S. Mitsushima, Y. Kuroda, submitted. Figure 1

Understanding the Role of Cracks in Active Oxygen Species Formation during Oxygen Evolution Reaction

Understanding the formation and location of catalytic intermediates is crucial for unraveling the mechanism of oxygen evolution reaction (OER), a key process in electrochemical water splitting. Despite the availability of various in-situ and ex-situ characterization methods, the formation and location of intermediates remain elusive, hindering the development of more efficient electrocatalysts. In this work, we discovered a stable static active oxygen species formed during the chemical oxidation of cobalt hydroxide flakes, providing a unique opportunity to probe the intermediates involved in OER. We are able to monitor the equilibrium conversion between stable peroxo structure and superoxo radical via EPR and Raman test, shedding light on the nature of the active oxygen species. In addition, CoOOH flakes with cracks were synthesized via controlled chemical oxidation, enabling the investigation of the role of crack/edge structures in the electrocatalytic activity. Statistical regression analysis combining morphological features, electrochemical performance, and Raman spectroscopy confirmed a strong correlation between morphology evolution, OER activity, and active oxygen species, highlighting the importance of controlling the morphology of electrocatalysts for enhancing their performance. Therefore, we propose that the source of active oxygen intermediates can be attributed to the presence of crack/edge structures. The crack-rich CoOOH exhibit significantly higher current density at a lower overpotential, providing a new direction for the design of efficient water oxidation electrocatalysts. Overall, this work offers important insights into the mechanism of OER and provides a basis for the development of more efficient and sustainable electrocatalysts for energy conversion and storage.

Comparative study of mixed ammonium fluoride complex-derived single metal hydroxides based on cobalt and nickel for energy storage applications

Zeolitic imidazolate framework 67 (ZIF67) have been intensively applied as efficient active materials for energy storage. Structure directing agents (SDA) play important roles on morphology and electrochemical performance of active materials. Incorporating SDA in synthesis is expected to confine growth of ZIF67 derivatives and create efficient active materials. Ammonium fluoride (NH4F) has been widely applied as an effective SDA for synthesizing active materials in electrochemical systems. Inspired by the confiner of NH4+ and the conductive agent of F−, two novel SDA of ammonium hydrogen fluoride (NH4HF2) and ammonia borane fluoride (NH4BF4) are introduced to synthesize Ni-based or Co-based ZIF67 derivatives via a one-step solution process at room temperature. Substituting 2-methylimidazole with HF2− and BF4− improves conductivity of ZIF67. Effects of NH4HF2 to NH4BF4 ratio for synthesizing ZIF67 derivatives are investigated. The main compositions of ZIF67 derivatives are cobalt and nickel hydroxides. The largest specific capacitance (CF) of 1112.4 F/g is attained for the optimized Ni-based ZIF67 derivative (NiHB) at 20 mV/s. An asymmetric supercapacitor with the NiHB and activated carbon electrodes shows a maximum energy density of 32 Wh/kg at the power density of 750 W/kg, and the CF retention of 70% and Coulombic efficiency of 90.6% after 10,000 cycles.

Interfacial P–O covalent bonds regulated electronic configuration in black phosphorus for improving oxygen evolution activity

Black phosphorus (P(black)) shows impressive physicochemical features for electrocatalysis including adjustable bandgap and high charge carrier mobility. However, the existence of solitary electron pairs in exfoliated P(black) nanosheets (EP(black)) leads to rapid surface degradation, resulting in unfavorable durability. Herein, a P–O bridge was created in the heterostructure EP(black)/vanadium-doped cobalt hydroxide with oxygen vacancy (EP(black)/V–CoO2-xH2) to stabilize and expedite oxygen evolution reaction (OER) activity. By bonding the solitary electron pairs of EP(black) and oxygen species (OH*) of V–CoO2-xH2, the distinctive P–O bridge resulted in important ligand effects that improved not merely the stability of EP(black) but effectively regulated the electron configuration of V–CoO2-xH2. DFT simulations revealed that directional interfacial electron migration from V–CoO2-xH2 to EP(black) facilitated the formation of pivotal OER intermediates and hence boosted OER activities. This study proposes a novel strategy to enhance the electrochemical properties of EP(black), which could be extended to a wide range of high-performance electrocatalyst systems.