Efficient Electrocatalytic Water Oxidation Research Articles

Ternary ZnO/Co3O4/CuO heterostructure nanocomposites derived from trimetallic metal-organic frameworks for efficient electrocatalytic water oxidation

Enhancing the electrocatalytic performance of transition-metal oxide catalysts by optimizing the active center at the multi-component heterointerface is a daunting task. Herein, the three-component ZnO/Co3O4/CuO heterostructure composite catalyst was effectively produced through a room-temperature precipitation reaction, followed by calcination in air. The ZnO/Co3O4/CuO ternary heterostructure catalyst showed superior oxygen evolution reaction (OER) performance, characterizedby a low overpotential (312 mV at 10 mA cm−2) and Tafel slope (83.5 mV dec-1) compared to the ZnO, Co3O4, ZnO/CuO, ZnO/Co3O4, and Co3O4/CuO catalysts. The research shows that the property of electrocatalytic oxygen evolution is greatly enhanced due to the combined impact of each component.

Interface Synergistic Effect of NiFe-LDH/3D GA Composites on Efficient Electrocatalytic Water Oxidation.

Currently, NiFe-LDH exhibits an excellent oxygen evolution reaction (OER) due to the interaction of the two metal elements on the layered double hydroxide (LDH) platform. However, such interaction is still insufficient to compensate for its poor electrical conductivity, limited number of active sites and sluggish dynamics. Herein, a feasible two-step hydrothermal strategy that involves coupling low-conductivity NiFe-LDH with 3D porous graphene aerogel (GA) is proposed. The optimized NiFe-LDH/GA (1:1) produced possesses a 257 mV (10 mA cm-2) overpotential and could operate stably for 56 h in an OER. Our investigation demonstrates that the NiFe-LDH/GA has a three-dimensional mesoporous structure, and that there is synergistic interaction between LDH and GA and interfacial reconstruction of NiOOH. Such an interface synergistic coupling effect promotes fast mass transfer and facilitates OER kinetics, and this work offers new insights into designing efficient and stable GA-based electrocatalysts.

A Proton-Conductive Co(II)-Polyoxometalate Acts as a Precatalyst for Efficient Electrocatalytic Water Oxidation.

A cobalt(II)-containing polyoxometalate, [H3O]5[{Co(H2O)4}3{Na(H2O)4}W12O42]·3H2O (Co-POM), has been isolated in a one-step facile aqueous synthesis and characterized unambiguously using single-crystal X-ray crystallography along with routine spectral analysis. The paratungstate cluster anion [W12O42]12- coordinates with {CoII(H2O)4}2+ and {Na(H2O)4}+ complex cations resulting in the formation of the water-insoluble Co-POM compound having three-dimensional (3-D) extended structure. Motivated by the protonated water molecules existing as the counter cations in Co-POM, herein, we demonstrate the detailed proton conductivity studies of the Co-POM, reaching a value of 1.04 × 10-2 S cm-1 at 80 °C and 98% relative humidity (RH). The temperature- and humidity-dependent proton conductivity in Co-POM is governed by Grotthus mechanism with Ea = 0.25 eV. In addition, we examined the electrochemical behavior of Co-POM, in an alkaline borate buffer where it is found to be electrochemically unstable and acts as a precatalyst (and not a true catalyst) for oxygen evolution reaction (OER). We also discuss the "post-mortem" analysis of the postelectrolysis sample to identify the active species which turns out to be a cobalt oxide material (Co3O4) incorporating small amounts of tungsten. Thus, in the present electrocatalysis work, the Co-POM molecule transforms into an efficient water oxidation catalyst (WOC).

Tuning built-in potential of NiP/NiFe LDH p-n junction towards efficient electrocatalytic water and urea oxidation

Oxygen evolution reaction (OER) and urea oxidation reaction (UOR) are critical half-reactions to realize sustainable hydrogen production. However, the sluggish dynamics derived from the multi-electron pathways necessitate the exploration for efficient catalysts. Herein, a p-n junction nanorod array composed of Mo doped NiP nanorod and ultrathin NiFe LDH nanosheets (NiMoP/NiFe LDH) is proposed to regulate charge distribution of interface for triggering decomposition of water and urea. The p-n junction with a powerful built-in potential (EBI) of 1.2 V at the interface facilitates the adsorption and fracture of chemical group in water and urea molecules. Consequently, the heterostructured electrode demonstrates exceptional electrochemical performance with ultralow potentials of 1.43 and 1.33 V (vs. RHE) at 10 mA cm−2 for OER and UOR, respectively. The overall urea electrolysis driven by NiMoP/NiFe LDH needs only 1.51 V to deliver 100 mA cm−2. This work demonstrates a promising strategy to regulate the EBI of semiconductor heterostructure for energy conversion and sewage treatment.

Built-in electric field construction and lattice oxygen activation for boosting alkaline electrochemical water/seawater oxidation

Oxygen evolution reaction (OER) remains a bottleneck for hydrogen production by water-alkali electrolysis at high industrial current density, but the structure–activity relationship of the catalyst and the underlying catalytic mechanism are still debated, which always limits the design of efficient catalysts. Herein, we report a proof-of-concept hierarchical hydroxide/sulfide (NiFe LDH/Ni3S2) heterostructure as model catalyst to simultaneously adjust the electronic states and activate lattice oxygen. As-activated NiFe LDH/Ni3S2 electrode displays promising OER capability with an ultra-low overpotential of 295 mV at the industrial current density of 500 mA·cm−2. The interface-induced built-in electric field effect promotes the asymmetric charge distribution on both sides. In-situ/ex-situ characterization demonstrates the adjusted intermediates adsorption/desorption and accelerated OER kinetics due to rapid electron transfer. A series of electrochemical probe experiments reveal that the OER mechanism of NiFe LDH/Ni3S2 follows the lattice oxygen mechanism. Especially, the super-strong wettability electrode design and structural advantages effectively enhance mass transfer and promote O2 desorption in alkaline water/seawater splitting systems. This work provides an avenue to break through OER limitations for efficient electrocatalytic water oxidation.

Highly efficient electrocatalytic water oxidation based on non-precious metal oxides/sulfides derived from a FeCoNi-metal organic framework

One of the main challenges for oxygen evolution reaction (OER) is to develop electrocatalysts with high performance, suitable stability, and low cost. First-row transition metal compounds have received attention due to their high electrocatalytic activity and diverse electronic structure. Meanwhile, metal-organic frameworks (MOFs) have emerged as promising alternative for OER due to their porous structure and unsaturated metal sites. In this study, FeCoNi-MOF based on MIL-88B was synthesized by a hydrothermal method. Then, the performance of the catalyst was investigated and improved by calcination and sulfidation at three temperatures of 250 ℃, 350 ℃, and 450 ℃. The phase development and crystal structure parameters of the synthesized samples were confirmed through X-ray diffraction. Additionally, the intensity of the peaks increased with the rise in calcination temperature. Field emission scanning electron microscopy revealed well-defined and uniformly distributed nanorods and nanospheres particles of calcinated and sulfides samples. The weight percentage (wt%) of the elements in the samples were verified to align with their stoichiometric ratios. The synthesized catalysts were loaded onto a nickel foam by a one-step method, and their electrocatalytic properties were examined in the OER process in 1.0 M KOH alkaline solution. The (FeCoNi)-O250 ℃ electrocatalyst, maintaining its nanorod morphology, exhibited an overpotential of 313 mV at a current density of 10 mA.cm-² and a small, stable Tafel slope of 31.5 mV.dec−1 and good charge transfer of 0.73 mF. Cm−2. However, the (FeCoNi)-S250 ℃ electrocatalyst showed better performance in the OER process with an overpotential of 298 mV at a current density of 10 mA.cm-² and a small and stable Tafel slope of 29 mV.dec−1 and good charge transfer of 0.82 mF. Cm−2. In other words, a higher Cdl increased reaction rates or lower overpotentials required for the reaction to occur. Furthermore, the activity of this catalyst remained constant at a fixed current density of 10 mA.cm-² for 18 hours. Based on the electron microscopy observations, and electrochemical evaluations, this superior performance can be attributed to the morphological change from nanorods to porous nanospheres due to sulfidation, resulting in increased electrochemically active sites and decreased charge transfer resistance.

Rich phosphorus vacancies N-doped C high-entropy metal phosphides for efficient electrocatalytic water oxidation

High-entropy materials have received increasing attention due to their unique physicochemical characteristics and remarkable properties for oxygen evolution reaction (OER). The synthesis of high-entropy metal phosphides (HEMPs) has rarely been reported owing to the incompatibility between different metal ions and phosphorus. Herein, the phosphorus vacancies (Pv) enriched N-doped C HEMPs (N-C@CoNiMnCuFeP/NF) for OER were prepared by a facile ZIF-derived phosphide method. Abundant Pv and amorphous structures increase the active sites and modulate the electronic structure of electrocatalyst to improve the OER performance. Besides, the synergistic effect among the metallic elements is beneficial for enhancing the electrocatalytic activity. Accordingly, HEMP-450 shows outstanding catalytic performance with the overpotential of 199 mV and continuously reacts for 140 hours without performance degradation for OER at 100 mA cm−2. This work demonstrates a simple template strategy for reasonably preparing HEMPs electrocatalyst with rich Pv.

Synergistic modulation of the localized electrons and lattice distortion of cobalt-nickel phosphide motivates intrinsic activity through heteroatoms for efficient electrocatalytic water oxidation

The development of non-precious metal-based catalysts for efficient renewable energy conversion remains a significant challenge. In this study, we synthesized petal-shaped spherical electrocatalysts based on cobalt–nickel phosphate (NiCoP) doped with Mo at different concentrations (Mo-NiCoP; 0.05 %, and 0.1 %) using a facile process. Mo doping provides abundant active sites for electrochemical water oxidation. The 0.1 %Mo-NiCoP electrocatalyst exhibited superior electrocatalytic activity for the oxygen evolution reaction (OER), with a low overpotential of 277 mV, compared to NiCoP (313 mV), 0.05 %Mo-NiCoP (292 mV), and noble-metal catalysts for OER. Additionally, the long-term stability of 0.1 %Mo-NiCoP under a fixed voltage for 20 h revealed only a minor decline in current density. The results of density functional theory calculations suggest that the exceptional electrocatalytic activity of Mo-NiCoP is due to the optimized adsorption energy barrier of intermediates in the OER process, the modulation of the electronic structure, and the introduction of rich lattice disorder defects in NiCoP by the Mo heteroatoms. This work presents a practical and economical approach to fabricating ternary transition-metal phosphates for water oxidation.

Tunable Pt-NiO interaction-induced efficient electrocatalytic water oxidation and methanol oxidation.

Metal-support interaction engineering is considered an efficient strategy for optimizing the catalytic activity. Nevertheless, the fine regulation of metal-support interactions as well as understanding the corresponding catalytic mechanisms (particularly those of non-carbon support-based counterparts) remains challenging. Herein, a controllable adsorption-impregnation strategy was proposed for the preparation of a porous nonlayered 2D NiO nanoflake support anchored with different forms of Pt nanoarchitectures, i.e. single atoms, clusters and nanoparticles. Benefiting from the unique porous architecture of NiO nanosheets, abundant active defect sites facilitated the immobilization of Pt single atoms onto the NiO crystal, resulting in NiO lattice distortion and thus changing the valence state of Pt, chemical bonding, and the coordination environment of the metal center. The synergy of the porous NiO support and the unexpected Pt single atom-NiO interactions effectively accelerated mass transfer and reduced the reaction kinetic barriers, contributing to a significantly enhanced mass activity of 5.59 A mgPt -1 at an overpotential of 0.274 V toward the electrocatalytic oxygen evolution reaction (OER) while 0.42 A mgPt -1 at a potential of 0.7 V vs. RHE for the methanol oxidation reaction (MOR) in an alkaline system, respectively. This work may offer fundamental guidance for developing metal-loaded/dispersed support nanomaterials toward electrocatalysis through the fine regulation of metal-support interactions.

Phosphorus doping to promote the reconstruction of NiS nanorods for efficient electrocatalytic water oxidation

Transition metal sulfides have been verified as effective precatalysts for OER in alkaline conditions, and the in-situ reconstructed metal (oxy)hydroxides on their surface were the real active sites. The rational reconstruction can regulate the amount and chemical state of the metal (oxy)hydroxides and thus promote the OER performance efficiently, but also remains a challenge. Herein, we report a unique rationally controllable in-situ anodic electrochemical activation (AEA) strategy to promote the surface reconstruction for the formation of amorphous NiOOH layer onto the P-doped NiS nanorod arrays on nickel foam (P-NiS@NiOOH-aea/NF). The doping of P atom promotes the dissolution of S and accelerates the reconstitution of NiOOH on its surface. The optimized P-NiS@NiOOH-aea/NF through the unique AEA strategy exhibits outstanding OER activity requiring ultra-low overpotentials of 203 and 349 mV to reach 10 and 1000 mA cm−2, respectively, together with robust electrocatalytic stability and satisfactory selectivity (nearly 100% Faraday efficiency) in 1.0 M KOH solution. The density functional theory (DFT) calculations further demonstrate that heteroatomic P-doping reduces the adsorption free energy of intermediate species and enhances the OER intrinsic activity of adjacent nickel active site. This work has a guiding significance for the rational design of introducing anions in the in-situ reconstruction process.

Engineering high-entropy alloy nanosheets toward efficient electrocatalytic water oxidation

Fabricating advanced materials with a high-entropy concept imparts a result in efficient energy conversion and storages, as the configurations of high entropy alloys (HEAs) are optimized through incorporating different atomic species. Herein, we synthesize FeCoNiCrMn HEAs with nanosheet structure through a facile salt-templated approach. Extensive characterizations reveal that the introduction of sodium chloride is beneficial to the formation of high-entropy and nanosheet structures, and the chemical compositions can be modified via the designed annealing temperature. As an example application, the FeCoNiCrMn HEA nanosheets that annealed at 750 ℃ exhibit outstanding electrocatalytic performances for water oxidation, which possess the ultralow overpotential of 294 and 434 mV at the current density of 10 and 300 mA cm−2, respectively, accompanied with long-term electrochemical durability with a negligible decay in alkaline at the current density of 100 mA cm-2 for 100 h. Our work not only offers insights into high-entropy syntheses, but also provides robust electrocatalysts for water splitting.

Versatile bimetallic metal-organic framework with nanocutting channels tailored for efficient electrocatalytic water oxidation and glucose detection

Metal–organic frameworks (MOF) with outstanding properties have shown great potential for electrochemical water splitting, particularly for the oxygen evolution reaction (OER) and nonenzymatic glucose detection. In this study, a facile method was used to synthesize CoNiMOF (with 5-aminoisophthalic acid as the organic linker) as electrocatalyst for the OER and glucose oxidation reaction (GOR). In-depth structural and microstructural analyses confirmed the formation of the MOF via metal–ligand (electron donor–acceptor) coordination. Among the different CoNiMOFs, CoNi(1:3)MOF shown to have nanocutting channels along the edges of the microstructural sheets, exhibited good catalytic activity toward the OER and GOR. CoNi(1:3)MOF delivers the best electrocatalytic performance in 1 M KOH with an overpotential of 348 mV at 20 mA cm−2 for the OER, benefitting from the specific morphology and electronic control. Moreover, the electrocatalyst was remarkably stable after 5000 cyclic voltammetry cycles and chronopotentiometric (20 h) analysis. As glucose sensor, CoNi(1:3)MOF exhibits a remarkably low glucose detection limit (1.03 μΜ) and wide detection range (2–500 μΜ and 1–15 mM, respectively). In addition, CoNi(1:3)MOF performed efficiently in an interference study, which revealed the selectivity of the developed sensor. The active formation of bimetallic MOF structures and the synergistic effect between the two metals in the electrocatalyst is attributed to the efficient modulation of the electronic structure, which effectively influenced the OER and GOR performance.

Bifunctional organic cobalt phosphonates nanoplates with efficient photocatalytic peroxymonosulfate activation and electrocatalytic water oxidation

The exploration of efficient and inexpensive transition metal phosphonates-based materials with multifunctional applications has increasingly urgent and meaningful. Herein, the organic cobalt phosphonates nanoplates (CoPPA) catalyst was achieved via a solvothermal process without employing any additives. The CoPPA catalyst proceeds nanoplates architecture with minimal sheet thickness, which not only reduce the transfer distance for charge carriers to the surface of catalyst and realize the separation of the charge carriers, but also provide numerous active sites for surface reaction. As a result, the optimal CoPPA catalyst not merely accelerated the photocatalytic activation of peroxymonosulfate (PMS) for tetracycline hydrochloride removal in CoPPA/PMS/Vis system, but also effectively electric-catalyze the oxygen evolution reaction. This work provides fresh insights for exploring high-efficiency dual-functional transition metal phosphonates-based materials and is expected to contribute to purify recalcitrant contaminants and energy conversion.

Under-Coordinated CoFe Layered Double Hydroxide Nanocages Derived from Nanoconfined Hydrolysis of Bimetal Organic Compounds for Efficient Electrocatalytic Water Oxidation.

Hierarchically structured bimetal hydroxides are promising for electrocatalytic oxygen evolution reaction (OER), yet synthetically challenging. Here, the nanoconfined hydrolysis of a hitherto unknown CoFe-bimetal-organic compound (b-MOC) is reported for the controllable synthesis of highly OER active nanostructures of CoFe layered double hydroxide (LDH). The nanoporous structures trigger the nanoconfined hydrolysis in the sacrificial b-MOC template, producing CoFe LDH core-shell octahedrons, nanoporous octahedrons, and hollow nanocages with abundant under-coordinated metal sites. The hollow nanocages of CoFe LDH demonstrate a remarkable turnover frequency (TOF) of 0.0505s-1 for OER catalysis at an overpotential of 300mV. It is durable in up to 50h of electrolysis at step current densities of 10-100mAcm-2 . Ex situ and in situ X-ray absorption spectroscopic analysis combined with theoretical calculations suggests that under-coordinated Co cations can bind with deprotonated Fe-OH motifs to form OER active Fe-O-Co dimmers in the electrochemical oxidation process, thereby contributing to the good catalytic activity. This work presents an efficient strategy for the synthesis of highly under-coordinated bimetal hydroxide nanostructures. The mechanistic understanding underscores the power of maximizing the amount of bimetal-dimer sites for efficient OER catalysis.

Silver nanoparticles embedded in phosphorus and nitrogen-doped hierarchical hollow porous carbon for efficient supercapacitor and electrocatalytic water oxidation

Supercapacitor (SC) and oxygen evolution reaction (OER) require highly efficient multifunctional catalysts prepared from non-noble metals and heteroatoms. In this work, we have developed silver (Ag) decorated on phosphorus (P), nitrogen (N) -doped hollow porous carbon (HPC) prepared through hydrothermal followed by pyrolysis method. The prepared bifunctional electrocatalyst was studied through different characterization techniques. As-prepared HPC-UD, P-HPC-UD, and Ag@P-HPC-UD integrate high-level P-doping, large specific surface areas (up to 1452, 1247, and 528 m2 g−1), and hierarchical multipores of cross-linked micro and mesopore channels. As a result, the Ag and P modified the active sites and electronic structure of the HPC bifunctional catalyst, which is beneficial for the electrocatalytic process. As a result, the Ag@P-HPC-UD catalyst provides an outstanding specific capacitance value of 388 F g−1 at 0.5 A g−1 when used as a SC electrode. Furthermore, the Ag@P-HPC-UD electrocatalyst exhibited efficient OER behavior with a lower overpotential of 165 mV at 10 mA cm−2 current density and a lower Tafel value of 55.46 mV dec−1, which is remarkably superior to commercial RuO2 electrocatalyst. Therefore, the Ag@P-HPC-UD electrocatalyst pathway for a new revolution in developing a highly impressive carbon-based electrode towards both SC and electrocatalytic OER performance.

Amorphous NiFe Oxide-based Nanoreactors for Efficient Electrocatalytic Water Oxidation.

Synergy engineering is an important way to enhance the kinetic activity of oxygen-evolution-reaction (OER) electrocatalysts. Here, we fabricated NiFe amorphous nanoreactor (NiFe-ANR) oxide as OER electrocatalysts via a mild self-catalytic reaction. Firstly, the amorphousness helps transform NiFe-ANR into highly active hydroxyhydroxides, and its many fine-grain boundaries increase active sites. More importantly, as proved by experiments and finite element analysis, the nanoreactor structure alters the spatial curvature and the mass transfer over the catalyst, thereby enriching OH- in the catalyst surface and inner part. Thus, the catalyst with the structure of amorphous nanoreactors gained excellent activity, far superior to the NiFe catalyst with the structure of crystalline nanoreactor or amorphous non-nanoreactor. This work provides new insights into the applications and mechanisms of amorphousness and nanoreactors, embodying the "1+1>2" synergy of crystalline state and morphology.

Amorphous NiFe Oxide‐based Nanoreactors for Efficient Electrocatalytic Water Oxidation

AbstractSynergy engineering is an important way to enhance the kinetic activity of oxygen‐evolution‐reaction (OER) electrocatalysts. Here, we fabricated NiFe amorphous nanoreactor (NiFe‐ANR) oxide as OER electrocatalysts via a mild self‐catalytic reaction. Firstly, the amorphousness helps transform NiFe‐ANR into highly active hydroxyhydroxides, and its many fine‐grain boundaries increase active sites. More importantly, as proved by experiments and finite element analysis, the nanoreactor structure alters the spatial curvature and the mass transfer over the catalyst, thereby enriching OH− in the catalyst surface and inner part. Thus, the catalyst with the structure of amorphous nanoreactors gained excellent activity, far superior to the NiFe catalyst with the structure of crystalline nanoreactor or amorphous non‐nanoreactor. This work provides new insights into the applications and mechanisms of amorphousness and nanoreactors, embodying the “1+1>2” synergy of crystalline state and morphology.

Single atomic Ru in TiO2 boost efficient electrocatalytic water oxidation to hydrogen peroxide

Electrocatalytic two-electron water oxidation affords a promising approach for distributed production of H2O2 using electricity. However, it suffers from the trade-off between the selectivity and high production rate of H2O2 due to the lack of suitable electrocatalysts. In this study, single atoms of Ru were controllably introduced into titanium dioxide to produce H2O2 through an electrocatalytic two-electron water oxidation reaction. The adsorption energy values of OH intermediates could be tuned by introducing Ru single atoms, offering superior H2O2 production under high current density. Notably, a Faradaic efficiency of 62.8% with an H2O2 production rate of 24.2 μmol min−1 cm−2 (>400 ppm within 10 min) was achieved at a current density of 120 mA cm−2. Consequently, herein, the possibility of high-yield H2O2 production under high current density was demonstrated and the importance of regulating intermediate adsorption during electrocatalysis was evidenced.

Spin-state inversion in non-precious Na single atoms decorated NiFe-LDH monolayer for efficient electrocatalytic water oxidation

Preparing highly efficient electrocatalysts via structural or electronic manipulation always holds great interest in water electrolyzers. Here, we introduce the non-precious Na atoms to NiFe-LDH and investigate the effect of electronic configuration changes on electrocatalytic water oxidation. The electrochemical tests reveal that the NiFe-LDH monolayer decorated with Na atoms (Na/NiFe-LDH) possesses superior oxygen evolution reaction (OER) performance, achieving an overpotential of 279 mV at the current density of 100 mA cm−2. The experimental characterizations highlight the effect of the Na-O3 motif on improving the intrinsic OER activity and facilitating surface charge transfer kinetics. Further theoretical calculations confirm that the formation of the Na-O3 motif reduces the strength of the Fe-O bond in the NiFe-LDH skeleton and induces the spin-state inversion for Fe 3d orbitals, which accounts for the enhanced OER performance. This work demonstrates an effective method to enhance the OER activity of NiFe-LDH through spin-state regulation.

Kinetics of Active Oxide Species Derived from a Metallic Nickel Surface for Efficient Electrocatalytic Water Oxidation

Kinetics of Active Oxide Species Derived from a Metallic Nickel Surface for Efficient Electrocatalytic Water Oxidation