Efficient Electrocatalyst For Water Oxidation Research Articles

Bioinspired octanuclear copper cubane complex as an efficient molecular electrocatalyst for water oxidation

Water oxidation catalysts (WOCs) with excellent activity and stability are highly desired. Numerous efforts have been dedicated to develop WOCs mimicking the cubic structure and activity of Mn4CaO5 cluster in oxygen-evolving center (OEC) of photosynthesis system II (PSII). Herein, a octanuclear Cu cluster [Cu8(dpy{OH}O)8(OAc)4]4+ (1, dpy{OH}O− = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone) that contains two Cu4O4 cubic fragments with bioinspired structure mimicking the Mn4CaO5 cluster of OEC of natural PSII is developed as efficient homogeneous catalyst for electrochemical water oxidation under near neutral condition for the first time. It exhibits outstanding water oxidation catalytic activity via accelerating oxygen evolution with onset overpotential of 730 mV and appreciable turnover frequency of 20.1 s−1. Collective experiments together confirmed the homogeneity and stability of cluster 1 under long-term water oxidation catalytic cycle. Kinetic study reveals the water nucleophilic attack (WNA) catalytic mechanism occurs on the coordination unsaturated Cu center of the cluster. This work provides the inspiration of the development of robust bioinspired catalyst for electrochemical water oxidation.

ZnAl2O4 decorated on graphitic carbon nitride (g-CN) composite as efficient electrocatalyst for water oxidation in alkaline medium

The main purpose of this research is to form highly effective and novel electrocatalysts for water splitting procedure, a pivotal step in the generation of sustainable energy. Cost-effective metal oxides exhibited superior benefits compared to alternative materials when used for oxygen evolution reactions (OER) in alkaline electrolyte. Our study focuses on the preparation of ZnAl2O4@g-CN composite by utilizing hydrothermal approach for electrocatalytic water splitting. The electrocatalytic potential of prepared electrocatalyst was observed by a comprehensive series of tests. Numerous electrochemical approaches such as chronoamperometry and electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were implemented to analyze catalytic procedure and durability in basic medium. The electrocatalytic tests of ZnAl2O4@g-CN composite reveal a remarkable overpotential of 209 mV, enabling the attainment of current density (Cd) 10 mA/cm2. Additionally, the composite shows significantly lower Tafel value (36 mV/dec) and has remarkable durability for 30 h. These characteristics mutually designate that electrocatalyst is well-suited for OER procedure. Therefore, the fabricated composite exhibited excellent efficacy in OER procedure as well as for several other upcoming applications.

New Nanocomposites Derived from Cation-Nonstoichiometric Bax(Co, Fe, Zr, Y)O3−δ as Efficient Electrocatalysts for Water Oxidation in Alkaline Solution

New Nanocomposites Derived from Cation-Nonstoichiometric Ba_<i>x</i>(Co, Fe, Zr, Y)O_3−δ as Efficient Electrocatalysts for Water Oxidation in Alkaline Solution

Multihole Ce-doped NiSe2/CoP hybrid nanosheets for improved electrocatalytic alkaline water and simulative seawater oxidation

The investigation of cost-effective and highly efficient electrocatalysts for alkaline water and simulative seawater oxidation is essential to the conversion and storage of renewable energy. In this paper, the Ce–NiSe2/CoP catalyst with multihole and ultrathin nanosheet structure is generated. The unique structural characteristics of Ce–NiSe2/CoP heterojunction nanosheets contribute the excellent OER performance under different alkaline 1 M KOH and simulated seawater (1 M KOH + 0.5 M NaCl) electrolytes. Specifically, this catalyst exhucture is generated. The unique structural characteristics of Ce–NiSe2/CoP heterojunction nanosheets conibits the low overpotentials of 287 and 304 mV at the current density of 10 mA cm−2, along with the Tafel slopes of 87.1 and 78.8 mV dec−1 in two solutions, respectively. Moreover, the Ce–NiSe2/CoP target product also displays good stability. The present study introduces a promising strategy for the advancement of high-performance electrocatalysts in green energy field.

Effect of Rh Doping on Optical Absorption and Oxygen Evolution Reaction Activity on BaTiO3 (001) Surfaces.

In the present work, we investigate the potential of modified barium titanate (BaTiO3), an inexpensive perovskite oxide derived from earth-abundant precursors, for developing efficient water oxidation electrocatalysts using first-principles calculations. Based on our calculations, Rh doping is a way of making BaTiO3 absorb more light and have less overpotential needed for water to oxidize. It has been shown that a TiO2-terminated BaTiO3 (001) surface is more promising from the point of view of its use as a catalyst. Rh doping expands the spectrum of absorbed light to the entire visible range. The aqueous environment significantly affects the ability of Rh-doped BaTiO3 to absorb solar radiation. After Ti→Rh replacement, the doping ion can take over part of the electron density from neighboring oxygen ions. As a result, during the water oxidation reaction, rhodium ions can be in an intermediate oxidation state between 3+ and 4+. This affects the adsorption energy of reaction intermediates on the catalyst's surface, reducing the overpotential value.

In situ transformation from metal-organic framework into iridium-iron hollow hexagonal rod to promote oxygen evolution reaction

Developing highly efficient and durable electrocatalysts for water oxidation in alkaline media is crucial for hydrogen production in industrialization. IrO2 is a highly promising electrocatalyst for oxygen evolution reaction (OER), but its large-scale is still limited to the sluggish OER kinetics in alkaline solution due to the multi-steps adsorption of -OH and H2O. Herein, we reported a novel in-situ generation from metal-organic framework strategy for preparing hollow hexagonal rod IrFex electrocatalysts (IrFex HHRs). Specifically, the optimized IrFe3 HHRs shows an excellent OER electrocatalytic activity, including low overpotential of 265, 295 and 307 mV at the current density of 10, 50 and 100 mA cm−2, and high stability (100 h). The experimental results revealed that the existent interfacial Fe-O-Ir bonds between Ir and MIL-88A (Fe) can promote electrons transport to improve the electrocatalyst activity. This work represents a new strategy for designing an efficiency electrocatalysts with low iridium content derived from Ir doped-bimetal MOF material.

Insights into the role of Co3O4/Ti3C2 MXene hybrid material in photoelectrochemical water oxidation over BiVO4 photoanode

Developing efficient hole transport layers and water oxidation electrocatalysts is vital for improving the performance of photoelectrochemical (PEC) devices for water-splitting. In this work, we synthesized Co3O4 nanoparticles/Ti3C2-MXene hybrid material and utilized it as a dual-function material to transport the photogenerated holes and catalyze the water oxidation reaction. It was found that the modification of BiVO4 with Co3O4/Ti3C2-MXene prolonged the lifetime of the photogenerated holes by 13.7-fold (i.e. from 0.26 s for BiVO4 to 3.56 s for Co3O4/Ti3C2/BiVO4) and significantly reduced the charge transfer resistance. The modification of BiVO4 with only Ti3C2-MXene resulted in significant surface recombination more likely due to the high concentration of the accumulated holes in the Mxene layer because of its low electrocatalytic activity toward water oxidation reaction. Employing the Co3O4/Ti3C2-MXene hybrid material significantly reduced the rate constant of surface recombination and dramatically enhanced the charge transfer efficiency (i.e. from 0.17% for BiVO4 to 14.0% for Co3O4/Ti3C2/BiVO4 at 0.65 VRHE). Under optimized conditions, the Co3O4/Ti3C2/BiVO4 photoanode was able to deliver 5.05 mA cm−2 at 1.23 VRHE and outperforms Ti3C2/BiVO4 and Co3O4/BiVO4 photoanodes. Moreover, it showed high stability for over 50 hours and reached a Faradaic efficiency of 90%. An applied bias photo-to-current efficiency (ABPE) value of 1.71% at 0.62 VPt was obtained for the overall water splitting. This work provides a facile method to reduce surface recombination and enhance the stability and PEC efficiency of BiVO4 photoanodes via the modification with dual-function oxygen evolution catalyst/hole transport layer hybrid material.

Bioinspired Tetranuclear Manganese Cubane Complex as an Efficient Molecular Electrocatalyst for Two-Electron Water Oxidation Towards Hydrogen Peroxide.

Stable homogeneous two-electron water oxidation electrocatalysts are highly demanded to understand the precise mechanism and reaction intermediates of electrochemical H2O2 production. Here we report a tetranuclear manganese complex with a cubane structure which can electrocatalyze water oxidation to hydrogen peroxide under alkaline and neutral conditions. Such a complex demonstrates an optimal Faradaic efficiency (FE) of 87 %, which is amongst (if not) the highest FE(H2O2) of reported homogeneous and heterogeneous electrocatalysts. In addition, active species were identified and co-catalysts were excluded through ESI-MS characterization. Furthermore, we identified water binding sites and isolated one-electron oxidation intermediate by chemical oxidation of the catalyst in the presence of water substrates. It is evident that efficient proton-accepting electrolytes avoid rapid proton building-up at electrode and substantially improve reaction rate and selectivity. Accordingly, we propose a two-electron catalytic cycle model for water oxidation to hydrogen peroxide with the bioinspired molecular electrocatalyst. The present work is expected to provide an ideal platform to elucidate the two-electron WOR mechanism at the atomic level.

Three-dimensional ordered FeTe-SmCoO3 nanocomposite: As efficient electrocatalyst for water oxidation

In this work, FeTe-SmCoO3 is fabricated through a hydrothermal method and then coated on a stainless steel (SS) substrate to enhance the electrocatalytic performance. The crystal structure, surface chemical state, and morphological features of pure (FeTe and SmCoO3) and heterogeneous catalysts (FeTe-SmCoO3) are determined via XRD, XPS, and TEM/EDX techniques. The fabricated FeTe-SmCoO3 electrocatalyst is attributed to the particular morphological design resulting from the synergistic effect of FeTe and SmCoO3 phases. The as-developed high exposure level of active sites with structural transformation greatly promoted the oxidation property with an overpotential only of 199 mV to derive a current density of 10 mA/cm2, also observed a small Tafel slope of 72 mVdec−1 with extraordinary stability of 90 h. The modified heterogeneous catalyst provides outstanding catalytic behavior toward OER in the alkaline solution, due to flexibility and multiple accessible oxidation states of samarium, cobalt, and iron ions. The catalyst not only acquires additional reaction sites and opens up new channels through the dispersion of the metal centers, but also achieves quick electron transfer in FeTe-SmCoO3 nanocomposite through the interconnection between two phases.

Multiwall carbon nanotubes supported rhenium doped Co3O4 as an efficient electrocatalyst for water oxidation in alkaline medium

The recent trends for the development of efficient and low cost transition metal (TMs) based anode catalysts for water splitting is crucial and important. Even though, research is continuously progressing in different directions to design catalyst; however, catalytic OER (oxygen evolution reaction) activity has remained insufficient. Till now, various transition metal oxides (TMOs) have been used as efficient and cost-effective electrocatalyst for the oxygen evolution reaction. The catalytic performance of TMOs could be enhanced by doping with the metal, which increases the catalyst's charge transfer and electronic conductivity. Decoration of TMOs with the multi-wall carbon nanotube (MWCNT) further improves catalytic activity by providing numerous active sites. Here, Co3O4/MWCNT and Rhenium (Re) doped Co3O4/MWCNT composite were prepared by simple hydrothermal process and used as electrocatalyst for OER in alkaline medium. Different concentrations of Re (0.05 mmol, 0.1 mmol, 0.2 mmol, 0.3 mmol) were doped and it was observed that the electrochemical results of the 0.2 mmol Re doped Co3O4/ MWCNT (R0.2CO) was most efficient electrocatalyst which offers the OER overpotential of 298 mV/dec to attain the 10 mA cm−2 current density, lower Tafel slope (70 mV/dec), higher value of turn over frequency (0.95), lower value of the charge transfer resistance (3.10Ω) and good stability, demonstrating the better OER catalytic activity as compared to un-doped Co3O4/MWCNT (R0.0CO) catalyst. The investigated catalyst R0.2CO is more efficient catalyst than most of the reported similar type of catalysts and offers comparable electrocatalytic activity with benchmark electrocatalyst RuO2.

Active Sites Engineered Bimetallic Iron–Vanadium Oxide (FeVOx) Thin Film Electrocatalyst for Efficient and Sustainable Water Oxidation

Active Sites Engineered Bimetallic Iron–Vanadium Oxide (FeVO_<i>x</i>) Thin Film Electrocatalyst for Efficient and Sustainable Water Oxidation

Nickel Hydroxide-Based Electrocatalysts for Promising Electrochemical Oxidation Reactions: Beyond Water Oxidation.

Transition metal hydroxides have attracted significant research interest for their energy storage and conversion technique applications. In particular, nickel hydroxide (Ni(OH)2 ), with increasing significance, is extensively used in material science and engineering. The past decades have witnessed the flourishing of Ni(OH)2 -based materials as efficient electrocatalysts for water oxidation, which is a critical catalytic reaction for sustainable technologies, such as water electrolysis, fuel cells, CO2 reduction, and metal-air batteries. Coupling the electrochemical oxidation of small molecules to replace water oxidation at the anode is confirmed as an effective and promising strategy for realizing the energy-saving production. The physicochemical properties of Ni(OH)2 related to conventional water oxidation are first presented in this review. Then, recent progress based on Ni(OH)2 materials for these promising electrochemical reactions is symmetrically categorized and reviewed. Significant emphasis is placed on establishing the structure-activity relationship and disclosing the reaction mechanism. Emerging material design strategies for novel electrocatalysts are also highlighted. Finally, the existing challenges and future research directions are presented.

FeCoCuMnRuB Nanobox with Dual Driving of High-Entropy and Electron-Trap Effects as the Efficient Electrocatalyst for Water Oxidation.

High-entropy borides hold potential as electrocatalysts for water oxidation. However, the synthesis of the tailored nanostructures remains a challenge due to the thermodynamic immiscibility of polymetallic components. Herein, a FeCoCuMnRuB nanobox decorated with a nanosheet array was synthesized for the first time by a "coordination-etch-reduction" method. The FeCoCuMnRuB nanobox has various structural characteristics to express the catalytic performance; meanwhile, it combines the high-entropy effect of multiple components with the electron trap effect induced by electron-deficient B, synergistically regulating its electronic structure. As a result, FeCoCuMnRuB nanobox exhibits enhanced OER activity with a low overpotential (η10 = 233 mV), high TOF value (0.0539 s-1), small Tafel slope (61 mV/dec), and a satisfactory stability for 200 h, outperforming the high-entropy alloy and low-entropy borides. This work develops a high entropy and electron-deficient B-driven strategy for motivating the catalytic performance of water oxidation, which broadens the structural diversity and category of high-entropy materials.

Erbium doped samarium oxide nanoballs functionalized cluster surface as a robust electrocatalyst for efficient water oxidation

The oxygen evolution reaction (OER) is a crucial energy-storing and energy-changing half-process in water splitting. It is critical to expand the availability of renewable energy reservoirs, and effective electrodes must be robust and possess a high level of catalytic activity. However, it is difficult to eliminate overpotential and improve the performance of OER. In this study, Erbium (Er)-doped samarium oxide (Sm2O3) was synthesized by a facile co-precipitation technique. Using X-ray diffraction analysis, it was determined that a Sm2O3 cubic structure was formed when sharp peaks were observed. Using Fourier-transform infrared (FTIR spectroscopy) and scanning electron spectroscopy (SEM) pictures, the existence of Sm2O3 crystals was detected and surface geometry was observed. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) confirm the successful Er doping in Sm2O3. The OER activities of pure Sm2O3 and Sm2O3 coupled with Er were determined using electrochemical. In comparison to pure Sm2O3, a high amount of Er-doped Sm2O3 possessed a low overpotential (365 mV for the OER) and a small Tafel slope (47 mV/dec). Consequently, OER became extremely active, metal oxide's structure and catalytic capabilities were altered by inclusion of rare earth metals. Erbium is an essential component when doped in Sm2O3 that improves the performance of OER. Among all 2% Er doped Sm2O3 is an excellent material for energy conversion.

Modulating redox transition kinetics by anion regulation in Ni−Fe−X (X = O, S, Se, N, and P) electrocatalyst for efficient water oxidation

Modulating redox transition kinetics by anion regulation in Ni−Fe−X (X = O, S, Se, N, and P) electrocatalyst for efficient water oxidation

Surface oxygen vacancy engineering of Cr-doped FeNi3/NiFe2O4 Mott-Schottky heterojunction as efficient electrocatalyst for high current density water oxidation

The defect engineering at the surface by filling of oxygen vacancies during OER causing surface reconstruction is considered to be a unique way to boost up intrinsic electrocatalytic activity, especially towards oxygen evolution reaction (OER) mechanism. The present study aimed creation of large number of oxygen vacancies by Cr-doping into FeNi3/NiFe2O4 Mott-Schottky heterojunction electrocatalyst causing much desirable surface engineering and electronic modulation in favour of OER activity. The optimized heterojunction nanoparticles exhibited an excellent catalytic activity with low overpotential of 246 mV at the current density of 20 mA cm−2 with low Tafel slope value of 55 mV dec−1 for OER. Such oxygen vacancy-aided surface reconstruction during OER demonstrated an outstanding durability over 200 h even at high current density of 1000 mA cm−2 in 1 M KOH electrolyte. The surface oxygen vacancy engineering with the help of ex-situ Raman spectroscopy at different anodic potentials reveals the filling of vacancies and generation of MOOH as surface reconstruction of electrocatalyst during OER, also supported by XPS, TEM and EELS analyses.

Oxygen defect engineering on low-crystalline iron(iii) oxyhydroxide as a highly efficient electrocatalyst for water oxidation

The defects optimized the adsorption capacity of the reaction intermediates during the catalytic process and finally improved the catalytic efficiency.

Electrodeposited CoNi-LDH nanosheets supported on halloysite nanotubes as a robust and highly efficient electrocatalyst for water oxidation

This work demonstrates electrodeposited CoNi-LDH nanosheets with variable Co/Ni molar ratios supported on halloysite nanotubes as efficient electrocatalysts toward the alkaline OER.

Low-coordinated surface nickel oxide as electrocatalyst for efficient water oxidation

Ni-based compounds represent promising candidates as high-performance electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. Here, a new Ni oxide electrocatalyst developed via a simple electrodeposition method is reported, exhibiting enhanced catalytic activity for OER. Structural and activity analysis of the fresh and post-reaction samples reveals that the Ni2+ center has low coordination with pyramidal symmetry (NiO5). The bulk metallic Ni readily undergoes oxidation under OER conditions to generate more low-coordinated Ni2+ and high-valence state Ni (Ni3+) species, thereby facilitating the OER reaction. This study provides new insight into the active structure of Ni-based oxide electrocatalysts and offers a simple pathway for the design and development of cost-effective and high-performance electrocatalysts for applications in OER.

Atomic Layer Deposition of NiO Using Different Precursors with Different Oxygen Sources

NiO thin films have attracted tremendous attention owing to their outstanding chemical stability, good magnetic and catalytic properties1. It is also considered an efficient electrocatalyst for water oxidation, and is one of the few p-type semiconductive oxides with optical transparency due to its wide bandgap of 3.6 eV. Furthermore, NiO films can control high and low conductive states under an external electric field, which is very useful for developing resistance-switching random-access memory devices2.NiO films have been prepared by different deposition techniques, including sputtering, sol-gel, pulsed laser deposition, spray pyrolysis, and chemical vapor deposition (CVD), atomic layer deposition (ALD). Among these, ALD is a powerful technique to grow thin conformal films with fine-tuning of both composition and thickness. The commonly used nickel precursors for ALD process are Ni(Cp)2, Ni(MeCp)2, Ni(EtCp)2, Ni(dmamp)2, Ni(dmamb)2, Ni(acac)2, Ni(apo)2, Ni(dmg)2, Ni(thd)2, and Ni(amd)2 in combination with ozone, water, hydrogen peroxide, or oxygen plasma1. However, ALD of NiO is not well developed yet. The major disadvantages associated with these nickel precursors are low volatility, thermal instability, and poor reactivity or narrow ALD window. Some of these precursors are expensive or very difficult to synthesize. The aforementioned situations indicate that developing a new ALD process for the NiO film with new precursors is pertinent.In this work, we explored different Ni-precursors such as Ni ketoiminates, Ni(ipki)2 and Ni(eeki)2 (their synthesis has been proposed earlier3), and Alanis, provided by Air Liquide. These different reactants combined with different oxygen sources (H2O and O3) resulted in high-quality NiO thin films. Surface analyses indicate NiO films are stoichiometric. They are uniform and exhibit a columnar morphology as determined by TEM (Fig.1a). From the growth characteristics, it is found that the Ni precursors have a strong effect on the GPC. Similarly, the oxygen source affects GPC but it also influences the morphology of the layer leading to significant roughness variations (observed by XRR and AFM). The use of H2O can also result in a nucleation delay. Polycrystalline films are observed when the reaction temperature reaches 125°C, and the crystallinity is further enhanced with deposition temperature (Fig.1b). After comprehensive optimization of the ALD process with Alanis precursor, it has been possible to reach one of the highest growth rate of 1.5 Å/cy, which is nearly seven times higher than that obtained with Ni(EtCp)2 based reaction with the same ALD reactor and having a wide temperature window (100 to 175 °C) with ozone. The same precursor also reacted well with water, giving a GPC of 0.9 Å with an initial nucleation delay. With the use of Ni-ketoiminates, the growth rate could be enhanced considerably with a GPC of 0.7 Å in combination with O3 at a higher temperature.The NiO layers were subsequently used as catalysts for water photooxidation in alkaline medium. The electrochemical properties are better when compared to layers grown by PVD. References Y. Zhang, L. Du, X. Liu, and Y. Ding, A high growth rate atomic layer deposition process for nickel oxide film preparation using a combination of nickel (II) diketonate-diamine and ozone, App. Surf. Sci., 2019, 481, 138-143.H.L. Lu, G. Scarel, X.L. Li, M. Fanciulli, Thin MnO and NiO films grown using atomic layer deposition from ethylcyclopentadienyl type of precursors, J. Cryst. Growth, 2008, 310, 5464-5468.3. D. Zywitzki, D.H. Taffa, L. Lamkowski, M. Winter, D. Rogalla, M. Wark, and A. Devi, Tuning coordination geometry of nickel ketoiminates and its influence on thermal characteristics for chemical vapour deposition of nanostructured NiO electrocatalysts, Inorg. Chem., 2020,59, 14, 10059-10070. Figure 1