Oxygen Evolution Catalysts Research Articles

Striking Stabilization Effect of Spinel Cobalt Oxide Oxygen Evolution Electrocatalysts in Neutral pH by Dual‐Sites Iron Incorporation

Developing stable and efficient nonprecious‐metal‐based oxygen evolution catalysts in the neutral electrolyte is a challenging but essential goal for various electrochemical systems. Particularly, cobalt‐based spinels have drawn a considerable amount of attention but most of them operate in alkali solutions. However, the frequently studied Co–Fe spinel system never exhibits appreciable stability in nonbasic conditions, not to mention attract further investigation on its key structural motif and transition states for activity loss. Herein, we report exceptional stable Co–Fe spinel oxygen evolution catalysts (~30% Fe is optimal) in a neutral electrolyte, owing to its unique metal ion arrangements in the crystal lattice. The introduced iron content enters both the octahedral and tetrahedral sites of the spinel as Fe2+ and Fe3+ (with Co ions having mixed distribution as well). Combining density functional theory calculations, we find that the introduction of Fe to Co3O4 lowers the covalency of metal‐oxygen bonds and can help suppress the oxidation of Co2+/3+ and O2−. It implies that the Co–Fe spinel will have minor surface reconstruction and less lattice oxygen loss during the oxygen evolution reaction process in comparison with Co3O4 and hence show much better stability. These findings suggest that there is still much chance for the spinel structures, especially using reasonable sublattices engineering via multimetal doping to develop advanced oxygen evolution catalysts.

Generation of Pure Oxygen from Briny Water by Binary Catalysis.

Whereas the emphasis of water splitting is typically on hydrogen generation, there is value in the oxygen produced, especially in the undersea environment and for medicinal applications in the developing world. The generation of pure and breathable oxygen from abundant and accessible sources of water, such as brine and seawater, is challenging owing to the prevalence of the competing halide oxidation reaction to produce halogen and hypohalous acids. We show here that pure O2 may be generated from briny water by using an oxygen evolution catalyst with an overlayer that fulfills the criteria of (i) possessing a point of zero charge that results in halide anion rejection and (ii) promoting the disproportionation of hypohalous acids.

A Conformal Carbon Nanolayer Coated Fe2 O3 Cocatalyst for the Promoted Activity of Plasma-Sputtered BiVO4 Photoanode.

To simultaneously improve the hole extraction ability of the BiVO4 photoanode and accelerate the surface reaction kinetics, herein, a carbon nanolayer conformally coated Fe2 O3 (C-Fe2 O3 ) as oxygen evolution catalyst (OEC) is loaded on the H2 plasma treated nanoporous BiVO4 (BVO(H2 )) surface by a hydrothermal reaction. It is found that the H2 plasma induced vacancies in BVO remarkably increases the conductivity, and the C-Fe2 O3 enables hole extraction from the bulk to the surface as well as efficient hole injection to the electrolyte. As a result, the C-Fe2 O3 /BVO(H2 ) photoanode achieves a photocurrent density of 4.4 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) and an ABPE value of 1.5 % at 0.68 V vs. RHE, which are 4.8-fold and 13-fold higher than that of BVO photoanode, respectively.

POM@ZIF Derived Mixed Metal Oxide Catalysts for Sustained Electrocatalytic Oxygen Evolution.

The design of efficient and stable oxygen evolution reaction (OER) catalysts based on noble-metal-free materials is crucial for energy conversion and storage. In this work, it was demonstrated how polyoxometalate (POM)-doped ZIF-67 can be converted into a stable oxygen evolution electrocatalyst by chemical etching, cation exchange, and thermal annealing steps. Characterization by X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy indicate that POM-doped ZIF-67 derived carbon-supported metal oxides were synthesized. The resulting composite shows structural and compositional advantages which lead to low overpotential (306 mV at j=10 mA ⋅ cm-2 ) and long-term stability under harsh OER conditions (1.0 M aqueous KOH).

Advances in Spin Catalysts for Oxygen Evolution and Reduction Reactions (Small 5/2023)

Advances in Spin Catalysts for Oxygen Evolution and Reduction Reactions (Small 5/2023)

Tailored BiVO4/In2O3 nanostructures with boosted charge separation ability toward unassisted water splitting

AbstractThe development of new heterostructures with high photoactivity is a breakthrough for the limitation of solar‐driven water splitting. Here, we first introduce indium oxide (In2O3) nanorods (NRs) as a novel electron transport layer for bismuth vanadate (BiVO4) with a short charge diffusion length. In2O3 NRs reinforce the electron transport and hole blocking of BiVO4, surpassing the state‐of‐the‐art photoelectrochemical performances of BiVO4‐based photoanodes. Also, a tannin–nickel–iron complex (TANF) is used as an oxygen evolution catalyst to speed up the reaction kinetics. The final TANF/BiVO4/In2O3 NR photoanode generates photocurrent densities of 7.1 mA cm−2 in sulfite oxidation and 4.2 mA cm−2 in water oxidation at 1.23 V versus the reversible hydrogen electrode. Furthermore, the “artificial leaf,” which is a tandem cell with a perovskite/silicon solar cell, shows a solar‐to‐hydrogen conversion efficiency of 6.2% for unbiased solar water splitting. We reveal significant advances in the photoactivity of TANF/BiVO4/In2O3 NRs from the tailored nanostructure and band structure for charge dynamics.

IrO2 Nanoparticle-Decorated Ir-Doped W18O49 Nanowires with High Mass Specific OER Activity for Proton Exchange Membrane Electrolysis.

The oxygen evolution reaction (OER) severely limits the efficiency of proton exchange membrane (PEM) electrolyzers due to slow reaction kinetics. IrO2 is currently a commonly used anode catalyst, but its large-scale application is limited due to its high price and scarce reserves. Herein, we reported a practical strategy to construct an acid OER catalyst where Iridium oxide loading and iridium element bulk doping are realized on the surface and inside of W18O49 nanowires by immersion adsorption, respectively. Specifically, W0.7Ir0.3Oy has an overpotential of 278 mV at 10 mA·cm-2 in 0.1 M HClO4. The mass activity of 714.10 A·gIr-1 at 1.53 V vs. the reversible hydrogen electrode (RHE) is 80 times that of IrO2, and it can run stably for 55 h. In the PEM water electrolyzer device, its mass activity reaches 3563.63 A·gIr-1 at the cell voltage of 2.0 V. This improved catalytic performance is attributed to the following aspects: (1) The electron transport between iridium and tungsten effectively improves the electronic structure of the catalyst; (2) the introduction of iridium into W18O49 by means of elemental bulk doping and nanoparticles supporting for the enhanced conductivity and electrochemically active surface area of the catalyst, resulting in extensive exposure of active sites and increased intrinsic activity; and (3) during the OER process, partial iridium elements in the bulk phase are precipitated, and iridium oxide is formed on the surface to maintain stable activity. This work provides a new idea for designing oxygen evolution catalysts with low iridium content for practical application in PEM electrolyzers.

Solar‐Driven Water Splitting in Photovoltaic Electrolysis Systems Using Copper Terpyridine Complexes as Oxygen Evolution Catalysts

Copper complexes, as kinds of molecular catalysts bioinspired from the copper O2‐activating enzymes, are attractive targets for water oxidation, which can undergo facile and reversible OO bond formation and cleavage under mild conditions. Herein, three copper(II) complexes of Cu(tpy), Cu(ctpy), and Cu(pctpy) are investigated as oxygen evolution catalysts, which are designed and synthesized using α,α′,α″‐terpyridyl(tpy) derivatives as ligands. In the electrochemical measurements, the carboxylic‐functionalized catalysts of Cu(ctpy) and Cu(pctpy) exhibit high water oxidation turnover frequencies of 1027 and 3363 s−1, respectively. The astonishing rates of O2 production exceed the oxygen evolution complex in natural photosystem II. Moreover, the photovoltaic electrolysis (PVE) system is constructed by connecting Si solar panels with the copper complex‐decorated electrodes. Under the irradiation of AM1.5G‐simulated sunlight, a high photocurrent density of 5.47 mA cm−2 and solar‐to‐hydrogen efficiency of 6.81% are achieved for solar water splitting without external bias. This is the first report PVE system using copper complex as a oxygen evolution catalyst molecular catalyst, which is of great significance to simulate the catalytic water oxidation process of natural enzymes and build an artificial photosynthesis system to achieve green, efficient, and stable decomposition of aquatic oxygen.

Operando Reconstruction toward Dual‐Cation‐Defects Co‐Containing NiFe Oxyhydroxide for Ultralow Energy Consumption Industrial Water Splitting Electrolyzer

AbstractNickel–iron oxygen evolution catalysts have been under the spotlight as substitutes for precious metals, however, they rarely operate efficiently in practical industrial electrolyzers due to their moderate activity. Guided by density functional theory, the interaction of cation vacancies and dopants can manipulate d band centers, thus gaining near‐optimal binding energies of the oxygenated intermediates and ultralow potentials. This principle is implemented experimentally by catalysis operando variations synthesis, more specifically, in situ Mo leaching from high‐entropy Co, Mo co‐doped NiFe hydroxide precursors form Co dopant and cation vacancy coexistent NiFe oxyhydroxide. Operando electrochemical spectroscopy uncovers that dual‐cation‐defects promote the readier oxidation transition of metal sites, thus contributing to a low overpotential of 255 mV at 100 mA cm−2. Furthermore, dual‐regulated NiFe oxyhydroxide electrodes operate stably at 8 A in practical industrial electrolyzers with ultralow energy consumption of ≈4.6 kWh m−3H2, verifying the feasibility of lab‐constructed novel catalysts towards industrialization.

Surface reconstruction of Fe(III)/NiS nanotubes for generating high-performance oxygen-evolution catalyst

Designing high-performance and cost-effective oxygen-evolution electrocatalysts is highly required toward sustainable water electrolysis. Surface reconstruction is a promising strategy to realize the improvement of the oxygen-evolution reaction (OER) performance of transition metal-based electrocatalysts. Herein, we present a simple electrospinning-post treatment route to construct a novel Fe(III)/NiS electrocatalyst and investigate the key role of the surface reconstruction to significantly promote the OER performance. Owing to the unique tubular morphology and the formation of the highly efficient electrochemical active species of Ni(Fe)OOH during OER process, the prepared Fe(III)/NiS nanotubular catalyst exhibits a low overpotential of 264 mV at 10 mA cm−2, superior to the benchmark RuO2 and many other metal sulfide electrocatalysts. Furthermore, the catalyst also presents an excellent durability with no distinct activity reduction for over 70 h. This study offers a reliable surface reconstruction way to fabricate high-efficiency and outstanding durable OER electrocatalyst, enabling it promising prospect for water electrolysis with a reduced energy consumption.

Oxygen-evolution reaction in the presence of cerium(IV) ammonium nitrate and iron (hydr)oxide: old system, new findings.

Solar fuel production by photosynthetic systems strongly relies on developing efficient and stable oxygen-evolution catalysts (OECs). Cerium(IV) ammonium nitrate (CAN) has been the most commonly used sacrificial oxidant to investigate OECs. Although many metal oxides have been extensively investigated as OECs in the presence of CAN, mechanistic studies were rarely reported. Herein, first, Fe(III) (hydr)oxide (FeOxHy) was prepared by the reaction of Fe(ClO4)3 and KOH solution and characterized by some methods. Then, changes in Fe oxide in the presence of CAN during the OER were tracked using in situ Raman spectroscopy, in situ X-ray absorption spectroscopy, in situ visible spectroscopy, and in situ electron paramagnetic resonance spectroscopy. FeOxHy in the presence of CAN and during the OER converted to γ-Fe2O3 and [Fe(H2O)6]3+, and a small amount of oxygen was formed. A maximum turnover frequency and turnover number of 10-6 s-1 and 1.3 × 10-3 mol(O2)/mol(Fe) (for half an hour) in the presence of CAN (0.20 M) and FeOxHy were observed.

Promoting the electrocatalytic activity through the introduction of oxygen vacancies to core–shell NiO hollow sphere catalysts for efficient oxygen evolution

The contribution of oxygen vacancies for improving the OER activity of NiO.

Experimentally revealed and theoretically certified synergistic electronic interaction of V-doped CoS for facilitating the oxygen evolution reaction.

Since electrocatalytic oxygen evolution (OER) is a four-electron transfer reaction with very slow kinetics, there is great competition to develop cheap, durable and efficient catalysts for oxygen evolution. A molecular model is designed for density functional theory (DFT) simulation calculations to guide the experiment, and this hypothesis is fully supported by the experimental data. Herein, regulating the composition and morphology of the bimetallic VCo and MoCo sulfide and monometallic sulfide nanoparticles (NPs) at the oil-water interface was achieved via a one-step hydrothermal method for efficient and durable OER electrocatalysts. Compared to CoS and MoCoS, the VCoS NPs show superior OER performance. By adjusting the atomic composition ratio of the VCoS nanoparticles, the VCoS NPs (1 : 2 : 1.5 mole ratio) showed a significant OER overpotential η = 255 mV (10 mA cm-2), and their outstanding stability was demonstrated after 48 h of continuous testing. The CoS and MoCoS NPs were also tested for comparison. Density functional theory (DFT) calculations showed that appropriate V doping (VCoS) can heighten the density of states (DOS) of the Fermi level, which generates more charge density and reduces the intermediate adsorption energy. This study not only provides efficient and powerful integrated catalysts, but also details a DFT calculation model guided by experiments to regulate the oxygen insertion technology, thus leading to the design of ideal materials and enabling more far-reaching applications in electrocatalysis.

Robust FeCoP nanoparticles grown on a rGO-coated Ni foam as an efficient oxygen evolution catalyst for excellent alkaline and seawater electrolysis.

Electrochemical water splitting is a potential green hydrogen energy generation technique. With the shortage of fresh water, abundant seawater resources should be developed as the main raw material for water electrolysis. However, since the precipitation reaction of chloride ions in seawater will compete with the oxygen evolution reaction (OER) and corrode the catalyst, seawater electrolysis is restricted by the decrease in activity, low stability, and selectivity. Rational design and development of efficient and stable catalysts is the key to seawater electrolysis. Herein, a high-activity bimetallic phosphide FeCoP, grown on a reduced graphene oxide (rGO)-protected Ni Foam (NF) substrate using FeCo Prussian Blue Analogue (PBA) as a template, was designed for application in alkaline natural seawater electrolysis. The OER activity confirmed that the formed FeCoP@rGO/NF has high electrocatalytic performance. In 1 M KOH and natural alkaline seawater, the overpotential was only 257 mV and 282 mV under 200 mA cm-2, respectively. It also demonstrated long-term stability up to 200 h. Therefore, this study provides new insight into the application of PBA as a precursor of bimetallic phosphide in the electrolysis of seawater at high current density.

Tungsten-Doped NiFe-Layered Double Hydroxides as Efficient Oxygen Evolution Catalysts

Tungsten-Doped NiFe-Layered Double Hydroxides as Efficient Oxygen Evolution Catalysts

Interfacial microenvironment modulation enhancing catalytic kinetics of CoNiP@NiFe LDH heterostructures for highly efficient oxygen evolution reaction.

The development of highly active and robust OER catalysts is the key to address the constraints on the efficiency of electrocatalytic water splitting technology. Herein, CoNi-pristine was synthesized by a simple hydrothermal method, further phosphorylation treatment and construction of heterojunctions to synthesize efficient oxygen evolution catalysts. The OER catalytic performance of the material was greatly enhanced by the advantages of proper self-supporting 3D morphology, formation of heterogeneous interfaces and the synergistic effect of CoNiP and NiFe LDH. In 1 M KOH, CoNiP@NiFe LDH/NF only requires an overpotential of 207 mV to reach a current density of 10 mA cm-2 and operates at high current densities for more than 120 h without significant decay. It provides assistance for the rational design of interface-engineered heterostructures based on the synthesis of OER catalysts with high catalytic activity.

One-step electrodeposition of V-doped NiFe nanosheets for low-overpotential alkaline oxygen evolution.

As a non-noble metal electrocatalyst for the oxygen evolution reaction (OER), the binary NiFe layer double hydroxide (LDH) is expected to replace Ru-based and Ir-based anode materials for water decomposition. To attain threshold current density, nevertheless, a somewhat significant overpotential is still needed. In this work, layered double hydroxides of NiFe LDH are doped with V to form the terpolymer NiFeV LDH, which greatly increases the intrinsic activity of NiFe LDH and improves OER performance. This process is a straightforward and quick one-step electrodeposition process. Notably, NiFeV/NF has a low overpotential (218 mV at 10 mA cm-2) and faster kinetics (Tafel slope of 31 mV dec-1) as well as excellent durability and stability in 1 M KOH solution. In addition, the OER performance of the catalyst prepared in this work is better than that of a non-valuable metal catalyst that was recently reported. The V-doped NiFe LDH layered double hydroxides and the investigation of electrodeposition electrocatalytic methods in this work offer a fresh opportunity for the advancement of electrochemical technology.

Novel high-entropy layered double hydroxide microspheres as an effective and durable electrocatalyst for oxygen evolution

High entropy oxygen evolution catalysts with high efficiency and long life.

ZIF-L-derived autocatalytic growth of Fe, N co-doped carbon nanotubes to form a hierarchical porous structure as an efficient oxygen reduction and oxygen evolution catalyst for Zn–air batteries

The hierarchical porous Fe–N–C catalyst with self-catalytic growth of carbon nanotube coated nanoparticles exhibited satisfactory electrocatalytic performances for the reactions in charge–dischargeable Zn–air batteries.

Stable seawater oxidation with a self-healing oxygen-evolving catalyst

Stable seawater oxidation at a large current density of 500 mA cm−2 for 1000 h is achieved with a self-healing borate-intercalated nickel–cobalt–iron oxyhydroxide (NiCoFe-Bi) catalyst in highly alkaline artificial seawater at pH 14.95.