Interface engineered Co, Ni, Fe, Cu oxide hybrids with biphasic structures for water splitting with enhanced activity
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Oxygen evolution
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Oxygen evolution
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Two-dimensional (2D) layered materials are currently one of the most explored materials for developing efficient and stable electrocatalysts in energy conversion applications. Some of the 2D metal phosphorous trichalcogenides (M2P2X6 or MPX3 in its simplified form) have been reported to be useful catalysts for water splitting, although results have been less promising for the sluggish oxygen evolution reaction (OER) due to insufficient activity or compromised stability. Herein, we report the OER catalysis of a series of M2P2X6 (M2+ = Mn, Fe, Co, Zn, Cd; X = S, Se). From the series of MPX3, CoPS3 yields the best results with an overpotential within the range of values usually obtained for IrO2 or RuO2 catalysts. The liquid-phase exfoliation of CoPS3 even improves the OER activity due to abundant active edges of the downsized sheets, accompanied by the presence of surface oxides. The influence of the OER medium and underlying substrate electrode is studied, with the exfoliated CoPS3 reaching the lowest overpotential at 234 mV at a current density of 10 mA/cm2, also able to sustain high current densities, with an overpotential of 388 mV at a current density of 100 mA/cm2, and excellent stability after multiple cycles or long-term operation. Quantum chemical models reveal that these observations are likely tied to moieties on CoPS3 edges, which are responsible for low overpotentials through a two-site mechanism. The OER performance of exfoliated CoPS3 reported herein yields competitive values compared to those reported for other Co-based and MPX3 in the literature, thus holding substantial promise for use as an efficient material for the anodic water-splitting reaction.
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Abstract The energy‐efficiency loss with high overpotential during hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), as well as economic inefficiencies including high‐cost materials and complicated processes, is considered the major challenge to the implementation of electrochemical water splitting applications. The authors present a new platform for electrocatalysts that functions in an unprecedented way to turn a catalyst into substrate. The NiFe alloy catalyzed substrate (NiFe‐CS) described herein is substantially active and stable electrocatalyst for both HER and OER, with low overpotential of 33 and 191 mV at 10 mA cm −2 for HER and OER, respectively. This structure enables not only the maximization of electrochemically active sites, but also the formation of hydroxyl species on the surface as the active phase. These outstanding results provide a new pathway for the development of electrocatalysts used in energy conversion technology.
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SrTiO3 (STO) is a widely used photocatalyst for water splitting, which has no photoactivity without a cocatalyst. The reason for this unclear. Here, we performed an oxygen evolution reaction (OER) on clean and oxygen deficient (100), (110), and (111) surfaces on STO by density functional theory. Combining our results with experimental results in the literature, we demonstrated that the overpotential is small enough for OER to occur on (100) surfaces. There is no photoactivity due to the photogenerated holes that cannot migrate to the (100) surfaces. On the (110) and (111) surfaces, the overpotential is very high, which prevents the OER from taking place on these two surfaces. Our work gives a guidance principle to understand the water splitting from the overpotential of OER and migrating photogenerated carriers. It may be helpful to design high efficiency photocatalysts based on STO.
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The oxygen evolution reaction (OER) is limited by the inherent linear scaling relationships of its reaction intermediates. Manipulating the spin configuration of the water oxidation intermediates allows us to overcome these constraints. Cobalt hexacyanoferrate (CoFe-PB) is an efficient and robust water oxidation catalyst and further known as a magnetic switch. Its versatile electronic structure renders it a potential candidate for magnetic tuning of the OER. Herein, we used first-principles density functional theory calculations to describe the OER on two different CoFe-PB model systems and evaluated the possibility for spin-crossover (SCO) of their resting states. We show that SCO during OER can significantly lower the overpotential by 0.7 V, leading to an overpotential of around 0.3 V, which is in agreement with the experimentally measured value. Applying an external potential >1.5 V vs SHE, the SCO-assisted pathway becomes largely favored and most likely the predominant reaction pathway.
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Considerations about thermodynamic and kinetic requirements for water splitting at n-type semiconductors are presented. A main point in water photooxidation concerns the catalytic role that the semiconductor must play in order to minimize the overpotential for oxygen evolution. On the basis of our previous results about water splitting at n-TiO/sub 2/ electrodes, and of the literature data on the electrocatalytic evolution of oxygen at RuO/sub 2/, the best metallic catalyst known up to date for this reaction, the minimum overpotential for water photooxidation is estimated to be of the order of 0.6 eV, which fixes the minimum semiconductor bandgap at about 1.8 eV. Implications of the model in photoreactions competing with water splitting are discussed.
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Photoelectrochemical cell
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Oxygen evolution reaction (OER) is a very complex process with slow reaction kinetics and high overpotential, which is the main limitation for the commercial application of water splitting. Thus, it is of necessary to design high-performance OER catalysts. NiFe based layered double hydroxides (NiFe-LDHs) have recently gained a lot of attention due to their high reaction activity and simple manufacturing process. In this study, a novel electrocatalyst based on NiFe-LDH was constructed by introducing Ti
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