Introduction of iron in various catalytic systems has served a crucial function to significantly enhance the catalytic activity toward oxygen evolution reaction (OER), but the relationship between ...material properties and catalysis is still elusive. In this study, by regulating the distinctive geometric sites in spinel, Fe occupies the octahedral sites (Fe3+(Oh)) and confines Co to the tetrahedral site (Co2+(Td)), resulting in a strikingly high activity (ηj = 10 mA cm−2 = 229 mV and ηj = 100 mA cm−2 = 281 mV). Further enrichment of Fe ions would occupy the tetrahedral sites to decline the amount of Co2+(Td) and deteriorate the OER activity. It is also found that similar tafel slope and peak frequency in Bode plot of electrochemical impedance spectroscopy indicate that Co2+(Td) ions are primarily in charge of water oxidation catalytic center. By means of electrochemical techniques and in situ X‐ray absorption spectroscopy, it is proposed that Fe3+(Oh) ions mainly confine cobalt ions to the tetrahedral site to restrain the multipath transfer of cobalt ions during the dynamic structural transformation between spinel and oxyhydroxide, continuously activating the catalytic behavior of Co2+(Td) ions. This material‐related insight provides an indication for the design of highly efficient OER electrocatalysts.
Iron doping in geometrical octahedral sites would significantly enhance the catalytic ability toward oxygen evolution reaction. Geometrical‐site confinement of iron ions leads to the cobalt ions in tetrahedral sites continuously activated under an activation process, achieving a strikingly high activity (ηj = 10 mA cm−2 = 229 mV and ηj = 100 mA cm−2 = 281 mV).
Efficient and earth abundant electrocatalysts for high‐performance oxygen evolution reaction (OER) are essential for the development of sustainable energy conversion technologies. Here, a new ...hierarchical Ni–Co oxide nanostructure, composed of small secondary nanosheets grown on primary nanosheet arrays, is synthesized via a topotactic transformation of Ni–Co layered double hydroxide. The Ni3+‐rich surface benefits the formation of NiOOH, which is the main redox site as revealed via in situ X‐ray absorption near edge structure and extended X‐ray absorption fine structure spectroscopy. The Ni–Co oxide hierarchical nanosheets (NCO–HNSs) deliver a stable current density of 10 mA cm−2 at an overpotential of ≈0.34 V for OER with a Tafel slope of as low as 51 mV dec−1 in alkaline media. The improvement in the OER activity can be ascribed to the synergy of large surface area offered by the 3D hierarchical nanostructure and the facile formation of NiOOH as the main active sites on the surface of NCO–HNSs to decrease the overpotential and facilitate the catalytic reaction.
A new hierarchical Ni–Co oxide nanostructure composed of small secondary nanosheets grown on primary nanosheet arrays is synthesized via a topotactic transformation of Ni–Co layered double hydroxide (LDH). The Ni3+‐rich surface benefits the formation of NiOOH, acting as the main active site for effective oxygen evolution reaction (OER).
Electrochemically converting water into oxygen/hydrogen gas is ideal for high-density renewable energy storage in which robust electrocatalysts for efficient oxygen evolution play crucial roles. To ...date, however, electrocatalysts with long-term stability have remained elusive. Here we report that single-crystal Co3O4 nanocube underlay with a thin CoO layer results in a high-performance and high-stability electrocatalyst in oxygen evolution reaction. An in situ X-ray diffraction method is developed to observe a strong correlation between the initialization of the oxygen evolution and the formation of active metal oxyhydroxide phase. The lattice of skin layer adapts to the structure of the active phase, which enables a reversible facile structural change that facilitates the chemical reactions without breaking the scaffold of the electrocatalysts. The single-crystal nanocube electrode exhibits stable, continuous oxygen evolution for >1,000 h. This robust stability is attributed to the complementary nature of defect-free single-crystal electrocatalyst and the reversible adapting layer.
Plasmonic nanostructures are capable of driving photocatalysis through absorbing photons in the visible region of the solar spectrum. Unfortunately, the short lifetime of plasmon‐induced hot carriers ...and sluggish surface chemical reactions significantly limit their photocatalytic efficiencies. Moreover, the thermodynamically favored excitation mechanism of plasmonic photocatalytic reactions is unclear. The mechanism of how the plasmonic catalyst could enhance the performance of chemical reaction and the limitation of localized surface plasmon resonance devices is proposed. In addition, a design is demonstrated through co‐catalyst decorated plasmonic nanoparticles Au/IrOX upon a semiconductor nanowire‐array TiO2 electrode that are able to considerably improve the lifetime of plasmon‐induced charge‐carriers and further facilitate the kinetics of chemical reaction. A thermodynamically favored excitation with improved kinetics of hot carriers is revealed through electrochemical studies and characterization of X‐ray absorption spectrum. This discovery provides an opportunity to efficiently manage hot carriers that are generated from metal nanostructures through surface plasmon effects for photocatalysis applications.
Surface plasmon resonance (SPR) of metal is a promising avenue for application to solar energy. Thermodynamics and kinetics of hot carriers generated by the SPR effect limit the photocatalytic performance. Using the synergistic effect of co‐catalyst IrOX, the photoelectrochemical performance is enhanced by 100% due to the accelerated charge transfer of hot holes and massive hot‐electron injection into TiO2.
Display omitted
•Fe-, Co-, Ni-, and Cu-doped α-MnO2 nanowires were synthesized by a one-step hydrothermal method.•All doped MnO2 nanowires exhibited much enhanced CO oxidation activity.•The Cu-doped ...MnO2 nanowires had a maximum TOF of 9.1×10−3s−1 at 70°C.•Cu-doped MnO2 could maintain 50h without obvious deactivation with 2% water moisture.•Cu doping makes the formation of oxygen vacancies easier in MnO2.
Replacing a small fraction of cations in a host metal oxide with a different cation (also known as doping) provides a useful strategy for improving the catalytic activity. Here, we report transition metal (Fe, Co, Ni, and Cu)-doped α-MnO2 nanowires synthesized by a one-step hydrothermal method as CO oxidation catalysts. The as-prepared catalysts displayed morphology, crystal structure, and specific surface area similar to those of the pure MnO2 nanowires. A catalytic activity test showed that all doped MnO2 nanowires exhibited much enhanced CO oxidation activity, with the Cu-doped ones being the most active (TOF of 9.1×10−3s−1 at 70°C). The Cu-doped MnO2 nanowires showed nearly 100% conversion of CO at 100°C at an hourly gas space velocity of 36,000mLg−1h−1, which could last for 50h without obvious deactivation even in the presence of 2% water vapor. Density functional theory calculations suggested that Cu doping could make the formation of oxygen vacancies in MnO2, which is the rate-determining step for CO oxidation reaction, easier than for Fe-, Co-, and Ni-doped and pristine MnO2. Our work demonstrates a facile and promising strategy for improving the catalytic activity for oxide-based catalysts, which should be applicable for a variety of different chemical reactions.
Metal oxides of the spinel family have shown great potential towards the oxygen evolution reaction (OER), but the fundamental OER mechanism of spinel oxides is still far from being completely ...understood, especially for the role of the metal ions. Owing to various coordinated sites of divalent/trivalent metals ions and surface conditions (morphology and defects), it is a great challenge to have a fair assessment of the electrocatalytic performance of spinel systems. Herein, we demonstrated a series of MFe
O
(M = Fe, Co, Ni, Zn) with a well-controlled morphology to achieve a comprehensive study of electrocatalytic activity toward OER. By utilizing several in situ analyses, we could conclude a universal rule that the activities for OER in the metal oxide systems were determined by the occurrence of a phase transformation, and this structural transformation could work well in both crystallographic sites (T
and O
sites). Additionally, the divalent metal ion significantly dominated the formation of oxyhydroxide through an epitaxial relationship, which depended on the atomic arrangement at the interface of spinel and metal oxyhydroxide, while trivalent metal ions remained unchanged as a host lattice. The metal oxyhydroxide was formed during a redox reaction rather than being formed during OER. The occurrence of the redox reaction seems to accompany a remarkable increase in resistance and capacitance might result from the structural transformation from spinel to metal oxyhydroxide. We believe that the approaching strategies and information obtained in the present study can offer a guide to designing a promising electrocatalytic system towards the oxygen evolution reaction and other fields.
Artificial photosynthesis using semiconductors has been investigated for more than three decades for the purpose of transferring solar energy into chemical fuels. Numerous studies have revealed that ...the introduction of plasmonic materials into photochemical reaction can substantially enhance the photo response to the solar splitting of water. Until recently, few systematic studies have provided clear evidence concerning how plasmon excitation and which factor dominates the solar splitting of water in photovoltaic devices. This work demonstrates the effects of plasmons upon an Au nanostructure–ZnO nanorods array as a photoanode. Several strategies have been successfully adopted to reveal the mutually independent contributions of various plasmonic effects under solar irradiation. These have clarified that the coupling of hot electrons that are formed by plasmons and the electromagnetic field can effectively increase the probability of a photochemical reaction in the splitting of water. These findings support a new approach to investigating localized plasmon-induced effects and charge separation in photoelectrochemical processes, and solar water splitting was used herein as platform to explore mechanisms of enhancement of surface plasmon resonance.
The formation of μ-OO peroxide (Co–OO–Co) moieties on spinel Co3O4 electrocatalyst prior to the rise of the electrochemical oxygen evolution reaction (OER) current was identified by in situ ...spectroscopic methods. Through a combination of independent in situ X-ray absorption, grazing-angle X-ray diffraction, and Raman analysis, we observed a clear coincidence between the formation of μ-OO peroxide moieties and the rise of the anodic peak during OER. This finding implies that a chemical reaction step could be generally ignored before the onset of OER current. More importantly, the tetrahedral Co2+ ions in the spinel Co3O4 could be the vital species to initiate the formation of the μ-OO peroxide moieties.
A well-defined co-catalyst system TiO2 nanotube-Au (core)-Pt (shell) was demonstrated to be the combination of the localized surface plasmon effect of gold and excellent proton reduction nature of ...platinum. Furthermore, surface engineering by the descending Fermi energies of gold and platinum was beneficial to electron transfer.
A unique functional electrode made of hierarchal Ni-Mo-S nanosheets with abundant exposed edges anchored on conductive and flexible carbon fiber cloth, referred to as Ni-Mo-S/C, has been developed ...through a facile biomolecule-assisted hydrothermal method. The incorporation of Ni atoms in Mo-S plays a crucial role in tuning its intrinsic catalytic property by creating substantial defect sites as well as modifying the morphology of Ni-Mo-S network at atomic scale, resulting in an impressive enhancement in the catalytic activity. The Ni-Mo-S/C electrode exhibits a large cathodic current and a low onset potential for hydrogen evolution reaction in neutral electrolyte (pH ~7), for example, current density of 10 mA/cm(2) at a very small overpotential of 200 mV. Furthermore, the Ni-Mo-S/C electrode has excellent electrocatalytic stability over an extended period, much better than those of MoS2/C and Pt plate electrodes. Scanning and transmission electron microscopy, Raman spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy were used to understand the formation process and electrocatalytic properties of Ni-Mo-S/C. The intuitive comparison test was designed to reveal the superior gas-evolving profile of Ni-Mo-S/C over that of MoS2/C, and a laboratory-scale hydrogen generator was further assembled to demonstrate its potential application in practical appliances.
PDF
