Improving charge transport and reducing bulk/surface recombination can increase the activity and stability of BiVO4 for water oxidation. Herein we demonstrate that the photoelectrochemical (PEC) ...performance of BiVO4 can be significantly improved by potentiostatic photopolarization. The resulting cocatalyst‐free BiVO4 photoanode exhibited a record‐high photocurrent of 4.60 mA cm−2 at 1.23 VRHE with an outstanding onset potential of 0.23 VRHE in borate buffer without a sacrificial agent under AM 1.5G illumination. The most striking characteristic was a strong “self‐healing” property of the photoanode, with photostability observed over 100 h under intermittent testing. The synergistic effects of the generated oxygen vacancies and the passivated surface states at the semiconductor–electrolyte interface as a result of potentiostatic photopolarization reduced the substantial carrier recombination and enhanced the water oxidation kinetics, further inhibiting photocorrosion.
Potentiostatic photopolarization was induced on BiVO4 to improve charge transport, reduce interface recombination, and improve the water oxidation kinetics. The undoped BiVO4 photoanode exhibited a record‐high photocurrent of 4.60 mA cm−2 at 1.23 VRHE with an onset potential of 0.23 VRHE in borate buffer without a cocatalyst or a sacrificial agent. Strong “self‐healing” characteristics enabled photostability over 100 h under intermittent testing (see picture).
The oxygen evolution reaction (OER), as an important process involved in water splitting and rechargeable metal–air batteries, has drawn increasing attention in the context of clean energy generation ...and efficient energy storage. This review concerns the progress and new discoveries in the field of Ni/Fe‐based micro/nanostructures toward electrochemical and photo‐electrochemical (PEC) water oxidation during last few years. First, toward the design and construction of new electrocatalysis, different types of current Ni/Fe‐based compounds for OER are summarized. The mechanism studies of the active phases and positions of Ni/Fe‐based micro/nanostructures are further introduced to understand the properties of catalytic active sites, which could facilitate further improving the performance of Ni/Fe‐based OER electrocatalysts. Second, splitting water using sunlight with low overpotential is another important target in making solar‐to‐hydrogen micro/nanodevices, and thus attention is then focused on the development of several important Ni/Fe‐based PEC catalysts. Third, the recent theoretical calculations on the OER mechanism during water splitting and insights into electronic structures are analyzed; finally, the future trends and perspectives are also discussed briefly.
The oxygen evolution reaction, as an important process involved in water splitting and rechargeable metal–air batteries, has drawn increasing attention in the context of clean energy generation and efficient energy storage. This review concerns the progress and new discoveries in the field of design of Ni/Fe‐based micro/nanostructures toward electrochemical and photo‐electrochemical water oxidation during the last few years.
Increasing long‐term photostability of BiVO4 photoelectrode is an important issue for solar water splitting. The NiOOH oxygen evolution catalyst (OEC) has fast water oxidation kinetics compared to ...the FeOOH OEC. However, it generally shows a lower photoresponse and poor stability because of the more substantial interface recombination at the NiOOH/BiVO4 junction. Herein, we utilize a plasma etching approach to reduce both interface/surface recombination at NiOOH/BiVO4 and NiOOH/electrolyte junctions. Further, adding Fe2+ into the borate buffer electrolyte alleviates the active but unstable character of etched‐NiOOH/BiVO4, leading to an outstanding oxygen evolution over 200 h. The improved charge transfer and photostability can be attributed to the active defects and a mixture of NiOOH/NiO/Ni in OEC induced by plasma etching. Metallic Ni acts as the ion source for the in situ generation of the NiFe OEC over long‐term durability.
Flex your PECs: A facile plasma etching approach was utilized to reduce both interface/surface recombination at NiOOH/BiVO4 and NiOOH/electrolyte junctions for photoelectrochemical (PEC) catalysis of water splitting. Addition of Fe2+ into the borate buffer electrolyte alleviated the active but unstable character of etched‐NiOOH/BiVO4, leading to an outstanding photostability over 200 h.
A photocharge/discharge strategy is proposed to initiate the WO3 photoelectrode and suppress the main charge recombination, which remarkably improves the photoelectrochemical (PEC) performance. The ...photocharged WO3 surrounded by a 8–10 nm overlayer and oxygen vacancies could be operated more than 25 cycles with 50 h durability without significant decay on PEC activity. A photocharged WO3/CuO photoanode exhibits an outstanding photocurrent of 3.2 mA cm−2 at 1.23 VRHE with a low onset potential of 0.6 VRHE, which is one of the best performances of p‐n heterojunction structure. Using nonadiabatic molecular dynamics combined with time‐domain DFT, we clarify the prolonged charge carrier lifetime of photocharged WO3, as well as how electronic systems of photocharged WO3/CuO semiconductors enable the effective photoinduced electrons transfer from WO3 into CuO. This work provides a feasible route to address excessive defects existed in photoelectrodes without causing extra recombination.
A photocharging/discharging strategy is used to initiate the WO3 electrode and prolong charge carrier lifetime for the oxygen evolution reaction. A WO3/CuO photoanode exhibited an outstanding photocurrent with a low onset potential. The prolonged charge carrier lifetime of photocharged WO3 and the electronic systems of photocharged WO3/CuO semiconductors were clarified using the nonadiabatic molecular dynamics combined with time‐domain DFT.
Photostability is one of the most essential properties for evaluating photoelectrochemical (PEC) water splitting performance on semiconductors. Herein, the oxygen‐deficiency conditions are applied to ...tune and activate BiVO4 photoanodes with a class of oxygen vacancies across the whole bulk material, and regulate the electronic occupancy of these states upon the charge carrier processes that determine PEC water oxidation activity. Through the experimental results and nonadiabatic molecular dynamics with time‐domain density functional theory calculations, the charge carrier lifetime can be influenced by the oxygen vacancies concentration on BiVO4, and the semiconductor can be flexibly photoactivated under oxygen‐sufficient and deficient atmospheres for enhancing the charge carrier density and photovoltage. The PEC performance of BiVO4 is further boosted by Pt doping, which exhibits a record photocurrent density of 5.45 mA cm–2 at 1.23 VRHE with solar conversion efficiency of 2.1% at 0.65 VRHE. The Pt can prevent the unnecessory charge recombination on the defected BiVO4, which also enhances the majority charge carrier density, resulting in one of the best charge separation efficiencies, close to 100%, among the steady‐state PEC performance for BiVO4. More importantly, the resulting Pt:BiVO4 presents long‐term stability over 50 h at 0.8 VRHE.
Herein, oxygen‐deficiency conditions are applied to tune and activate BiVO4 photoanodes with a class of oxygen vacancies across the whole bulk material, and regulate the electronic occupancy of these states upon the charge carrier processes that determine photoelectrochemical (PEC) water oxidation activity. The material is doped with Pt, which further enhances the majority charge carrier density, resulting in one of the best charge separation efficiencies, close to 100%, among the steady‐state PEC performance for BiVO4 photoanodes.
Hydrogen economy has emerged as a very promising alternative to the current hydrocarbon economy, which involves the process of harvesting renewable energy to split water into hydrogen and oxygen and ...then further utilization of clean hydrogen fuel. The production of hydrogen by water electrolysis is an essential prerequisite of the hydrogen economy with zero carbon emission. Among various water electrolysis technologies, alkaline water splitting has been commercialized for more than 100 years, representing the most mature and economic technology. Here, the historic development of water electrolysis is overviewed, and several critical electrochemical parameters are discussed. After that, advanced nonprecious metal electrocatalysts that emerged recently for negotiating the alkaline oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are discussed, including transition metal oxides, (oxy)hydroxides, chalcogenides, phosphides, and nitrides for the OER, as well as transition metal alloys, chalcogenides, phosphides, and carbides for the HER. In this section, particular attention is paid to the catalyst synthesis, activity and stability challenges, performance improvement, and industry‐relevant developments. Some recent works about scaled‐up catalyst synthesis, novel electrode designs, and alkaline seawater electrolysis are also spotlighted. Finally, an outlook on future challenges and opportunities for alkaline water splitting is offered, and potential future directions are speculated.
The hydrogen economy has emerged as a very promising alternative to the current hydrocarbon economy, which involves the process of harvesting renewable energy to split water into hydrogen and oxygen and then further utilization of hydrogen fuel. Alkaline water splitting represents the most mature and economic technology for clean hydrogen production, making high potential for successful implementation of hydrogen economy.
Transition‐metal phosphides have stimulated great interest as catalysts to drive the hydrogen evolution reaction (HER), but their use as bifunctional catalytic electrodes that enable efficient ...neutral‐pH water splitting has rarely been achieved. Herein, we report the synthesis of ternary Ni0.1Co0.9P porous nanosheets onto conductive carbon fiber paper that can efficiently and robustly catalyze both the HER and water oxidation in 1 m phosphate buffer (PBS; pH 7) electrolyte under ambient conditions. A water electrolysis cell comprising the Ni0.1Co0.9P electrodes demonstrates remarkable activity and stability for the electrochemical splitting of neutral‐pH water. We attribute this performance to the new ternary Ni0.1Co0.9P structure with porous surfaces and favorable electronic states resulting from the synergistic interplay between nickel and cobalt. Ternary metal phosphides hold promise as efficient and low‐cost catalysts for neutral‐pH water splitting devices.
Sheets and paper: Ternary Ni0.1Co0.9P porous nanosheets anchored onto conductive carbon fiber paper, can be used as a bifunctional catalytic material for driving both water reduction and oxidation reactions efficiently in neutral‐pH electrolyte under ambient conditions.
A considerable challenge in the conversion of carbon dioxide into useful fuels comes from the activation of CO2 to CO2.− or other intermediates, which often requires precious‐metal catalysts, high ...overpotentials, and/or electrolyte additives (e.g., ionic liquids). We report a microwave heating strategy for synthesizing a transition‐metal chalcogenide nanostructure that efficiently catalyzes CO2 electroreduction to carbon monoxide (CO). We found that the cadmium sulfide (CdS) nanoneedle arrays exhibit an unprecedented current density of 212 mA cm−2 with 95.5±4.0 % CO Faraday efficiency at −1.2 V versus a reversible hydrogen electrode (RHE; without iR correction). Experimental and computational studies show that the high‐curvature CdS nanostructured catalyst has a pronounced proximity effect which gives rise to large electric field enhancement, which can concentrate alkali‐metal cations resulting in the enhanced CO2 electroreduction efficiency.
The needle has landed: CdS nanostructures with sharp tips can generate large electric fields that lead to increased CO2 concentrations for CO2‐to‐CO conversion. The localized electric fields are significantly enhanced when two nanoneedles are in close proximity. These advantages result in CO2 electrocatalytic reduction with a 95.5±4.0 % CO Faraday efficiency.
Tuning and optimizing the efficiency of light energy transfer play an important role in meeting modern challenges of minimizing energy loss and developing high-performance optoelectronic materials. ...However, attempts to fabricate systems giving highly efficient energy transfer between luminescent donor and acceptor have achieved limited success to date. Herein, we present a strategy towards phosphorescence energy transfer at a 2D orderly crystalline interface. We first show that new ultrathin nanosheet materials giving long-afterglow luminescence can be obtained by assembling aromatic guests into a layered double hydroxide host. Furthermore, we demonstrate that co-assembly of these long-lived energy donors with an energy acceptor in the same host generates an ordered arrangement of phosphorescent donor-acceptor pairs spatially confined within the 2D nanogallery, which affords energy transfer efficiency as high as 99.7%. Therefore, this work offers an alternative route to develop new types of long-afterglow nanohybrids and efficient light transfer systems with potential energy, illumination and sensor applications.
Transition metal dichalcogenide materials have been explored extensively as catalysts to negotiate the hydrogen evolution reaction, but they often run at a large excess thermodynamic cost. Although ...activating strategies, such as defects and composition engineering, have led to remarkable activity gains, there remains the requirement for better performance that aims for real device applications. We report here a phosphorus-doping-induced phase transition from cubic to orthorhombic phases in CoSe
. It has been found that the achieved orthorhombic CoSe
with appropriate phosphorus dopant (8 wt%) needs the lowest overpotential of 104 mV at 10 mA cm
in 1 M KOH, with onset potential as small as -31 mV. This catalyst demonstrates negligible activity decay after 20 h of operation. The striking catalysis performance can be attributed to the favorable electronic structure and local coordination environment created by this doping-induced structural phase transition strategy.
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