A molecular cobaloxime cocatalyst and ultrathin FeOOH nanolayers co-modifiedBiVO_(4) photoanode for efficient photoelectrochemical water oxidation

BiVO_(4) has been attracting a lot of interest in photoelectrochemical (PEC) water oxidation due to its efficient solar absorption and appropriate band positions.So far,sluggish water oxidation kinetics and fast photogenerated charge recombination still hinder the PEC performance ofBiVO_(4) .In this study,a novel PEC photoanode was designed by depositing ultrathin FeOOH nanolayers on the surface of nanoporousBiVO_(4) electrode,followed by modification with a cobaloxime (Co(dmgH)_(2)(4-COOH-py)Cl) molecular cocatalyst.Under irradiation of a 100 mW cm^(-2)(AM 1.5G) Xe lamp,the photocurrent density of the cobaloxime/FeOOH/BiVO_(4) composite photoanode reached 5.1 mA cm^(-2)at 1.23 V vs.RHE in 1.0 M potassium borate buffer solution (pH=9.0).The onset potential of the optimal cobaloxime/FeOOH/BiVO_(4) photoanode exhibited a 460 m V cathodic shift relative to bareBiVO_(4) .In addition,the surface charge injection efficiency of the composite photoanode reached~80%at 1.23 V vs.RHE and the incident photon-to-current efficiency (IPCE) reached~88%at 420 nm.

Sulfide@hydroxide core–shell nanostructure via a facile heating-electrodeposition method for enhanced electrochemical and photoelectrochemical water oxidation

Designing low-cost,easy-fabricated,highly stable and active electrocatalysts for oxygen evolution reaction(OER) is crucial for electrochemical(EC) and solar-driven photoelectrochemical(PEC) water splitting.By using a facile heating-electrodeposition method,here we fabricated a porous but crystalline Fe-doped Ni3 S2.A thin porous surface NiFe hydroxide layer(~10 nm) is then formed through OER-running.By virtue of the core Fe-doped Ni3 S2 with good conductivity and the shell NiFe hydroxide surface with good electrocatalytic activity,the core-shell nanostructure on Ni foam exhibits excellent OER activity in 1 M NaOH,needing only 195 and 230 mV to deliver 10 and 100 mA/cm^(2),respectively,much more superior to those of 216 and 259 mV for the sample deposited under normal temperature.The enhanced photo-response of the sulfide@hydroxide core-shell structure was also demonstrated,due to the efficient transfer of photo-generated carriers on the core/shell interface.More interestingly,it shows a good compatibility with Si based photoanode,which exhibits an excellent PEC performance with an onset potential of 0.86 V vs.reversible hydrogen electrode,an applied bias photon-to-current efficiency of 5.5% and a durability for over 120 h under AM 1.5 G 1 sun illumination,outperforming the state-of-the-art Si based photoanodes.

Chelation-mediated in-situ formation of ultrathin cobalt(oxy)hydroxides on hematite photoanode towards enhanced photoelectrochemical water oxidation

In this work,a facile chelation-mediated route was developed to fabricate ultrathin cobalt(oxy)hydroxides(CoOOH)nanosheets on hematite photoanode(Fe_(2)O_(3)).The route contains two steps of the adsorption of[Co-EDTA]^(2-)species on Fe_(2)O_(3) nanorod array followed by the hydrolysis in alkaline solution.The resulting CoOOH/Fe_(2)O_(3) exhibits a remarkably improved photocurrent density of 2.10 mA cm^(-2) at 1.23 V vs.RHE,which is ca.2.8 times that of bare Fe_(2)O_(3).In addition,a negative shift of onset potential ca.200 mV is achieved.The structural characterizations reveal the chelate EDTA plays important roles that enhance the adsorption of Co species and the formation of contact between CoOOH and Fe_(2)O_(3).(Photo)electrochemical analysis suggests,besides providing active sites for water oxidation,CoOOH at large extent promotes the charge separation and the charge transfer via passivating surface states and suppressing charge recombination.It also found CoOOH possesses some oxygen vacancies,which could act as trapping centers for photogenerated holes and facilitate the charge separation.Intensity modulated photocurrent spectroscopy(IMPS)shows that,under low applied potential the water oxidation mainly occurs on CoOOH,while under high applied potential the water oxidation could occur on both CoOOH and Fe_(2)O_(3).The findings not only provide an efficient strategy for designing ultrathin(oxy)hydroxides on semiconductors for PEC applications but also put forward a new insight on the role of CoOOH during water oxidation.

Synergy of porous structure and cation doping in Ta3N5 photoanode towards improved photoelectrochemical water oxidation

Herein,a cross-linked porous Ta3N5 film was prepared via a simple solution combustion route followed by a high-temperature nitridation process for photoelectrochemical(PEC) water oxidation.Meanwhile,the metal cations(Mg2+ and Zr4+) were incorporated into the porous Ta3N5 to enhance the PEC performance.The porous Mg/Zr co-doped Ta3N5 photoanode yielded a photocurrent density of 1.40 mA cm^(-2) at 1.23 V vs RHE,which is 5.6 times higher than that of the dense Ta3N5 photoanode.The enhanced performance should be ascribed to the synergistic effect of porous structure and cation doping,which can enlarge the electrochemical active surface area and accelerate the charge transfer by introducing ON substitution defects.Subsequently,Co(OH)2 cocatalyst was loaded on the Mg/Zr-Ta3N5 photoanode to negatively shift the onset potential to 0.45 V vs RHE and further improve the photocurrent density to 3.5 mA cm^(-2)at 1.23 V vs.RHE,with a maximum half-cell solar to hydrogen efficiency of 0.45%.The present study provides a new strategy to design efficient Ta3N5 photoelectrodes via the simultaneous control of the morphology and composition.

Rationally designed/constructed MnO_x/WO_3 anode for photoelectrochemical water oxidation

Photoelectrocatalytic water splitting is an effective way to utilize the solar energy to solve the energy shortage. The valence band edge of WO3 located at 3V vs. normal hydrogen electrode（NHE）, which can offer enough potential to kinetically oxidize water for oxygen evolution reaction. However, water oxidation reaction kinetics is sluggish when only WO3 is used as the photoanode. It is highly desirable to use cocatalyst to promote the kinetics. Mn Oxloaded on the WO3 photoanode through photodeposition methods improves the photoelectrochemical water oxidation performance. A maximum photocurrent density of composite photoanode is achieved with a deposition time of 3 min, which is higher than that of pristine WO3 photoanode around 40%. Mn O2 is not only a cocatalyst for water splitting but also for improving oxidation selectivity. We tried to use two means to load Mn Oxon WO3 photoanode material. It is observed that loading a moderate amount of Mn Oxon the WO3 by photodeposition can promote the performance of the WO3 photoanode.

Boosting the photoelectrochemical water oxidation performance of bismuth vanadate by ZnCo_(2)O_(4) nanoparticles

Due to the involvement of four-electron transfer process at photoanode,water oxidation is the ratelimiting step in water splitting reaction.To settle this dilemma,ZnCo_(2)O_(4)nanoparticles are combined with BiVO_(4)to form a p-n ZnCo_(2)O_(4)/BiVO;heterojunction photoanode,which is proved by an input voltage-output current test.The built-in electric field formed within the heterojunction structure promotes the effective separation of electrons and holes.ZnCo_(2)O_(4)is also an effective water oxidation cocatalyst,since it could cause the holes entering the electrode/electrolyte interface rapidly for the subsequent water oxidation reaction.The photocurrent density of ZnCo_(2)O_(4)/BiVO_(4)composite photoanode reaches 3.0 mA/cm^(2) at 1.23 V vs.RHE in 0.5 mol/L sodium sulfate under AM 1.5 G simulated sunlight,about 2.1 times greater than that of BiVO_(4)(1.4 mA/cm^(2)).These results suggest the potential of ZnCo_(2)O_(4)nanoparticles for improving photoelectrochemical water splitting anode materials.

High-performance Bi_(2)S_(3)/ZnO photoanode enabled by interfacial engineering with oxyanion for efficient photoelectrochemical water oxidation

In the present contribution,we demonstrate that the sluggish kinetics of oxygen evolution reaction(OER)over the bismuth sulfide(Bi_(2)S_(3))photoanode,which severely restricts its photoelectrochemical activity,is markedly accelerated by employing a sulfatecontaining electrolyte.First-principle calculation points to the spontaneous adsorption of sulfate(SO_(4)^(2−))on Bi_(2)S_(3)and its capacity of stabilizing the OER intermediates through hydrogen bonding,which is further reinforced by increasing the local density of states near the Fermi level of Bi_(2)S_(3).Meanwhile,the electron transfer is also promoted to synergistically render the ratedetermining step(from O*to OOH*)of OER over Bi_(2)S_(3)kinetically facile.Last but not least,benefitting from such enhanced OER activity and efficient charge separation resulted from depositing Bi_(2)S_(3)on the zinc oxide nanorods(ZnO NRs),forming a core–shell heterojunction,its photocurrent density achieves 8.61 mA·cm^(−2)at 1.23 VRHE,far surpassing those reported for additional Bi_(2)S_(3)-based and several state-of-the-art photoanodes in the literature and further exceeding their theoretical limit.The great promise of the Bi_(2)S_(3)/ZnO NRs is in view of such outperformance,the superior Faradaic yield of oxygen of more than~80%and the outstanding half-cell applied bias photon-to-current efficiency of~1%well corroborated.