Visible Light Induced Photoelectrochemical Properties of n-BiVO₄and n-BiVO₄/p-Co₃O₄

Abstract

The visible light induced photoelectrochemical properties of the pressed powder electrodes n-BiVO 4 , p-Co 3 O 4 , and n-BiVO 4 /p-Co 3 O 4 containing 0.8 wt % cobalt were investigated. At pH 7 flatband potentials of -0.30 and +0.54 V vs NHE were measured for the bismuth vanadate and cobalt oxide, respectively, whereas -0.31 V was obtained for BiVO 4 /Co 3 O 4 . At a bias of 0.1 V vs Ag/AgCl the n-type photocurrent of BiVO 4 changes to p-type upon prolonged irradiation, whereas it remains n-type at the much higher bias of 1.0 V vs Ag/AgCl. The change in conductivity type can be rationalized by invoking oxidation of water to a surface peroxide species. From the photocurrent decay of BiVO 4 under chopped irradiation the presence of efficient charge recombination is indicated. It can be suppressed by addition of iodide, thiocyanate, or methanol, leading to about twice as large incident-photon-to-current efficiencies (IPCE). Different from that, in the case of the BiVO 4 /Co 3 O 4 electrode the IPCE values do not change in the presence of iodide or thiocyanate and are 4 times higher. This distinct difference is rationalized by the assumption that the photogenerated charges are efficiently separated at the BiVO 4 -Co 3 O 4 interface forming a type of n-/p-junction. Whereas electrons migrate to the n-type component, holes move to the p-type material. In summary, modification of n-BiVO 4 by p-Co 3 O 4 stabilizes the photocurrent, increases the efficiency of its generation, and leads to a compartmentalization of interfacial reduction and oxidation at the n-type component and p-type component, respectively.

Facile fabrication of an efficient BiVO 4 thin film electrode for water splitting under visible light irradiation

“…Calcination of this film at 573-723 K for 2 h in air gave a yellow BiVO 4 thin film. Cobalt oxide cocatalyst was loaded on the BiVO 4 film with an area of 2.5 cm 2 by an impregnation method with calcination at 673 K for 1 h in air using an aqueous solution (5 μL, 80 mmol L −1 ) of CoðNO 3 Þ 2 (Wako Pure Chemical; 99.5%), if necessary (17,18).…”

“…Development of a photoelectrode material with visible light response has been sought for efficient utilization of solar energy. It has been reported that Fe 2 O 3 (9-11), WO 3 (12)(13)(14), BiVO 4 (15)(16)(17)(18)(19)(20)(21)(22)(23)(24), and SrTiO 3 ∶Rh (25) of metal oxide electrodes respond to visible light. Recently, some (oxy) nitride materials such as TaON (26,27), Ta 3 N 5 (27,28), SrNbO 2 N (29), and Ta 0.9 Co 0.1 N x (30) have also been found to be visible light responsive photoelectrodes for water splitting.…”

“…Modification with Co 3 O 4 by precipitation method increases the photocurrent of BiVO 4 electrode (18). Recently, cobalt phosphate (CoPi) prepared by an electrodeposition has been reported as an oxygen evolving electrocatalyst (37).…”

Visible-light sensitive cobalt-doped BiVO4 (Co-BiVO4) photocatalytic composites for the degradation of methylene blue dye in dilute aqueous solutions

“…In this study, we prepared Co-doped BiVO 4 using the amorphous heteronuclear complexation technique. The heteronuclear complex precursor is stable and its chemical composition is easy to control comparing with that prepared by other methods such as solidstate reaction [28], sol-gel [29], coprecipitation [30], metalorganic decomposition [31], and solution combustion [32]. Furthermore, the crystallization step can be readily controlled at low calcination temperatures.…”

Structural and electronic properties of oxygen defective and Se-doped p-type BiVO4(001) thin film for the applications of photocatalysis

“…For instance, the tetragonal BiVO 4 possesses a band gap of 2.9 eV and mainly absorbs UV region, while the monoclinic clinobisvanite (m-BiVO 4 ) exhibits a much higher photocatalytic activity due to its ideal band gap (2.4−2.5 eV) which absorb the UV and visible regions of the electromagnetic spectrum, having an ideal valence band edge position for driving water oxidation [9]. However, it has been recently reported that m-BiVO 4 , an n-type semiconductor [10], exhibits poor photocatalytic property which is stem to low mobility of the photogenerated charge carriers (electron−hole pairs), positive potential of CB (vs NHE) and high charge recombination rates which significantly limit its practical applications. The photocatalytic activity of m-BiVO 4 can be tuned either with metal or non-metal doping, semi-conductor recombination (heterojunction formation), depositing the co-catalysts, defect formation (oxygen vacancy creation), and crystal-facet control or morphological modification.…”