2. Introduction BiVO 4 is an effective photocatalytic material for solar water oxidation reaction because of nontoxicity and photochemical stability However, bare BiVO 4 exhibits low water photo-oxidation due to an inefficient separation of photoexcited electron-hole pairs Through impurity doping into BiVO 4, significant improvements in the water photo-oxidation ability of BiVO 4 structure have been reported

3. Introduction In particular, incorporation of tungsten or molybdenum into BiVO 4 was shown to significantly improve its photoactivity for the water oxidation reaction However, there has been neither a systematic screening study to find other suitable dopants nor one on the relative magnitude of the effect of different dopants Thus, in this study, 12 dopants (Mo, W, Ti, Cr, Fe, Zn, Nb, Ru, Pt, Sn, Ce, and Ta) are screened and a drastic improvement in the visible-light-induced water oxidation activity of bare BiVO 4 only with W or Mo doping is observed

4. Results

5. Relative to undoped BiVO 4 powder, the photocatalytic water oxidation activity of W: BiVO 4 or Mo: BiVO 4 powder is dramatically improved Mo doping shows a greater photoactivity improvement than that of W doping Both W and Mo impurities are efficient dopants to enhance the visible-light-induced water oxidation activity of a BiVO 4 photocatalyst

6. Results The high intensity and sharp peak patterns of all three powder samples are well matched to a monoclinic phase of BiVO 4 Both W and Mo impurities have been effectively incorporated into the crystal lattice of BiVO4 W or Mo doping has no significant effect on the light absorption characteristics of a bare BiVO 4 structure

7. Results W or Mo doping into the V sites of the monoclinic BiVO4 lattice increased the PEC activity by five to six times

8. Results The IPCE values of W or Mo-doped BiVO4 photoanodes are higher than that of bare BiVO4

9. Results To find any changes in the transport properties of the carrier, M- S analysis for capacitance and electrochemical impedance spectroscopy (EIS) measurements for charge-transfer resistance were carried out for the all three photoanodes

10. Results Mo-doped BiVO4 has the best charge-transfer efficiency, as seen by the low value of R CT whereas the high R CT value of an undoped BiVO4 photoanode indicates poor charge-transfer ability The results of EIS measurements

11. Results The results of capacitance measurements

12. Results The carrier density can be obtained by the slope of tangent lines of the M-S plots A smaller slope means a higher carrier concentration Thus, W or Mo doping increases the carrier density and reduces the electrical resistance of a monoclinic BiVO 4 system

13. Results The DOS moves to a lower energy and the Fermi level (E F ) moves closer to the CB edge in W- or Mo-doped BiVO 4

14. Results The extra electron donated by the dopants like W or Mo will enhance carrier density when they substitute for V positions of BiVO 4 system Such increased carrier density can accelerate charge transfer and superior photoactivity

15. Conclusions A remarkable doping effect was confirmed in Mo- or W-doped BiVO 4 for visible-light-induced photocatalytic O 2 evolution from water and PEC current generation W- or Mo-doped BiVO 4 photoanodes exhibited high photocurrents and incident photon-to-current conversion efficiency Relative to bare BiVO 4, a carrier concentration is about 1.6-2 times higher and charge-transfer resistance suppressed by 3-4 times Mo functions as a more efficient electron donor than W