Photocatalytic and Photoelectrochemical Water Oxidation over Metal‐Doped Monoclinic BiVO4 Photoanodes

Abstract

The visible‐light‐induced water oxidation ability of metal‐ion‐doped BiVO 4 was investigated and of 12 metal ion dopants tested, only W and Mo dramatically enhanced the water photo‐oxidation activity of bare BiVO 4; Mo had the highest improvement by a factor of about six. Thus, BiVO 4 and W‐ or Mo‐doped (2 atom %) BiVO 4 photoanodes about 1 μm thick were fabricated onto transparent conducting substrate by a metal–organic decomposition/spin‐coating method. Under simulated one sun (air mass 1.5G, 100 mW cm−2) and at 1.23 V versus a reversible hydrogen electrode, the highest photocurrent density (JPH) of about 2.38 mA cm−2 was achieved for Mo doping followed by W doping (JPH≈1.98 mA cm−2), whereas undoped BiVO 4 gave a JPH value of about 0.42 mA cm−2. The photoelectrochemical water oxidation activity of W‐ and Mo‐doped BiVO 4 photoanodes corresponded to the incident photon to current conversion efficiency of about 35 and 40 % respectively. Electrochemical impedance spectroscopy and Mott–Schottky analysis indicated a positive flat band shift of about 30 mV, a carrier concentration 1.6–2 times higher, and a charge‐transfer resistance reduced by 3–4‐fold for W‐ or Mo‐doped BiVO 4 relative to undoped BiVO 4. Electronic structure calculations revealed that both W and Mo were shallow donors and Mo doping generated superior conductivity to W doping. The photo‐oxidation activity of water on BiVO 4 photoanodes (undoped<W doped<Mo doped) was in accordance with the results from electrochemical impedance spectroscopy, Mott–Schottky analysis, and theoretical electronic structural calculations. Thus, Mo or W doping enhanced the photocatalytic and photoelectrochemical water oxidation activity of monoclinic BiVO 4 by drastically reducing its charge‐transfer resistance and thereby minimizing photoexcited electron–hole pair recombination.