Enhanced Performance of β-Bi₂O₃by In-Situ Photo-Conversion to Bi₂O₃-BiO_2-xComposite Photoanode for Solar Water Splitting

Ordered nanoporous bismuth oxide layer consisting of metastable β-Bi 2 O 3 phase that showed n-type semiconductivity was synthesized by a simple electrochemical anodization of bismuth substrate. When the anodic nanoporous β-Bi 2 O 3 samples were tested as photoanodes for solar water splitting application in 0.5 M Na 2 SO 4 (pH:5.8), and 1 M KOH (pH:13.7), the photocurrent decayed continuously with time from an initial value of 0.95 mA/cm 2 under 1-sun illumination at a bias potential of 1.5 V RHE . Accumulation of photo generated holes at the photoanode/ electrolyte was attributed to the photocurrent decay. Addition of methanol as sacrificial hole scavenger was not found to be effective for the bismuth oxide photoanodes. When hydrogen peroxide was added to the 0.5 M Na 2 SO 4 electrolyte, the photocurrent density increased to ∼4 mA/cm 2 and was stable for more than 1 h of illumination of AM1.5 global light at 1.5 V RHE . Addition of hydrogen peroxide to the 1 M KOH solution showed a gradual increase in the photocurrent density for the first 300 seconds of light illumination to a maximum value of ∼10 mA/cm 2 at 0.65 V RHE and then it decreased continuously. The high photocurrent density of nanoporous β-Bi 2 O 3 in 1 M KOH + 0.3 M H 2 O 2 was be attributed to the presence of photo-converted Bi 2 O 4-x phase which harvested more light in the visible wavelengths.