Solution-Processed Nb-Substituted BaBiO₃ Double Perovskite Thin Films for Photoelectrochemical Water Reduction

Photoelectrochemical (PEC) water reduction is a long-term strategical technology for hydrogen production. In this work, we synthesize a series of compact and nano/mesoporous Nb-substituted BaBiO 3 [i.e., Ba 2 Bi(Bi 1– x Nb x )O 6, 0 ≤ x ≤ 0.93, BBNO] thin films using cost-effective chemical solution methods. The synthesized BBNO alloy based thin films demonstrate tunable bandgaps from 1.41 eV ( x = 0) to 1.89 eV ( x = 0.93) to efficiently absorb the solar spectrum and p-type conductivities suitable for hydrogen production. The photoelectrodes with a configuration fluorine-doped SnO 2 /BBNO (0 ≤ x ≤ 0.93)/Pt produce cathodic photocurrents of 0.05–1 mA·cm –2 at 0 V RHE (volt versus reversible hydrogen electrode) measured in a neutral (pH = 7.2) phosphate buffer and under simulated AM 1.5G illumination (100 mW·cm –2 ). The BaBiO 3 without Nb alloying based electrode delivers the best photocurrent of 1 mA·cm –2 at 0 V RHE but is subjected to severe corrosions during the PEC related tests. Alloying Nb has an obvious influence on enhancing the material stability against corrosion. With Nb alloying, the screen-printed nanoporous BBNO ( x = 0.6, bandgap = 1.62 eV) based photoelectrode generates a better photocurrent of 0.2 mA·cm –2 at 0 V RHE with a highly positive onset at 1.5 V RHE enabling unbiased water reduction.