Dense/nanoporous bilayer BiVO4 photoanode with outstanding light-absorption efficiency for high-performance photoelectrochemical water splitting

This study designs a dense/porous bilayer-structured BiVO4 photoanode to achieve a high photoelectrochemical (PEC) performance. Monolayer photoanodes have their respective limitations; the dense monolayer BiVO4 (d-BVO) photoanode has high reflectance, and the porous monolayer (p-BVO) photoanode has high transmittance, which limits light absorption. Conversely, the dense/porous bilayer structure maximizes the light-absorption and increases PEC efficiency by combining these layers. The dense and porous layers of the bilayer photoanode (b-BVO) were manufactured using the simple processes of sputtering deposition and solution spin coating, respectively. The light absorption of b-BVO increased to approximately 92 % (at wavelengths of 300-500 nm). This resulted in an increase in the absorption efficiency (eta abs) to 81.4 %, which was 21.9 % and 24.5 % higher than those of d-BVO and p-BVO, respectively. The photocurrent density of b-BVO was 2.43 mA cm-2 at 1.23 V versus a reversible hydrogen electrode, which was 31.4 % and 102.5 % higher than those of d-BVO and p-BVO, respectively.