Inverse Opal CuBi₂O₄ Photocathodes for Robust Photoelectrochemical Water Splitting

In general, p-type CuBi2O4 (CBO) photocathodes demonstrate excellent solar-to-hydrogen conversion efficiencies but have low quantum yields near the band-edge region (i.e., above 600 nm), which substantially impedes achieving photocurrent densities that match the theoretical values. This is the main obstacle in the construction of photoelectrochemical (PEC) water-splitting cells. To overcome this difficulty, we fabricated inverse opal-like structured CBO (IO-CBO) photocathodes using a layered self-assembly approach. The fabricated photocathodes have an interconnected macroporous structure that supports enhanced visible-light-harvesting capabilities and improves intrinsic charge-carrier transport properties. Optimized IO-CBO cathodes exhibit a high photocurrent density of 2.95 mA cm–2 at 0.6 V versus a reversible hydrogen electrode with stability over 2 h of operation. Furthermore, IO-CBO cathodes have exceptional near-band-edge photon harvesting and quantum yields of 15% at 600 nm, which is unprecedented for CuBi2O4-type photocathodes. We believe that the present work promotes the application of ternary-based nanostructures in solar-driven hydrogen production.