Facilitating hole transfer on electrochemically synthesized p-type CuAlO2 films for efficient solar hydrogen production from water

Delafossite CuAlO2 photoelectrodes are synthesized via the electrodeposition of Cu(II) and Al(III) onto fluorine-doped tin oxide (FTO) substrates in water and dimethylsulfoxide (DMSO) solvents, followed by annealing in air and Ar. The surface properties, crystalline structure, and photoelectrochemical (PEC) performance of the as-synthesized samples are significantly affected by the synthetic conditions. Optimized CuAlO2 electrodes (synthesized in DMSO and annealed in air) possess suitable energetics for H-2 production under sunlight (an optical bandgap of similar to 1.4 eV and a conduction band level of -0.24 V-RHE). They exhibit a photocurrent onset potential of similar to+0.9 V-RHE along with a faradaic efficiency of similar to 70% at +0.3 V-RHE in an alkaline solution (1 M KOH) under simulated sunlight (AM 1.5; 100 mW cm(-2)). The addition of sacrificial hole scavengers (sulfide and sulfite) significantly improves the PEC performance of CuAlO2 by a factor of eight, along with providing a faradaic efficiency of similar to 100%. This indicates that the hole transfer limits the overall PEC performance. This issue is addressed by employing a similar to 150 nm-thick Au film-coated FTO substrate for the CuAlO2 deposition. In the absence of hole scavengers, the H-2 productiown with the Au-underlain CuAlO2 photoelectrode (Au/CuAlO2) is three-fold higher than that with bare CuAlO2, while the faradaic efficiencies at +0.3 and +0.55 V-RHE are similar to 100%. The time-resolved photoluminescence emission decay spectra of the CuAlO2 and Au/CuAlO2 confirm the facilitated charge transfer in the latter.