Protection of Si photocathode using TiO₂ deposited by high power impulse magnetron sputtering for H₂ evolution in alkaline media

Si is an excellent absorber material for use in photoelectrochemical (PEC) hydrogen production. Only a few studies have been done using Si in alkaline electrolyte for hydrogen evolution due to its poor chemical stability in high pH electrolyte, indicating that a chemically stable protection layer is essential. Here we investigate thin TiO₂ films deposited by high power impulse magnetron sputtering (HiPIMS) as a protection layer for a p-type silicon photocathode for photoelectrochemical H₂ evolution in a high pH electrolyte. The X-ray reflectometry analysis reveals that the HiPIMS process provides improved film density for TiO₂ films (4.15 g/cm³), and consequently results in a significantly less corroded Si surface. The Si photocathode protected by the HiPIMS grown TiO₂ film along with Pt as co-catalyst produced a photocurrent onset potential of ~0.5 V vs. RHE in 1 M KOH and showed a 4% decay over 24 h in KOH. In contrast, the sample with the TiO₂ deposited using conventional DC sputtering technique of similar thickness shows 20% loss in photocurrent for the same time interval. Considering the fact that the experiments were carried out not in the cleanroom, much less corrosion loss can be obtained if done in dust-free condition. Hence, these results suggest the HiPIMS technique as an improved approach for the protection of photoelectrodes, which are unstable in alkaline solution.