Influence of solution pH on the dynamics of oxygen bubbles on the surface of TiO₂-NTAs electrodes

The rise of concentration resistance caused by bubble growth is a key factor affecting the photoelectrochemical water splitting efficiency. In this research, we employed an electrochemical workstation, a synchronized measuring system, and a CCD camera to investigate the in-situ evolution of oxygen bubbles on the surfaces of TiO₂-NTAs and C/TiO₂-NTAs electrodes. The connection among the critical nucleation, growth and departure behavior of a single bubble on the photoanode surface and photocurrent curves at different solution pH (1–13) has been investigated. For TiO₂-NTAs, it was found that strong alkalinity significantly reduces the voltage required for critical bubble nucleation. The photocurrent rises approximately 1.5 times when the control voltage is 0.10 V (vs. Ag/AgCl) by pH increasing from 1 to 13 and while the bubble evolution cycles decline by approximately 3.2 times. The photocurrent rises by 10.4 times compared with pH = 9 and by 7.3 times compared with pH = 13 when the control voltage is 0.71 V (vs. RHE), respectively. We also found that the oxygen bubble evolution of C/TiO₂-NTAs is similar to TiO₂-NTAs. When pH = 3–13, the average photocurrent of C/TiO₂-NTAs electrode is higher than that of TiO₂-NTAs, and the average bubble evolution cycles are lower than those of TiO₂-NTAs at the same pH. According to the results, carbon films can rise the absorption capacity of TiO₂-NTAs and significantly improve the effectiveness of photogenerated holes and electrons departure. Meanwhile, based on the oxygen bubble force balance model on the photoanode surface, the concentration Marangoni force rises with the increase of pH, which leads to the growth of bubble departure diameter. The outcomes demonstrate that oxygen bubbles on the photoanode surface can be successfully eliminated in strongly alkaline settings.