Boosting the stability of BiVO4 photoanodes: in situ cocatalyst passivation and immobilization by functional fluorine anions

In photoelectrochemical water splitting, little attention is paid to the volume change of the cocatalyst on photoelectrodes during long-term testing, which is one of the important reasons for the decay of stability of photocorroded electrodes. Tuning the electrolyte composition (e.g. Fe2+ additives) has been demonstrated to be an efficient approach for in situ cocatalyst regeneration and photocorrosion inhibition. Photoelectrode stabilization by surface passivation is adopted as the most vital approach for obtaining high stability. Herein, we challenge the traditional strategy to in situ passivate the surface states with a "surface-protected etching" process for tuning the electrolyte composition via employing F- anions in borate buffer. The F- species could incorporate into the Co-catalyst to activate catalytic sites for cocatalyst reconstruction, improving the charge transport of BiVO4. More importantly, the dynamic migration of F- anions with strong chemical bonds suppresses the volume change of the cocatalyst, passivates the surface states of BiVO4/cocatalyst, and minimizes the dissolution of BiVO4 over long-term measurement, which further inhibits the photocorrosion of electrodes. The resulting photoanode allows stable oxygen evolution over 100 h at a low potential of 0.6 V-RHE, which is superior to the traditional NiOOH/FeOOH double layer cocatalyst. This finding on in situ etching and passivation engineering shines a light on boosting the stability of photoelectrodes in such electrolyte systems.