Tailoring of bulk oxygen vacancies in BiVO₄ photoanodes via crystallization dynamics engineering for boosted photoelectrochemical water oxidation

Oxygen vacancies (Ov) in metal oxides is of critical importance in photoelectrochemical water splitting due to its unique capability on modulating the carrier density and charge separation. A challenge remains however currently on generating bulk Ov in metal oxides since surface Ov faces awkward photochemical instability. We herein demonstrate a facile way of creating the bulk Ov in Mo:BiVO₄ (MBVO) photoanodes simply from altering Bi/V in MBVO with non-stoichiometric ratio, which significantly modifies the crystallization dynamics of MBVO and tailors the amount of bulk Ov in MBVO. It is proposed that the bulk O_V significantly increase the majority carrier density due to the additional photoexcitation of O_V, and reduce the recombination constant (k_rec) due to the efficient trapping of excess holes in the stable deep-level inter-band Ov²⁺ states. It is further demonstrated that the tailored bulk O_V leads to a 1.6-fold increased photocurrent density and 50 h operational stability at 1.23 V_RHE, indicating the potentials for tailoring bulk Ov in photoanodes via crystallization dynamics engineering for viable photoelectrochemical water splitting.