Distinguished heterojunction and co-catalyst behaviors on tungsten doped BiVO₄ for photoelectrochemical catalytic water splitting reaction

Bismuth vanadate (BiVO₄) is one of the most promising photocatalysts for water oxidation. The short charge transfer path of BiVO₄ limits its electrochemical performance. Incorporating foreign materials into BiVO₄ is widely usedto resolve this problem. The heterojunction or co-catalyst/photocatalyst system can possibly be established in the foreign material/BiVO₄ system. However, the definition of these two systems is sometimes misleading. It is necessary to distinguish the behavior of the foreign material and understand its effects on water oxidation catalytic ability. In this study, three metal organic frameworks or their derivatives, MIL(Fe), ZIF67, and oxidized ZIF67, are coupled with BiVO₄ as the catalysts for water oxidation. By observing optical properties and linear sweep voltammetry curves, the behavior of foreign materials can be simply defined. The in-situ synthesized MIL(Fe)/W doped BiVO₄ (MIL/W:BVO) shows a heterojunction behavior, while the ex-situ synthesized ZIF67-decorated and oxidized ZIF67-decorated W:BVO present co-catalyst behaviors. The highest photocurrent density of 4.14 mA/cm² at 1.23 V_RHE and the smallest charge-transfer resistance of 67.0 Ω are obtained for the MIL/W:BVO electrode, implying a better modification of heterojunction with effective charge transfer cascades. Agood long-term stability with a current retention higher than 90% is also obtained for MIL/W:BVO after 5000 s under illumination.