Engineering Interfacial Band Alignment in a CoWO4/Bi2MoO6 Heterostructure for Enhanced Photoelectrochemical Performance

Achieving efficient charge carrier separation remains a fundamental challenge in improving the performance of photoelectrochemical (PEC) systems. Rapid charge recombination within pristine semiconductor photoelectrodes severely limits the efficiency of these systems. To overcome this limitation, a novel CoWO4/Bi2MoO6 binary heterostructure was tailored via a facile solvothermal route. Integrating these two semiconductors creates a favorable band alignment that accelerates interfacial charge transfer and suppresses carrier recombination. The comprehensive structural and optical analyses confirmed the seamless integration of both phases. Consequently, the optimized CoWO4/Bi2MoO6 heterostructure demonstrated a remarkable PEC performance, achieving a photocurrent density of –0.89 mA cm–2 at –0.20 V vs RHE, corresponding to a 22-fold enhancement over bare CoWO4. Electrochemical impedance spectroscopy revealed a low charge-transfer resistance of 310 Ω, indicating facilitated interfacial charge transfer. Moreover, ultrafast transient absorption spectroscopy revealed a prominent 17.8 ps decay component, highlighting rapid interfacial charge transfer and efficient charge separation, followed by a long-lived 4590 ps component associated with stabilized charge carriers. The heterostructure delivered a maximum applied bias photon-to-current efficiency of 3.6% at –0.41 V vs RHE. These findings underscore the efficacy of rational interface engineering in boosting charge separation and transport for advanced solar energy conversion.