A novel type I-like F-scheme heterojunction for improving H2 generation from water: A case modelled by physically-attached ZnCdS-Cu2O composite

Type-I heterojunction has been long-perceived non-effective in photocatalytic research. Nonetheless, this work holds an opposite belief, suggesting the possibility of securing improved photo-activity even with heterojunction possessing Type-I-like band alignment. Such concept was deliberately verified over a F-scheme heterojunction modelled by ZnCdS-Cu₂O, with their intimate interface yielding interesting interaction and improved optical properties. Electronically, the wide bandgap ZnCdS possesses relatively higher Fermi level (E_f). Contacting them would, therefore, induce ZnCdS-to-Cu₂O electron shuttlings, enabling an auspicious interfacial band alignment with upward-bended ZnCdS's bands alongside oppositely bending Cu₂O's bands. Such band structure realizes two facilitated pathways which thermodynamically direct photo-holes towards Cu₂O while immobilizing photo-electrons at the conduction band of ZnCdS. Spatial separation of photo-charges can, therefore, be achieved, with the robust photo-reductive capability of composite preserved. At surficial level, ZnCdS-Cu₂O promises expedient hydrophilicity and facile H₂ desorption; these help to accelerate H₂ generation during photoreaction. 940 % activity improvement against ZnCdS is, therefore, realized by ZnCdS-Cu₂O_10%. Astonishing AQY of 94.3 % (365 nm) and 72.1 % (420 nm) was also attained by the same photocatalyst, in conjecture to its highly sustainable activity that could last for 10 photoreaction cycles. Meanwhile, practicality evaluation suggested the high resilience of ZnCdS-Cu₂O_10% against alkaline condition and intermittent production halts in dark. More importantly, its applicability to H₂ generation from seawater was also validated, demonstrating a net positive energy production of 205 % even with ethanol added. Overall, this work verifies the productivity of Type-I-like F-scheme heterojunction, offering new avenues for future research to photocatalytic community.