Microwave-Induced Interfacial Engineering of AC/Bi2S3 Composites for Enhanced Thermoelectric Performance

The development of low-cost and scalable thermoelectric materials is critical for efficient waste heat recovery and sustainable energy conversion. However, bismuth sulphide (Bi2S3), despite its favourable Seebeck coefficient and low thermal conductivity, suffers from intrinsically poor electrical conductivity, limiting its thermoelectric performance. Herein, we report a rapid microwave-assisted strategy to engineer activated carbon (AC)/Bi2S3 composites with enhanced charge transport properties. The microwave approach enables uniform nucleation and strong interfacial coupling between conductive carbon networks and semiconducting Bi2S3, facilitating improved carrier mobility and transport pathways. Structural and spectroscopic analyses confirm the successful formation of defect-tolerant heterostructures without disrupting the graphitic framework of AC. Thermoelectric evaluation reveals that the optimized AC/Bi2S3_9:1 composite exhibits a significantly enhanced electrical conductivity of 2.5 × 105 S cm-1, while maintaining a positive Seebeck coefficient of +4.4 μV K-1, indicating a transition from n-type (Bi2S3) to p-type behaviour induced by carbon incorporation. The composite also demonstrates a low thermal conductivity of 0.95 W m-1 K-1, resulting in an improved figure of merit (ZT) of 0.158 at room temperature, outperforming other compositions and pristine Bi2S3. The enhanced performance is attributed to synergistic effects of interfacial charge transport, increased carrier concentration (~4.5 × 1023 cm-3), and improved mobility (~1200 cm2 V-1 s-1), enabled by the optimized composite architecture. This work highlights microwave-assisted processing as a scalable route for engineering carbon-chalcogenide heterostructures toward cost-effective thermoelectric applications.