Enhanced Thermoelectric Performance in Li-Intercalated PdPS.

Pentagonal 2D materials like penta-palladium-phosphorus-sulfur (PdPS) are renowned for their intriguing physical properties stemming from their unique Cairo pentagonal tiling topology. In this study, we explored the enhancement of thermoelectric properties in exfoliated penta-PdPS layers through lithium intercalated penta-PdPS (LixPdPS), derived from bulk crystals produced via chemical vapor transport (CVT). We present a systematic examination of the effects of Li⁺ intercalation on the in-plane electrical conductivity and thermoelectric power factor across various stages of intercalation (2.5, 10.5, and 20.5 cycles) and over a temperature range from 20 to 380 K. Our findings reveal that both the Seebeck coefficient (|S|) and electrical conductivity (σ) are optimally tuned at intermediate Li⁺ intercalation stages. At 10.5 cycles, |S| increases by 50% and σ by 1.6 times relative to pristine PdPS, yielding a peak power factor (PF) of 80 μW m⁻¹ K⁻² at 380 K, over 3-fold higher than the pristine value (24 μW m⁻¹ K⁻²). Thicker LixPdPS flakes further enhance PF by accommodating more Li⁺ ions, which raise carrier concentration and promote energy filtering. These improvements arise from pseudorecrystallization of grain boundaries and chemical doping, effectively decoupling σ and |S|. Controlled Li⁺ intercalation thus offers a powerful means to modulate electronic and lattice structures, enabling high-efficiency thermoelectric performance in 2D penta-PdPS and related layered materials.