Liquid-like ionic conductors in the copper selenide family represent a promising class of thermoelectric materials capable of recycling waste heat into electrical energy with an exemplary figure-of-merit (zT > 1.4) above 800 K. Ion diffusion, however, is enhanced at such high temperatures and drives a non-reversible phase segregation that inhibits practical applications. In tandem, the thermoelectric performance at moderate temperatures (500 − 750 K) where ion diffusion is less problematic, is not optimal for real-world applications (zT < 1). In this work, we demonstrate that incorporating a small weight fraction of carbon using various carbon sources can significantly enhance the zT of Cu₂Se at both middle and high temperatures. All the carbon-doped Cu₂Se samples exhibit weak temperature dependent zT higher than 1.0 over a broad temperature range from 600 to 900 K, with the 0.6 wt% Super P doped Cu₂Se sample achieving a zT of 1.85 at 900 K. Furthermore, the 0.3 wt% carbon fiber doped Cu₂Se shows zT > 1 for T > 520 K and reaches a record level of zT of ~ 2.4 at 850 K. These values for the carbon doped Cu₂Se are comparable or superior to those for the current state-of-the-art thermoelectric materials. Microstructure studies on graphite incorporated Cu₂Se revealed that graphite nanostructures interspace between Cu₂Se nanoscale grains being responsible for the significantly enhanced zT. The low thermal conductivity in the nanostructured composite is attributed to the high density of interfaces caused by the small grain diameters (30 − 60 nm), along with the strong acoustic mismatch between Cu₂Se and carbon phonon states which enhances the thermal boundary resistance. This discovery indicates strong prospects for engineering carbon thermoelectric nanocomposites for a range of energy applications.

中文翻译：

---

碳增强的Cu ₂ Se纳米晶固体的品质因数显着提高

硒化铜家族中的液体状离子导体代表了一种有前途的热电材料，能够将废热回收为电能，其典型的品质因数（zT > 1.4）高于800K。如此高的温度并导致不可逆的相分离，从而阻碍了实际应用。同时，离子扩散问题较少的中等温度（500-750 K）的热电性能并不是现实应用的最佳选择（zT <1）。在这项工作中，我们证明了使用各种碳源掺入少量碳可以显着提高Cu ₂的zT硒在中温和高温下均如此。所有的碳掺杂Cu ₂ Se样品在600至900 K的宽温度范围内均表现出弱于温度的zT值，高于1.0，而0.6  wt％的Super P掺杂Cu ₂ Se样品在900 K时的zT为1.85。中，0.3 重量％的碳纤维的掺杂的Cu ₂硒节目的zT > 1 Ť > 520 K和到达的记录电平的zT〜2.4的在850 K.这些值用于该碳掺杂的Cu ₂Se与当前最先进的热电材料相当或更好。对掺入Cu ₂ Se的石墨的微观结构研究表明，Cu ₂ Se纳米级晶粒之间的石墨纳米结构的间隙是显着增强zT的原因。纳米结构复合材料的低导热性归因于小粒径（30-60 nm）引起的界面高密度，以及Cu ₂ Se和碳声子态之间的强烈声失配，从而增强了热边界电阻。这一发现表明，工程碳热电纳米复合材料在一系列能源应用中具有广阔的前景。