Interfacial charge transfer effects in rare earth oxide composites: Work function modulation and electron transpiration cooling performance

Electron transpiration cooling (ETC) is an innovative active cooling mechanism that utilizes thermionic emission and recovery to achieve thermal management, offering new design strategies for thermal protection in hypersonic vehicles. Materials with lower work function enhance electron emission and thus improve ETC efficiency. In this study, we present a novel coating system based on rare earth oxides that leverages interfacial effects to modulate work function effectively. Gd₂O₃ was employed as a coating on graphite via in situ synthesis to fabricate a low work function Graphite-Gd₂O₃ (G-Gd₂O₃) material. Experimental results show that by controlling the synthesis parameters, the work function of G-Gd₂O₃ is significantly reduced by 24–39% compared to pristine graphite. Density functional theory calculations indicate that this reduction originates from the formation of an interfacial composite structure, which facilitates electron delocalization and promotes interfacial charge transfer. Furthermore, a simplified computational fluid dynamics model incorporating ETC was developed. Simulations demonstrate that a 1.92 eV reduction in work function leads to a 31.3% decrease in stagnation temperature. This work provides valuable insights into the design of ETC cathodes, supporting its practical application in hypersonic thermal protection.