Improved thermoelectric metal-organic frameworks via electronic modulation in aluminum fumarate

Aluminum fumarate (AlFum) is a metal-organic framework (MOF) with a facile and scalable synthesis route, but its low electrical conductivity due to its wide band gap (4.9 eV) limits its use in charge-transport applications. Here, an interfacial strategy is used to examine how in situ silver incorporation modifies insulating AlFum within a PEDOT:PSS conductive backbone to produce a thermoelectric composite. The in situ process produces a heterogeneous AlFum-Ag composite in which silver nanoparticles and a silver-fumarate coordination phase coexist at the AlFum surface. Synchrotron WAXS reveals a persistent lattice shift, indicating local structural distortion induced by interfacial interaction. UV-Vis analysis further shows that the Urbach energy increases from 0.159 eV for AlFum to 0.337 eV for AlFum-Ag, consistent with enhanced band-edge tailing and interfacial energetic disorder. When processed into pellets, the in situ AlFum-Ag composite delivers a fourfold increase in electrical conductivity (0.20 to 0.80 S cm^-1) with only a 26% decrease in Seebeck coefficient, resulting in a 2.2-fold enhancement in power factor (0.386 to 0.849 µW m^-1 K^-2). These findings establish a potential pathway for MOF-based thermoelectric composites development and identify Urbach energy as a useful descriptor of interfacial electronic modification.