Interfacial phonon thermal transport properties of plasmonic-metal-semiconductor composite electrodes

Plasmonic solar water splitting is produced on the composite electrode with plasmonic metal nanoparticles loaded on semiconductor, where the localized heating generated by relaxation of the metal’s localized surface plasmon resonance (LSPR) under light excitation enhances hydrogen production efficiency. To optimize composite photoanodes for photoelectrochemical water splitting system, the non-equilibrium molecular dynamics simulations are conducted to obtain the interfacial thermal conductivity between plasmonic metals (Cu, Ag, Au) and semiconductors (TiO<sub>2</sub>, ZnO, MoS<sub>2</sub>) at varying temperatures. The relationship between interfacial thermal conductivity and phonons at different frequencies is investigated via vibrational density of states which is calculated from the velocity autocorrelation functions and subsequent phonon participation ratio. The results indicate that as he temperature increases, the interfacial thermal conductivity of all composite electrode configurations is enhanced. When Cu and Ag are combined with TiO<sub>2</sub> into Cu-TiO<sub>2</sub> and Ag-TiO<sub>2</sub>, respectively, the thermal transport performances of Cu-TiO<sub>2</sub> and Ag-TiO<sub>2</sub> are superior to Au-TiO<sub>2</sub>, and the interfacial thermal conductivity of Cu-TiO<sub>2</sub> reaches 973.56 MW·m<sup>–2</sup>·K<sup>–1</sup> at 800 K. With Au as the fixed plasmonic component, Au-ZnO shows that its interfacial thermal conductivity reaches 324.44 MW·m<sup>–2</sup>·K<sup>–1</sup> at 800 K, which is higher than those of Au-MoS<sub>2</sub> and Au-TiO<sub>2</sub>. Based on the obtained interfacial thermal conductivity of different composite photoanodes, it is predicted that Cu-ZnO is the optimal composite, but its interfacial thermal conductivity is 547.69 MW·m<sup>–2</sup>·K<sup>–1</sup> at 800 K, second only to Cu-TiO<sub>2</sub>. The analysis of vibrational density of states and phonon participation ratio shows that the low-frequency region (0—10 THz) is the main region for thermal transport, and both interfaces exhibit a high phonon participation ratio range of 0.7—0.8. However, the Cu-TiO<sub>2</sub> possesses much higher vibrational density of states than Cu-ZnO within this critical band. Although Cu-ZnO exhibits a higher phonon participation ratio range in the high-frequency range, its lower overall interfacial thermal conductivity is attributed to the minimal contribution of high-frequency phonons to interfacial thermal conductance. The findings provide optimization strategies based on interfacial thermal transport mechanisms for constructing efficient photoanodes for solar water splitting.