Nickel nanoparticles individually encapsulated in densified ceramic shells for thermally stable solar energy absorption†
While non-noble transition metal nanoparticles are widely explored in the field of solar energy harvesting and conversion at high temperatures, their high tendency to diffuse and oxidize may cause a substantially reduced lifetime of devices. To address this issue, herein, we demonstrate that Ni nanoparticles individually encapsulated in a densified ceramic shell, achieved by a SiO2 coating and a subsequent densification process, possess significantly enhanced stability at high temperatures. Ni diffusion is effectively prevented at temperatures as high as 800 °C, and the oxidation of the Ni nanoparticles is suppressed at 500 °C when exposed to air. A spectrally selective absorbing film fabricated with these densified Ni@SiO2 NPs exhibits high optical absorption with reflectance <20% in the main solar radiation region, superior to that of semiconductor Si-based solar absorbing films. It also exhibits high thermal stability at 500 °C in air, a temperature at which thermal degradation begins for most selective solar absorbers with high-melting-point metals and metal nitrides. The Ni@SiO2 absorbing film developed in this work outperforms state-of-the-art high-temperature solar absorbers, suggesting its applicability in high-temperature solar-thermal conversion systems.