Study on solar full-spectrum absorption regulation by staggered peak doping spinelalumina composite particles

The inert segmented calcination process was proposed to form bimetallic doped spinel-alumina-based composite particles as novel high-temperature heat transfer and thermal energy storage (TES) medium in concentrated solar power (CSP). Optimized preparation process came from thermal tests of the precursors under different conditions. Accurate characterizations were conducted on crystal phase, composition, surface morphology, optical characteristics, specific heat, and stability. The absorption regulation mechanism of doping and oxygen vacancies is revealed based on the density functional theory +U (DFT+U) method. The results show doping bimetallic elements have a synergistic effect on promoting the Al2O3 phase transition, lowering α-Al2O3 phase change temperature of 986°C in the air. Doping with staggered absorption peaks compensates for the shortcomings of selective absorption to improve solar full-spectrum absorptivity. In the co-doped system, new secondary main peaks are formed around 3-4eV in the ε(hν) and N(hν), and increased oxygen vacancies by inert treatment results in a red shift in the absorption coefficient, broadening the absorption waveband. The particles have good thermophysical properties with a maximum specific heat of 1.12kJ/(kg·K) and a mass loss of 0.21% from 30-1200°C. In situ formation of alumina-based spinel compounds effectively improves particle high temperature stability. The absorptivity maintains a high level after long-term thermal test. The synthetic composite candidates with low preparation cost, excellent stability, and high absorptivity can be used as a solar absorption, heat transfer, and TES medium in direct radiation solar receivers, further improving efficiency and reducing the levelized cost of electricity (LCOE).