Synergistic Defect Engineering in Ca-Based Pellets for Durable and High-Absorptance Solar Thermochemical Energy Storage.

Abstract

Solar thermochemical energy storage (TCES) holds immense promise for a carbon-neutral future. However, its large-scale, low-cost implementation is severely hampered by the poor solar absorptance, rapid performance degradation, and low volumetric energy density of conventional calcium carbonate/oxide materials. Herein, a multi-scale synergistic defect engineering strategy is proposed to resolve this conflict fundamentally. Guided by predictive ray-tracing models and density functional theory calculations that pinpoint dopant d-electron effects as the key modulator of optical properties, Mn/Mg co-doped pellets are rationally designed. These engineered pellets demonstrate a suite of outstanding properties: a dramatic leap in solar absorptance from a mere 3.4% to 78.5%, a 1.54-fold enhanced thermal conductivity, and exceptional cycling durability. Over 123 cycles, the pellets achieve a remarkable average volumetric energy density of 877.9 <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mi>MJ</mi> <mspace></mspace> <msup><mi>m</mi> <mrow><mo>-</mo> <mn>3</mn></mrow> </msup> </mrow> <annotation>$\rm {MJ\ m^{-3}}$</annotation></semantics> </math> (2.1 times that of the pristine powder), maintaining a high average of 848.3 <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mi>MJ</mi> <mspace></mspace> <msup><mi>m</mi> <mrow><mo>-</mo> <mn>3</mn></mrow> </msup> </mrow> <annotation>$\rm {MJ}\ {\rm m}^{-3}$</annotation></semantics> </math> over 217 cycles. This unprecedented performance comes from a unique multi-scale defect synergy, where 0D point defects induce beneficial lattice strain, while in situ formed 3D nano-precipitates strategically pin 2D grain boundaries to suppress high-temperature sintering effectively. This work not only delivers a record-performing TCES material but also establishes a promising, theory-guided strategy for the intelligent design of next-generation energy storage materials.