Session: 06-03: CSP Receivers and Reactors II

Paper Number: 168673

168673 - High-Absorptance, Thermally-Robust Surfaces for Receivers 

Abstract: 

Thermal radiative energy transport is essential for high-temperature energy harvesting technologies, including thermophotovoltaics (TPVs) and concentrating solar power (CSP). However, the inherently low absorptivity of conventional high-temperature materials constrains radiative energy transfer, thereby limiting both system performance and technoeconomic viability. Most conventional approaches for creating high-temperature absorbers use coatings with desired absorption properties, which achieve their optical properties through hierarchical structures, multilayer materials, or metamaterials. However, coatings are prone to delamination and substrate compatibility challenges, such as from mismatched coefficients of thermal expansion or poor chemical adhesion, reducing practicality, especially at very high temperatures (>1000C). Decoupling optical properties from bulk material properties would significantly expand the viable design space, enabling the use of high-temperature and scalably machinable refractories.

Here, we demonstrate ultrafast femtosecond laser-material interactions to transform diverse materials into high-absorptance surfaces with spectral absorptivity above 0.96. We have laser-patterned materials from diverse classes including metals, Ni-alloys, and carbon materials, demonstrating the above improvement in absorptivity for all classes. The laser ablation process fires a 1.5W laser for 500 fs 2,000 times at a fixed location, then pans to the next location spaced 35 microns away and repeats the laser process. The laser causes the surface to vaporize, creating micro-scale hills and valleys, dotted with nanoparticles of resolidified material.

These hierarchically engineered microstructures enriched with nanoscale features result in effective light-trapping. We have conducted finite-difference time-domain simulations to theoretically verify that the resulting hierarchical structures interact with light in such a way that results in minimal reflection. Further, by tuning the laser parameters to change the geometry of the surface, we can obtain either broadband or spectrally selective absorptivity. This flexibility ensures the surfaces are useful for various applications.

These laser-blackened surfaces (LaBS) exhibit exceptional thermal stability, retaining high absorptivity for over 100 hours at temperatures exceeding 1000°C, even in oxidizing environments. We have tested Ta LaBS at 1500C and 2000C for 100 hours in an Ar environment, noting a small reduction in absorptivity from 0.98 to 0.95 and 0.92, respectively. We also tested a RA602CA LaBS at 1000C for 150 hours in air, similarly noting a small reduction from 0.98 to 0.95. These are the highest-temperature, longest-duration tests of stability for a structured absorber to the authors' knowledge.

While integration into a CSP system remains to be shown, we have conducted preliminary tests for Ta LaBS when applied as TPV thermal emitters. Ta LaBS double electrical power output from 2.19 to 4.10 W cm^-2 at 2200°C while sustaining TPV conversion efficiencies above 30%.

This versatile, largely material-independent technique offers a scalable and economically viable pathway to enhance absorptivity for advanced thermal energy applications.

Presenting Author: Shomik Verma Massachusetts Institute of Technology

Presenting Author Biography: Shomik Verma is a Mechanical Engineering PhD student at the Massachusetts Institute of Technology, working with Prof. Asegun Henry in the Atomistic Simulation & Energy Research Group, as a PD Soros and NSF GRFP Fellow. He is fascinated by the future of energy and has worked in a variety of fields including electric vehicles, solar cells, fuel cells, hydrogen production, thermal energy storage, and thermophotovoltaics. At MIT, his current projects are modeling how a thermal energy grid storage system can best improve the reliability of renewables and designing a next- generation power plant based on hydrogen combustion and thermophotovoltaic power generation.
Previously, Shomik completed 2 MPhils in Materials Science at Imperial College London and the University of Cambridge as a Marshall Scholar. He obtained his Bachelors in Mechanical Engineering from Duke University in 2019, where he helped build 2 electric vehicles ended up breaking Guinness World Records for efficiency.