Piezoelectric materials have been studied for nearly a century now. Initially employed in sonar technology, piezoelectric materials now have a vast set of applications including energy harvesting, sensing and actuation, and have found their way into our everyday lives. Piezoelectric material properties are being further enhanced to improve their performance and be used in novel applications. This review provides an overview of piezoelectric materials, and offers a material science and fabrication perspective on progress towards the development of practical piezoelectric energy harvesters and sensors. Piezoelectric materials have been divided into the three following classes for this review: ceramics, polymers and composites. The prominent materials under each class are examined and compared, with a focus on their linear piezoelectric response in the d33 mode. The three classes of piezoelectric materials are also compared qualitatively for a range of metrics, and the applications that each material class are best suited for is discussed. Novel piezoelectric materials such as ferroelectrets and nanogenerator devices are also reviewed here. It is shown that ceramic piezoelectric materials have strong piezoelectric properties but are stiff and brittle, whereas polymer piezoelectric materials are flexible and lightweight but do not exhibit very good piezoelectric performance. Composite materials are concluded to possess the advantages of both ceramic and polymer materials, with room to tailor-fit properties by modifying the structure and composition.

We encapsulated six solvents with novel physical and chemical properties for CO2 sorption within gas-permeable polymer shells, creating Micro-Encapsulated CO2 Sorbents (MECS), to improve the CO2 absorption kinetics and handling of the solvents for postcombustion CO2 capture from flue gas. The solvents were sodium carbonate (Na2CO3) solution, uncatalyzed and with two different promoters, two ionic liquid (IL) solvents, and one CO2-binding organic liquid (CO2BOL). We subjected each of the six MECS to multiple CO2 absorption and regeneration cycles and measured the working CO2 absorption capacity as a function of time to identify promising candidate MECS for large-scale carbon capture. We discovered that the uncatalyzed Na2CO3 and Na2CO3-sarcosine MECS had lower CO2 absorption rates relative to Na2CO3-cyclen MECS over 30 min of absorption, while the CO2BOL Koechanol appeared to permeate through the capsule shell and is thus unsuitable. We rigorously tested the most promising three MECS (Na2CO3-cyclen, IL NDIL0309, and IL NDIL0230) by subjecting each of them to a series of 10 absorption/stripping cycles. The CO2 absorption curves were highly reproducible for these three MECS across 10 cycles, demonstrating successful absorption/regeneration without degradation. As the CO2 absorption rate is dynamic in time and the CO2 loading per mass varies among the three most promising MECS, the process design parameters will ultimately dictate the selection of MECS solvent.

Hollow fiber membrane contactors (HFMCs) can effectively separate CO2 from post-combustion flue gas by providing a high contact surface area between the flue gas and a liquid solvent. Accurate models of carbon capture HFMCs are necessary to understand the underlying transport processes and optimize HFMC designs. There are various methods for modeling HFMCs in 1D, 2D, or 3D. These methods include (but are not limited to): resistance-in-series, solution-diffusion, pore flow, Happel’s free surface model, and porous media modeling. This review paper discusses the state-of-the-art methods for modeling carbon capture HFMCs in 1D, 2D, and 3D. State-of-the-art 1D, 2D, and 3D carbon capture HFMC models are then compared in depth, based on their underlying assumptions. Numerical methods are also discussed, along with modeling to scale up HFMCs from the lab scale to the commercial scale.

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We have developed polymer composite inks that may be three-dimensionally (3D) printed to produce new reactor designs for CO2 capture. These inks are composed of solid sodium carbonate particles dispersed within an uncured silicone and are printed using direct ink writing (DIW). After printing, the silicone is cured, and the structures are hydrated to form aqueous sodium carbonate domains dispersed throughout the silicone. These domains enable high CO2 absorption rates by creating domains with a high surface area of the solvent per unit volume in the printed structures. These results demonstrate an order-of-magnitude improvement in CO2 absorption rates relative to a liquid pool of sodium carbonate. The results from this class of composite inks demonstrate the potential for the use of 3D printing to shape new and advanced CO2 capture reactors.