Additive manufacturing and two-step redox cycling of ordered porous ceria structures for solar-driven thermochemical fuel production. (31st December 2021)

• Record Type: Journal Article
• Authors: Haeussler, Anita; Abanades, Stéphane
• Is Part Of: Chemical engineering science. Volume 246(2021)
• Publication Date: 2021-12-31
• Subjects: CO2 utilization -- Thermochemical hydrogen production -- Solar reactor -- Ceria redox cycle -- Porous media -- Hierarchically ordered structure -- 3D-printing -- Reticulated foam; Chemical engineering -- Periodicals; Génie chimique -- Périodiques; Chemical engineering; Periodicals; Electronic journals; 660
• DOI: 10.1016/j.ces.2021.116999
• Languages: English
• ISSNs: 0009-2509

Abstract

Graphical abstract: Highlights: Additive-manufactured porous ceria structures were investigated for solar fuels production. The hierarchically-ordered porous architectures were prepared from 3D-printed scaffolds. The structures were integrated in a solar-heated reactor for two-step redox cycling. The 3D-ordered architected geometry enhanced volumetric radiation absorption. Ordered structure with struts micro-scale porosity enhanced the thermochemical performance. Abstract: This study focuses on thermochemical H2 O and CO2 -splitting processes using non-stoichiometric metal oxides and concentrated solar energy to produce solar fuels. The redox process involves two distinct reactions: (i) a thermal reduction at high temperature of the oxide with creation of oxygen vacancies in its crystallographic structure, resulting in released O2 ; (ii) a re-oxidation of the metal oxide by H2 O and/or CO2, yielding H2 and/or CO. Hierarchically-ordered porous ceria materials offer high potential for solar-driven thermochemical fuel production based on two-step redox cycles for H2 O and CO2 -splitting. The emergence of additive manufacturing processes allows to develop architected reactive materials with 3D-ordered geometry and hierarchical structure (porosity gradient), able to enhance the volumetric solar absorptivity and provide homogeneous heating of the oxygen carrier. The investigation of additive-manufactured ordered porous ceria monoliths made from 3D-printed polymer scaffolds was performed in a solar reactor. In comparison with reticulated ceria foams, an improvement of the oxygen yields was achieved with 3D-ordered porous structures. A low total pressure during the reduction step (inducing low p O2 ) favored the reduction extent and associated fuel yields. The fuel production rate during the exothermal oxidation step was enhanced by decreasing the temperature and by increasing the CO2 partial pressure. In addition, since the oxidation step is a surface-controlled reaction, a natural pore former (woody biomass) was used to create µm-size pores within the struts of ceria scaffolds. This enhanced the oxidation kinetics with a maximal CO production rate of 4.9 mL/min/g and fuel yield up to 333 µmol/g (with a reduction step at 1400 °C under ~0.10 bar of total pressure). Thus, using a 3D-ordered open-cell geometry with addition of micro-scale porosity in the struts enhanced the thermochemical performance.