Session: 01-02: Decarbonizing Commodity Chemicals and Emissions Analyses

Paper Number: 169901

169901 - Unlocking New Routes to Thermochemical H2 and So2 Production via Sulfur Redox Cycling 

Abstract: 

Two-step solar driven redox cycles for H₂ or syngas production have been proposed as a means to thermochemically split water since at least 1975. Originally, the process was based on stoichiometric redox reactions using oxides such as Fe₃O₄ or ZnO, but more recently much of the focus has been on nonstoichiometric oxides such as ceria and perovskite oxides. There has been extensive material investigation to identify new materials that enable lower temperatures than the state-of-the-art nonstoichiometric ceria, or CeO_2-d, including efforts have focused on high throughput computation, machine learning and empirical testing strategies. Yet there remains an inherent thermodynamic barrier due to the high water splitting enthalpy (~285 kJ/mol), which necessitates that candidate materials have even higher enthalpy. Thus, efforts to decrease temperature have so far resulted in incremental improvements because of this barrier, and universally have come at the expense of low H₂O conversions because of less favorable water splitting thermodynamics.

Typically, these two-step reactions occur at extreme temperatures 1400 °C, and when driven by concentrating solar thermal (CST), are accompanied by large radiative and optical losses. In this work, we present a novel sulfur reforming redox cycle in which a conventional STCH water splitting material (e.g. ceria or Fe₃O₄) is reduced and sulfur simultaneously oxidized to produce SO₂, at temperatures less than 1200 °C. The resulting reduced oxide is then exposed to steam or carbon dioxide to produce H₂ or syngas. The produced SO₂ is a valuable commodity integral to the fertilizer sector and heat may be supplied by sulfur combustion, thus reducing the typically large radiative and optical losses. In this work we demonstrate the viability of this new process through computational and experimental validation, coupled with a technoeconmic analysis. In total, we demonstrate the potential for efficient and scalable H₂ production at 200-400 ^oC lower than traditional two-step cycles, while also maintaining high H₂O to H₂ conversions (approaching 100%) with limited inert gas requirements. This process, when taken as a whole, represents a step change in the thermochemical H₂ technology space that has significant industrial relevance for the fertilizer and energy sectors.

Presenting Author: Jonathan Scheffe University of Florida

Presenting Author Biography: Jonathan Scheffe is an Associate Professor in the Department of Mechanical and Aerospace Engineering at the University of Florida. Prof. Scheffe is Principle Investigator of the Renewable Energy Conversion Laboratory that is focused on research in the area of energy conversion and storage. Applications include the production of renewable fuels/electricity, H2 production and fuel reforming. He is the former chair of the American Society of Mechanical Engineers (ASME) Solar Energy Division, an ASME fellow and has co-authored more than 50 peer reviewed publications in the field of solar thermal energy conversion. Prof. Scheffe has received research funding from the U.S. Department of Energy Solar Energy Technology Office, U.S. Department of Energy Hydrogen and Fuel Cell Technology Office, Duke Energy, Synhelion SA, Peregrine Hydrogen, Florida Department of Transportation, and Qatar National Research Foundation.