(Invited) Solar Thermal Electrochemical Production of Energetic Molecules: Efficient STEP Solar Water Splitting, Carbon Capture, and Solar Metals, Fuel and Bleach Production

Abstract

The Solar Thermal Electrochemical Production of energetic molecules converts solar energy at high efficiency. Rather than electricity, a variety of useful chemicals, including solar fuels and iron without CO 2 emission, are produced by this STEP process. A synergy of solar thermal and solar-electric and other renewable energy electronic charge transfer, forms an alternative higher efficiency solar energy conversion process. For example, STEP can split CO 2 with >50% solar efficiency. Previously, we demonstrated STEP carbon capture, STEP fuels and STEP iron. Here we expand the STEP process portfolio to include the solar production of magnesium and bleach. IntroductionSTEP, the Solar Thermal Electrochemical Production of energetic molecules is an efficient process for converting solar energy. In STEP, the product of the solar energy conversion is useful chemicals, rather electricity. The STEP approach for solar energy conversion (1) is based on our theory and experimental observation, that even a semiconductor with bandgap smaller than the water splitting potential (E(H 2 O)=1.23V at 25°C) can split water at elevated temperature (2-4). Hence, silicon (bandgap 1.1 eV) was used to directly form hydrogen fuel from water at elevated temperature in a novel molten alkali hydroxide electrolyzer. As represented in Fig. 1 STEP generalizes the advantage of this energy conversion process to the endothermic formation of all useful, energetic molecules (1), is and includes STEP cost effective production of hydrogen (5), iron (6,7) fuels and carbon capture (8,9).The STEP process uses solar thermal energy to heat and decrease the energy of enodothermic electrolysis reactions (Figure 1), and applies the low requisite, remaining energy, by non-fossil fuel electronic charge. This process captures sunlight with conversion efficiency greater than either photovoltaic or solar thermal electric processes, through the use of the global (visible + thermal) sunlight. For example, energy sufficient, visible, sunlight drives photovoltaic charge transfer, and available heat, infrared sunlight, and excess visible sunlight, heats, and decreases the energy of, an electrolysis reaction (1). Figure 1. Left: A conventional, efficient photovoltaic generates a voltage too low to drive many useful electrochemical reactions, such as water or carbon dioxide splitting, or the indicated generic redox transfer, at ambient temperature. Right: The STEP process uses solar thermal energy to drive down the required electrolysis. This forms an energetically allowed pathway to drive charge transfer, as detailed in (1). Figure 2. CO 2 is easily captured as solid carbon at 750°C, or at 950°C as carbon monoxide using a molten Li 2 CO 3 electrolysis cell powered by sunlight, as detailed in (7).In the STEP process, rather than electrical generation, solar energy directly provides the chemical products needed by society. This original process is derived for the solar generation of energetically rich chemicals, including chlorine, metals, hydrogen and to ECS Transactions...

Modeling and design guidelines of high-temperature photoelectrochemical devices

“…To date, there is no experimental or theoretical research of solid-state PEC devices, only PV-driven high-temperature electrolysis has been investigated. [1][2][3] Licht et al 4,5 conducted a theoretical analysis of solar thermal electrochemical photogeneration of energetic molecules. They used part of the absorbed solar spectrum (superbandgap energy) to drive a photovoltaic component while the remaining solar spectrum (super and sub-bandgap energy) was used for heating the electrolyzer components.…”