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Off Grid Energy Independence
Posted on May 10, 2018 by Dr Peter Harrop

High yield syngas production from solar carbon dioxide recycling?

There is currently much debate about how to use photovoltaic solar power which is increasingly the lowest cost zero emission renewable source of electricity. It is particularly an issue when wasted due to the electricity not being needed at that time of day, batteries being an expensive, toxic, short lived, dangerous and unreliable option much of the time. Making chemicals such as hydrogen for fuel cells and industry is an option and an elegant form of this might be a circular economy making emitted carbon dioxide into fuel.
Dr.-Ing. Félix Urbain studied Materials Science at RWTH Aachen University. He pursued his PhD at the Institute of Photovoltaics in the Jülich Research Centre. His attention was focused on hydrogen production via H2O splitting. In 2016, he was awarded with the degree Dr.-Ing. summa cum laude, sustaining the world record in solar-to-hydrogen conversion efficiency of 9.5% for thin film silicon based systems. Currently, he works as a Post-Doc at IREC in Spain, and his activity is dedicated to photoelectrochemical CO2 recycling. He is author of 22 papers on ISI international journals, 24 conference contributions (4 invited talks), and one patent.
For ICREN Barcelona April 20018, he wrote: "The photo-electrochemical recycling of CO2 emerged as alluring way to store intermittent renewable energy whilst converting it back into chemical fuels. In this contribution, we report on a novel prototype reactor device for high yield conversion of CO2 to syngas (H2 + CO), which by design, is integrated, scalable to large areas, and compatible with state-of-the-art photovoltaics and electrocatalysts. Within this contribution, mainly three aspects will be addressed: adaption and integration of silicon based solar cells as photoanodes, cathode material development, and prototype reactor assembly.
The application of silicon photovoltaic cells as photoanodes requires meeting challenges, such as increasing the photovoltage without impairing the photovoltaic efficiency; protection of the solar cell by robust coatings to increase the stability in aqueous electrolytes; and the decoration with catalysts ensuring an efficient oxygen evolution reaction (OER). Under photoelectrolysis conditions, the photovoltage can be adjusted up to 2.4 V by connecting up to four solar cells in series. We demonstrate that this high photovoltage of the photovoltaic structure enables the usage of earth-abundant catalyst materials for the OER, such as Ni.
The CO2 reduction reaction is performed by large scale three-dimensional metallic foam cathodes, which are decorated with highly active nanosized catalysts for selective syngas production. We investigate the deposition of Zn and Ag catalysts on Cu- and Ni-foams. The performance of the as-produced (gas-diffusive) cathodes is evaluated in terms of product selectivity, Faradaic efficiency, overpotentials, and stability. Stable and tunable H2:CO ratios between 5 and 1 along with high CO Faradaic efficiencies of up to 96% and CO current densities of 39.4 mA/cm2 are measured.
In the complete integrated reactor assembly we combine the optimized silicon photoanode and the gas diffusive cathode (both with 10 cm2 active surface area) and investigate the most efficient membrane configuration, in terms of low overall cell voltage. Additionally, we stepwise optimize the reactor, regarding clever packaging, efficient gas management, and electrolyte flow. Finally, we demonstrate a bias-free operation of the complete reactor device providing a photocurrent density of 5.0 mA/cm2 measured under 100 mW/cm2 illumination. This corresponds to a solar-to-syngas conversion efficiency of 4.3%." However, he did not release his slides.
In its report, Battery Elimination in Electronics and Electrical Engineering 2018-2028 IDTechEx notes that storing finished product is increasingly seen as more efficient and lower cost that intermediate storing of electricity in zero emission off grid production of chemicals and indeed in desalination it is often practiced, the clean water being made during daylight and supplies ensured by storing that water without having batteries for intermediate electricity storage. An example is the mobile photovoltaic desalinators being deployed by MIT is disaster zones such as Puerto Rico.
Dr Peter Harrop

Authored By: Dr Peter Harrop


Posted on: May 10th 2018