A New Hybrid Fuel Cell with Both Water Purification and Power Generation

­Due to the growing problems of environmental degradation and energy scarcity, there is an increasing demand for sustainable and renewable energy technology development. Over the past few decades, energy extraction from wastewater to develop efficient energy conversion technologies had been extensively studied. Employing the complex organic pollutants in wastewater that serve as carbon and energy sources for power generation, generating electricity from wastewater while degrading the pollutants is more than three times the amount of energy required to treat them. Photocatalytic fuel cell (PFC) is a more common design process for successfully capturing energy from wastewater, compared to Microbial fuel cell (MFC), proton exchange membrane fuel cell (PEMFC), solar-driven power extraction from salinity gradient and galvanic cells, which is driven by solar energy. In the PFC system, under light irradiation, rapid generation of electron/hole pairs would occur at photoanode and bring a fast and direct charge-transfer. Pollutants are oxidized and degraded by photogenerated holes, while photogenerated electrons at anode can pass through the external circuit to cathode for electricity production. Photoanodes directly determine the efficiency of photocatalytic degradation of pollutants and power generation.

BiOCl is a promising photoanode material, its unique layered structure that greatly accelerates the separation and migration of photogenerated electron-hole pairs, and its excellent photocatalytic activity has been widely used in the degradation of various refractory organic pollutants in wastewater. Polyoxometalates are considered to be excellent electron buffers, trapping electrons and storing several electrons per molecule. Their unique charge transfer properties can facilitate photocatalytic degradation of pollutants. In order to solve the problem that separated photogenerated electrons by composite BiOCl-based catalysts need to be temporarily stored and migrated to the cathode with minimal loss. Therefore, the preparation of BiOCl/POMs composites was considered to investigate whether combining the advantages of both to improve the electron transfer and charge separation properties for pollutant degradation and synchronous power generation.

Using BiOCl-NH4PTA as photocatalyst combined with an air cathode, researchers from the Research Center for Eco-Environmental Sciences and Tsinghua University School of Environment prepared a novel photocatalytic hybrid fuel cell with flow-through field (F-HFC). Their work achieved the purpose of removing organic pollutants in water and synchronous electricity generation. The mechanism of F-HFC had been systematically clarified, which provided an important theoretical basis for water purification and waste water energy recovery. This study entitled “A hybrid fuel cell for water purification and simultaneously electricity generation” is published online in Frontiers of Environmental Science & Engineering in 2023.

In this study, the research team found that dyes and biomass could be directly degraded in F-HFC, with enhanced pollutant degradation and electricity generation. Nearly 100% of the dyes could be removed within 90 minutes of irradiation. BiOCl-NH4PTA photocatalyst greatly improved electron transfer and charge separation. They found that BiOCl-NH4PTA composite has enhancement on photocatalytic oxidization ability over pollutants as well as power outputs compared to pure photocatalysts BiOCl. In addition, the generator theory of F-HFC system was further elucidated. Their study demonstrated that polyoxometalate (NH4PTA) act as the acceptor of photoelectrons and could retard the recombination of photogenerated electrons and holes, which lead to superior photocatalytic degradation.

This study investigated successfully constructed an electron and mass transfer enhanced photocatalytic hybrid fuel cell with flow-through field (F-HFC) by utilizing BiOCl-NH4PTA as photocatalysts and Pt/C air-cathode. This work not only advances the design of high-performance photocatalysts coupled with fuel cell system with flow-through field, but also provides new solutions for the treatment of refractory wastewater and simultaneous energy recovery.

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