The solar-wastewater fuel cell (SWFC) is an emerging technology capable of harnessing direct electricity from the process of wastewater remediation (Fig. 1). The technology has great potential in many different aspects depending on its target applications: From reducing the carbon footprints in urban wastewater treatment plants, capitalizing on the otherwise unusable residual biomass wastestreams, to serving as a low-cost, decentralized electricity generation unit for the most remote locations. One of the early challenges facing SWFC lies in its adaptation to wastewater environments, and in particular, the prediction of performance in an environment comprising of a large cocktail of organic substrates. By carefully examining the physical and electrochemical interactions of different organic substrates with the electrode surface, we found that strong adsorbates and direct hole scavengers (e.g., carboxylic acids), generated higher photocurrents compared to hydroxyl radical scavengers (e.g., alcohols). Simple and short-chained molecules are the most efficient as a result of their fast degradation kinetics. Based on this, we derived for the first time, a theoretical model that accurately predicts the photocurrent generated from any arbitrary mixture and concentrations of organic substrates. Because the open-circuit voltage of the SWFCs is dependent on the Fermi level of the photoanode, this was maximized through the selection of materials used in the construction of photoanodes. Lastly, we show the long-term performance of the SWFCs in the treatment of actual wastewater collected from different sewage treatment plants.

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